Using a star configuation for Jaguars on CAN

[Peter Johnson]

Originally Posted by Dale

We went so far as to buy the best RJ10 crimpers we could and buying a RJ10-45 cable tester. We tested each cable before putting it on the robot wiggling around the wire while we were doing it. We still had problems.

You make a good point about the RJ45 connectors not seeming to fail though there are always the unexplained loss of coms on the field so who knows. Maybe they are dropping in and out too?

I love the way the daisy chain cleans up the control board, I just don't like having, in our case, 18 flaky connectors in that chain any one of which can bring down the whole robot.

Most of the comm issues on the field were due to one of 3 reasons:
1) Radio reset button getting hit (black button on the front of the old radios). This could happen simply from the mass of the button if the shock was large enough (e.g. going over a bump hard, even kicking could do it if the axis of the shock was in line with the button).
2) cRIO or radio power disconnect. The radio power connection was friction fit. The cRIO power connector uses non-locking screws that like to back out under vibration.
3) Driver station ethernet disconnect (less common).

The FMS this year had really good reporting on radio issues: e.g. it showed whether the disconnect was on the robot or driver station side.

We used CAN this year to 7 Jaguars. We only had two issues with CAN disconnecting: in one, going over the bump hard, some of our pneumatic brass came loose and fell onto one of the RJ11 tabs, neatly disconnecting the cable. We also had one unexplained failure which we believe was a cable working its way loose. Another common failure on the CAN bus we saw on our practice base but not on our main robot was the terminator resistor leads shorting: the way they have you make the terminator seems to be vulnerable to the leads being too long and vulnerable to touching each other (as the pins are adjacent).