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More torque at high speeds.

The new Model 2300 series of motors from ThinGap, LLC, of Ventura, Calif., combine very smooth operation and no measurable cogging with very low eddy current or hysteresis losses and a high peak-to-continuous-torque ratio. The series' eight motors have peak torques of 250 to 600 ounce-inches and maximum continuous speeds of 2,710 to 16,305 rpm.

Behind their performance lies an unusual design. Like all ThinGap motors, they feature a stator made of etched copper sheets. This replaces conventional slotted stator designs, which wind copper wire around stacked iron laminates. Because the copper is continuous rather than separated by gaps between slots, the motors do not hunt between poles when running slowly.

ThinGap separates the etched copper sheets of the stator with insulating layers and laminates the stack into a freestanding, 3-millimeter-thick composite stator with no iron backing. Changing the etching pattern alters the stator's magnetic properties, providing one way to tailor the motor to its application.

"Our motor is very, very smooth. There are no forces between the rotor and stator, so there is no cogging whatsoever. There are no radial stator-to-rotor forces to create wobble. There are no eddy currents and no hysteresis," Colleen Ballew, a marketer at ThinGap, said.

Open frame stator construction provides several advantages. Eliminating gaps boosts copper packing density and the ratio of copper to total coil volume. This raises both torque and peak torque.

[ILLUSTRATION OMITTED]

Ordinarily, torque declines when motors overheat. Eliminating the iron backing enables heat to escape the thin laminated coil more efficiently. In fact, ThinGap claims that the amount of cooling actually rises as motor speed increases. "Because the cooling increases with rpm, the torque increases with rpm, creating very high power and power/weight at high rpm," Ballew said.

As a result, the faster the motor runs (within its rated range), the more continuous torque it produces.

Also, eliminating iron prevents magnetic saturation, which can lower torque. As a result, continuous torque is limited only by cooling. By adding active cooling, engineers can push the thermal limit back even further for even more torque.

The rotor consists of an inner and outer iron ring. Permanent magnets can be attached to either or both rings, which are then bonded together. Since the rotor's inner and outer irons turn together, they generate no eddy currents or hysteresis.

ThinGap describes the model 2300 series as "embedded" motors because of their flexible mechanical design. The company sells both complete motors and stator/rotor sets that buyers can mount on their own custom hubs, mounts, and shafts.

The motors assemble easily because there are no magnetic forces between the rotor and the all-copper coil stator. Users can install motors back to back on a common shaft to boost torque or to produce counter-rotating movements on inner and outer shafts.

This section was edited by Associate Editor Alan S. Brown

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Title Annotation:TECH FOCUS: Power Transmission & Motion Control
Comment:More torque at high speeds.(TECH FOCUS: Power Transmission & Motion Control)
Author:Brown, Alan S.
Publication:Mechanical Engineering-CIME
Geographic Code:1USA
Date:Jul 1, 2011
Words:477
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