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Originally Posted by apalrd
My opinions on the topic:
-The serial bridge is ~1/8th the speed of the 2can, yes (115,200baud serial vs 1M?) - That's fairly significant if you update the Jaguars fast enough
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Yep, you'd be right. However, we've run at least 6 Jaguars in CAN mode on a robot for the last couple of years now, and the serial to CAN interface has not been considered slow. How often do you plan on updating a Jaguar anyway? To give you an idea, the Jaguar messages that are sent are only 32-bits long. The therefore theoretical maximum bandwidth of messages is 3600 commands PER SECOND. In PWM mode, the Jags can be updated every 5ms or so and the Victors every 10ms. So that's only 200 and 100 commands per second, respectively. Assuming 10 Jaguars and a 60% efficiency, you still get about 200 updates per second per Jaguar. And with fewer, the update rate is higher. My point was that I can't justify the $200 cost for update speeds that I already get.
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-We have yet to use a CAN jaguar, or have any features we cannot do with purely a Victor and some software on our end. We like it this way for some things, as we can modify the control loop to fit our robot (a PID loop isn't great for everything), or add multiple control loops and add the output (e.g. control to distance + control to heading over the two sides).
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Sometimes it's just nice to tell a Jaguar to go to a position using a Set() command rather than having to write or use a PID in your code for it.
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-We will never use a Jaguar in drivetrains because of their high-current shutdown. We had a lot of issues on our Lunacy bot post-season, because after 5 minutes of driving (with super low cof wheels, remember) the shooter could randomly (predictably after a few minutes) shut down due to the extended current draw of forward-reverse slams.
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This year, rate limiting (built-in) will solve most of those issues. However, we have run Jaguars on the drive train for the last couple years and we could not make them reset when using a joystick to thrash the motors back and forth. We only run into those issues when the command for full forward is immediately followed by full reverse. And even THEN we only had that issue because we were doing that with five motors simultaneously. (It was a swerve drive train without completely rotating modules). Even THEN the issue was a voltage dip because of the HUGE current spike of 5 CIM motors reversing direction immediately. Rate limiting solved that issue nicely. It's typically considered unnecessary to slam them back and forth since even a quick rate limit will be imperceptible to humans.
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-I've heard the black jags are far more reliable than the grey ones. We are willing to use a black jag if it gives us an advantage, but we haven't found an advantage yet. They are functionally the same over PWM, but if you only use PWM control, the Jaguars are physically bigger and can't handle the extended high-current draw that the Victors can.
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I think that probably has to do with people removing the screws on the Grey Jags even though they aren't meant to be removed - and thus leaving metal shards in the case.
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-In my time on 33, I've only seen 1 Victor die, ever. We have some of the really old Victor 883's which we still use for practice and mock up robots, and they still work after many years of use. The Jaguars don't yet have that kind of track record, especially after the really bad grey jags.
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Now that, I'd agree with. Jags just need some babying and there are a few fundamental rules that have to be followed to have success. They have their problems, but they're pretty great at the same time.
- Bryce