How absolutely necessary is the 120 ohm resistor at the end of the canbus on this canivore wiring documentation:
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Pretty necessary. If you go more than a foot or two without termination (CAN FD), you’ll lose communications or have inconsistent communications.
120Ohm resistors are pretty cheap and not too difficult to wire in, is there a particular concern you are worried about?
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we just dont have one right now and have everything else wired up, will it break anything if it isnt there?
Break? No. Work? Also No.
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The CANivore CANFD is pretty fussy, it really wants a true 120+/-5% with a high quality electrical connection to the bus. I’ve gotten away with sketchy nonsense on the RIO bus (bending and sticking bare thru-hole 100Ohm resistor into female header pin contacts) that doesn’t fly on the high speed CAN.
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I am curious about how we wire the 120-ohm resisters on the canbus. My team is mounting a CANivore on our robot, but are unsure on how to wire the resister to the end of the can chain.
Are there any videos or documentation we can look at on how to do it?
You can either solder each end of the resistor to the yellow/green can wires of the last device or use a Wago splicer
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Just verifying you know that modern Power Distribution boards have a CAN terminator built in. Check on yours.
The PDP2 doesn’t. I can only assume that’s why this diagram in particular was changed.
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Those won’t work with the CANivore CAN-FD bus (non-FD-aware devices throw errors on the bus when they see FD messages).
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the source of hours of pain for me 
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I believe we did run into the problem of losing communication after a foot or two, the devices are able to be seen when the wires aren’t too long.
We will order some resistors would these suffice?
we would order some from specifically ctre, but the shipping cost is too high for just ordering some resistors
Those will be fine. Even a 1/16th Watt, 10% resistor would be fine. (Basically, it’s hard to find a nominally 120 ohm resistor that wouldn’t work here.)
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If you want your stuff to work reliably, it is 100% necessary to terminate the far end of both CAN networks in this diagram.
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If you need to, you could also bundle multiple different resistors (we did 3 480ohm resistors in parallel, but you could do other combinations or in series) to get to 120 ohms if you do not currently have a 120 ohm resistor
If you are in the land of prime shipping, you should be able to get them on Amazon probably with lots of friends. Attach them to the ends with solder and heat shrink, wagos, or connects of your choice.
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I recommend these : Playing With Fusion - CAN Network 120-ohm Terminator Resistor simply solder, heat shrink and your good to go !
In short, YES. You need it.
I had a very simple swerve robot that utilize all CTRE compliments (8 kraken + 4 cancoder + pigeon) on CAN FD from CANivore. pigeon is the second device after CANivore, than 4 swerve module all with Kraken - cancoder - Kraken in terms of device in the chain. All cables used are CAN cable come with kraken and built in cable from pigeon. cancoder were soldered using cable came with kraken so there is no connecter within a swerve module.
From my test, resistor inside CANivore needs to be turned on or nothing would work. For just CANivore + pigeon, no resistor at the end is needed and everything works just fine. However, once I start to connect swerve modules in daisy chain, as soon as about the second module is connected, without resistor at the end of the line, the whole CAN bus starts to get funky (fail randomly). Once the third module is connected, nothing would work without the termination resistor at the end of the line.
I’m pretty sure for an actual robot in competition, there will be more device in this CAN bus compared to what I have here.
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Our experience with the CANivore is the bus does not work reliably without termination resistor on both end of the line. To the point of we add a temporary terminating resistor for segment testing. I have a life time supply of 120 ohm resistors.
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I just happened to saw this video. It’s pretty inspiring regard why we need a termination resistor at the end of CAN bus.
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