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Oct 24, 2004, 07:51 PM
Boston, Mass
Joined May 2001
6,463 Posts
Motor Constants & Static Tests For Micro Motors

I've been meaning to finish this up, put it on my web site, and do the related tests. But, I've been too busy with other things, most notably small children. There have been enough questions about micro motors in a few different threads that I thought I should post these two work-in-progress (not much progress lately) tables. Some motors need to be double checked, and others are not done yet, and weights and resistances need to be filled in. However, many motors are done and the data is useful.

These tables apply the method in Jochen Bergmeyer's Feb 2003 Inside Story article. To simplify the presentation of lots of motors in one table I give the max efficiency rpm, max power rpm, and amp draw and power and efficiency for these two points. Note that it is output power that is given.

To see how to use these values, I would suggest reading Jochen's excellent article. To see how to simply apply the max power and max rpm points, I suggest reading my March 2004 Inside Story article on pager motors, where I illustrate how to use this information specifically for the Didel 4.5 ohm pager. The concept is the same for other motors.

What do you need to have to make use of this information? You need a tachometer (cheap at about \$30) and an amp meter. Eventually I'll get around to doing static tests for some of the motors in these tables, and writing it all up as an article. But for now if you want to take the trouble to measure your propulsion setup you can answer basic questions about how close to max power or efficiency you are with that gearing and prop. All the caviets about static tests apply. To see exactly which prop will work best in flying conditions, you need to fly it.

There are two tables. The 3.5V corresponds to one-cell applications, generally in the first minute or two of discharge. The 7.0V corresponds to two-cell applications. Only motors that won't quickly burn out on two cells are included in the 7.0V table, although with a sufficiently high gearing some of the lower volt motors might be able to be used at 7.0V.

Enjoy,
Gordon