Understanding BLDC Motors and Direct Drive Motors

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BLDC motors (Brushless DC electric motors), also referred to as electronically commutated motors (EC motors, ECMs), are synchronous motors. They get their power from a DC electrical source, through an integrated switching energy supply/inverter. This power source creates an AC electrical signal to operate the motor. This signal is a bi directional current that has no waveform limitations, rather than a sinusoidal waveform. Extra electronics and sensors control the waveform and output amplitude of the inverter.

Frequently, motor areas of BLDC motors are permanent magnet synchronous motors. However, they can be induction, or switched reluctance motors. A BLDC motor could be defined as a stepper engine. Nonetheless, usually, stepper motors are used in motors which are regularly stopped, with their rotors in specified angular positions. With BLDC motors, a couple of the main performance parameters are motor constants Km and Kv. In SI units, these constants are numerically equivalent.

Direct drive motors are engines that take their power from motors with no reductions (like rotary torque sensor). The benefits of these include superior efficiency, as the power does not get wasted by friction (from the chain, gearbox or belt). Also, direct drive motors are less noisy, because they are simple devices, and have less vibrating parts. Thus, normally, the system’s overall noise output is much lower.

Furthermore, direct drive engines have a longer lifespan. With fewer vibrating parts, these are far less likely to fail. Typically, problems in other motors are caused by stress, or by component aging (like stretched belts). These engines generate substantial torque at a small rpm as well.

Direct drive types of motors feature quicker and more exact positioning. The low inertia and high torque facilitates quicker times for positioning on synchronous servo permanent magnet motors. In addition, the feedback sensors are fixed directly onto the rotary part, which enables the exact sensing of angular positions. Better still, in these motors, hysteresis, elasticity and mechanical backlash are all eliminated, because they do not use ball screw or gearbox mechanisms.

The primary drawback of these systems are that they require special features. Normally, motors are constructed to produce optimum torque at fast rotational speeds, invariably 3,000 or 1,500 rpm. This is helpful for many appliances, like electric fans. However, other appliances require reasonably high torque at extremely slow speeds. Phonograph turntables are a good example of this, as they require an extremely precise and constant 45 rpm, or 33.3 rpm.

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