Hello to all,

I would like to know if anyone has measured the actual efficiency of our setups. That is, not measuring only U*I = P [Watt], but also the actual efficiency based on prop RPM and n100W-values, where available. I'm interested in this because many posts are about Watts measured U*I, but that's "P_in" (Watts as measured at the battery leads), not "P_out", which is IMHO a completely different story altogether - ESC heat, motor heat and prop efficiency do play a big part in getting the most out of our setups.

One crucial question: are n100W-values of our props (18' to 22' or even bigger) available, and if so, where? I'm eager to measure my Plettenberg setup with this method.

Regards
-Fabrizio

A couple people on rcgroups' Power Systems forum have built their own motor testing system. It is a device which mounts the motor on the front of a metal tube and has a strain gauge on a thin section of the tube. This measures motor output torque. Then a hand-held tachometer tells angular speed, so output power is known independant of prop efficiency. A standard wattmeter tells input power. The device I saw pictures of was good to about 1600W with a 17" prop, so not quite large enough for a 2m pattern motor, but it could easily be scaled up.

Hi,
There is a commercially available dynamometer available for wet power.
I don't remember the manufacturer's name, but it was a beautifully made item: made with fine plywwod, like the sort used for piano pin-blocks.
The torque meter was a simple arm and weight. No fancy instrumentation was required, just a protractor and a tach.
later,
Dean P.