CAN Bus Connectors

We use Talon SRX exclusively (for now) and have a breakout board With lockin .100 spaced connectorsSchematic_PCB-5.0_Sheet-1_20190501155513.pdf (34.0 KB)
PCB_PCB-6.0-drawingguyFINALSUCCESS_20190501161412.pdf (9.8 KB)
SANY0055

Makes finding and fixing and preventing problems easy. Each board plugs into the next one and if you need to diagnose some - no cutting, crimping or soldering etc. just unplug one board and plug a different one in or a jumper etc. Plus all the limit switches and encoders etc plug in with locking .100 spaced connectors too. We had one talon act up this year and just replaced it in less than a minute

I’m looking at this wagon connector, we have a few , but we don’t really understand how they work, and the website isn’t very revealing. Are these simply for terminating the CAN bus loop? How would you use this to connect 2 CAN devices (maybe I’m just blind and tired and can’t see the obvious)

No, in one wago lever nut, all connections are electrically linked. Each 2 position lever nut, should have (for can) two of the same color wires. I can take a photo of how ours are wired tonite. If you put one yellow and one green, or a pair of each into the same connector, your can bus will not work.
Yes, one per pair of same colored wires will work.

Sorry for the stupidity, I just don’t know how those work, if you have a picture, that would be amazing

The connectors you are specifying may be fine, I have not used them.
I have used these connectors:


and I’ve had issues where a misalignment cut through the trunk wire, causing an intermittent connection at first then total disconnection.

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I split the large tangential discussion about topology to this thread: Merits of Star Topology for CAN Bus

Feel free to use this thread to discuss connectors.

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I’ve always took R77 to mean there cannot be another intelligent device between the roboRio and the motor controller. In any of the topologies discussed in this thread the controllers are all directly (logically and electrically if not mechanically) connected to the roboRio. One would hope the inspectors interpret this similarly. Despite my obvious preference I would argue star-type wiring is compliant with R77.

@supermcmatrix I’ve seen several teams using Andersons and I’m curious how it works for your team. Do you use the green/yellow housings and 15 amp contacts? Have you had any connection issues?

The team I have been mentoring this season uses the smallest Anderson PP (15A?) with green and yellow housings. They use a longer strip length, twist the exposed strands togehter and fold the wire over multiple times (4x, I think). They worked well when crimped and assembled correctly, just like with all the other connection methods.

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For clarity, the “CTRE-specified daisy-chain topology” is a 2-wire CAN bus topology. CTRE’s implementation of this bus is including two sets of twisted pair wiring, which are tapped off of on a board in their controller. By daising chaining these wires together, you create a bus.

You can achieve a 2-wire CAN bus in other ways, including through the use of wire taps. See my post in the other thread - Merits of Star Topology for CAN Bus

The wire taps pierce the wire’s insulation, but are not designed to pierce the wire itself. I still wouldn’t attempt to re-use the wire (or at least that section of wire) if you’ve removed a tap from it, as you’ve created a shorting risk.

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We use Powerwerx Anderson powerpoles. To crimp the tiny wires into the PP, we use ferrules.

We used to use Anderson powerpoles for CAN. The 15 amp contacts work, but they have to be squished completely solid (with the flat portion of the crimper) to adhere to the 20 AWG can bus wire. Take extra care to make sure the connection is solid on such a small wire.

[edit] Strain relief is important too. We found such a heavy connector on such a small wire can cause the wire to repeatedly bend at the crimp and eventually fail in fatigue.

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I don’t have a photo of them in use, but did some quick googling…

Something like this, but imagine yellow and green wires.
Does that help clarify?

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Currently my team is using ferrules and then snapping them into wago connectors.(https://www.wago.com/221/us/) however we’re not the happiest with this method because the wagos take up a lot of space and are not inline. But it has worked very well and if you need a step up from wire-nuts (like we did) then I highly recommend this as a quick fix, although my team is currently looking for the next step up.

The lever wagos are great for CAN stuff. We use them particularly often on practice and prototype bases because it allows for quite a bit of flexibility. I think the ferrules are probably unnecessary, the wago lever is designed specifically for stranded wire and I’ve been pretty happy with their performance with just bare wire (both professionally and in robot world).

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Yeah, we use the green and yellow housing with the 15 amp contacts. Occasionally the wire will come out of the housing, but I think if we do what @philso described, that will be prevented, so I’ll try that in the future

Apparently I posted on the wrong fork of the thread …

For 2019, FRC #1018 primarily used the JST connectors that mate to the REV SparkMAX motor drives. I suspect there is a stub length associated with these, probably in the mm range. Where we used the Talons, we used interlocking PWM style connectors for the CAN communications.

We did suffer one can failure over 4 events; we had a connector pull loose from the SparkMAX as the cable was too tight.

We used the built in terminations at the PDP and the RoboRIO for the two bus terminations.

From a physical standpoint, the JST connectors provided very convienient test points to validate CANbus termination.

A growing concern I have with the CANbus are the message identifiers. We need to make sure that we have the ability to specify CAN message identifiers independent from the equipment supplier. This will allow FRC teams to assure that command messages always take priority over response or monitor messages. I suspect that most teams that are using CAN are already encountering collisions on the CANbus.

By the way I found a student that could fabricate the No-See-ums JST contacts, and what a job he did! I would guess 100 terminations and none failed!

The FRC CAN arbitration ID specification is detailed here: https://s3.amazonaws.com/screensteps_live/attachment_assets/assets/001/647/611/original/FRC_CAN_Device_Specifications.docx?1529014633

Note that, since in the CAN protocol clear bits are dominant, a motor controller frame will take priority over a PDP frame (for example).

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Perhaps a better explanation is why CTRE should take precedence over REV

Well, first of all, the manufacturer field is less significant than the device type field, so for example a Rev motor controller will take priority over a CTRE IMU. The choice to have manufacturer field in the arbitration ID at all goes back to the original CAN spec developed for the Jaguars: http://carlosgj.org/Lorentz/7870.SW-RDK-BDC24-UG-7243.pdf

I believe FIRST simply hands out successive manufacturer codes in the order they are requested.

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