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Unread 08-02-2011, 11:41
dyanoshak dyanoshak is offline
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AKA: David Yanoshak
FRC #2158 (ausTIN CANs)
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Re: Why are Limit Switches outlawed with PWM, but not CAN?

Quote:
Originally Posted by Al Skierkiewicz View Post
If motors are in motion due to the state of the limit switch(es), then the FMS cannot stop them.
That's not how it works. When a NC limit switch opens the circuit, the Jaguar shuts off the motor, regardless of the commands being sent to it.

When the limit switch closes the circuit (or the jumpers are in place), the Jaguar responds to commands. When the FMS sends a disable command, the cRIO shuts off the PWM signal going to the Jaguar. The Jaguar needs to see a signal every 100ms or else it shuts off and goes into a no-signal safe state. Therefore, when the cRIO shuts off PWM at the request of the FMS, the Jaguar shuts off within 100ms.

You can think of the same thing happening with CAN, however it is implemented differently.

I hope this clarifies things.

-David
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