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Topic: A few questions related to a random project concept (Read 1 time) previous topic - next topic


Sep 11, 2011, 12:38 am Last Edit: Sep 11, 2011, 12:44 am by sciguy Reason: 1
A few questions:

I want to have motors that can be rotated by hand (with an attached wheel or something) but also accurately rotated by the motor.

Could this motor:  30:1 gearmotor, assuming it was disconnected, be turned by hand? (not directly to the shaft, there'd be some kind of wheel attached.)  There wouldn't be very fast, jerky movements. What about the higher ratio motors of the same type, like the 50:1?

Second, a motor driver such as this:  dual h bridge driver would allow me to move the motor and stop it in place, but also set the outputs to a high impedance mode, so the motor could be turned by hand, right?

Third, the back extended shaft of that motor could be used to control a quadrature encoder made of a disk half white, half black, and 2 photodetectors put at 90 degrees from each other from the shaft, right?

So if the answer to all these questions is yes, I could use the mentioned things to make a motor that would be turnable by hand, but also able to accurately move itself (not while being turned by hand obviously)


The only problem I se with the plan is the difficulty of turning the shaft of a 30:1 or 50:1 gearmotor.  When you turn the output shaft by hand you are turning the motor 30 or 50 times as fast.  That's a lot of momentum.

A better choice might be a stepper motor with a shaft encoder.  The encoder will allow you to track the current position and the motor is fairly easy to turn when the windings are not powered.
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If you use a 50:1 a 30:1 motor then you run the risk of wearing out the motors prematurally because instead of just turning the shaft 90 degrees, the shaft will turn 90 degrees, but the motor will turn 25 times, which will wear out the brushes in the motor pretty quickly.

The setup you are thinking about with the encoders seems to be pretty solid, but you might want to consider an H-bridge with motor enable pins so that when you want to turn the motors by hand, you can turn off the motor enable pins off so that the motors will be easier to turn and won't create any back emf through the circuit.

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