Is there a CANFD limitation

Behrouz-AKT

I am planning to use Duet 3 6HC for a PNP setup with 30 feeders . The communication between Duet 3 6HC and the feeders is CANFD . Somewhere in online documentation documentation I read that there is a limit of 20 CANFD devices on the network. Was the limitation based on traffic or something else? Can you elaborate on the limitation?

dc42

@Behrouz-AKT currently there is a limit of 4 CAN-connected expansion boards in the Duet 3 Mini build of RRF, and 20 CAN-connected expansion boards for the MB6HC and MB6XD boards. It's not currently a hard limit, however if there are more CAN-connected expansion boards than that, and they all have motors connected, then sequences of movement commands involving more than that number of expansion boards might get delayed.

Are you planning for each feeder to have its own CAN address? Might it not make sense for one processor to control e.g. 4 feeders?

Behrouz-AKT

@dc42 Thanks for your response. Based on your comments i understand that these limits are based on Duet expansion boards . Correct?

If I am building my own custom board for feeder control there is no physical limits beyond the CANFD limits. I would address each feeder individually and the commands are simple command like "advance to next position" and in relation to a 3D printer it is fairly simple operation. The sequence of operation would be

Move head to position above feeder
Pick component
Advance the feeder
Repeat 1-3 for next head

The feeder are compact devices and therefore would need to have its own board. I seem to recall reading in RFF that there is a CANID range for 3rd party custom boards. Was I dreaming?

dc42

@Behrouz-AKT you can choose whatever CAN addresses you like for the expansion boards. The total number available is 126 but I suggest you avoid using 120 and above as they are default addresses for Duet3D expansion boards.

There are electrical limits on the total length of a CAN bus and the number of devices that you connect to it, however I don't think ~30 nodes would be a problem in this respect.

Behrouz-AKT

@dc42 Thanks for the response. Much appreciated