Trying to figure out what connectors should be used for a CAN bus. The vampire T clips are the only ones I have seen used. Could a couple of 3 wire Wago connectors be used (bus in, bus out and line leading to device) or would that mess up the signal?
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So it depends on the layout. Using a 3-wire Wago to connect the wires would create a āBusā topology, rather than a daisy chain, which does work (and Iāve used it for years on FRC robots without issues) but has some cable length limitations, so itās best to know what youāre doing before attempting.
Most teams use PWM connectors (like the kind that come with new Rev and Vex motor controllers) and use cable holders to keep the connections together in a daisy chain. This year my team plans to use these Molex connectors (basically PWM but with integrated locking tabs):
Female Pins
Male Pins
Female Housing
Male Housing
In the past weāve also used Anderson PowerPole connectors for CAN wires, though these are pretty overkill, so it wouldnāt be my first choice (we used them because they were compatible with the āCAN Busā Hubs we were using, but have since upgraded).
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My team uses two 2-pole lever nuts between each device to daisy chain them using both pairs of wires coming out of each device. Iām sure the method youāve described will work as well, though itās not officially recommended by any major FRC CAN device manufacturers.
Iāve officially given up on connector wars at this point, so just do what works for your team and youāll probably be fine.
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Actually, if you read page 46-47 of the Falcon 500 Users Manual, āBusā Topology is listed as an acceptable alternative layout.
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It appears I am using the wrong terminology. We are trying to set up whatever it is called that is not star topology. Where there is a main Bus with lines extending from it to the various devices. So that one CAN wire failure does not take down the whole bus.
Right, thatās a āBusā Topology, rather than a āStarā. The key difference is that in a Bus topology, the green wires are still kept separate from the yellow wires, rather than connecting all wires to a central bus.
So what youāre proposing (connecting each device through a 3-wire wago) would work as long as you use two of them for each device (one for the yellow wire and one for the green), and make sure that your terminators (generally the RoboRio and the PDP) are still on either end of the bus.
Personally, Iāve found it much more convenient to connect all the devices to a central distribution point (while keeping the two wire sets separate) so you donāt have a ton of wire sections. This can be accomplished with something like a pair of grounding bars (one for green, one for yellow) or with something like the power distribution block I linked in my first post. Essentially, either of these options become the āBusā, with the connecting wires being the āstubsā.
This year to save weight and money (Anderson PowerPoles get expensive after a while), we actually had some custom PCBs printed with 20x connections for CAN devices using the Molex connectors I linked above.
We went a slightly different direction with strips of Weidmuller connectors and optional termination shunts at each end. Multiple mounting hole patterns support cutting strips shorter where less connectivity is needed and still be able to use whatās left.
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Thatās sweet. Are those available for purchase?
We originally hadnāt made enough to share beyond a few local folks but maybe we can crank it up and make a few - Iāll refresh myself with the BOM and see what we might be able to do.
In general, responses have been positive - theyāre pretty useful little gizmosā¦
ā Chris Herzog
Note Playing with Fusion released a couple similar options this year, I have a couple of each on order.
I like the flexibility of your design to ācut and fitā exactly the right number of devices.
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Iād also be game to purchase a couple of them for 3468 if you do!
I still like these. Be sure to secure them, even if with duallock or velcro; they do snag on other things if you let them run free.
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But $5/connection 
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Nice, originally I wanted to go the Weidmuller connector route but I had trouble finding a source for the PCB terminals. That said, the Molex connectors we ended up going with have the added benefit of being able to connect them to each other (instead of just the PCB terminals) in case you need a slightly longer length for something, so weāre happy with what we got.
These are a very good choice - latching, inexpensive and close to the proper shape. We use them as well. I know teams like the tee connectors to minimize the effects of a single bad connection but these connectors are very similar (just latching) to the PWM connectors used in FIRST for many years. If you crimp them correctly with the right tool and test them (pull test and continuity test) afterwards they are very reliable.
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I was always under the impression that CAN had to be from one device to the next, no central Bus.
If I used a Bus configuration, how does that wire up? If I had 3 talons, would I wire up the RoboRio -> Talon -> Talon -> Talon? Or would I do RoboRio -> bus, Talon -> bus, Talon -> bus, Talon -> bus. If the bus config, what happens both of the can wires that comes out of a talon? Does one not get used?
It sounds like the bus configuration is safer to use in case one of the devices cuts out
Correct, one set of wires from the speed controllers would not get used.
As to how to wire it, hereās a pair of diagrams I made a while back for this:
One would have to ensure that the ends of the two unused wires are suitably insulated so they donāt short on something. If they do, it will take down the whole CAN network.
This is really a response to the last post by @Chadfrom7226.
Yes, this is correct. In the past we simply left the female PWM connectors that the controllers come with on the unused set of wires and spooled them up to avoid any issues (technically, you could just trim off the extra wires, but we kept them as spares in case something happened to the pair we were using). Covering the unused wires/connectors with electrical tape is also a good practice.
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On my younger sonās team, we used these latching connectors from Hansen Hobbies, or possibly the same part from DigiKey. We used the same crimping tool as for crimping the contacts onto PWM cables. We had zero problems with these in the recommended daisy-chain CAN configuration.
Those worried about a CAN connection going bad and disabling part of their robot need to see if they really need to improve their electrical construction standards. It does not take much effort to get connections with a level of reliability that far exceeds what is needed for an FRC robot. If the quality of the workmanship is such that one is worried about losing even one peripheral (motor controller, PCM, PDP) then one should be worried about the connection at the Roborio where a failure means one loses everything.
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