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The big problem with many small motors is that they lack torque. Engineers at maxon precision motors inc., Fall River, Mass. (www.maxonmotorusa.com), changed this with their EC4, a 4-mm-diameter brushless-dc motor and gearhead. They used the latest winding technology and the most-powerful magnets available to design a motor with 0.5 W of power. (The longer version EC4 generates 1.0 W of power.) The motor also puts out 0.4 mNm of torque.
The GP4 gearhead has a ceramic gearhead carrier, which lets it handle high input speeds and drive torques. The speed/torque gradient of the motor and gearhead is 50,000 mNm-1. The drive uses no mechanical commutation and there is no cogging.