Even through CIM motors are usually on 40A breakers, they can draw significantly more current for brief periods of time. The breakers do not trip instantly at 40.00001A, they trip after X seconds depending on the ambient temperature and current being drawn. Thus, your slip rings should be rated to handle the stall current of a CIM motor.
I don’t think you need slip rings that can handle stall current of a CIM those would be pretty insane 180amps? … Just like the breakers I am sure the slip rings aren’t going to melt at 40.00001 amps. I would contact the manufacture for a more detailed answer on what they can handle.
Bomb squad if I remember correctly uses one of the Mercotac models…
The 12 gauge wiring required by FRC rules for circuits on 40A breakers is also only rated for ~40A. The breaker is designed to trip in a way that reflects how the wiring is heating up. I imagine the conductors in a slip ring have similar behavior and can be similarly rated and protected by the breaker. Basically, if the wiring only needs a 40A rating (130A would require 4 gauge wire…), then a slip ring should be fine with that as well. Please correct me if this reasoning doesn’t work.
Can someone chime in on any differences between these parts of the circuit and their current ratings?
The 2014 robot rules allow slip rings as part of branch circuits “as long as the entire electrical pathway is via appropriately gauged/rated elements.” Since a branch circuit is rated for 40 amps and 12/10 AWG wire, the slip ring should be rated accordingly.
we can’t even find slip rings rated for 40A much less the hundreds of amps stall current. those things would be the size of a truck. and i imagine slip rings can also handle higher peaks as well anyway, i’m just trying to get as close numbers based on continuous ratings as I can.
well our design not only has a cim rotating with it but also a servo(we are doing a 2 speed shifting swerve, or at least attempting to) so we need some kind of slip ring with 5 channels 2 of which needs to be 40A for the cim. i mean we could just stick wires through the center as people have pointed out but we don’t want to have to deal with all the issues related to untangling the wires.
If you look at Pwnage’s CIM in wheel swerve ( I think), they have a piece of code that, depending on how far the swerve module has rotated (with three complete rotations in one direction being the max IIRC) automatically turns the wheel the opposite direction to compensate for rotation of the wires. It’s a fairly simple fix, and they said it had a minimal impact on reaction speed of the robot.
This would remove the need for slip-rings, which would bring the overall cost of the modules down quite a lot while simplifying construction.
Also, if you don’t mind me asking, exactly how are you planning on packaging this swerve module?