Falcon 500 Brake Mode

Does anyone know how much torque a Falcon 500 applies in brake mode?



A mechanism driven by a permanent magnet DC motor with the leads shorted together will generate a braking force proportional to the velocity (if you want a torque analysis, just do everything in angular units):

F = mv\frac{k_v}{k_a}

Where m is the robot mass, v is the velocity, and k_v and k_a are motor parameters described in the SysId documentation. You can probably get good estimates for these from ReCalc for whatever mechanism you have.

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While the Falcon is enabled, you should be able to get significantly more torque than shorting the leads - tell the falcon to go into a speed PID and set the target speed to zero. This should cause the embedded motor controller to actively counter any motion.

I’m mostly concerned about when it is disabled … but I suppose brake mode doesn’t do anything when there is no power?

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Ok, thanks

Brake mode is active when disabled if you set it to be. However, It does not actively prevent movement, it increases resistance as movement increases. This is because the motor is attempting to generate current when it spins and you are feeding that current back into fighting against the rotation.

It is very easy to slowly turn a motor in brake mode and very hard to turn it quickly.

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Ok, that makes sense. Thank you.

These are two different conditions. Disabled means power with no PWM input. Additionally, I have no confidence that all motor controllers are designed to perform the same way in all of the edge cases, especially as legal FRC controllers range from essentially analog devices filtering a digital input to simple digital devices to smart digital devices. My advice is that if you are expecting a given behavior from a motor controller (or other device) that the vendor does not explicitly state, test it yourself. Or ask the vendor directly. Or even better, both.
And I know that testing can be difficult, especially for low resource teams. But the bottom line is that if the difference is enough to matter, it’s enough to figure out a test.

OBTW: Not directly germane, but a case where even the experts incorrectly assumed that old and [then] new motor controllers performed equally:


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