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Unread 24-01-2017, 12:53
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FRC #3310 (Black Hawk Robotics)
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Re: Velocity Control - Battery Compensation Term

Quote:
Originally Posted by Ether View Post
Consider the following thought experiment:

Take a CIM whose free speed is 5310 rpm at 12 volts and connect it to a good quality properly assembled and lubed 2:1 gearbox whose output shaft is connected to nothing (no load).

Using the same computation you did above, the CIM's speed would now be 5310*0.8 = 4248 rpm.

Now go to the motor curves for CIM and you'll see that CIM is drawing 29 amps.

Do you believe that? If not, where is the error?


An unloaded, well lubed, 2:1 gearbox has a much higher efficiency factor and thus I would expect a higher CIM speed and lower current. If you lube the gearbox with toothpaste you might create enough friction to draw 29 amps at 4248 RPM.

The 0.8-0.9 factor approximates typical losses seen in FRC for gearboxes + belt/chain + bearing friction + wheel/roller windage.
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