What is the “best” way to connect devices to the Can Bus? We’ll be using Spark Controllers mostly.
Thanks,
-Brian
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Some will say soldering, as this creates a ‘perfect’ connection that more or less cannot fail. It does make it harder to replace if you need to for another reason, such as a wire getting damaged / replacing a motor with non-removable can wires like falcons.
The best connector is probably the Molex SL. It’s gaining popularity in FRC, especially since the crimping tool can be gotten from FIRST CHOICE. Andymark has started selling pre-crimped Molex SL wires.
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I am biased against the Molex because I hate crimping it.
Last year we used WAGOs, they worked well but have created reliability issues in the off season.
This year we intend to solder and use WAGOs as pit repairs. The proponents for soldering are very vocal about it. It’s reasonable though, it practically cannot fail, everything else can.
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I can’t stand the crimping of Molex. I haven’t played with the new awesome crimpers yet though.
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The crimpers are really nice and make it easier, but the biggest issue I’ve dealt with is strip length.
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Aside from soldering, the cheap alternative we use is crimping on ferrules and using cheap inline levernut connectors off Amazon. Has worked well for us.
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And you’ve opened one of the classic can of worms topics. 
Seriously, though, you’ll get a lot of opinions on this. Our team just solders CAN connections because we’ve had too many failures of other methods. We have in the past used: WAGO connectors of several types, including the WCP ones specifically meant for CAN wires; the small 3-pin connectors (like PWM cables); even very small molex connectors. All of these had problems at some point. The only connection that has never failed us is the simple soldered connection with shrink tube over it.
Now I’m going to duck the brick-bats that will be thrown by all those who will absolutely disagree with me on this. 
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We made an OA post on our wiring practices. Here are the highlights:
Out philosophy is that CAN connections need to be strong, secure, impossible to install incorrectly, and hot-swappable.
We use Deutsch DTM connectors for most CAN connections, which can join many (2 to 12) sets of wires (CAN and wires for sensors), and latch very well. We buy the non-waterproof versions because the waterproof ones are very expensive, and if our robot is getting wet, we’ve got bigger problems.
Wagos/lever nuts are good for prototyping, but too easy to yank out during the stress of competition or install the wires reversed. Molex connectors are fine and easy to disconnect but have been too fragile in our experience, especially if another robot is extending into your robot, they can be smashed easily.
Multiple wires per connection makes swerve wiring and swapping easier, since putting all of one type of wire in one connector makes it impossible to plug motors in wrong when swapping modules.
Soldering should be a great option in theory, but usually, in our experience, due to the difficulty involved we end up with weaker connections than a properly soldered butt joint should be. We use open barrel crimps now which are stronger and easier than soldering.
I’m not saying that you have to go as far as we have, but we were plagued by wiring/connection issues for years, and we made this change for 2024 and never had a single issue, despite a very rough game.
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I wish there were a Deutsch connector that wasn’t nearly so bulky. Something 3x - 4x the size of an SL would be great. DTMs seem huge compared the function they’d serve on a robot. (I will say that I’ve done a lot of them on boats and cars and never seen one fail “unexpectedly”. I have mis-crimped some pins, but those tend to show up in your hand/at the bench/at the dock rather than in service.)
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Deutsch connector’s are definitely bigger and more expensive than standard connectors used by most FRC teams. But the cost of playing a single match is hundreds of dollars (registration + robot build cost / number of matches), and having your robot die because we went with smaller and cheaper connectors feels very shortsighted. We feel they’re worth the tradeoffs.
I believe these are the ones we use for CAN btw, 4 pin for the each swerve module (turn and drive combined into one connector), and we use some 2 pin for other mechanisms with a single motor, and then we have used a 12 pin connector to make a single detachment point for our pivot last year so that we could combine CAN with several sensors.
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Last season we used some “knock off WAGOs”. They were THE worst.
We switched to these XT60 Connectors - Male/Female Pair and they seem much better.
And they are much smaller than the DTM’s (which are also a great choice).
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Strain-relieving the wires on both sides of the connector and tying down the connector body will prevent strain from being applied to the connector.
Last season, the momentum of the Wago lever-nut connectors was sufficient to pull them off the wires.
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I second the use of Molex SL connectors. Here’s our post from last year on our build thread with more details.
As you can see there are varying opinions on this topic and no one right answer, but you should decide what is the right answer for your team.
My team is also firmly in the MolexSL camp. We have had a very high degree of success in building reliable CAN bus (and other) connections with this, and have been able to train many students - even ones new to the work - to make reliable crimps and assemble connections properly. Using the official crimp tool has been key to this. We also own good strippers that can be adjusted with a stop to make getting the strip length right easy, and we buy only name-brand Molex terminals and shells, never clones. Our students are also trained to always have someone experienced inspect their crimps before assembly.
If you didn’t manage to snag a MolexSL crimper from FIRST Choice but want to try MolexSL anyway, I recommend this positioner for an inexpensive Iwiss crimper as a viable alternative. We had the Iwiss on hand and printed/attached one of the positioners to compare to the real thing. It’s not quite as foolproof but still very usable; at less than 1/10th the cost it is a decent way to get started, or as a backup tool.
While I know many teams have gone the solder route, we don’t solder our CAN bus nor do we recommend that approach for others. Why not?
- It is much harder to replace components or reconfigure.
- We don’t like the safety implications of a hot soldering iron on the robot cart, which you will end up needing to have in order to make repairs on the fly. The potential for burns or damage to parts/tools from accidental contact with a not-yet-cooled soldering iron is off-putting for us.
- Fatigue where the solder ends in a stranded wire can lead to breaks, especially for wires that move with mechanisms. Soldering can fail - this is one way, and the other is simply a bad solder joint.
@BFasano since you’re using Spark controllers, I will add some specific advice:
- For SparkMAX, zip-tie the CAN (and motor encoder) wires to the power wires 1-2" away from the controller. This strain-relief reduces flexing at the JST connector, which is where these wires frequently break. Also put a bit of hot glue on the JST as insurance against it being pulled out.
- If at all possible, avoid using the DuPont connectors that come on the CAN wires. They provide absolutely no mechanical support for the connections and are prone to coming apart. The clips that go over them (or a wrap of electrical tape) do help, but only to a point. In my view, the best thing you can do to improve your CAN is to stop relying on these!
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I am curious if anyone has tried using bullet connectors. Pretty solid connections if crimped correctly and colour coding them with a bit of heat-shrink is easy.
Bullet connectors used to be quite common in the 2000’s and perhaps even the early 2010’s but have since fallen out of favor.
Bullet connectors are typically singletons? So you have to disconnect and reconnect each wire individually.
It seams like a small thing, but the move to a keyed single connector is attractive in terms of 1 operation to connect/disconnect both circuits, and also prevent miss-wiring/connection.
I can definitely recommend the Molex SL connectors. They are compact, easy to mate and unmate, feature a locking mechanism, and are keyed to prevent incorrect installation. The main drawback is the cost of the crimp tool.
You can drop to xt30 for CAN 5013 went to those last year, don’t know what they are doing this year though.
We love the Molex connectors. We got the crimper last year and it makes it so easy to make good connections. Just purchased some four pin housings so will see how that goes.
One thing that hasn’t been mentioned is the quality of your wire matters a lot. Look at the number of strands and the gauge. Smaller wires make it harder to get a good crimp.
The other aspect is training. Regardless of your method if you don’t have good training or don’t build in quality control you will have failures.
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I’m pretty sure 2056 used something like this?