Solar Thermal Motor

Step 9 Final Step!

Make a notch in the rim of the two tin cans (note: In the picture I used foam cups instead of cans, because I didn't have any cans, but this does not work as well.)
Rest the axle pins in the notches of the cans.

Although your solar motor might be ready to use now, it is a good idea to balance test it first. Give it a spin. If it looks like it if heave on one side, add weight (pins, small brads, etc) to the opposite side until it is balanced.
Note: add the weight to the Styrofoam Back disc, Not to flywheel.

You are done!
Put the whole assembly in the sun - if everything is built right, if will begin the rotate. The more balanced it is, the faster it will spin.

Comments

[DanYHKim]

I'd love to see a video of this in action.
Would it be able to move air through a passive solar air heater? It could complement some of the other solar air projects that rely on thermosiphon effects to circulate air through them.

[justajo]

I saw this just the other day on the PopSci archive, February 1980 (as referenced earlier), before I saw it here. It works...but after a few minutes quit working. After a good deal of tweeking it seems that the stretched plastic only goes through so many re-heatings until there is no stretch left. Re-stretching does not help. You have to make new strips. Or at least that has been my experience. Maybe too much sunlight or heat. As to power, it has very VERY little, just barely able to make the thing turn. That's why it has to be a lightweight as possible and in balance with friction from the axle points to a minimum, thus the styrofoam building material and straight pins. Maybe others have had better luck at making this thing operate for more than a few minutes. Fun and educational, but no practical application to power anything.

[HowTutorial.com]

This is a very clever concept. How did you discover the stretched black plastic shrinks in heat property?

[macrumpton]

The first time I saw this motor was in the 70's in popular science magazine.

[n0ukf]

Most plastics tend to shrink in the presence of heat. Black is used here because it will absorb more heat than others. White or clear will either reflect or pass the heat rays more than absorbing them.

[Mr.NHRA]

This may sound like an unintelligent question but does the motor always rotate the same direction?

[andros1200]

It probably depends on which way the light hits it.