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Unread 04-06-2010, 11:16
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JamesCH95 JamesCH95 is offline
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Re: Most Powerful FIRST Team created T-Shirt Cannon

Quote:
Originally Posted by billbo911 View Post
Continuously running any motor in a stalled state is never a good idea. Even a hobby servo doesn't like it. Position feedback keeps the servo in a set position. Once the desired position is achieved, motor current is removed.

Your best bet is to keep the mechanism you are positioning in balance. That way, the motor is primarily used to move the mechanism, not hold it.
After doing a little more research I found that some motors have a published "Maximum Continuous Stall Torque" rating, usually a small fraction of their maximum rated torque. It would be safe to operate the motor under these conditions, though a non-KOP motor designed for this purpose would be capable of a higher sustained torque.

On GOOGLE Books one can find Handbook of Electric Motors By Hamid A. Toliyat, G. B. Kliman which has many of its pages readable and searchable for more information. It has block diagrams and equations one could use to start making a PID loop to control a DC motor.

I heartily agree with your second point, mounting the servo so it is close to the CG of what it's manipulating will undoubtedly reduce the load on whatever motor or servo is used.
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