works like a charm for a small rover, cheers mate

Not a rover but I was hoping this would work for my train. And it does, for the engine, but not once I add carriages. I connect carriages via merge blocks and use Whip's Subgrid Wheel Script so ALL the wheels give propulsion. With Whip's script on or off your script can hardly move the train. Not really your problem as it is outside your advertised use but thought I would mention it. Probably works great for a rover.