Talon SRX CAN Issue?

Hello everyone!

Recently we have been setting up our electrical/control system, and I believe I have encountered a problem.

So we are going to be daisy chaining the Talon SRX motor controllers by using CAN. So we have a HL(Yellow/Green) set of wires going from the roboRio to the one Talon to another, which is then connected to another talon, which in turn is connected to another Talon.

I didn’t use a termination resistor at the end yet because I wanted to see if the TalonSRX lights would turn orange (indicating a CAN bus was connected…) and the first two Talons did that. So I decided to add another Talon to the link and when I turned on the system the LEDs where flashing orange and red quite oddly…

If I add a termination resistor to the end of the CAN bus would that solve this issue, or are the Talons damaged forever…?

Please help!

Thank You so much!

Terminate the end of the bus (preferably with a PDP since it’s easier than adding a 120 ohm resistor). That should be the first step.

If they still blip red momentarily make sure you don’t have common-ID talons.
It’s better explained in section 2.2 in Talon software reference manual and section 16.4). Basically use the web interface to choose a unique ID for each Talon, that is most likely why they are blipping red. Talons default to ID0, so having multiple Talons with the same ID will cause that exact condition.

And then finally recheck your connections. I like to flick each connection point and see if the SRXs blip red at the same time. Just start at the top and wiggle each connection point until you work down to the other end. If the blips are synchronous with you touching the cable then its a wiring issue.

How are you connections being made?

Thank you! I will try what you say :slight_smile:

You described the red as blip, and I think that’s an accurate description of what is taking place here…

Currently we are using PowerPole connectors for the motor outputs and power inputs. As for the CAN connectors I have just spliced them, and then temporarily crimped them with a butt connector.

I will try to assign each a unique ID (can this be done once I have the whole network wired up, or do I have to do it individually like the manual describes?)

I will try to flick the connections too, but just for clarification, are the talon’s damaged or is it an fixable issue?

There is no reason to think they are damaged. You can short CANBus (yellow/green wires) to 12V or ground and it won’t harm the Talon SRX (or any CTRE CAN device).

For proper communication you need 120ohm at each end. Generally the roboRIO provides this at one end, and the PDP (check the jumper) at the other. Not having this MAY be the culprit.

Without 120ohm at each end, you will see some red blips IF the CAN bus is long enough. Though if the CANBus is only a couple feet and you are just playing/learning/testing you can often get away with just terminating one side with no red blips. HOWEVER you are currently in the position of troubleshooting a negative symptom that you are seeing. So the goal is to remove/rule-out each problem one at a time. So the next step is to terminate the floating green/wire pigtail with the PDP, or place a 120ohm resistor (PDP is easier), reproduce the problem, and move to the next and most likely causes (common device IDs or just wiring).

Forgetting to terminate will not damage anything.

Check the recommended gauge on the butt-connectors. I’ve once seen a team use a similar connector, but the connector-size was for a much thicker wire, so the crimps were not deep enough for constant connection.

You can absolutely resolve the common-IDs even with everything connected together. The is no need to separate each Talon (also explained in section 2.2 of talon srx software reference manual).

Also FYI we sell a connector strategy to make mating everything simple, and not permanent…
…and other teams have found ways to connect their CAN Devices that I think are also worth looking at.

Oh hey you actually started one of the threads.

To add to the list, terminations give the majority of CAN problems for all teams. The terminations when viewed as a load model for the transceiver chips terminates the bus in 60 ohms. This happens to be the approximate impedance of twisted pair #22 wire. When the terminations are not present as required, not only are reflections present, but the bus impedance rises to the point where the shunt capacitance starts playing havoc with rise times and noise.
Here is a TI paper on CAN…

Take a look at page 7 & 8.

Thank You!

After some diagnosis and terminating, I was able to assign each Talon SRX an unique ID, and start programing!

Your steps were very helpful, and I feel I gained some valuable knowledge!

Al Skierkiewicz:
I will look into the documentation further to get a deeper understanding of the electrical components.

Again thank you both very much!