Quote:
Originally Posted by dradel
We need the motor to go so far and then stop. It is controlling an arm in our intake system. Thinking of trying a spike, but would like to vary the speed of the motor
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Do you use a sensor to tell you where to stop?
Is it the same spot(s) every time?
What motor are you using?
The Talons brake by effectively shorting together the leads of the motors. If it is a Permanent Magnet motor, like the CIMs (or retains the residual magnetism) the motor acts like a generator and creates power. This provides the braking force. It only works above a certain speed (push a robot on the ground, and if you get it going fast enough, you WILL know when the braking kicks in). It can't brake at a stand still and requires power to maintains position.
Back in logomotion we used some limit switches and a window motor to hold an arm in place. The window motor is not easily backdriveable so we didn't have to worry about brake/coast. If we had to redo this today, I'd try using a Jaguar as the limit switches on that work even in PWM mode. As it was, we implemented software limits in labview.
If you're trying to brake any other motor, you'd probably need an external brake.