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I am working on a prop for a film -- I have to make a sign spin in a circle (simple attachment to a motor) and have variable speed.

I know enough to wire the thing, but am having a hard time getting and answer on what size motor to use. The sign will be 20x30 in and made of coroplastic--so light weigh. I can not puncture the sign to attach it to the shaft of the motor, so will have to rig an attaching mechanism. Seems to me the load should be no more than 2 lbs.

Any recommendations for size of motor or which equation I should use to suss it out would be a great help. Thing is due on Friday...

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  • \$\begingroup\$ You need to find/specify the rotational speed, the required acceleration, the voltages and currents that are available. "Size" is a very limited parameter, either as a requirement or an answer. It's about the power and control of power to achieve your goals, constant power comes from rotational speed at the total load, peak power comes from control mechanism and acceleration. \$\endgroup\$
    – Asmyldof
    Aug 25, 2015 at 23:30
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    \$\begingroup\$ At 20x30 inches, unless the sign spins in its own plane, you'll have a lot of wind resistance too. \$\endgroup\$
    – user16324
    Aug 25, 2015 at 23:43

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Everything really depends on how the sign is mounted to the motor. If the sign is centered, then barring a requirement for top speed or how quickly it will spin up, just about any motor will do. If the sign is not centered then at torque calculation is needed. To calculate the torque multiply the weight of the object by the distance away from the center of the shaft. For example one pound two feet away would be two foot-pounds of torque.

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It sounds like you might want something like the turntable from a microwave oven. Find an old microwave that has a turntable motor that still works and take it apart or cut out the parts that you need.

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