Originally Posted by
howardcano
It's not difficult nor terribly expensive to use an electronic current sink (controlled by a microprocessor, of course!) on the slave motor to vary the load on the motor under test. That's how the fancy dynos for brushed motors worked. But torque output needs to be measured with a separate sensor like a strain gauge to get good accuracy. Just measuring the current loading the slave motor isn't good enough.
The slave motor could simply replace the propeller as the load on the RCBenchmark dyno, since it already has a strain gauge to measure torque.
The flywheel dyno still gives more complete data in a shorter time, but if one needs to run a motor under a continuous load for an extended period of time (perhaps for stress testing), then the absorption dyno the proper device.
What I meant was to try to have the slave motor give a (high enough) constant load, and rather than run the tested motor continuously, as you normally would with a slave motor setup, instead do a full-throttle acceleration, like you would with a flywheel? You'd then analyze the data the same way as you would with a flywheel.
Like I said, calculating "real" torque won't be easy (or maybe even possible), and it won't spin up all the way to the free-spinning RPM, but for the range covered, you should be able to get data to compare different timing settings at the same RPM, and come up with some sort of reasonable timing advance curve.
Maybe the data at the top of the RPM range could be gathered with a lower load setting on the slave motor, and yet more runs?