Our CAN Tale of Woe

[duane]

The moral of our story is - get the right connectors and the right crimpers.

We spent nearly three weeks trying to get the computer to connect to the CAN network.

On our first pass we purchased standard off the shelf 4 wire telephone cables and connectors. Wire everything up and of course got nothing.

I really don't like that the CAN cables are non-standard telephone cables. I also dislike that we have to make our own cables. This is the primary cause of our problems.

After re-reading the data sheets we purchased a few 6-wire connectors and made new cables for the serial-to-CAN cable. We'll worry about the others later. It still didn't work. Turns out the crimper we purchased is a 4-wire crimper.

We found an RJ-45 crimper and tried that. It looked like it worked, but testing the cable showed that one wire (white) didn't connect properly. The RJ-45 crimper is 8-wires. The outside wires could not be crimped properly due to the shape of the connector.

So, back to the store to find a proper 6-wire crimper. The 6-wire crimper has finally worked for us. We have now re-made all of the cables, flashed all of the Jaguars, and assigned them addresses. Now for some LabView testing with the CAN VIs.

We have one Black Jaguar that is still not responding. I'm glad we got a spare. (Although now we have no spare. )

So the moral of this story is to get the right connectors and the right crimpers. The cables are the key to successful use of CAN.

I like that CAN is a positive locking network. I dislike that it requires non-standard cables to operate. Success would have been much more satisfying if we could just use off-the-shelf cables.

We're off to do more robot testing.

[Shinigami2057]

You can use off-the-shelf cables - CAN-to-CAN connections (not serial-to-CAN) use 6P4C connectors, which means you can use standard RJ-11/RJ-12/RJ-25 phone cable. The only "non-standard" cable is the serial RS-232 cable you make for using the Black Jaguar as a bridge. This can be made with (standard) RJ25 phone cabling, a DB9 modular adapter, and a 100 ohm resistor as show in the Getting Started Guide. All of these were listed with corresponding Digikey part numbers.

I think the moral of the story is for teams to read the directions, twice (perhaps there is an EE analogue of 'measure twice, cut once'). The Jaguar manuals were very clear in the requirements for making the bridge cable. If you try and hack together hardware like many teams (including our team) hacks at code, without reading the directions, you'll get bitten pretty hard.

[duane]

I believe that this is incorrect. Standard RJ-11/12/25 cables (ie for my phone at home) are NOT the same as CAN cables. Look at the wiring diagram for CAN cables and the wiring for standard cables. They are not the same.

[duane]

From MDL-BDC24_GSG.pdf.

--
Use CAN cables to daisy-chain the network between Jaguar modules. Standard off-the-shelf modular RJ11/12/14 cables can be used. Cables must be “straight-pinned,” which means Pin 1 > 1, Pin 2 > 2, and so on. This is also referred to as a reverse-cable because the tabs on the connectors are on the opposite sides of the cable. The CAN cable needs only 4 conductors, but it is acceptable to use a 6-conductor cable and plugs. A suitable 6-ft off-the-shelf 6P4C cable is Digikey Stock No. A2662R-07-ND.
--
While this guide uses the term off-the-shelf, this is not the description of a standard telco modular cable. Standard telco modular cables might be termed "reverse-pinned" and "straight-cable" that is the modular connectors face the same direction, instead of the way that they are shown in figure A-3 of the document.

Sure, you can buy these cables through digi-key. But off-the-shelf means I can walk into any store and buy a telco cable and have it work. It doesn't seem like that is the case.

I would love to be corrected on this point.