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Unread 04-03-2012, 19:27
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Re: Your take on CAN...

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Originally Posted by mikets View Post
Correct me if I am wrong. If the cause is really over current (not because of loose wires etc) and the breakers got cut off, your robot will be cut out no matter if you are using Jaguars or Victors (CAN or PWM for Jaguars). The only difference between Jaguars and Victrors (or CAN vs PWM) is that when the breaker resets, Victors (and Jaguars with PWM) will work again versus Jaguar with CAN may not work because its configuration has been cleared by the "brownout". If that is really the cause, software may be able to help to recover by detecting brownout and reconfiguring the Jaguars if necessary.
I really do like this effort and the value it adds.

However, there is a slight catch. If the system often browns-out the problem will degrade the battery charge and possibly the battery life.

So this is absolutely great for situations where something unusual happens and the drive train is operating within a reasonable range, but it's no fix for a drive train that often draws too much current under normal operation. If a drive train can't move forward on a flat rug surface without any interference and without flowing 60A all this will do is buy you a little time. Maybe you can use it to extend things to the end of a match for a design pushing just past the limit but it'll have consequences later.
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Unread 04-03-2012, 21:20
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Re: Your take on CAN...

Agreed. Software recovery is meant to safeguard rare occassions that browned out Jags such as short stall situatoins. If this happens a lot in normal operations, it must be root caused and fixed.
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Unread 06-03-2012, 18:05
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Re: Your take on CAN...

We had a similar issue last year with our lifter mechanism. It was strictly a mechanical issue. The motors were really on the ragged edge of being able to run the lifter smoothly over the entire range of motion. To help the drivers avoid burning out the motor, we added to our dashboard a current graph. We polled the Jaguars for the current, and had a nice chart. If we saw it going into the red zone (> 40 amps) for any extended period, the driver could dial back on the motor. This detected stalls and binds in the lifter, and had nothing to do with the Jaguars or CAN bus other than to give us the ability to peer into them and see what was happening.
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