[KensRedZed]

Hi Johnno,

A digital tachometer in around the $30 US range will do the job perfectly. The tach comes with reflective tape. Stick it on a gear or round plate that can be secured to the motor shaft.

You can also stick a piece of reflective tape to a tire and multiply by your gear ratio to figure out the final motor RPM.

Walmart or equivalent type store will have one. This is what they look like.

   

Link here.

https://www.walmart.ca/en/ip/OUTAD-Non-c...WETTP1IQOO

I hope this helps?
Ken