CAN

[arthurlockman]

What do people think about the CAN system? Last year, we used the built in can-serial system, and it was awful. It jittered way too much, and no matter what we did, it wouldn't stop. At competition, we heard about the 2CAN system, which, according to the team we talked to, fixed their jitter and oscillation. My question is, what do other teams use? Given the price of the 2CAN, our mentors are hesitant to buy one without getting more recommendations. What do you think?
-Arthur

[ratdude747]

Never had serial can issues... the only jittering we had was due to a programming bug (slow code and PID do not mix).

It went so well (once we figured it out) that I even wrote a whitepaper on it...

BTW, the robot ran mecanum to drive, and had 4 other motors in use on CAN (2 arm lift motors, a wrist motor, a claw motor, and a minibot launch motor). everything was smooth.

[Phalanx]

We used CAN for our drive system last year with 4 Jaguars & 2CAN on PORT2 of our CRio and didn't have any problems or issues with CAN.

The keys are:

1) 100% proper wiring and termination for the CAN network. Any faultiness with that you will have issues.

2) A good charged battery. Low battery will cause brown outs.

3) Make sure your Telop code is executing under 20ms.

We'll be using CAN again this season with 2CAN on PORT1 with the new 4 port CRIO.

[apalrd]

A few comments on CAN:

-The serial bridge is speed limited. The 2CAN can talk much faster on the CAN bus, so theoretically you can update more motor controllers faster without lag.

-I spent a good deal of time over the summer working on an automotive/military CAN bus (I can't talk about), and termination and bus design is VERY IMPORTANT for CAN. If you don't terminate the bus, or have weird splits and branches (e.g. you try to star wire it instead of daisy-chain, or your taps are too long relative to the bus length), it will hate you.

-I have yet to find an FRC robot that *NEEDED* a Jaguar instead of a Victor, the need for CAN is (to me) yet to be seen.

[ratdude747]

Originally Posted by apalrd

I have yet to find an FRC robot that *NEEDED* a Jaguar instead of a Victor, the need for CAN is (to me) yet to be seen.

well, technically all you *need* is a STAMP based (pBASIC) IFI controller (2003 and earlier).

That said, the cRIO and CAN make life a lot easier. Not needed, but still nice.