Does anybody have a way of buffering the motor drive to a larger motor given that it polarity switches to change motor rotation ?
(Later) After some research I thought a high current H-bridge should do the trick, but when I scope the rover motor drive signal this wont work. When the motor rotates forward the drive signal looks OK, one side 0 volts and the other PWMing to +5 volts, but in reverse BOTH sides of the drive PWM with respect to ground. Couldnt find any explanation for this as any schematics of the rover dont show how the PWM signal is generated. Gave it more though and am going to use the forward PWM buffered to drive the larger motor and a relay driven by a discrete output to select forard/reverse, diagram attached.
Why not attach a link to the data sheet for the driver instead of a picture? A motor driver does not use the system ground because it is NOT attached to a motor winding. You seem to be measuring something other than what is being sent to the motor. You must use an oscilloscope on the motor leads to see the drive being sent to the actual motor, since the motor leads will switch polarity to each other, not in relation to the system ground.
Not sure what you think high current is, but to me it is in the hundreds of amps. If you can get by for under 40A and want to spend less then $10.00 US get one these at your favorite china supplier. Take a look at the BTS7960 Bridge module, it will drive decent size motors. I use them for LED drivers also.