CAN tutorial

[Aren Siekmeier]

We tried out CAN this year via a Serial to CAN cable to a Black Jag. We had a 6 motor drive train and one motor for the elevator (2 black jags, 5 grey). Our CAN code worked beautifully with the drive train; we had not yet wired up the Jag for the elevator. When we did and started running elevator at the same time, we got lots of lag issues, with safety timeouts and CAN bus errors all over the place, resulting in system watchdogs beyond belief. We had it later confirmed (not sure where) that the Serial CAN bus on the cRio can only handle 6 jags efficiently, so we had it switched out for PWM. Unfortunately, due to <R49> and <R58> we couldn't have the limit switches on the elevator jag, which was a big sad face for the programmers.

Have other people had issues with more than 6 jags on the Serial bus? Is the 2CAN able to handle it? (I've heard it's bus speed, anyway, is much much faster, at about 800MHz?)

We also had one Jag (grey) that gave nothing but a Vbus fault in BDC-COMM and didn't accept any image. It worked flawlessly with PWM, so it was probably a firmware issue.