Optimizing Method Applied

June 1, 2000
Consider, for example, specifying the lightest possible three-phase dc-brushless motor for use in a miniature aircraft.

Consider, for example, specifying the lightest possible three-phase dc-brushless motor for use in a miniature aircraft. The stator ID and stack length is set by the design at 0.38 and 0.17 in., respectively. The motor is to be fitted with a gear reducer and an electronic controller. Required power output is 2 W at 5,000 rpm with at least 80% efficiency. Because high-power density is an important factor, use high-energy neodymium magnets with an air gap flux density of 10,500 gauss, and Hyperco stator iron with a flux density of 15,000 gauss. The combination results in a b of 0.7. A four-pole stator seems reasonable given the small motor size. In general, pole count scales with motor size. The peak of the b = 0.7 curve on the four-pole plot gives a CMO = 0.2, and = 0.5.

Next, calculate KO, a factor directly related to the tightness of the stator windings, and therefore to the manufacturing cost. Estimate the following parameters:

K = about 1.2.
= 0.45 to 0.65 typically; choose 0.5
KW = 0.7 to 1.0 for motors in the power range of 1-1,000 W; choose 1.0

Next, calculate KET = 2.580, and finally KO = 0.402. Substituting these values into the KM expression gives:

Because the required power output at 5,000 rpm is 2 W, the output torque is 0.541 oz-in. Use a 6:1 gear reducer so that the torque at the motor is approximately 0.090 oz-in. From the definition of KM, the losses in the motor windings are 0.21 W, or about 10% of the required output. Motor efficiency is 90%, allowing for a total of 10% for motor friction and transmission losses.

Sponsored Recommendations

The entire spectrum of drive technology

June 5, 2024
Read exciting stories about all aspects of maxon drive technology in our magazine.


May 15, 2024
Production equipment is expensive and needs to be protected against input abnormalities such as voltage, current, frequency, and phase to stay online and in operation for the ...

Solenoid Valve Mechanics: Understanding Force Balance Equations

May 13, 2024
When evaluating a solenoid valve for a particular application, it is important to ensure that the valve can both remain in state and transition between its de-energized and fully...

Solenoid Valve Basics: What They Are, What They Do, and How They Work

May 13, 2024
A solenoid valve is an electromechanical device used to control the flow of a liquid or gas. It is comprised of two features: a solenoid and a valve. The solenoid is an electric...

Voice your opinion!

To join the conversation, and become an exclusive member of Machine Design, create an account today!