Quote:
Originally Posted by jhersh
No... this is a start-up issue only. Can you describe as much about your setup and the behavior you see?
Thanks,
-Joe
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We usually don't have connectivity issues at startup. We'll be driving and all of a sudden we'll loose one or more Jaguars off the bus with timeout or communications errors (haven't looked at the debug information myself, relying on the student feedback for the specific details).
The odd part is that in many cases these Jaguars are performing similar tasks to other Jaguars in the system, so it's not something specific to their actuators.
The Jaguar will drop off the bus, it'll come back and won't respond to further adjustments until we soft boot it. Hence we detect when they fail like this and automatically force a soft boot at this point.
Our most specific issue with this has been on the drive system. We have 2 Jaguars per side connected to CIM motors in the CIMiple gear boxes. We split the encoders and they are 100% isolated from each other and we want to run PID to target a velocity setpoint (it works fine when we don't get timeouts), but even with potentiometers we've seen this (but those Jaguars are high ratio shallow pitch worm drives). It seems to happen less when we use CAN for Vbus and hence loose the external reference, but it still does happen.
Given that we'll be fine for protracted periods of time, then suddenly experience a timeout under hard driving conditions this is what leads me to believe we have some sort of noise issue at work. Obviously if there was a spike that reached logic level on the CAN bus it would cause issues as the CAN bus is basically unmodulated single ended open collector digital. However, when using PWM, the worst you'd get is a shorter than expected pulsewidth at a frequency that is possibly wrong unless you have a periodic source of interference (unlikely in this case at the normal center frequency this system uses). So basically PWM would be more noise immune mostly because the Jaguars aren't fast enough or powerful enough electrically to instantly decompose it and overcome the load's inertia in response.
For the most part, the biggest problem we've had at startup with the cRIO using JAVA has been the bridge Jaguar just outright failing or the bus being improperly terminated. We had one Jaguar that just literally up and died once we turned it off. It was raining that day, we thought maybe water got into it somehow, but I inspected it and it was dry.