Issue with Talons

[RyanN]

We too seem to be having an issue like this.

The problem is noted as a drive train twitch. We're using the default drive code (tank) without any modifications.

The issue is experienced with the Talons; however, we're only using the PWM interface with the Talons. All other motor drivers are connected using the CAN bus.

No one is near the controls when this occurs. It is just a brief twitch. I'm a bit worried reading this because we haven't had a good chance to run the robot much yet.

I looked at the schematic for the Digital Sidecar, and I'm not seeing how it can be an intermittent problem with the DSC.

Link for the schematic can be found here.

The PWM signals originate directly from the NI 9403, so the DS isn't actually supplying the PWM signals. There are three 'chips' that touch the PWM signal.

1. A 10K pullup resistor used for a disconnected DSC. Resistors don't intermittently fail. However, a cold solder joint might cause an intermittent connection; however, this would only affect the system IF AND ONLY IF the 32-pin cable becomes disconnected.
2. A disable chip. There is a chip, in line, with the PWM signals. This relies on a signal defined as OUTPUT_EN. If this signal toggles while sending a NEUTRAL PWM signal to the speed controllers, this could cause the speed controllers to 'twitch.' However, the OUTPUT_EN line should remain HIGH while the robot is ENABLED.
3. A current limiting resistor. It's placed between the disable chip and the actual output. Again, resistors don't intermittently fail, and the only issue I can imagine is a bad soldering job.

Just going on a wild hunch... How many of you experiencing this issue are using the home-made DSC cable that connects your DSC to the NI 9403? It's possible that there is an intermittent or high resistance (bad connection) pin that is causing this issue. Looking at the pinout, OUTPUT_EN is DIO_21 on the NI 9403. First, try a different (real) cable. I don't see much failing in the DSC, so I'm pointing my finger at the cables right now.