Originally published at: https://boingboing.net/2018/05/22/good-explainer-video-for-how-s.html
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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.
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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:
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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.
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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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