Three mainboards

[kuon]

Hello,

I am working on a large machine and I am using 2 6XD board to control 8 servo.

I need to add 6 stepper drivers for additional functions. Can I use one 6HC (and if yes, how should I wire the canbus?) or do I need to use 2x3HC?

Thanks

[Phaedrux]

Not sure it's been done before. Will check.

[jay_s_uk]

@kuon I think the difficulty will come in that the 6XD/HC boards have CAN termination resistors pre-soldered in place.
You may end up having to go the route of 2 x 3HC's

[kuon]

@Phaedrux Any official stance on that? Thanks

[dc42]

@kuon the 6XD boards (and recent 6HC boards) have traces on the underside that can be disconnected to remove the CAN termination resistors. You need to gently twist a small (e.g. 2mm) drill bit in each of the 2 holes to remove a small amount of copper so as to disconnect the two pads from each other.

CAN1 is the main CAN connection so it's CAN1_TERM that you need to change in this way.

[kuon]

@dc42 I just noticed that 6HC and 6XD have 2 CAN BUS. Could I just use RJ11 CAN1 to connect daughter boards and use CAN0 to bridge two mainboards? So it would be something like this:

6XD -> CAN1 -> CAN distribution board (toolboards) -> CAN  6XD
|
\ - CAN0 -> 6HC

[T3P3Tony]

@kuon no, CAN0 is not sued for the main CAN bus

[Thorpydo]

@T3P3Tony
As I understand, 2 conductors will need to go to each pin for CAN1_L and CAN1_H for the middle main board(s).

I've created a diagram as I understand the wiring should be. Is it correct?
How is it recommended to make the junction? Insert two wires into the RJ11 connector for each pin? They are made for 1... seems like it will be wonky or not work when inserting two.

https://imgur.com/a/CbCiCU1

(if it's helpful for reference, cross posting from https://forum.duet3d.com/topic/31190/increase-maximum-number-of-axii-to-30)

[dc42]

@Thorpydo it's acceptable to have a short stub (less than 1m long) between a board and the backbone CAN bus.

[Thorpydo]

@dc42
Thanks, that helps.

I think I will use something like these RJ11 phone splitters to keep the junctions easy, clean, and (maybe shielded?)
https://www.amazon.com/Phone-Splitter-Telephone-Suitable-Machine/dp/B0B1D9775P/ref=sr_1_19?hvadid=409957000450&hvdev=c&hvlocphy=9031520&hvnetw=g&hvqmt=b&hvrand=13040326026356310989&hvtargid=kwd-11735544458&hydadcr=19108_11276318&keywords=rj11%2Bline%2Bsplitter&qid=1689094335&sr=8-19&th=1

@kuon
How has your project turned out? What did you do here? Any issues with CAN communication?

[dc42]

@Thorpydo many flat RJ11 cables are crossover cables. This doesn't matter for telephone or broadband use, but it does matter for CAN. So you should check that there is no overall crossover between each pair of boards.