servo motor/testing

I have a few servos with no amp/voltage/kv.ke etc. markings
haven't been able to get anything from manf.
I saw a post once on how to calculate based on the voltage and
resistance[?] readings when spinning the motors at a given rpm.
Two of these motors are yaskawa RM78 4 pole brushed.
three are QMC brushless.

can anyone point me to that old post or tell me how to test??

thanks
Carl