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Unread 21-01-2016, 09:56
philso philso is offline
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Re: Gearing a Rotating Arm

Quote:
Originally Posted by Chris is me View Post
Arms can be tricky!

I would avoid driving a long lever arm with a live 1/2" hex axle, ...

If you must motorize a long lever arm, it's probably best to do the final reduction for the arm using chain, with the sprocket bolted to the arm to transmit torque. 973 RAMP has some good videos on how to design a simple durable arm power transmission system. The chain can deal with some of the shock loading the arm will face a bit better than a final gear stage could, as there is some flex in the chain and the sprockets are engaged at multiple teeth versus 1 or 2 teeth for a geared system.
A team here in Houston twisted some 1/2" hex so that it looked like part of a wrought iron railing last year by transmitting the torque from the sprocket to the arm through the 1/2" hex.


Quote:
Originally Posted by JamesCH95 View Post
3) Arms can usually stall to hold position, but you must make sure this current is acceptable (see JVN calc for this). I've designed arms that stalled RS775s to hold position with no issues, use your judgement here
The RS550 and RS775's rely on fan cooling. If the stall current is high enough, the windings will start smoking pretty quickly, possibly causing permanent damage to the motor.