Zumo chassis and quadrature encoders

[markroth8]

I’m interested in the Zumo Chassis for a project, but I’d like to get fairly accurate feedback on the distance each tread has moved. It seems like the quadrature encoders do just that but I’m not sure if they will fit into the chassis. Can anyone confirm whether they do (and what else I might need to order), and if not can anyone recommend alternate ways of getting feedback on actual tread movement?

[MrDreamBot]

It may be difficult to mount quadrature encoders on the zumo due to lack of space. A DIY approach I can think of is to paint the tracks with white stripes (across the track) and use QTR reflectance sensors to count the stripes on each track when the zumo moves.

[markroth8]

It may be difficult to mount quadrature encoders on the zumo due to lack of space. A DIY approach I can think of is to paint the tracks with white stripes (across the track) and use QTR reflectance sensors to count the stripes on each track when the zumo moves.

Nice idea - I opened an inkjet printer once and saw something similar for head positioning. Where would I mount the sensors?

[jwatte]

paint the tracks with white stripes (across the track) and use QTR reflectance sensors to count the stripes

That is brilliant

I’d put the sensors in the center of the treads, between the wheels. You can paint the teeth of the belt/tread white, and keep the bottoms black, for example.

[hybernaut]

I looked into this a few days ago, as well. Pololu do make encoders to go with these sprockets (https://www.pololu.com/catalog/product/1217) but they are unlikely to work with the tracks unmodified:

Although the drive sprockets are identical to the hubs used in the Pololu 42×19mm wheels, they will not work reliably with the quadrature encoder associated with those wheels. The tracks do not block enough ambient light around the teeth of the sprocket, so the encoders will be unable to achieve a good contrast between black and white unless you take special measures to shield them.

from https://www.pololu.com/catalog/product/1415

The other approach to wheel encoders is to use micromotors with extended wheel shaft like these:
https://www.pololu.com/catalog/product/2214. Then you can attach an encoding device inside the chassis.

I have not been able to find an off-the-shelf encoder that would attach to these motors, but research is quite fascinating. For example, here’s the Austriamicrosystems AS5040, a contactless magnetic rotary encoder on a chip in the $10 range: http://docs-europe.electrocomponents.com/webdocs/0d59/0900766b80d59dc8.pdf

[Erich]

I had the same need for quadrature encoders for the Zumo chassis.
I’m using successfully the Pololu optical quadrature encoders in my project.
See this post:
https://forum.pololu.com/t/zumo-chassis-with-quadrature-encoders/5994/1

I hope this helps,
Erich