Comment by hydrogen7800
5 days ago
When I was about 13 I took apart a broken servo from a hobby RC car I had. What a revelation to me. The circuit board was pretty mysterious to me, but I noticed the encoder (didn't know what it was called then) on the output shaft, and immediately realized its purpose. It looked to me a bit like a volume knob. I wondered why the servo motor didn't keep turning, but I realized this thing must be telling the motor "a little more" or "a little less", and it would have to keep making small oscillations back and forth to compensate for external forces, etc, which explained all the twitching noises it made. It was a great discovery at that age.
It's amazing how many parts they fit into such a tiny space, isn't it? Those things are little marvels.
It's a potentiometer most of the time, BTW. Encoders are on the spendy "digital servos"
Yeah, it was a potentiometer. Is an encoder not simply any device that provides a signal proportional to its position or displacement? It had wiper arms (brushes?) that dragged along a conducting surface on a PCB below the rotor.
An encoder is a device that encodes the position -- absolute or relative -- of its shaft as a set of digital outputs.
Most common type uses optical sensors internally, although there are also magnetic types. A quadrature encoder is the most popular and provides two output signals, phase separated by 90 degrees. The phase separation allows the reader to determine which direction the shaft is moving.
A potentiometer used for position feedback is usually just called a potentiometer. I guess it's technically an encoder, but I don't think I've ever heard it referred to that way.
There are also resolvers, discussed somewhere else in this thread, but we won't go there!
HTH
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