What is the acceptable tolerance of a can terminating resistor? Our 120s are reading 117-118. I think this will be good but just wanted to verify.
The length of FRC Robot CAN networks is generally considered small, and CAN when implemented properly is fairly robust. Termination resistance should be nominal 120Ω and depending on the exact network speed and number of devices communicating I have seen values in the kΩ and over-termination down to 30Ω total bus resistance be functional on CAN networks.
117-118Ω will be perfectly fine if you are choosing not to utilize the built in termination resistors of the PDH/PDP and RoboRIO.
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For the Rio bus that is more than adequate. The Carnivore is higher speed so more picky. But even that should be fine. Otherwise they would specify tight tolerance resistors
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The idea is to match the characteristic impedance of your CAN wiring. This varies by quite a bit, especially in FRC.
Not specifically for this but people should make sure the last band on the resistor is gold because that has +/- 5% tolerance.
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As long as the CAN bus is happy, I’m happy. I don’t look into it much more than that. I think at one point I ran a CANivore at 60 ohms instead of 120 and it was fine.