Just a thought.
The speed controller designed to be used on the electric scooter, which uses one 250 watt motor for propulsion and costs less than 15 bucks, work as a speed controller for the tanks?
One controller for forward and one for reverse, on each motor?
2 contollers for each motor
$15 x 4 = $60.
Full proportional control in forward and reverse.
One servo should move a thumb contol lever forward and backward. May need a leverage assist though.
The controllers are designed to work with 12v to 36v and up to 30 amps.
For those of us who know how to make expensive smoke....maybe a more knowlegeable builder can review their specs?
Hope this helps .
Dan "cheap" Whitney