So I pulled one motor off the incomplete arm. The wiring is actually labeled hall effect. I took the motor and placed it in the lathe to try to carefully cut the end cap off to inspect the board and it does appear that there’s a hall effect sensor setup inside of it. That said, even if it’s not useable, the output shaft side of the gearbox seems to be accessible at all the joints and seems to all have some form of magnetic encoder mounted to them.