Good explainer video for how servo motors work

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There are several completely different types of servo motors. This RC airplane servo motor works great for steering a model. This type of servo system is rarely used in industry (other than automotive and HVAC), because it’s not precise enough, and tends to ‘hunt’ for position.

The servo motors that I work with on telescopes are typically driven with a velocity feedback loop, rather than position feedback. This results in much smoother and more accurate control - down to less than an arc-second of angular error. But the angle encoders cost $10k each.


Pretty arduino specific, and doesn’t get into the internals of the motors, but nonetheless very informative! Very worthwhile for the arduino peeps, I’m sure.

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I was also hoping for more information about the internals of the motors, specifically the internal control circuit (and why feed PWM into a controller rather than I2C, SPI, or more direct control & feedback; the answer likely being that this allows for simple open-loop control with a single PWM or digital output). Here’s a more comprehensive video, with table of contents in the description:


PWM is used because it’s a standard left over from the seventies, when transistors allowed proportional control with servo motors. The older controllers from the fifties that used vacuum tubes used a ratchet to step through three or five different control settings, rather than providing the proportional control as you get with these fancy modern servos.


Thank you, I’ve been wondering!

Pulse Width Modulation has applications in battery management and electric compressor efficiency optimization, but I’ve been puzzled by its ubiquity in modern robots.

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