Electric motor converts electrical energy into rotational mechanical power through electromagnetic forces, forming the most widespread actuation technology in modern robotics.
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Electrical motors operate by applying current-carrying conductors within magnetic fields, generating Lorentz forces that produce rotational torque. Brush DC Motors maintain brushes in contact with a rotating commutator to reverse current direction and maintain constant torque direction; this simple mechanism enabled early robot development but requires brush maintenance. Brushless DC Motors (BLDCs) employ electronic commutation via Hall sensors or back-EMF feedback, eliminating brush wear and enabling higher speeds and efficiency, making them the dominant choice in contemporary robotics.
Motor selection depends on application requirements: slow, high-torque applications favour large-diameter, low-speed (LSHS) direct-drive motors; fast, light-load applications employ small, high-speed motors with gearbox reduction. Stepper Motors provide open-loop positioning for discrete motion without encoders, suitable for simple manipulation tasks. Servo Motors integrate feedback control electronics enabling precise position or velocity tracking. Linear Motors eliminate mechanical power transmission, directly producing linear rather than rotary motion at the expense of higher cost and complexity.
Modern electric motors in robotics emphasise integration: embedded encoders provide position feedback, integrated drivers enable communication via CAN Bus or Ethernet fieldbus reducing wiring complexity, and active thermal management preserves performance under continuous high-power operation. Research advances include direct-drive motors reducing transmission losses, in-wheel motors for Mobile Robots eliminating intermediate mechanics, and soft motors using electroactive polymers for compliant interaction. Control innovations exploit motor back-EMF for sensorless speed feedback, model-based current control enabling rapid force changes, and machine learning-based efficiency optimisation that adapts motor operation to varying loads.