It was a surplus potentiometer from my electronics repair shop for older tv's which was easy to mount because of the twist tabs, 2000 ohms was the value.
l left it on the unit because under different size batteries, I wanted to vary the back emf -coil collapse voltage (more resistance = less current draw from source supply but less work output fan rpms but increased output voltage charge rate. )
There are no blue prints but the schematic is on the video ,download the video, the instructions to download with firefox browser and download helper links should be in this forum post.
Then pause and screen print if you would like to.they are in hi-definition so
should be clear on larger screens. and print well. good luck on your experiments