Hi Irving,

1. This explains far better than I could:
http://www.servocity.com/html/how_do_servos_work_.html

2. Servo tester is £5 - £15
http://www.fast-lad.co.uk/store/prod...oducts_id=1716
The potentiometer on the tester controls the width of the pulses, and replaces the signal it would otherwise get from the reciever. This signal moves the output arm of the servo motor to the required position, or for the throttle, the engine to the required speed. It is fully proportional.

I wondered, with my limited electronics knowledge, whether the pot could be removed (which must just provide the pulse generating part of the servo tester with a 0 - 4.8v output) and via a magic box the Mach3 0-10v could be connected instead.
I'm sure you could come up with something along these lines or better !

Does this help you with a better plan?

Ah, you've already replied. Looks like you have it in hand!