[pasta]

I know servos don't step, but doesn't the decoder 'count' steps?

But I totaly agree with you, they are completely different. Maybe in this case it was not very clever to oversimplify the problem.

By the way: you point out what I think is great about this business. So much work has been done to control motors very accurate. It's amazing what CNC machines can do today. And also how software optimized motion paths (gcode). And now this hardware. Great stuff!

[jacquesm]

Encoders (not decoders) typically contain a glass disc which contains two 90 degree out-of-phase sinusoidal patterns of light/dark, these are digitized to some arbitrary precision to give you a number of 'steps' around one revolution of the encoder axis. The 90 degree out-of-phase signal is used to be able to determine the direction of motion.

[pasta]

Ah! Thank you for that info. I always thought they used binary disks (black and white or holes).

[TaylorAlexander]

So the term "losing a step" is used on stepper motors, which can be mechanically overpowered to lose positioning. Encoders however will typically always measure the position accurately even if you overcome motor torque and disturb the motor. So in that sense "lose a step" simply does not apply here. Steppers can lose positioning by being pushed beyond their holding torque, while brushless servos will not lose their positioning in the same situation.

[jacquesm]

The fix for that was to bolt an encoder onto the stepper just as with the servo, but in practice these systems do not work very well.