Variable speed

Hello,

I am a wanna-be electronics guy and want to install a variable speed regulator on my tennis ball machine. The schematics can be found at:

https://www.electro-tech-online.com/custompdfs/2011/03/401_switch_box.pdf

I wanted to regulate the current/speed of the rotor motor. Thanks, to anyone who can help, and/or give advice.

All that skem shows is a bunch of connectors and their interwiring. For the task, that's nearly zero information. Need the motors and other circuitry for anything here to be of use.