Isolated CAN Bus layout with 6xODrives and 2xBatteries

[Cython]

I’ve read all the forum posts on this topic but I still want to make sure what I plan is working.

My Plan: I want to use an RPI with an Isolated CAN hat. That is connected to two times → 3 Outdrives (24V) and a 4s LiPo. (the RPI is powered by one of the two batteries using a DC-DC converter).
I am playing to run at a high current limit (30A on all 12 Motors) so I also installed some fans.

Some things I learned from other forum posts that I will implement:
I will also be using ferrite rings on the motor leads. I will use shielded cables for the encoders and thick cables for power delivery that will be kept as short as possible. The power delivery will also be arranged in a BUS pattern to have shorter runs.
In addition, I will use XT90S connectors to help with Inductance issues.
I am also using a 4s battery to keep well below the 24V current limit.

To clarify: The CAN bus is planned as one continuous BUS connecting all 6 ODrives, the picture could suggest otherwise.

My question:

1. I read conflicting information regarding the ground connection when using Isolated CAN do I need it or not?
2. Using two batteries, should I connect the two grounds so that there is no voltage difference between them?
3. Anything else I missed regarding ground loops or other dangers?
   
   

Thank you for the help!

[towen]

So first thing is, if you connect all the grounds, there are some obvious loops.

I would connect the ground between the two batteries (this could even be via the chassis, if you have a metal chassis), but leave off the grounds on the CAN bus itself.
With the battery grounds connected via the power wiring, there will no gross potential difference between any of the grounds, so it should all be within the few volts that CAN can tolerate.
If you were to connect the grounds of the CAN, then you risk huge currents flowing in wires that shouldn’t carry current.

@madcowswe do you agree with that assessment?

Also, 12 axes… that’s a lot… What is your application?

[Cython]

Thank you for the answer.
I’m building a quadruped robot dog with my Univeristy. I will make sure to share my results here, as soon as I’m finished.

[madcowswe]

So conceptually I would suggest separating “DC-” from “logic GND”. Connect all DC- together (connect - of both batteries together), and connect all logic GND together. Then only connect DC- to logic GND in a single point. I made this diagram to show the idea: