Use a toy radio control to control big motors for tank-like control.
On the receiver, cut the toy car/tank motor wires off at the motors and connect those wires to the 5 volt relay coils as shown in the schematic for the PIC..
Any speed control can be connected, like a PWM. Use heavy guage wires on all relay contact lugs.
Step 1: RELAY BOARD PHOTOS
Step 2: Toy Radio Control Now Controls "monster Car"
The toy receiver and motors probibly ran on 4 penlight batteries. Now the same toy controls 12 volts to power a car big enough for you to ride.