Donkey car odometer

[UPDATE 2019-10-09]: After multiple tests, disk with 3 holes is enough and best to have good velocity estimator with the recommended hall sensor from aliexpress (cf video description below: https://fr.aliexpress.com/item/32925980105.html?productId=32925980105 and magnets are https://fr.aliexpress.com/item/32950950068.html?productId=32950950068). I didn't updated the photos above but I the final version is 3 holes and not 6 holes.

This is an odomometer kit install for Donkeycar HSP-94186, one of the most popular donkeycar.

https://www.robocarstore.com/products/hsp-94186-for-donkey-car

This design has been inspired by Tawn Kramer Odomoter video title "Odometer Install on an Exceed Magnet Rc Car"
https://www.youtube.com/watch?v=l0KUXxfalIQ
I'm using hall sensor from Aliexpress referenced in comments section below video

Magnet( 4*3) and hall board is referenced in Tawn Kramer video description.

But why a kit install ? because the HSP-94186 doesn't have any hole in the mai