Can I branch the CAN to go to two separate places?

[techhelpbb]

Originally Posted by Andrew Schreiber

It's good to know the limits of the system so you know what you can get away with should you have the need to. Or there's the argument of knowing points of failure... Or there's just the general concept of liking to know things.

True but knowing all the points of failure and liking to know things usually does not play well with a 6 week build. There are many examples of KISS in FIRST builds.

[Andrew Schreiber]

Originally Posted by techhelpbb

True but knowing all the points of failure and liking to know things usually does not play well with a 6 week build. There are many examples of KISS in FIRST builds.

I've never had a terribly good sense of time, did I miss the game release again? Crap, I hate it when I do that.

[techhelpbb]

Originally Posted by Andrew Schreiber

I've never had a terribly good sense of time, did I miss the game release again? Crap, I hate it when I do that.

LOL, yeap it is almost bag and tag already.
Time for robot delivery heroics!

Seriously, not to discourage those who have the time and motivation but there is nothing wrong with the recommended way. So most of those I know that made Jaguars work and other interesting unusual CAN things on an FRC robot (including my Propeller based CAN ESC) leveraged the off season, or knowledge acquired by someone off season, or even knowledge and resources outside of FRC channels.

It is wonderful to give that extra dimension, but as the complexity climbs you leave the common denominator behind. FIRST picked a design for the CAN bus that should make everyone work in the 6 week build season and then made sure to build process around it. We should acknowledge potential alternatives exist but not create a situation where the CSA job requires a CAN BERD/BERD in the spare parts kit.

[FrankJ]

Originally Posted by techhelpbb

...I am not being overly critical of the Jaguar, but FRC11 finally decided to stop fielding them and they now are in a box in my one shop as a result. ...

I look at branches and star in a similar way. It would seem to be an interesting rabbit hole. The recommended design does work so why invest in the alternative?

The CRio Canbus was RS232 to the first jaguar. That limited throughput to the CRio to 9600 BPS. There were significant programming gotchas on the CRio Canbus implementation. For instance it didn't do well with being loaded with more data than the throughput could handle. I think many issues blamed on Jaguars and wiring was actually programming. Anyway as a system the Canbus Jaguars were problematic. The current Roborio/Talon SRX is way better.

By standard, the maximum recommended stub length is .3 M. Which limits star configurations. Although with the short bus length of your typical FRC robot, you can get away with a lot, but I would stick to the standard. TI has a good application paper on CANBUS here.

[techhelpbb]

Originally Posted by FrankJ

I think many issues blamed on Jaguars and wiring was actually programming. Anyway as a system the Canbus Jaguars were problematic. The current Roborio/Talon SRX is way better.

Agreed there were a lot of issues programming could have addressed with the Jaguars and cRIO, and software fixes have been released to the RoboRIO and accessories, but it is hard on students trying to learn programming to address that sort of thing especially with the time it takes to reload test code into the cRIO and to some extent the RoboRIO.

Programmers without deep hardware/firmware familiarity and knowledge often face these kind of issues when they do embedded work and robotic systems. It becomes extremely important to have clear disclosure and support.

In a way, more CAN devices puts pressure and focus on the system providers to find, resolve and support lest we accumulate risk. I am much more comfortable with how we use CAN now.

[FrankJ]

Originally Posted by techhelpbb

..., but it is hard on students trying to learn programming to address that sort of thing especially with the time it takes to reload test code into the cRIO and to some extent the RoboRIO....

I agree completely. I didn't mean to sound as if I was throwing programmers under the bus.

It is one of those gotchas that you do have to look for in real life. Which generally made PWM a better choice unless you really needed something that canbus gave you.

[wireties]

Originally Posted by philso

Yes, it would be better to put the termination at the end of the longest branch. I am not sure if the termination resistors in the RoboRio and PDP can be disconnected easily so this might not be possible.

You just move a jumper. They made it pretty easy!