Quote:
Originally Posted by slibert
We do see (via 2Can diagnostics page) the voltage dropping to around 7 amps at the same time the Amps jump to ~40 when the shutdowns occur - so this hypothesis is very plausible. I'll see if we can get an onboard voltage history made to monitor the minimum voltage on the VBus.
- Via BDC-Comm, after one of these events, we didn't see any other faults than the "comm" faults in the Jaguar. No indication of voltage faults (too bad, because this is the only indicator that makes me question the under-voltage brown-out hypothesis). In the case of a brown-out, what indication should we see via BDC-Comm? Or put another way, is there a deterministic way via on-board Jaguar logs to prove this is what's happening?
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In order to see a fault on the BDC-COMM or 2CAN interface, 3 things need to happen:
- The fault condition occurs
- The Jaguar senses and records the fault
- Either BDC-COMM or the 2CAN polls the Jaguar for the fault status
Faults can happen very fast. Sometimes faster than the information can be polled for and sometimes faster than the Jaguar can sense/record the fault.
Voltage faults are especially tricky because a dropping bus voltage will trigger a fault and then shortly after cause the Jaguar to brown out. If the bus voltage is dropping fast enough, the Jaguar will not have time to sense and record the fault. A Jaguar will brown out just below 6V, so the fact that you're seeing 7V right before the issue most likely indicates a brown-out.
Unfortunately, the rate at which BDC-COMM or the 2CAN can poll for the bus voltage is probably too slow to see the voltage drops that are related to spikes in motor current (when changing speeds rapidly). An oscilloscope would be able to see those short dips, but I wouldn't want to put an o-scope on a robot that's moving around
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Quote:
Originally Posted by slibert
- How to best deal with this case, which is surely going to happen in tele-op mode during competition? After reading further on ChiefDelphi, I'm thinking of detecting the "possibility" we're in that state by exception-handling on commands to the motors. Thereafter, to poll the Jaguar's GetPowerCycled() state (which I assume should transition to TRUE after a reset completes), and if it does indicate the Jaguar was power cycled, to re-initialize it so speed mode works again. Does that sound like a good approach to you?
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You are correct, checking for the PowerCycled state is what you should do. That way you can reset your configuration parameters and regain control of the Jaguar.
Hopefully you can prevent further brownouts by following these tips:
- Inspect crimped contacts and make sure they are making good electrical connections.
- Make sure electrical connections are secure and not vibrating.
- Reduce overall power wire length.
- Make sure your battery is fully charged.
- Make sure your battery is "healthy" (old batteries may look charged, but their voltage drops rapidly under use).
- Implement a ramp in software or use the Jaguars ramp settings to prevent rapid (sub-second) changes in speed.
- Make sure your gearing isn't too low. A low gear ratio can make it easier to stall your motors, therefore dropping the battery voltage lower and more often.
Quote:
Originally Posted by slibert
- Are you aware of any support for a "persistent configuration" (configurable startup defaults) in the Jaguar so that after reboot, in our case, it could enter speed mode automatically?
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There currently isn't a way to do this in the Jaguar firmware.
In addition to all of this, I would encourage you to look at the
2012 Jaguar FAQ and
Jaguar Getting Started Guide. Both of these documents (and more) can be found at
www.ti.com/jaguar. They provide lots of useful information.
-David