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As Printed in MOTION CONTROL supplement to Machine Design

Examples of Extreme Temperature Motors

More and more motion applications are going into the deep freeze.

Computerized railroad crossing gates with northern climates must operate at –40°C, high flying aircraft can subject motors and associated electronics to –70°C, military systems need to function properly in arctic conditions.

Successful applications in these temperature extremes depend on engineers paying close attention to the details of modern motor design.

Permanent magnet materials experience a change in field strength as the magnet temperature varies. Neodymium magnets typically exhibit a temperature co-efficient of –0.11%/°C, and samarium cobalt magnets –0.043%/°C, from 25°C to -40°C. A neodymium magnet undergoes a 7.15% change in strength. While this is a reversible effect it can have a profound effect on motor performance at low temperatures. The basic motor parameters of speed (Ke) and torque (Kt) will change in proportion to the change in the magnets. No-load speed and regulation constants will be affected. Motor speed/torque curves are shifted.

Open loop systems can have variations to speed and closed loop systems can run out of control margins. To make matters worse, lubricants in bearings and gearing thicken adding to the parasitic loading on the system. Frozen moisture can “glue” mechanical parts together and increase breakaway torque.

Magnets are also susceptible to irreversible performance degradation. Extreme cold coupled with peak and in-rush currents in the motor winding can cause permanent demagnetization.

Dynetic Systems overcomes these challenges of extreme temperatures with specialized design techniques, bearings, and gears. Lead screws and gearing can be lubricated with MIL-PRF-23827 aircraft quality synthetic ester grease capable of -75° C and extreme pressure operation.

Finite element analysis techniques are used to optimize the magnetic circuit design and to choose the most appropriate magnet material. Current limiting is used to avoid demagnetization problems. Additionally, integral-heating elements can be incorporated to maintain the motor above ambient temperature when applicable.

Often overlooked, motors subjected to cold temperatures require additional corrosion preventative treatments, and may require complete sealing due to condensing moisture, even when the motor is placed inside an enclosure.

Already known for their quality products, reliable delivery, and excellent sales/engineering support; Dynetic Systems specializes in integrating components into a comprehensive motion package. They offer excellent support for OEMs and manufacturers who need assistance in selecting, sizing or replacing motors.

As a U.S. based motor company with a complete small motor line, Dynetic is an excellent choice for customers with special military, medical, industrial or robotic applications seeking a single source for multiple types of motors.

Reprinted from Motion Control Magazine April 1, 2004

Manufacturer of Highly Engineered Motors and Motion Control Products
SL Montevideo
2002 Black Oak Ave., Montevideo, MN 56265 USA

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