I am curios to know if I can utilise the Lego Power range to rotate a transducer to a set point and return to its original position and if so is it able to cycle the movements repetitively? Ideally I would like to set the motor to run to between say 0 degrees around to 240 degrees and then back to 0, 100 times although these figures could change.

Any advice/help is greatly appreciated!


2 Answers 2


It would be difficult to get the exact rotations that you are talking about using Power Functions parts. The servo motor would be your best option, but its range is fixed to +/- 90 degrees from center. If you use a controller with variable speed, it will rotate through 7 steps to get to 90 degrees in either direction.

If you're willing to look at Mindstorms, there is a servo motor with a built-in rotation sensor that was released with both NXT and EV3. These can both be rotated to and from any position, and they are accurate within 1 degree. It sounds like that's the best option to meet your needs.

EV3 servo


If you don't need constant speed motion a better idea would be to use a crank running from any modern motor (ie, geared down internally). That way you can guarantee the end points. For a 240° rotation you might need to gear up after the crank, but as long as there's a spring or constant load in one direction backlash shouldn't be an issue.

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Here;s a really quick sketch of what I mean. Your motor drives the black axle in the foreground, and that rotates a full 360° (continuously). That pushes the cyan lever backwards and forwards, rotating the black gear. Which in turn drives the grey gear which is your output. By judicious fiddling with the gear ratio and the crank lengths you'll be able to get just about any output rotation you want.

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