Motor Testing: Volts vs RPM

Today I was able to test the motors under no load to get a general idea of how they work. I tested some Turnigy 860kV motors with a bench top power supply, and the eagle tree RPM sensors. I used an RC airplane remote set at full throttle for all tests.

Volt	RPM	Amps
9	8640	0.6
10	9600	0.64
11	10560	0.685
12	11520	0.73
13	12480	0.78

From this graph, a few things are clear:

• RPM and current vary linearly with voltage.
• No load current is very low (~675 mA)
• The kV rating is off by a bias, but a very good predictor of no load.

Concerning the kV rating I found that with 

expected rpm / measured rpm

I came up with .895833 for every result. The measured kV can be calculated by

measured rpm / measured voltage

This resulted in a measured kV of 960, a full 100 more rpm than the manufacturer specified 860kV.

This test is important because it indicates that we can test the other characteristics of the motors (thrust, torque, etc.) and reliably extrapolate the results to different voltages.