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Unread 29-01-2012, 21:57
Ether's Avatar
Ether Ether is offline
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Re: Resilience of Motors using PID

Quote:
Originally Posted by Spirator View Post
... PG71 gearmotor. Our shooter requires 6Nm of torque to be held up and the PG71 is capable of approximately 22Nm.

...will the motor draw stall current as it's holding an angle or will it only draw current required to move 6Nm? Is this a reliable way to run the motor?
This is the kind of problem I wrote the motor calculator for.

See attached PDF. To hold 6Nm at zero RPM will take about 3.3 volts. The motor will be generating about 20 watts of waste heat at that operating point.

To get some idea of what this means, the motor is generating 21 watts of waste heat when it is running at 12 volts at maximum efficiency. Of course, at that operating point the motor's internal fan is spinning quite fast and cooling the motor's innards.

If you stall the PG71 at 12 volts, the waste heat is 264 watts. So your scenario is generating only 7.5% of that.

Bottom line, I don't think it will smoke immediately. How long do you intend to hold it like that? Could you add some surgical tubing to relieve some of the load?

Attached Files
File Type: pdf pg71.pdf (31.1 KB, 33 views)

Last edited by Ether : 29-01-2012 at 22:01.
 


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