Animation Fundamentals: Motors

Save for the rare cases where movement is provided directly by hand, there wouldn't be animation without motors. They come in a mind-bogglingly vast array of sizes, require many different forms of electrical power, operate at countless different speeds, and deliver equally as many different levels of torque. They also operate on multiple principles, although modelers will most often encounter three varieties: direct current, alternating current, and stepper motors.

My animations rely exclusively on DC motors, although they could work using other motor types. The selection of motor depends mostly on three factors: available space, required speed, and required torque. In every case, I use geared motors. This is because a motor's natural speed is much too fast for animation purposes; also, smaller motors don't have a lot of torque, and gearing them down increases it.

I have an enormous stockpile of geared motors scrounged from VCRs, toys and other old tech; I also make bulk purchases of surplus motors. So called pager motors are a hot item, but while their small size is tempting, their speed is too high and torque much too low to be of much use. Geared pager motors are becoming increasingly available, however, and these can be quite useful where space is very limited.

One other factor that affects my choice is noise, although I know it's not a universal concern. When a geared motor is operating at high speed, it often creates a distracting racket. So, I'll usually look for the largest geared motor I can use, because the larger motor's higher torque means it can get the job done operating at a lower speed.

Ultimately, the selection process is most dependent on the output RPM of the geared motor. In some cases it can be further reduced by adding more gears, but this creates the burden of fabricating gear assemblies, which can be arduous. It's best to find a motor that comes closest to the target RPM straight out of the box.

Also, it bears repeating: slower is better. If you think an animation is the right speed, slowing it down some more often improves the effect.

This sub-micro geared motor is only 6 mm in diameter, and is available with gearbox ratios of 700:1, 136:1, 26:1, and 5.1:1. Typical cost is about $12 each.

This style of geared motor is widely available with a variety of gear ratios for as little as $3 each or less. They also come in right-angle versions. Search eBay for geared micro motor, and you'll see thousands of listings.

Testing and Evaluating

I built the ultimate small motor tester/evaluator; it's been one of my most useful tools.

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