Since I'm all about cooking, cooking is all about making stuff, and my blog is all about making I decided that it's time to add a recipe.
(Cross-posted to Cibatarian. My wife's foodie blog)
It's over 100 degrees outside, and that can only mean one thing: Hatch Chile Season! While everyone else in Texas is looking for anything at all to help them cool off foodies in the South are turning up the heat.
I was born in New Mexico, and I grew up in Texas. My mother was born in Arizona, and she grew up all around the American Southwest. To put it mildly I grew up with spicy food. My mother introduced me to the incredibly complex flavor of the green chiles from Hatch, New Mexico in a recipe her mother had taught her when she was young: green chile burritos. I hadn't seen the chiles since I moved away to go to college in 1992 until a few years ago when I happened, much to my surprise, upon a basket of rather sad looking Hatch chiles at a local super market, and my mouth began watering immediately. The smell of the peppers is unmistakable, and I took every pepper they had on the shelf. I roasted them myself once I got home by putting them on my barbeque grill and rotating frequently until the skins were blistered and blackened all the way around. Since then H. E. B. and the Central Market in Houston have begun annual Hatch Chile Festivals at which they fire roast the peppers by the bushel for you at the store and send them home with you piping hot. Temperature-hot, that is. Well also spicy-hot, of course. Why did we have to use the same word for both in English? It's so much easier in Spanish where "caliente" means temperature-hot and "picante" means spicy-hot. Picante sauce therefore just means "hot sauce", and "hot" picante sauce is redundant. Not that I speak Spanish fluently. I don't even have any Latin or Spanish heritage. I just like the food, and growing up in Texas I've learned more than a little Spanish.
The following recipe is the first with which I have ever come up on my own. It's really simple, which is why I chose to lead with it. It takes about forty minutes from prep to table, but about half that time is waiting while the potatoes boil. It's perfect if you happen to be doing other things at the same time.
Ingredients:
- 5 pounds of potatoes cut into 3/4 inch cubes (skins-on is my preference)
- one stick of butter
- one cup plus one shotglass of cream (I didn't say this recipe was diet friendly)
- five to ten minced, roasted Hatch green chiles with the stems and seeds removed (hot or mild, I like hot)
- salt and pepper to taste
Boil the potatoes in a large stock pot with a tablespoon of salt and oil. When the potatoes squish easily between two spoons (about twenty minutes) drain the potatoes and return them still hot to the stock pot. Add the butter, Hatch chiles, and cream and mash with a potato masher or ricer to the desired smoothness.
If you decide to try this recipe at full strength your first time out (10 hot chiles) have the shotglass of cream right next to your plate. If it turns out that you've gotten in over your head with the heat of the chiles take the shot and swish it around in your mouth until the flames are extinguished. The fat in the cream will help dissolve the capsaicin (the naturally occurring chemical that gives peppers their characteristic heat; it just happens to be insoluble in water so no amount of water, soda, or beer will help). I accept no responsibility for the effects you may experience the following day (we've come to call it "afterburners" or "the ring of fire").
I'll be adding more recipes in the future. Especially recipes about Hatch chiles!
Saturday, August 18, 2012
Saturday, August 4, 2012
Work in Progress: A Dragon's Eyes (Assembly)
It's hard to believe that I've been at this for over a month now. I'm sure Dean and Adrienne think it's taking too long, but for me the time has flown by. I don't get to spend time on this project every day because of work and other commitments. The time I do have for it I spend mostly watching resin cure (it's kind of like watching paint dry but slower). Each time I cast a resin part almost 24 hours pass before I can do anything else with it. I brought the dragon home last week (his name is Zippy it turns out) so I could work on it in my workshop instead of having to take several trips to Dean's house.
Knowing now how I was going to make the eyes and needing a new, clean mold to do it I mixed up a batch of oogru and set to work. Previously I had taken a single mold of the entire face so I could have a copy from which to work. This time I did each eye individually since during final assembly that is all on which I would be working. I took care to work as much oogru into the fine details around the eyes as possible using a popsicle stick, and I came back with a second layer after the first had cured to thicken and reinforce the mold a bit more.
Once I had a satisfactory pair of molds I began cutting out the eyes from the original sculpture with a rotary tool. This turned out to be harder than I expected. The reproduction on which I'd practiced was less than 1/8" thick at its thickest point. The original was much thicker. I absolutely didn't want to make a mistake at this stage, so I took well over an hour for each eye to get them right.
Dean and I had discussed making the eyes with a clear, slit pupil and having the rest of the eye translucent white. I took a pair of similarly sized lenses (from my original experiments with the jeweler's resin) and marked them with some measurements I took from the molds I'd just finished. I used my band saw to cut roughly identical oblong shapes and then sanded them with an emery board until they were almost exactly the same size and shape I wanted. I placed one in a mold to confirm my measurements, and I realized I had a problem. The little piece of resin wouldn't stand on its own in the mold. I would have to prop it with something while the resin around it cured, and that simply wasn't an option in the tight space inside the dragon's head.
I decided to resolve this issue by "gluing" the piece to the mold with some liquid resin. I put the two molds face-up on a table, propped the pupil pieces in the molds using popsicle sticks, and mixed up a small batch of resin. I became concerned that if I tried making the translucent resin as I had previously (by stirring in bubbles while the resin slowly cured) I wouldn't be able to get the exact density of bubbles in later batches resulting in visibly distinct layers when I poured the final section of the eye. I opted to use just a small amount of clear resin to glue the pupil component in place.
A day later the pupils were more or less secured in the molds. The fresh resin would hold them in place so long as I wasn't too rough with the mold. If I accidentally "unmolded" them I'd probably have to start all over. I used modeler's clay to create a wall around the eye hole on the inside of Zippy's head as I had done previously taking care to keep the flesh-colored polymer clay well back from the edge of the hole so it wouldn't be visible and wouldn't interfere with the resin bonding to the original sculpture. I carefully placed the eye mold back on the face and secured it with a pair of rubber bands. I laid the sculpture down and propped it with books so the eye on which I'd be working was level with the floor.
The inside of Zippy's head is a tight space around a sharp corner. It's impossible to see directly into the area in which I was working, so I used a small night-vision security camera I just happened to have laying around (something else in my weird-ass crap box). I placed the camera inside the cavity facing the inside of the eye on which I was working. This allowed me to observe indirectly what was going on inside the head. As soon as the camera was in place I noticed that I'd created a rather large well with the mold and the modeler's clay. I had been previously mixing jeweler's resin in 5ml batches, and it occurred to me that I would need a somewhat larger amount to fill the space I'd created. Alternatively I could make two separate batches and pour each individually.
Recall that my original plan (back in the very beginning) had been to create a complex eye with a cornea, iris, and retina. I had liked the effect, but the implementation in its original form was too difficult. Looking into the large void I had to fill I realized that I could make the complex eye in a series of pours rather than a series of parts. I mixed up a batch of clear jeweler's resin and drew it into a syringe. I plugged the end of the syringe and pulled back the plunger creating a partial vacuum inside. All of the bubbles suspended in the mix (and there were many more than I realized) swelled like balloons and rose slowly to the top of the fluid. I reached the syringe into the dragon's head and watched on my monitor as I slowly squirted the clear resin into the space around the pupil component that stood erect in the center. I took extreme care not to get any resin on the flat top of the pupil, and I stopped pouring when the fluid level reached the rim of the eye all the way around.
The next night I mixed up another batch of resin this time with bubbles. I've discovered that if I wait an hour after the initial mixing the viscosity of the resin increases considerably. This makes it easier to incorporate smaller, more uniform bubbles that don't float to the surface. Once again I used the security camera like a laparoscopic surgery camera inside the dragon's head, and once again I slowly poured the resin into the well this time stopping before the fluid level over-topped the pupil component. A day later I stood the sculpture up and unmolded the new eye. I was actually surprised at the result. Even without polish the eye had a nice three-dimensional appearance that made it look alive.
I repeated the entire process with the remaining eye using a single drop of the fresh, clear resin to polish the eye I'd just finished. This time positioning the sculpture to get the eye level was much more difficult however because the dragon's head is turned slightly, but when the two layers were complete the result was no less impressive. To be completely honest I wasn't expecting it to turn out as well as it did.
For those keeping score: it took a day to cast the lenses out of which I cut the pupil components, a day to "glue" the pupils into the molds, a day to pour the left cornea, another day to pour the left iris, a day to pour the right cornea and polish the left cornea, a day to pour the right iris, and a day to polish the right cornea. In all a week of pouring components after all the experiments I'd done to this point.
Almost done! When next I post on this subject it will be about the instillation of the lights and moving Zippy to his final home. Since that might take a couple of weeks expect that next week's post may be about a different subject entirely.
Knowing now how I was going to make the eyes and needing a new, clean mold to do it I mixed up a batch of oogru and set to work. Previously I had taken a single mold of the entire face so I could have a copy from which to work. This time I did each eye individually since during final assembly that is all on which I would be working. I took care to work as much oogru into the fine details around the eyes as possible using a popsicle stick, and I came back with a second layer after the first had cured to thicken and reinforce the mold a bit more.
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| First layer of the new mold. Even after it's cured oogru will bond solidly to new layers of oogru. It doesn't bond to much else however which makes it so good for mold making. |
Once I had a satisfactory pair of molds I began cutting out the eyes from the original sculpture with a rotary tool. This turned out to be harder than I expected. The reproduction on which I'd practiced was less than 1/8" thick at its thickest point. The original was much thicker. I absolutely didn't want to make a mistake at this stage, so I took well over an hour for each eye to get them right.
Dean and I had discussed making the eyes with a clear, slit pupil and having the rest of the eye translucent white. I took a pair of similarly sized lenses (from my original experiments with the jeweler's resin) and marked them with some measurements I took from the molds I'd just finished. I used my band saw to cut roughly identical oblong shapes and then sanded them with an emery board until they were almost exactly the same size and shape I wanted. I placed one in a mold to confirm my measurements, and I realized I had a problem. The little piece of resin wouldn't stand on its own in the mold. I would have to prop it with something while the resin around it cured, and that simply wasn't an option in the tight space inside the dragon's head.
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| The pupil component glued into a mold. I marked the end of the piece with a marker to make it more visible to the camera. |
A day later the pupils were more or less secured in the molds. The fresh resin would hold them in place so long as I wasn't too rough with the mold. If I accidentally "unmolded" them I'd probably have to start all over. I used modeler's clay to create a wall around the eye hole on the inside of Zippy's head as I had done previously taking care to keep the flesh-colored polymer clay well back from the edge of the hole so it wouldn't be visible and wouldn't interfere with the resin bonding to the original sculpture. I carefully placed the eye mold back on the face and secured it with a pair of rubber bands. I laid the sculpture down and propped it with books so the eye on which I'd be working was level with the floor.
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| The left eye mold strapped on with rubber bands. Notice how much thicker it is than in the image above. |
Recall that my original plan (back in the very beginning) had been to create a complex eye with a cornea, iris, and retina. I had liked the effect, but the implementation in its original form was too difficult. Looking into the large void I had to fill I realized that I could make the complex eye in a series of pours rather than a series of parts. I mixed up a batch of clear jeweler's resin and drew it into a syringe. I plugged the end of the syringe and pulled back the plunger creating a partial vacuum inside. All of the bubbles suspended in the mix (and there were many more than I realized) swelled like balloons and rose slowly to the top of the fluid. I reached the syringe into the dragon's head and watched on my monitor as I slowly squirted the clear resin into the space around the pupil component that stood erect in the center. I took extreme care not to get any resin on the flat top of the pupil, and I stopped pouring when the fluid level reached the rim of the eye all the way around.
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| This is the camera set-up I used. You can see the outline of the pupil component on the monitor. What's harder to see is the syringe hovering over the well that I'm using to drip resin in. |
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| Four phases of the build (left to right): The original eye, unmodified; The eye, cut out (notice the thickness of the resin at the front of the socket); The new eye fresh out of the mold; The new eye, all polished up. |
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| I lit the eye with an ultraviolet LED just to see how it looks. For some reason the UV light reacts strangely with my camera making it look like a bad special effect from the original Dune movie. The sculpture here is positioned to let the resin in the right eye cure. |
Almost done! When next I post on this subject it will be about the instillation of the lights and moving Zippy to his final home. Since that might take a couple of weeks expect that next week's post may be about a different subject entirely.
Saturday, July 21, 2012
Work in Progress: A Dragon's Eyes (proof of concept)
Alright. So I have this incredibly complicated design for a light-up eye involving three pieces of clear plastic in three different shapes (a rounded "cornea", a flat, etched and painted "iris", and a rounded "retina") and three LEDs in two different colors. How could this possibly go wrong!
I knew how all the parts were going to fit together if not how they were going to stay together. I also hadn't figured out was how I was going to fit it all in the eye socket of the dragon's head. I thought that I was going to have to cut one of my circular jeweler's resin lenses to fit in the almond-shaped eye-hole and then glue it in place to form the cornea. I started with what was essential: I made the eye-hole since I couldn't know what shape to cut the lens until I had that. I carved the existing eye out of my reproduction dragon face with a rotary tool (at this point I'm still working on proof-of-concept, not the actual dragon sculpture). I put the reproduction back in the original mold when I was done to check my work, and I had a sudden inspiration: I didn't have to re-shape anything to fit in the hole in the face. I could clamp the original mold on and simply pour clear resin in the void I'd just cut! As long as the part I was working on remained level and the mold was firmly clamped to the urethane reproduction the jeweler's resin should cure in the same exact shape as the eye I had just removed. Furthermore I expected that the jeweler's resin would even stick like glue to the urethane saving me from finding some invisible means by which to secure the cornea in the socket.
To make sure there was no spillage I created a wall around the hole with modeling clay. That would allow me to over-fill the space a little (it's easier to remove excess material than it is to add it). I clamped the mold and face together with spring clamps, and then I clamped the whole assembly to the table to keep it level over-night. I took care to mix the resin without incorporating any bubbles, and when I unmolded the piece the following day (re-unmolded?) the eye was exactly the right shape and securely and neatly bonded to the surrounding face. I repeated the technique I had used previously to polish the cornea (a few drops of resin on the rough surface), and another day later the results were even better than I had hoped!
I arranged with Dean a time to present my proof-of-concept so I could move on to working on the original sculpture. I suppose it should have been a warning as I was getting ready to take everything out to show him that I had to go to great lengths to pack everything in sealable containers so nothing would get damaged or lost en route. It took a bit of time to re-wire my demonstration electronics and to sort and stack all the parts I'd built. The result was a rickety pile that only displayed the illusion I was hoping for if the observer viewed it from directly above. Dean was non-plussed, and I can't say I disagreed with him. To be frank I had no idea at that point how I was going to get all those parts to remain together, and the stack was taller than half the width of the dragon's head into which I planned to fit two of them (the eyes are on opposite sides of the head).
On the positive side: Dean really liked the look of the clear resin cornea I'd poured in my reproduction of the dragon's face. There were a couple small bubbles in the resin that became more visible when the light was shone through, and the bubbles were causing the light to bounce in an interesting way. Dean actually liked how they looked, and he pointed out that if the resin was full of bubbles the light being refracted from all of them would diffuse the light shining through and make it visible from all directions.
Dean gave me the go-ahead to start cutting on the original to at least get that component started. Not having an iris however would mean the ultraviolet LEDs would have nothing to make them visible (reflect a visible wavelength), so I would have to switch to an LED with a color in the visible spectrum. I hadn't cancelled my order for the ultra-bright purple LEDs from China, so having an iris painted with fluorescent purple pigment won't technically be essential (assuming they ever arrive). I did experiment with etching the back of the resin cornea to make it resemble a slit-pupil iris though, and Dean wasn't entirely opposed to the way it looked.
Back at home I repeated the process I'd used to pour the first eye on the other side, but instead of taking my time to mix the resin gently I beat the hell out of it to incorporate as many bubbles as possible. As I was about to pour the resin I had an idea: rather than etching a slit-pupil I could cast one. The resin I had just mixed had a milky appearance from the quantity of bubbles, and the etching I'd used on the clear cornea wouldn't be visible anyway. I took one of the clear lenses I'd created previously as an experiment and cut it with my band saw into an oblong shape. This I set into the mold before I poured the new resin. Without all the bubbles the clear (old) resin was denser than the new, bubbly resin, so gravity held it in place while the resin cured. After a layer of polish was added the resulting eye actually looked rather nice (if I do say so myself) if a little rough (the mold is starting to show signs of wear).
I now have the original dragon sculpture in my workshop, so I have work to do. First I have to create a new mold that's easier to work with and in better shape than the one I currently have. Next I have to grind out the existing eyes (this could be difficult: the resin of the original sculpture is much thicker in some places than the reproduction with which I've been working). Then I have to pour new eyes (having a vastly different space in which to work than with my proof-of-concept). Finally I have to wire the electronic components.
Coming soon: Assembly!
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| The flesh-tone stuff around the eye is modeling putty. It stays pliable almost forever unless its heated. All it's for here is to prevent the resin from running out. |
To make sure there was no spillage I created a wall around the hole with modeling clay. That would allow me to over-fill the space a little (it's easier to remove excess material than it is to add it). I clamped the mold and face together with spring clamps, and then I clamped the whole assembly to the table to keep it level over-night. I took care to mix the resin without incorporating any bubbles, and when I unmolded the piece the following day (re-unmolded?) the eye was exactly the right shape and securely and neatly bonded to the surrounding face. I repeated the technique I had used previously to polish the cornea (a few drops of resin on the rough surface), and another day later the results were even better than I had hoped!
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| Right eye right out of the mold. The black spring clamp in the picture is just there to give some contrast to the eye. |
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| This is the right eye polished up. The iris is simply scratched in the back of the cornea with the tip of a screwdriver. I wish I had taken a picture before I'd scratched the iris in. |
I arranged with Dean a time to present my proof-of-concept so I could move on to working on the original sculpture. I suppose it should have been a warning as I was getting ready to take everything out to show him that I had to go to great lengths to pack everything in sealable containers so nothing would get damaged or lost en route. It took a bit of time to re-wire my demonstration electronics and to sort and stack all the parts I'd built. The result was a rickety pile that only displayed the illusion I was hoping for if the observer viewed it from directly above. Dean was non-plussed, and I can't say I disagreed with him. To be frank I had no idea at that point how I was going to get all those parts to remain together, and the stack was taller than half the width of the dragon's head into which I planned to fit two of them (the eyes are on opposite sides of the head).
On the positive side: Dean really liked the look of the clear resin cornea I'd poured in my reproduction of the dragon's face. There were a couple small bubbles in the resin that became more visible when the light was shone through, and the bubbles were causing the light to bounce in an interesting way. Dean actually liked how they looked, and he pointed out that if the resin was full of bubbles the light being refracted from all of them would diffuse the light shining through and make it visible from all directions.
Dean gave me the go-ahead to start cutting on the original to at least get that component started. Not having an iris however would mean the ultraviolet LEDs would have nothing to make them visible (reflect a visible wavelength), so I would have to switch to an LED with a color in the visible spectrum. I hadn't cancelled my order for the ultra-bright purple LEDs from China, so having an iris painted with fluorescent purple pigment won't technically be essential (assuming they ever arrive). I did experiment with etching the back of the resin cornea to make it resemble a slit-pupil iris though, and Dean wasn't entirely opposed to the way it looked.
Back at home I repeated the process I'd used to pour the first eye on the other side, but instead of taking my time to mix the resin gently I beat the hell out of it to incorporate as many bubbles as possible. As I was about to pour the resin I had an idea: rather than etching a slit-pupil I could cast one. The resin I had just mixed had a milky appearance from the quantity of bubbles, and the etching I'd used on the clear cornea wouldn't be visible anyway. I took one of the clear lenses I'd created previously as an experiment and cut it with my band saw into an oblong shape. This I set into the mold before I poured the new resin. Without all the bubbles the clear (old) resin was denser than the new, bubbly resin, so gravity held it in place while the resin cured. After a layer of polish was added the resulting eye actually looked rather nice (if I do say so myself) if a little rough (the mold is starting to show signs of wear).
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| The left eye. The mold has been damaged by constantly putting the reproduction in and out of it (my fault). Nonetheless, I like the result. I'll probably make the pupil narrower in the final version. |
I now have the original dragon sculpture in my workshop, so I have work to do. First I have to create a new mold that's easier to work with and in better shape than the one I currently have. Next I have to grind out the existing eyes (this could be difficult: the resin of the original sculpture is much thicker in some places than the reproduction with which I've been working). Then I have to pour new eyes (having a vastly different space in which to work than with my proof-of-concept). Finally I have to wire the electronic components.
Coming soon: Assembly!
Saturday, July 14, 2012
Work in Progress: A Dragon's Eyes (part 2)
As of Thursday three weeks ago I had a reasonable reproduction of an original dragon sculpture's face and eyes, but I had only a vague idea of what I was going to do to make the glowing eyes themselves. It was the eyes after all that I was originally consulted to make not the reproduction of the face (that was a fun side-project that I could alter if necessary). Dean and Adrienne want vibrant, purple eyes visible from the end of their block, and the inspiration for the modification had been a pair of edge-lit, cat's eyes goggles I had made for my wife as a costume piece.
The existing eyes of the dragon sculpture have a pronounced hemispherical curve, and I decided to maintain that shape as much as possible. Simply carving the eyes out and replacing them with pieces of flat Plexiglas would certainly accomplish the desired effect, but making the eyes look alive will require keeping the corneal curve. The best possible result I thought would involve making a complex eye out of three differently shaped components lit in different ways. I came up with the idea of a curved, clear cornea (replacing the existing eye) sitting on top of a flat, etched piece of edge-lit Plexiglas (etched to resemble an iris) backed by a third, curved piece of clear plastic or glass lit directly from behind by a differently colored LED (amber or red as the backing color behind the purple iris) to look like reflection off a retina.
I don't posses the equipment to grind a lens. What I needed therefore was to find something (either glass or a clear polymer) that already had the desired curve. That meant I needed to know what the curve of the existing eye is. I assumed that the curve matched the surface of a sphere. I took a couple measurements, used some basic geometry, and I estimated that the eyeballs of the dragon would be about 1.5 inches in diameter. Roughly the size of a ping pong ball. That's convenient.
As I was wandering aimlessly through a hobby store looking for a clear object with the shape I needed I happened to notice a package of clear epoxy resin on a shelf. It was packaged in two parts like the polyurethane I'd used to reproduce the dragon's face, and that made me think about the possibility of making a lens with the curve I wanted. Over the next few days I experimented with differently shaped molds and clear, pourable media (clear epoxy, acrylic cement, jeweler's resin, and even cyanoacrylate glue). I had the best results using an oogru mold I took of a ping pong ball (again, convenient) with jeweler's resin. This produced a clear, hemispherical object similar to a lens.
Jeweler's resin is a two-part, viscous resin that takes at least 24 hours to cure. This extended cure time prevents excessive heat production (which can cause cloudiness and discoloration I discovered with the clear epoxy) and gives any bubbles in the mix time to rise to the surface. The result is an optically clear plastic (unless you add dyes) with an amazingly durable and scratch resistant surface. It can be poured over a table or counter (for example) to create a laminate or into a mold (that may or may not contain other items, encasing them in the resin) to make jewelery or other plastic parts. The surface exposed to air is amazingly clear, but the surface in contact with the mold takes the texture of the mold. Since neither the ping pong ball nor the oogru out of which I made the mold are perfectly smooth the resulting lens when unmolded had a hazy surface that appeared to have been frosted. The curve was perfect, but I couldn't see anything through the rough surface.
I spent another day contemplating techniques that I could use to polish the surface of the lens to make it crystal clear. I was about to begin testing the resin's response to fire-polishing or using solvents to smooth the surface when I remembered that the flat part of the lens (the part that had been exposed to air while the resin cured) was already smooth and clear without polishing. I wondered what would happen if I layered the resin. Would there be a distinct difference between layers, or would old and new layers bond seamlessly?
I mixed up another batch of resin, dabbed a couple drops of liquid resin on the top of the dome of the lens (as it rested on the flat surface on a table), and smoothed it carefully over the entire frosted surface. The rest of the batch went into the same mold from which the first lens came just in case I ruined the one I was working on. I had hoped that the viscosity of the liquid resin would keep enough of it from simply running off the sides that it would leave a sufficiently thick coat, but with a cure time of 24 hours all I could do was wait and see. Much to my delight it worked almost perfectly! Some larger imperfections on the surface of the original lens were still visible, but for the most part the new resin had cured to a glass-smooth finish. I made new molds taking extreme care to eliminate as many imperfections in the mold as possible, and I poured new resin lenses.
As the new lenses cured I set to work making the next layer of the eye: the iris. I have a drill bit specifically made for cutting perfect circles. It's the scariest damn thing I've ever seen attached to my drill press. It looks like parts are going to come flying off at close to sonic speed at any moment. I take extensive safety measures each time I use it just in case one of the parts of the bit does come flying off. It cuts neat circles in Plexiglas though, and that's what I use it for. I cut a pair of one-and-a-half inch disks out of quarter-inch thick acrylic and drilled holes in the edges on opposite sides to accommodate a pair of 5mm LEDs. Etching and abrading the disks to resemble a slit-pupil iris was an afternoon project since I've done similar work previously (it's just like making the cat's-eyes goggles). Gluing the LEDs in and wiring them in series with a resistor was accomplished the following afternoon (never power a LED without a resistor in series or you're basically creating a short-circuit).
The electronic parts stores in town don't have purple LEDs, so I started with ultraviolet LEDs. Ultraviolet however is invisible to the human eye. The hints of purple you see when looking at an ultraviolet light are actually a different wavelength entirely "leaking" through. UV light does have the interesting property of changing its wavelength in response to many surface materials and reflecting back as a very different color (this isn't entirely accurate at the quantum level, but that discussion is a bit too involved for the scope of this project). Fluorescent colors (a.k.a day-glo or neon) are the most vibrant examples of this effect as can be seen at many nightclubs ("color brightening" fabric detergents and softeners also contain fluorescent compounds). My idea was to add a surface paint on the back of the acrylic disk that fluoresces purple under a black-light. This would serve two purposes: first it would convert invisible UV light into a vibrant purple, and second it would block any light coming from behind the iris everywhere except through the pupil (the only part of the disc not painted). The "retina" I was still planning to make would then be visible only through the slit pupil.
Do you have any idea how difficult it is to find fluorescent purple paint? For that matter do you have any idea how hard it is to find fluorescent blue paint for mixing with fluorescent red paint (which is easy to find) to make fluorescent purple? Red, orange, green, and yellow are all readily available. I searched for a week to find purple. I was about to give up, and I had even ordered ultra-bright purple LEDs from a supplier in China as a back-up plan. By luck however I found the only purple pigment (evidently) in existence in the form of a paint intended for use with an airbrush.
With the cornea and iris completed all that was left was the retina (and of course to mount the whole thing). Compared with the trouble I had been having with the other two components the retina was a breeze. All I needed was to use one of the spare jeweler's resin lenses with its flat side to the back of the iris component and to shine a red or amber LED from about an inch behind the curved side of the lens. This creates a watery glow rather than a pinpoint of light. I used a breadboard to assemble both an amber and a red LED for test purposes.
Up next: Putting it all together.
The existing eyes of the dragon sculpture have a pronounced hemispherical curve, and I decided to maintain that shape as much as possible. Simply carving the eyes out and replacing them with pieces of flat Plexiglas would certainly accomplish the desired effect, but making the eyes look alive will require keeping the corneal curve. The best possible result I thought would involve making a complex eye out of three differently shaped components lit in different ways. I came up with the idea of a curved, clear cornea (replacing the existing eye) sitting on top of a flat, etched piece of edge-lit Plexiglas (etched to resemble an iris) backed by a third, curved piece of clear plastic or glass lit directly from behind by a differently colored LED (amber or red as the backing color behind the purple iris) to look like reflection off a retina.
I don't posses the equipment to grind a lens. What I needed therefore was to find something (either glass or a clear polymer) that already had the desired curve. That meant I needed to know what the curve of the existing eye is. I assumed that the curve matched the surface of a sphere. I took a couple measurements, used some basic geometry, and I estimated that the eyeballs of the dragon would be about 1.5 inches in diameter. Roughly the size of a ping pong ball. That's convenient.
As I was wandering aimlessly through a hobby store looking for a clear object with the shape I needed I happened to notice a package of clear epoxy resin on a shelf. It was packaged in two parts like the polyurethane I'd used to reproduce the dragon's face, and that made me think about the possibility of making a lens with the curve I wanted. Over the next few days I experimented with differently shaped molds and clear, pourable media (clear epoxy, acrylic cement, jeweler's resin, and even cyanoacrylate glue). I had the best results using an oogru mold I took of a ping pong ball (again, convenient) with jeweler's resin. This produced a clear, hemispherical object similar to a lens.
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| Various lenses and molds in the experimenting phase of my design. |
I spent another day contemplating techniques that I could use to polish the surface of the lens to make it crystal clear. I was about to begin testing the resin's response to fire-polishing or using solvents to smooth the surface when I remembered that the flat part of the lens (the part that had been exposed to air while the resin cured) was already smooth and clear without polishing. I wondered what would happen if I layered the resin. Would there be a distinct difference between layers, or would old and new layers bond seamlessly?
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| The top lens is right out of the mold. The bottom lens is polished by adding another layer of resin. |
I mixed up another batch of resin, dabbed a couple drops of liquid resin on the top of the dome of the lens (as it rested on the flat surface on a table), and smoothed it carefully over the entire frosted surface. The rest of the batch went into the same mold from which the first lens came just in case I ruined the one I was working on. I had hoped that the viscosity of the liquid resin would keep enough of it from simply running off the sides that it would leave a sufficiently thick coat, but with a cure time of 24 hours all I could do was wait and see. Much to my delight it worked almost perfectly! Some larger imperfections on the surface of the original lens were still visible, but for the most part the new resin had cured to a glass-smooth finish. I made new molds taking extreme care to eliminate as many imperfections in the mold as possible, and I poured new resin lenses.
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| The scariest damn drill bit EVER! |
As the new lenses cured I set to work making the next layer of the eye: the iris. I have a drill bit specifically made for cutting perfect circles. It's the scariest damn thing I've ever seen attached to my drill press. It looks like parts are going to come flying off at close to sonic speed at any moment. I take extensive safety measures each time I use it just in case one of the parts of the bit does come flying off. It cuts neat circles in Plexiglas though, and that's what I use it for. I cut a pair of one-and-a-half inch disks out of quarter-inch thick acrylic and drilled holes in the edges on opposite sides to accommodate a pair of 5mm LEDs. Etching and abrading the disks to resemble a slit-pupil iris was an afternoon project since I've done similar work previously (it's just like making the cat's-eyes goggles). Gluing the LEDs in and wiring them in series with a resistor was accomplished the following afternoon (never power a LED without a resistor in series or you're basically creating a short-circuit).
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| The iris disks, front and back. The front is frosted by abrading with sandpaper, and the back is etched with radial lines to give it a three-dimensional appearance. There are holes drilled in the edges top and bottom for the LEDs. |
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| The iris all wired and lit-up. The UV LEDs for some reason are highly visible to the camera, but not to the naked eye. |
The electronic parts stores in town don't have purple LEDs, so I started with ultraviolet LEDs. Ultraviolet however is invisible to the human eye. The hints of purple you see when looking at an ultraviolet light are actually a different wavelength entirely "leaking" through. UV light does have the interesting property of changing its wavelength in response to many surface materials and reflecting back as a very different color (this isn't entirely accurate at the quantum level, but that discussion is a bit too involved for the scope of this project). Fluorescent colors (a.k.a day-glo or neon) are the most vibrant examples of this effect as can be seen at many nightclubs ("color brightening" fabric detergents and softeners also contain fluorescent compounds). My idea was to add a surface paint on the back of the acrylic disk that fluoresces purple under a black-light. This would serve two purposes: first it would convert invisible UV light into a vibrant purple, and second it would block any light coming from behind the iris everywhere except through the pupil (the only part of the disc not painted). The "retina" I was still planning to make would then be visible only through the slit pupil.
Do you have any idea how difficult it is to find fluorescent purple paint? For that matter do you have any idea how hard it is to find fluorescent blue paint for mixing with fluorescent red paint (which is easy to find) to make fluorescent purple? Red, orange, green, and yellow are all readily available. I searched for a week to find purple. I was about to give up, and I had even ordered ultra-bright purple LEDs from a supplier in China as a back-up plan. By luck however I found the only purple pigment (evidently) in existence in the form of a paint intended for use with an airbrush.
With the cornea and iris completed all that was left was the retina (and of course to mount the whole thing). Compared with the trouble I had been having with the other two components the retina was a breeze. All I needed was to use one of the spare jeweler's resin lenses with its flat side to the back of the iris component and to shine a red or amber LED from about an inch behind the curved side of the lens. This creates a watery glow rather than a pinpoint of light. I used a breadboard to assemble both an amber and a red LED for test purposes.
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| This is what it looks like completely assembled. The red LED shining through a convex lens set behind the slit pupil in the iris disk. I think it looks really amazing, but it's a very complicated arrangement. |
Up next: Putting it all together.
Saturday, July 7, 2012
Work in Progress: A Dragon's Eyes (part 1)
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| The image from the catalogue. |
Dean (my friend) had examined the decoration when it arrived, and he discovered that in addition to the long, hollow core there was also a fairly large void inside the dragon's head that's accessible from inside the 4X4 core. It's more than adequate he realized to contain some electronics for some kind of practical effect. Dean is a software developer and brewmaster (it's a long story) not a weird-ass projects developer, so as one of the weirdest people he knows naturally he called me (actually he'd seen another project I'd completed that's similar to what he wanted done here).
The idea he and his wife had and presented to me was to cut out the opaque resin eyes of the dragon with a rotary tool and replace them with super-bright LEDs. They initially wanted to power the lights from a battery that recharged daily via a solar cell (kind of like those garden stake-lights you can find at almost any hardware or garden store), but the location of the existing mailbox in the shade of a large tree made that difficult. Instead Dean suggested running a wire from an existing 24 volt power supply (for a koi pond in their front yard). It sounded like fun, so after a short brainstorming session to discuss possibilities I drove to his house to see the dragon for myself.
The device Dean had seen previously that had inspired him to bring me in on this project was a pair of steampunk goggles I'd made for my wife. I had hand-sewn the goggles entirely out of leather and used thick Plexiglas lenses. The lenses I had etched and frosted to resemble a cat's eyes (slit pupils), and I had edge-lit the lenses with a pair of bright, green LEDs (concealed by the leather rim). The effect is quite vibrant. Everywhere the lens is etched or frosted the light of the LEDs is refracted out of the acrylic and visible to viewers nearby. Everywhere the surface is undamaged the light isn't visible, and the surface appears dark. The deeper scratches of the etching grab more light and are therefore brighter than the shallower scratches of the frosted areas (which I created by abrading the surface with coarse sandpaper). The goggles actually put out enough light to see by in the dark, but the same amount of light goes in both directions making it impossible to see in the dark if you're wearing them (they're just a costume piece anyway). It was something along these lines that Dean and Adrienne wanted for their dragon.
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| The goggles, turned on. The batteries and wires are concealed inside the eyes. |
Since we didn't have an exact plan for what we were going to do we didn't want to start by damaging the original resin sculpture. I wanted to have a cheap duplicate I could carve up, and that meant making a mold of the original. I've experimented with mold-making a couple times using latex. It's a long, painstaking process of painting on layer after layer of liquid latex and letting it dry between layers before the mold is finally thick enough to survive being removed. A much quicker option is two-part pourable silicone available at our local hobby and craft store. I've played with that before as well, but pourable silicone mold material is fairly expensive. A third option I've been wanting to try that has become popular in the maker community in the last year or so for making rubber parts: Oogru.
Silicone caulk (silicone I) is an inexpensive and commonly available gel. It's available at any hardware store for sealing windows and doors. In thin layers it hardens quickly to form a flexible, water-tight seal. In large quantities, such as squirting a bunch into a cup, only the outside layer hardens forming a "skin" while everything on the inside of the mass remains liquid for a very long time. The reason for this is that silicone caulk requires moisture from the air in order to harden. When the outside layer cures it effectively blocks any additional moisture from getting to the inside. Some very clever individual discovered that if you mix common corn starch (available at any grocery store) with common silicone caulk (in nearly equal parts) moisture from the cornstarch (which is hygroscopic meaning it naturally and constantly absorbs water from the atmosphere) diffuses slowly and evenly into the silicone allowing it to cure throughout all at the same time. Mixed quickly and in equal parts the caulk remains a workable liquid with the consistency of cold cake frosting for about five minutes.
Oogru (the silicone caulk/cornstarch mixture) releases acetic acid as it cures producing some pretty potent fumes. It isn't really harmful (acetic acid is basically vinegar), but it can cause respiratory irritation (use only in well ventilated areas) and possibly skin irritation if it's applied to the skin. Don't use oogru to make molds of body parts!
I brought all the requisite materials with me and set to work making a mold of the dragon's face and eyes. I coated the surface of the resin with silicone lubricant so the mold wouldn't stick too tenaciously. I applied the oogru in two layers: the first layer thinner than the second in an attempt to get as much detail as possible. After the oogru had completely cured I mixed some plaster and soaked a piece of cloth in it, and I wrapped the plaster-impregnated cloth over the oogru mold to form a mother-mold. A mother-mold is essential when working with a flexible primary mold. When the primary mold is removed from the original there is nothing holding the shape of the mold, so reproductions from the mold will never be exactly like the original. A rigid mother-mold acts as a shell holding the flexible primary mold in its original shape once its removed from the original allowing for more accurate reproductions.
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| The mold on the right and the reproduction on the left. Not too bad for my first attempt, if I do say so myself. |
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| This is the side of the reproduction up close. Notice the pronounced curvature of the eye. |
In my next post: Creating a complex eye.
Saturday, June 30, 2012
Pneumatic Rocketry
The United States Civil Air Patrol (CAP) was founded December 1, 1941 (six days before bombs fell on Pearl Harbor). Up until that point US military pilots had been providing critical services around the country; services such as search and rescue, disaster surveillance, and transport of people and materials around the country. With the growing war in Europe however it was becomming increasingly likely that the US was going to have to commit forces to the conflict. Concerned that the roles served by military pilots to that point would be left vacant when the pilots were sent overseas a group of volunteer civilian pilots were recruited and trained to assume the roles. After the war that group of pilots were officially placed under the budget of the newly formed United States Air Force as their Civilian Auxiliary.
My maternal grandparents were pilots with the CAP in the 1960s. They lived in the Arizona/New Mexico area at the time and were involved in searches for missing planes and in flood and wildfire spotting for disaster response. When I became a pilot in 2001 my grandmother suggested that I join. A squadron was finally chartered in my area, and I joined the Civil Air Patrol as a Senior Member a few years ago.
In the past half-century the mandate of the CAP has expanded significantly. Today the focus of the organization is split into three main areas: Emergency Services (disaster response/recovery, transport of materials/people, and search and rescue), Cadet Services (think Boy Scouts with planes), and Aerospace Education. It's the last of these that my post this week covers.
Rocketry is one of the (many) subjects that CAP teaches as a part of our aerospace education program. Our cadets get to build and launch solid-fuel rockets during their training. An early precursor in their training however involves compressed air rockets. Working on a similar principle the air rockets, launched from a platform containing a volume of compressed air, are a safer alternative to pyrotechnic rockets, and they can be launched with far less restrictive safety requirements (such as near a building or during dangerously dry weather).
The Aerospace Education Officer for my squadron is a former employee of NASA. When she joined us she brought with her a pneumatic launch system developed by NASA educators exactly for the purpose of teaching rocketry. Basically it's a sealed pressure-vessel made from 1-1/2 inch PVC which is pressurized by a bicycle pump or air compressor through a tire valve in one end of the pipe. A ball-valve retains the pressure, and when the valve is opened the air rushes through a piece of 1/2 inch PVC pushing a paper rocket off the end of the tube.
There's a small design problem I've noticed with the NASA endorsed pneumatic launcher: the ball valve. It's a magnificant piece of hardware for what it does. It holds pressure very well, and when it's opened it causes little to no additional resistance to the fluid passing through (air is a compressable fluid). Between "off" and "on" however no matter how fast the valve is opened there's a brief period during which the valve is only partially opened. This allows air to escape at a much slower rate than it would when the valve is completely opened. For most applications this is irrelevant, but when the air begins flowing in a pneumatic rocket launcher the rocket begins to launch before the valve is completely opened. I haven't done high-speed video studies to confirm this, but I suspect that the rocket in most cases has been pushed off the end of the launch tube long before the valve has been completely opened. Additionally, because of safety concerns an adult educator has to be the one to turn the handle launching the rocket. It's exciting for kids to watch a paper rocket they've built get launched, but I bet they would have even more fun if they got to launch it themselves.
I had seen a post on Make Blog about someone who had made a home-built t-shirt launcher (similar to the ones used at sporting events). It was charged (pressurized) by a carbon dioxide tank worn as a backpack, and it had an electric push-button trigger that opened a sprinkler system solenoid valve that dumped the pressure all at once into the launch chamber. A solenoid valve is an electro-mechanical valve that uses a diaphragm rather than a ball-valve to regulate flow. It opens almost instantly, and when it's open it allows low-resistance flow almost as efficiently as the ball-valve. A single, hollow-core electromagnet (a solenoid) opens the valve when an electric charge passes through it, and the valve closes when the electricity stops. A screw on top of the valve allows it to be opened manually if the electricity ever fails or if the user just wants to test the system without bothering to apply a current.
My plan was to re-build the launcher completely from scratch, replace the ball-valve with a sprinkler system solenoid valve, and have a remote trigger of some kind that the students can hold and activate themselves. I found the perfect trigger at an auto parts store: a toggle switch covered by a bright red plastic shield that has to be opened in order for the switch to be thrown. I think it's intended for use with nitrous oxide systems, but I'm not certain. It was perfect. It was bright red, and it gave the impression of preparing to launch a missile like in old war movies from the '80s!
I assembled the PVC components in one afternoon. The instructions on the cement I used to glue everything together recommended waiting a day before putting any strain on the joints, so with the down-time I began building the remote trigger. One thing I was concerned about was battery life. I was fairly certain that the solenoid valve would consume an enormous amount of electricity making for short battery life. If someone left the firing switch in the "on" position for too long there wouldn't be enough charge left in the battery for more launches. It's not hard to change a battery. It's just unnecessarily wasteful. I decided to build a timer circuit that would deliver electricity for a very short time and then stop even if the switch was still in the "on" position, saving the battery in case someone forgot to turn the switch back off. For a timer I generally fall back on one of my favorites: the 555!
I designed a timer curcuit using the NE555 in monostable mode. An online calculator gave me the resistor and capacitor sizes I needed to time it for a half-second, and as I did with the feline behavior modification device I had previously built (in fact the circuits are nearly identical) I used a faster R-C circuit to trigger the 555 as soon as power was delivered to the system. It took me an hour to solder but several more hours to debug. On my hand-drawn schematic I had reversed the positions of the trigger resistor and capacitor making the 555 run non-stop. Once I had that problem ironed out I started assembling the timer, the trigger switch, and the power supply (a 9 volt battery) into a black plastic project box.
At this point I discovered a problem in my design. Some experimentation showed me that using a bicycle pump I could get the pressure in the launcher up to 70 psi with twenty pumps which was about as much effort as any reasonable person would probably want to put into launching a paper rocket. It turns out however that the greater the difference in pressure between the high pressure side of the valve and the low pressure side the more energy is needed to open the valve. The 9 volt battery I'd installed in the project box would fire the launcher if the pressure was below 50 psi, but if the pressure was any higher it just couldn't get the valve to open. The difference in effect between 50 and 70 psi was very noticable, so I really wanted to stick with the higher pressure. Some further experimentation taught me that 12 volts would open the valve at up to 100 psi (I really didn't want the pressures to get that high, but it was good to know), and I just happened to have an eight-cell AA battery pack in my random-crap box. The eight-cell battery pack wouldn't fit in the project box though, so I had to re-design the circuit.
Ultimately I decided to keep the 9 volt battery in the project box to power only the 555 timer circuit. That circuit didn't consume very much power, and I'd designed it to run on 9 volts anyway. I only had to re-solder three connections on my circuit board to isolate the 12 volt launch circuit (It would have taken a few more to replace the 9V battery entirely). The eight-cell battery pack I attached to the outside of the launcher with a pair of rubber bands so that the batteries could be easily changed when they got low.
I delivered the launcher at a meeting a few weeks later. Our Aerospace Education Officer was delighted, and testing demonstrated that the device worked just as I had planned. I should mention that I'm the Safety Officer of my squadron, and repeated testing of the launcher indoors (without a rocket on it) prompted some of the other officers to wonder if maybe they'd made the wrong choice in appointing me to the position of "Safety" Officer. I'm not entirely certain I disagree.
What I learned: I really need to spend some time thinking my projects through completely before I start assembling. If I'd done the experiments testing how much power was required to open the valve at different pressures I would have known to design the timer circuit to run on 12 volts instead of 9 or at the very least I wouldn't have been quite so committed to putting a battery inside the project box. I also need to think more critically when it comes to trouble-shooting. When I had the components reversed on the schematic I wired the circuit the same way. Rather than ever wondering if the schematic was wrong I just kept comparing the physical circuit to my hand-drawing and getting more frustrated because I couldn't figure out what was different.
All in all it was a good build. It was 100% successful on the first launch, and nobody has been injured by it yet. The entire project was completed in about two days, which is actually really fast for me.
A few things to note: Around the country a few launchers similar to the one I built (using NASA's plans) have burst when pressurized even after years of safe use. There are a couple reasons why this may be happening: Since the launchers are used outdoors, presumedly during daylight hours, it's possible that ultraviolet radiation (from the sun) has weakened the plastic, lowering the burst point without warning. Another possibility is that mechanical stress on the PVC, either from continuously pressurizing and depressurizing or just from normal wear and tear, has fatigued the PVC in much the same way a piece of metal will break if it's repeatedly bent back and forth. No matter what the cause NASA has removed the designs from their web site and no longer recommends using this launcher for educational purposes.
My maternal grandparents were pilots with the CAP in the 1960s. They lived in the Arizona/New Mexico area at the time and were involved in searches for missing planes and in flood and wildfire spotting for disaster response. When I became a pilot in 2001 my grandmother suggested that I join. A squadron was finally chartered in my area, and I joined the Civil Air Patrol as a Senior Member a few years ago.
In the past half-century the mandate of the CAP has expanded significantly. Today the focus of the organization is split into three main areas: Emergency Services (disaster response/recovery, transport of materials/people, and search and rescue), Cadet Services (think Boy Scouts with planes), and Aerospace Education. It's the last of these that my post this week covers.
Rocketry is one of the (many) subjects that CAP teaches as a part of our aerospace education program. Our cadets get to build and launch solid-fuel rockets during their training. An early precursor in their training however involves compressed air rockets. Working on a similar principle the air rockets, launched from a platform containing a volume of compressed air, are a safer alternative to pyrotechnic rockets, and they can be launched with far less restrictive safety requirements (such as near a building or during dangerously dry weather).
The Aerospace Education Officer for my squadron is a former employee of NASA. When she joined us she brought with her a pneumatic launch system developed by NASA educators exactly for the purpose of teaching rocketry. Basically it's a sealed pressure-vessel made from 1-1/2 inch PVC which is pressurized by a bicycle pump or air compressor through a tire valve in one end of the pipe. A ball-valve retains the pressure, and when the valve is opened the air rushes through a piece of 1/2 inch PVC pushing a paper rocket off the end of the tube.
I had seen a post on Make Blog about someone who had made a home-built t-shirt launcher (similar to the ones used at sporting events). It was charged (pressurized) by a carbon dioxide tank worn as a backpack, and it had an electric push-button trigger that opened a sprinkler system solenoid valve that dumped the pressure all at once into the launch chamber. A solenoid valve is an electro-mechanical valve that uses a diaphragm rather than a ball-valve to regulate flow. It opens almost instantly, and when it's open it allows low-resistance flow almost as efficiently as the ball-valve. A single, hollow-core electromagnet (a solenoid) opens the valve when an electric charge passes through it, and the valve closes when the electricity stops. A screw on top of the valve allows it to be opened manually if the electricity ever fails or if the user just wants to test the system without bothering to apply a current.
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| This is my set-up, unassembled. Notice that there is no ball-valve. The propane tank is just there for scale. The brass device in the upper left corner is a pressure-relief valve. It will open if the internal pressure exceeds 150 psi. The PVC is rated to over 200 psi. |
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| It's a black box with a red switch! Doesn't it look ominous?! |
I assembled the PVC components in one afternoon. The instructions on the cement I used to glue everything together recommended waiting a day before putting any strain on the joints, so with the down-time I began building the remote trigger. One thing I was concerned about was battery life. I was fairly certain that the solenoid valve would consume an enormous amount of electricity making for short battery life. If someone left the firing switch in the "on" position for too long there wouldn't be enough charge left in the battery for more launches. It's not hard to change a battery. It's just unnecessarily wasteful. I decided to build a timer circuit that would deliver electricity for a very short time and then stop even if the switch was still in the "on" position, saving the battery in case someone forgot to turn the switch back off. For a timer I generally fall back on one of my favorites: the 555!
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| This is the fully assembled launcher in launch configuration. The electronic components aren't attached yet. |
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| The electronic components arranged so they can be seen. The red trigger switch is shown opened. |
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| Here you can see how everything fits into the project box. Obviously there isn't room enough for eight AA batteries. |
Ultimately I decided to keep the 9 volt battery in the project box to power only the 555 timer circuit. That circuit didn't consume very much power, and I'd designed it to run on 9 volts anyway. I only had to re-solder three connections on my circuit board to isolate the 12 volt launch circuit (It would have taken a few more to replace the 9V battery entirely). The eight-cell battery pack I attached to the outside of the launcher with a pair of rubber bands so that the batteries could be easily changed when they got low.
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| I'm still learning the software I use to draw these schematics. That explains the differences between this and my Feline Behavior Modifier. The resistor-capacitor (RC) sequence is the simplest electronic timer. The resistor slows the rate at which the capacitor charges resulting in a time that can be easily calculated. I use them here to time the 555 and to trigger it. |
I delivered the launcher at a meeting a few weeks later. Our Aerospace Education Officer was delighted, and testing demonstrated that the device worked just as I had planned. I should mention that I'm the Safety Officer of my squadron, and repeated testing of the launcher indoors (without a rocket on it) prompted some of the other officers to wonder if maybe they'd made the wrong choice in appointing me to the position of "Safety" Officer. I'm not entirely certain I disagree.
What I learned: I really need to spend some time thinking my projects through completely before I start assembling. If I'd done the experiments testing how much power was required to open the valve at different pressures I would have known to design the timer circuit to run on 12 volts instead of 9 or at the very least I wouldn't have been quite so committed to putting a battery inside the project box. I also need to think more critically when it comes to trouble-shooting. When I had the components reversed on the schematic I wired the circuit the same way. Rather than ever wondering if the schematic was wrong I just kept comparing the physical circuit to my hand-drawing and getting more frustrated because I couldn't figure out what was different.
All in all it was a good build. It was 100% successful on the first launch, and nobody has been injured by it yet. The entire project was completed in about two days, which is actually really fast for me.
A few things to note: Around the country a few launchers similar to the one I built (using NASA's plans) have burst when pressurized even after years of safe use. There are a couple reasons why this may be happening: Since the launchers are used outdoors, presumedly during daylight hours, it's possible that ultraviolet radiation (from the sun) has weakened the plastic, lowering the burst point without warning. Another possibility is that mechanical stress on the PVC, either from continuously pressurizing and depressurizing or just from normal wear and tear, has fatigued the PVC in much the same way a piece of metal will break if it's repeatedly bent back and forth. No matter what the cause NASA has removed the designs from their web site and no longer recommends using this launcher for educational purposes.
Monday, June 18, 2012
A recurring source of inspiration.
Almost eight years ago exactly I was married to my lovely wife. When we moved-in together she brought with her two cats, orange tabbys, brothers. Although they're named after characters from the TV series Bonanza they have become known as "The Fat One" and "The Dumb One". That's not to imply that the Fat One is particularly clever or that the Dumb One is particularly svelte, but it's a completely accurate description of the two brothers. The Fat One outweighs a bowling ball, and the Dumb One could be (and has been) out-smarted by a grasshopper.
Cats adjust poorly to new homes. It takes a long time for them to become comfortable in the new, unfamiliar environment. Behavior issues often develop when an adult cat is moved. These two idiots manifested their discomfort by turning the furniture into a surrogate litter box. They pee'd or pooped on every upholstered surface to which they had access, but of particular interest to the two butterballs was my wife's papasan chair. It seems they took turns making trips to the water bowl and back to the chair. After only a month of repeated cleanings and efforts to appease or repel the cats there was no salvaging the cushion on the chair, and it had to be discarded to save the rest of the house from smelling like a dirty diaper.
We replaced the cushion on the chair with a brand new cushion in the vain hope that if it didn't smell like cat urine they might not treat it the same way. We moved the chair to a different part of the room hoping that they may forget it was there. My wife even made a water-proof cover for it just in case the behavior continued. Less than a day after the cushion had been replaced the accursed felines were at it again. It took them less than a week to realize that the water-proof cover was just a cover, and first the Fat One and then his not-quite equally obese brother managed to slip under the cover and hose the cushion once more.
It was time for a new approach.
I collect random stuff. When I go to a hardware or kitchen supply store I simply can't leave until I've looked at the clearance section, and more than once I've taken something home that I didn't need at the time with either the expectation that I might need it in the future or the hope that I could take it apart and learn something. It shouldn't be a surprise therefore that I happened to have a motion-detector driveway light and a servo motor in my random-crap box. I made a trip to the dollar store and Radio Shack to get everything else I needed. My design: a motion detector to "see" the cats, a spray bottle to "discipline" the cats, and a servo to pump the trigger on the spray bottle.
It took a bit of experimentation get all the parts to work together. I didn't want to have to build a servo-driver circuit in addition to everything else I was doing, so I modified the servo to be voltage driven rather than pulse-width modulation (PWM) controlled. Servos are designed to only have 180 degrees of motion which would be just fine if I were using it as a servo rather than just a gear-head motor. I modified it to make it turn continuously in either direction. (I'll make a special post on how I modify and control a servo at a later time) I made a special armature for the servo from a heavy washer and a small bolt since the factory armatures that came with the servo were light plastic that folded under the stresses involved. The bolt stands straight out from the washer so that as the servo turns it keeps hitting (and depressing) the trigger on the spray bottle.
I didn't have to do much to the motion detector. It's powered by mains current (110V AC house current), and when the passive infrared (PIR) sensor detects something the module passes mains current directly through to two light sockets (which I removed to expose the wires). I had hoped to power the servo directly from the motion detector (through a step-down transformer of course), but the shortest time I could get the motion detector to go "high" (conduct current to the wires previously intended for the lights) was five seconds which was WAY more time than I wanted the spray bottle to be continuously spraying.
A 555 timer is a very inexpensive, sturdy, and reliable integrated circuit that can be used to deliver a direct current (DC) of 3 - 12 volts for a precisely controlled period of time that can vary from extremely short to surprisingly long (milliseconds to hours). I use them frequently in my electronics circuits, so don't be surprised if they keep appearing in my blog entries. I won't bother posting a full tutorial about 555s on my blog. Quite simply there are many very well done tutorials elsewhere online. I'll put some links to a few at the bottom of this post.
I had a 9 volt power supply that had previously powered a neck massager I'd purchased at a thrift store (and subsequently took apart to scavenge components). The output wires from the motion detector I soldered to the primary winding of the transformer from the power supply so that each time the output from the motion detector went "high" (the motion detector detected something) the power supply could deliver a steady 9 volts to a 555 timer circuit.
I built a monostable circuit using a 555 timer, modified the circuit to trigger automatically as soon as it received power from the 9 volt power supply, and calibrated the resistor-capacitor (RC) series to run for about about three seconds (see the circuit schematic I used below). At 9 volts the modified servo would rotate completely three times without a load. I didn't want to risk burning-out the 555 timer, so to power the servo I had the output of the timer actuate an SPST solenoid through which the servo received power directly from the 9V power supply.
Long explanation shortened for the attention-span impaired: Motion detector detects something. It passes 110 volts AC for five seconds to a transformer that steps the current down to 9 volts DC. A 555 timer activates as soon as it gets power closing a solenoid switch for 3 seconds (instead of the full five seconds). Electricity passes through the closed solenoid switch powering a gear-head motor (a modified servo) which pushes the trigger on a spray bottle two to three times in three seconds.
Astonishingly, it worked perfectly the first time! I made a frame out of a piece of PVC pipe I cut and flattened, and I mounted the device on a camera tripod for stability and so the height of the sprayer could be adjusted. The cats learned very quickly that getting on the chair meant getting sprayed with cold water.
I wish I could say that the intended result of the entire project (behavior modification) had been achieved. Unfortunately while my contraption worked perfectly the noise made by the modified servo motor was obnoxious, and the massive field of view of the motion detector meant that is was regularly triggering when someone (human sized) walked behind the chair, around the chair, or pretty much anywhere in the same room with the chair. My wife got into the habit of unplugging the device when she got home in the evening, and she would neglect to plug it back in when she left the room. As a result what the cats learned was only that they couldn't get on the chair during the day, but in the evenings it was safe.
Project was ultimately a failure, but the device was a success. That's better than many of my results.
Suggested links:
It's kind of like this: http://twolumps.net/d/20110330.html
555 tutorial - http://www.sentex.ca/~mec1995/gadgets/555/555.html
One way to mod a servo (not mine): http://www.instructables.com/id/How-to-modify-a-servo-motor-for-continuous-rotatio/
I love Wikipedia. A quick lesson on motion detectors: http://en.wikipedia.org/wiki/Passive_infrared_sensor
Cats adjust poorly to new homes. It takes a long time for them to become comfortable in the new, unfamiliar environment. Behavior issues often develop when an adult cat is moved. These two idiots manifested their discomfort by turning the furniture into a surrogate litter box. They pee'd or pooped on every upholstered surface to which they had access, but of particular interest to the two butterballs was my wife's papasan chair. It seems they took turns making trips to the water bowl and back to the chair. After only a month of repeated cleanings and efforts to appease or repel the cats there was no salvaging the cushion on the chair, and it had to be discarded to save the rest of the house from smelling like a dirty diaper.
 |
| Here they are in the chair in question. Notice the size of the beast on the left is approximately that of a Thanksgiving turkey. |
We replaced the cushion on the chair with a brand new cushion in the vain hope that if it didn't smell like cat urine they might not treat it the same way. We moved the chair to a different part of the room hoping that they may forget it was there. My wife even made a water-proof cover for it just in case the behavior continued. Less than a day after the cushion had been replaced the accursed felines were at it again. It took them less than a week to realize that the water-proof cover was just a cover, and first the Fat One and then his not-quite equally obese brother managed to slip under the cover and hose the cushion once more.
It was time for a new approach.
I collect random stuff. When I go to a hardware or kitchen supply store I simply can't leave until I've looked at the clearance section, and more than once I've taken something home that I didn't need at the time with either the expectation that I might need it in the future or the hope that I could take it apart and learn something. It shouldn't be a surprise therefore that I happened to have a motion-detector driveway light and a servo motor in my random-crap box. I made a trip to the dollar store and Radio Shack to get everything else I needed. My design: a motion detector to "see" the cats, a spray bottle to "discipline" the cats, and a servo to pump the trigger on the spray bottle.
It took a bit of experimentation get all the parts to work together. I didn't want to have to build a servo-driver circuit in addition to everything else I was doing, so I modified the servo to be voltage driven rather than pulse-width modulation (PWM) controlled. Servos are designed to only have 180 degrees of motion which would be just fine if I were using it as a servo rather than just a gear-head motor. I modified it to make it turn continuously in either direction. (I'll make a special post on how I modify and control a servo at a later time) I made a special armature for the servo from a heavy washer and a small bolt since the factory armatures that came with the servo were light plastic that folded under the stresses involved. The bolt stands straight out from the washer so that as the servo turns it keeps hitting (and depressing) the trigger on the spray bottle.
I didn't have to do much to the motion detector. It's powered by mains current (110V AC house current), and when the passive infrared (PIR) sensor detects something the module passes mains current directly through to two light sockets (which I removed to expose the wires). I had hoped to power the servo directly from the motion detector (through a step-down transformer of course), but the shortest time I could get the motion detector to go "high" (conduct current to the wires previously intended for the lights) was five seconds which was WAY more time than I wanted the spray bottle to be continuously spraying.
A 555 timer is a very inexpensive, sturdy, and reliable integrated circuit that can be used to deliver a direct current (DC) of 3 - 12 volts for a precisely controlled period of time that can vary from extremely short to surprisingly long (milliseconds to hours). I use them frequently in my electronics circuits, so don't be surprised if they keep appearing in my blog entries. I won't bother posting a full tutorial about 555s on my blog. Quite simply there are many very well done tutorials elsewhere online. I'll put some links to a few at the bottom of this post.
I had a 9 volt power supply that had previously powered a neck massager I'd purchased at a thrift store (and subsequently took apart to scavenge components). The output wires from the motion detector I soldered to the primary winding of the transformer from the power supply so that each time the output from the motion detector went "high" (the motion detector detected something) the power supply could deliver a steady 9 volts to a 555 timer circuit.
I built a monostable circuit using a 555 timer, modified the circuit to trigger automatically as soon as it received power from the 9 volt power supply, and calibrated the resistor-capacitor (RC) series to run for about about three seconds (see the circuit schematic I used below). At 9 volts the modified servo would rotate completely three times without a load. I didn't want to risk burning-out the 555 timer, so to power the servo I had the output of the timer actuate an SPST solenoid through which the servo received power directly from the 9V power supply.
 |
| This is the whole system. There is no schematic symbol for a motion detector, and I didn't feel like drawing out the entire circuit for it. Some of these parts were simply what I had at the time I was building the circuit. The capacitors in particular. |
Long explanation shortened for the attention-span impaired: Motion detector detects something. It passes 110 volts AC for five seconds to a transformer that steps the current down to 9 volts DC. A 555 timer activates as soon as it gets power closing a solenoid switch for 3 seconds (instead of the full five seconds). Electricity passes through the closed solenoid switch powering a gear-head motor (a modified servo) which pushes the trigger on a spray bottle two to three times in three seconds.
Astonishingly, it worked perfectly the first time! I made a frame out of a piece of PVC pipe I cut and flattened, and I mounted the device on a camera tripod for stability and so the height of the sprayer could be adjusted. The cats learned very quickly that getting on the chair meant getting sprayed with cold water.
I wish I could say that the intended result of the entire project (behavior modification) had been achieved. Unfortunately while my contraption worked perfectly the noise made by the modified servo motor was obnoxious, and the massive field of view of the motion detector meant that is was regularly triggering when someone (human sized) walked behind the chair, around the chair, or pretty much anywhere in the same room with the chair. My wife got into the habit of unplugging the device when she got home in the evening, and she would neglect to plug it back in when she left the room. As a result what the cats learned was only that they couldn't get on the chair during the day, but in the evenings it was safe.
Project was ultimately a failure, but the device was a success. That's better than many of my results.
Suggested links:
It's kind of like this: http://twolumps.net/d/20110330.html
555 tutorial - http://www.sentex.ca/~mec1995/gadgets/555/555.html
One way to mod a servo (not mine): http://www.instructables.com/id/How-to-modify-a-servo-motor-for-continuous-rotatio/
I love Wikipedia. A quick lesson on motion detectors: http://en.wikipedia.org/wiki/Passive_infrared_sensor
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