How many teams plan on using CAN this year?

[Bryscus]

Originally Posted by taichichuan

I'm also interested in using a TouCAN Ethernet to CAN bridge this year. That should address some of the latency issues of the serial interface flavor that we encountered last season.

That's interesting that you experienced latency problems last year. We were using 6 Jaguars at one point and we did not experience any noticeable latency (any more than PWM connections anyway). Another help this year could also be the synchronous command - even though if it's truly a latency problem, you'll still experience a delay; all motors could be delayed the same amount however.

There was ONE minor (major at the time) issue we had that most teams should not run into. Last year SPAM used a swerve/crab drive train that used one position motor (to rotate all four wheel modules) and four wheel motors. We used off the shelf modules but we didn't get the ones that continually rotate. Instead, the modules would turn only so far and then spin 180 degrees and reverse the wheel direction. Every now and then when this happened the robot would stop moving for a second or two and then start again, but the position motor would no longer work. If we power cycled the robot it worked again.

Needless to say, it was VERRRRRYYYY frustrating that this was happening. What I finally determined was that when this reversal condition was happening a huge current spike would drop the voltage input to the Jags and reset them (especially when the battery was low). The position motor Jag was set up for position PID control using an encoder. Well, when the Jags reset they go back to open-loop voltage control - hence the reason it would no longer work. The Jag was receiving position commands and just ignoring them because it was in voltage mode! We found that we could even re-initalize a Jag and make it work without power cycling!

When we finally (correctly) diagnosed the problem, we limited the ramp up time of all the motors and corrected the issue. However, this has left a sore taste in our mouths. We will use CAN again this year, but be sure to limit current spikes because Jags CAN be reset when the input voltage dips.

- Bryce