Originally Posted by
gigaplex
Current and voltage generated by the driven motor doesn't give you mechanical power, without knowing the efficiency of the conversion. And that conversion efficiency is not linear.
If you could calibrate the driven motor with several loads it is possible to get real numbers. Also if you slowly raise up the revs you can still make a dyno like power graph and if you take such a graph from both sides and put them over each other. There is still a lot of info created to work with.