If you are looking for a neat science project involving electricity, this is a very unique and interesting option. I got the idea from a website put together by William Beaty that illustrated a "3-soda-bottle" design. You can go there for more background information on how an electrostatic motor works.

In this website I show a "2-soda-bottle" motor I designed and built, which is a modification on his original design. I estimate it spins at about 300 - 500 rpm. Click here to see pictures that show the various components of my design and how they fit together. Click to see a brief video clip showing the electrostatic motor in operation.

In the original 3-soda-bottle design, 2 of the soda bottles served as "stators" that interacted with a third "rotor" soda bottle, causing the rotor to spin. The 3 soda bottles were lined up side by side, with the rotor bottle sandwiched between the two stator bottles. In my design, the rotor bottle sits inside a slightly larger stator bottle on a common axle, such that the rotor bottle is completely enclosed within the stator bottle. The stator bottle has 2 aluminum foil plates (left and right) that take the place of the two separate stator bottles in the original design.

If you are interested in building my "2-soda-bottle" design, the following tips will help you be more successful:

• The rotor bottle should be about 1 cm smaller in radius than the stator bottle so they are close but there is still some "wobble room".
• The axle should be as straight and vertical as possible so that the rotor bottle is symmetrically spaced inside the stator.
• The axle should fit in the exact centre of the rotor's cap to avoid wobbling.
• The plastic tabs on the stator should be bent inward a little toward the rotor, but should not touch the rotor. Instead, extend a short piece of foil past the end of the tab to act as a brush that lightly touches the rotor.
• Timing is important. The brushes should make contact with the rotor plate just as it comes directly opposite the stator plate.
• Use a Van de Graaff generator if at all possible to delever the electrostatic charge.

I think this is a better design for a number of reasons:

• The curved shape of the stator and rotor are the same, maximizing the electrostatic force and impulse.
• The rotor is protected from breezes or drafts that may interfere with its motion.
• The aluminum foil plates on the stator and rotor bottles are separated by the insulating plastic of the stator bottle, allowing close separation while preventing unwanted static discharges across the gap.
• Friction between the axle and rotor cap are negligible, allowing very free-spinning motion.

Good Luck!
John Chase, Edmonton