Benefit of Direct Drive Motors
A direct-drive motor is defined as "a motor that fits within the spindle assembly and directly powers spindle rotation. Direct drive motors do not use a gearbox." This defining characteristic makes direct-drive motors well-suited for certain applications. Direct-drive motors boast numerous features that make them the best choice for many uses.
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How Direct-Drive Motors Work
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To get a rudimentary understanding of how a direct-drive motor works, consider the operation of a turntable. (For those under 35 or 40, a turntable is an old device for playing records.) In a turntable employing a direct-drive motor, the turntable is driven directly by the motor and may actually be part of the armature. This eliminates the need for intermediate drive belts or wheels. Some of the most renowned designs use this approach.
Why Use a Direct-Drive Motor?
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One of the defining features of a direct-drive motor it that it has no power-transmission elements between motor and drive load. This brings the advantages of high dynamic motion with essentially no backlash, and excellent static/dynamic load stiffness which allows for precise motion control. Incorporating large numbers of magnet pole pairs in the rotor aids in high torque generation.
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Benefits of Direct-Drive Motors
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One of the benefits of the direct-drive motor is its economy of moving parts. A gearbox, wheel, drive belt or other intermediate component in a drive-train is one more area for possible failure. As with all things mechanical, the more complex the device the more opportunities for malfunction; and usually the more difficult to repair. The direct-drive motor's relative simplicity of design is a major positive.
Uses for Direct-Drive Motors
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Direct-drive or torque motors are designed for three different types of operation. They provide "high stall torque" ("stand-still" operation) in positioning systems. They provide high torque at low speeds for speed-control systems and they provide optimum torque at high speed for positioning, rate or tensioning systems.
Advantages of Direct-Drive Motors
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A direct-drive motor provides the highest practical torque-to-inertia ratio where it counts the most---at the load. In a direct-drive DC motor, torque increases directly with input current at all speeds and angular positions. Another benefit is the low electrical time constant of torque motors which allows torque to develop very rapidly when voltage is applied. This fast response is an important aid to servo stiffness.
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- Photo Credit close up of professional DJ"s turntable image by TEA from Fotolia.com
