{"id":3844,"date":"2019-07-08T16:14:21","date_gmt":"2019-07-08T16:14:21","guid":{"rendered":"https:\/\/novanta.com\/robotics-automation\/technical-paper\/direct-drive-motors-frameless-resolvers\/"},"modified":"2026-01-29T04:40:45","modified_gmt":"2026-01-29T04:40:45","slug":"direct-drive-motors-frameless-resolvers","status":"publish","type":"novanta_tech_paper","link":"https:\/\/novanta.com\/robotics-automation\/technical-paper\/direct-drive-motors-frameless-resolvers\/","title":{"rendered":"Direct Drive Motors, Frameless Resolvers, Ring Encoders"},"content":{"rendered":"\n
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Direct drive motors have been around for many years but it is only very recently, with the demand for higher performance, that they have seen more widespread use. This article compares and contrasts the use of direct drives to more traditional motor arrangements and discusses the available position feedback options. <\/p><\/div>\n<\/div>\n\n

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Direct Drive Terminology<\/h2>\n\n

\u2018Direct Drive\u2019 can be applied to any motor which directly drives a load or rotor without transmission elements such as gears, pulleys or chains. More usually, the term refers to brushless, permanent-magnet, synchronous motors which transmit their torque directly to their load or rotor. Often, they have a short axial height compared to their diameter and a large through bore. \u2018Torque motor\u2019 is also a term that is sometimes used to describe direct drive motors which produce a constant torque when stationary or moving over short angular ranges.<\/p>\n\n

How do Direct Drive Motors Work?<\/h2>\n\n

Direct drive motors<\/a> work in much the same way as most brushless DC motors. Magnets are attached to the motor\u2019s rotor and windings are arranged on the motor\u2019s stator. As the windings are energized, they produce electromagnetic fields which either attract or repel the rotor\u2019s magnets. Appropriate switching or commutation of power to the windings produces a controlled motion. There are linear and rotary direct drive<\/a> motors but rotary versions are by far the most frequently used.<\/p><\/div>\n<\/div>\n\n

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Direct drive motors with diameters of >1m are possible, able to produce torque<\/a> of >10,000Nm. Many direct drive motors are \u2018frameless\u2019 which means that they are supplied without a housing, bearings or feedback sensor. This allows machine builders and system integrators to streamline their housing, shaft and bearing design to optimize overall size, shape, weight and dynamic performance.<\/p>\n\n

The two main reasons for a design engineer to choose a direct drive are dynamic performance and shape factor. Rather than dealing with a coupling, gearbox, belts, or chains, a direct drive motor attaches directly to the load so there is no hysteresis, backlash or \u2018lost motion\u2019 in any direction of movement. The design advantage that comes from motors that are fairly flat with a large hole in the middle \u2013 allowing slip-rings, pipes, and cables to pass through – should not be underestimated.<\/p>\n\n

The advantages of the direct drive approach include:<\/h2>\n\n