Brushless Hub Motor Feedback Question

General topics and discussions about the VESC and its development.
CorruptEnigma
Posts: 1
Joined: 08 May 2017, 14:55
Location: London

Brushless Hub Motor Feedback Question

Postby CorruptEnigma » 08 May 2017, 16:57

Hi

I am looking into building a differential drive robot platform using a pair of brushless hub motors similar to those used in hover boards http://www.uumotor.com/store/26-6-inch-small-hub-motor-250w-20kmh.html. These motors seem really great for this application as they provide a really compact easy solution compared to a geared motor.

I had a question regarding the hall sensor feedback, this is my first time using BLDC motors and I was wondering if the Hall sensors used to find the position of the poles provide sufficient resolution for odometry on a robot? I'm used to using motors with high resolution shaft encoders which provided hundreds to thousands of counts per rotation. So I'm really not sure whether I'll be able to get enough counts for useable odometry.

Thanks

Richard

rew
Posts: 937
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Brushless Hub Motor Feedback Question

Postby rew » 09 May 2017, 05:17

The term odometry to me means that you know how many miles you've gone since the start of the day. That's entirely possible.

The question is of the resolution. The hall sensors simply tell you what phase of an electrical revolution you are in. There are 6 phases. So, if your motor has 23 pole-pairs, there will be 6*23= 138 resolvable steps per revolution. If the wheel is 20cm in diameter, or 62.8 cm circumference, you would get 0.455 cm of resolution.

If that's accurate enough, is up to you.


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