A micro brushless DC motor

Model Airplane News, Dec 1999 by Aberle, Bob

Phil Smith is a retired electromechanical engineer in Adrian, MI. For those lucky enough to know him, every meeting or phone call is always a great learning experience. During the past half dozen years, Phil has concentrated his efforts on developing electronic circuitry to support the new thrust into micro R/C. When we meet every year at the KRC E-Fly, the Toledo Show, or the E-Nats, Phil Smith always has something new to show, such as his own version of an infrared micro R/C system, several types of tiny magnetic actuators, or even an electric-motor speed controller that weighs only a gram or two.

At the recent AMA E-Nats in Muncie, IN, Phil couldn't wait to show me his latest design creation:

a micro-size, brushless, DC electric motor. If that didn't catch your attention, let me say it one more time: a microsize brushless DC electric motor that's capable of powering an equally micro-size RIC or free-flight model aircraft. It's only a start and, as Phil describes it, this is only a proof-of-concept prototype.

The photos that I hastily took between contest flight rounds at the E-Nats tell most of the story. Four rare-earth magnets are placed on a rotating disc made out of printed circuit (PC) board. The magnets are roughly 1/4 inch in diameter and 1/8-inch thick. The PC board rotor is epoxied to a wheel-collar-type hub, then to an 1/8-inch-diameter shaft. This shaft is ballbearing-supported.

Phil operates this experimental brushless motor on 4 cells (5 volts) with a current drain of about 250mA (1/4 amp). Although the present configuration would lend itself well to a gear drive, this first prototype just uses simple direct drive.

Power output is claimed to be only on the order of 1 to 3 watts, but this could easily be increased to power some of the smaller parking-lot models. Phil bought a Hall effect surface-mount component from DigiKey, the national mail-order electronics parts specialists. In fact, everything Phil used on this project is readily available.

You might ask: why go to the trouble of making a tiny, brushless DC motor to power a 1- or 2-ounce indoor R/C model? Well, the brushless concept does offer certain advantages:

a wider voltage range (in this case, 3 to 7 cells);

zero break-in time;

long service life (something the little coreless motors can't claim!);

less chance of causing electric noise feedback into the micro R/C system;

a motor that can be retimed quite easily for optimum performance.

Phil's experimental motor is a little cumbersome, but he thinks that it can be improved. The final motor design won't end up as small as a pager motor (8/10 gram), but it will still be very light. He'd like to make it 1/2-inchsquare and possibly have up to several amps' motor current.

Phil would like to communicate with modelers who share his desire to experiment with this type of motor technology. His home phone number is (517) 263-4572, and he will gladly take calls weekdays from 10 a.m. till 9 p.m. EST. This is just another example of the kind of progress we look forward to in R/C model aviation during the next millennium.