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It turns out the bimetal "jumping disks" that used to be sold by the old Edmund Scientific required quite a bit of delta T to pop. But it also turns out that the delta T needed is inversely proportional to the radius of curvature of the disks. A big, shallow-dish shaped one wouldn't need much of a temperature
change to pop one way or the other. So apply a piezoelectric coating to one side of, say a 4in. dia. one and paint the other side black. Lay it in the sun, black side up and wait for it to "pop", whereupon it generates a small electric current. If some of this power was used to darken an LCD shutter (used in fast-acting welding masks) placed above it, the disk would cool and pop the other way. Shouldn't take much to turn off the LCD, so most of this half of the cycle is surplus and could be shunted to storage. When it heats up again the cycle repeats. An array would sound like popping popcorn!
[jutta, Oct 17 2004]
(?) I wondered how to power it.
[2 fries shy of a happy meal, Oct 17 2004]
paper heat engine [pashute, Feb 11 2011]
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Those things were great, and "you could put your eye out", which is probably why they vanished from the face of the earth.
You had to manually set the jumping disks after heating them -- they didn't "pop" until cooled. Still, a disk could be designed to pop back and forth, perhaps with not as much motion as the jumping disks had.
||It would be better if you could make the disk jump up onto a sloped, shaded area where it cools and regenerates and then slides back into the sunlight.
||Never heard of Spencer disks before. Excellent.
||solid solar stirling engine is deleted...
||Rather than having it LCD shutter, simply design it with a small hole in the center of the disk and use a solar concentrator. When the disk is unpopped, it's away from the focal plane, and the light is spread over the diameter of the disk. When it's popped, the center is in the focal plane, and the light passes cleanly through the hole, allowing the disk to cool.
||You would lose some power in the out of plane state from light passing through the hole, but the controls get much simpler, and there is no need for a power take off.