If you did that, it would be a FABRICATED ITEM, not COTS. Appropriate definitions from the glossary are below:
COTS: Commercial off the Shelf, a standard (i.e. not custom order) part commonly available from a VENDOR for all teams for purchase
FABRICATED ITEM: any COMPONENT or MECHANISM that has been altered, built, cast, constructed, concocted, created, cut, heat treated, machined, manufactured, modified, painted, produced, surface coated, or conjured partially or completely into the final form in which it will be used on the ROBOT
Additionally, note the last portion of R54:
as long as the entire electrical pathway is via appropriately gauged/rated elements.
So, to sum up… if you want to create a custom slip ring, you would need to make it out of properly rated COTS parts. For example, a COTS copper ring, electrically rated for the current (or more) of the associated breaker, and COTS brushes, also properly rated.
In theory, you could make a very rough (and poorly performing, I’m sure) slip ring by stripping a length of wire, forming a loop with it, and using the end of another piece of wire as a brush. Performance would suck (in terms of disconnects, high impedance likely tripping the breaker repeatedly, etc). Consider all that, and then consider R8:
ROBOT parts shall not be made from hazardous materials, be unsafe, cause an unsafe condition, or interfere with the operation of other ROBOTS
Any attempt at a custom electrical component like this would invite heavy scrutiny for safety, even if it passed the other rules.
So, instead I would ask: What’s the intended purpose of such a device? Why do existing COTS supplies not meet your needs? What requirements do you have in your design that could be slightly modified to allow for a different solution?