Digitrax Zephyr wireless Jump throttle

Jack has various broken remote control cars. i also bought a great little working one from Dick Smith (similar to Tandy) for twelve bucks! The Zephyr has a DC input that can be used as a second DCC throttle (in fact it has two of them) - brilliant design. So I figure put the two together.

the remote control gives up/down and left/right. the Jump wants DC voltage and polarity. Simple to connect the servos on the remains of the car to a little DC opamp: faster/slower, forward/reverse. In fact you only need faster/slower, with the opamp swinging from +12 to -12V

One day I'll do this...