FOC + encoder with no Index channel

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
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FOC + encoder with no Index channel

Postby teodor.rosca » 06 Sep 2017, 10:08

Hello people,

I am wondering if it is possible to somehow bypass the software procedures pertaining to finding index pulses for encoders. I am currently exploring an application where I'm interested in speed control only (no absolute position needed) and I am using a simple quadrature incremental encoder with no index pulse on a small outrunner.
From what I can see, an index pulse is expected in all cases, otherwise the motor is run in openloop until the index is found.
Has anyone tried using bare-minimum encoders with no index (and had any success) so far?

- if this is the wrong place to start this thread, let me know and I will move it where it belongs. -


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Re: FOC + encoder with no Index channel

Postby pf26 » 08 Sep 2017, 16:42

How many counts per rev do you have on the encoder, and how many poles per turn on the motor ?
Depending on these, it may not be possible to assume the rotor position accurately enough from the encoder for the FOC to work properly. I guess.

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Re: FOC + encoder with no Index channel

Postby rew » 08 Sep 2017, 19:28

I have an encoder like that. It has 600 pulses per revolution. That's quite enough to resolve "rotor position".

But if you don't know the starting position, there is a problem. You'd have to run the motor "sensorless" and at speed for a while to find the relationship with the encoder.

On the other hand, you could just ignore the encoder for driving hte motor and just use the encoder for the speed info that you need. (but if you're running at speed, the "tacho" is also available as a speed indication)

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