Hi Mike / Steve,
I prototyped a 'fly-by-wire' throttle control a while back which used a radio control type servo. The servo was a ball-raced unit with a 5kg pull and very fast acting. Remember that when you crack the chokes by hand, eg blipping the throttle, the revs out of gear climb instantly so the the servo has to be extremely fast.
I used a PIC micro controller, reading an analogue to digital converter that read the pedal position from a potentiometer (variable resistor). Once read, the processor generated a variable pulse width modulated signal that was used to directly drive the servo.
A mock-up was contructed and tested on a rig, but was never fitted to Roy's 500bhp Mk1 GTD. Mainly because we are always busy tinkering with some other bit of the car.
One very important thing to consider when attempting things like this is SAFETY!!.
SAFETY 1st! - SAFETY 2nd!! and even SAFETY 3rd!!!.
With this in mind I incorporated several failsafes including -
1)checking that the choke position, also read via A/D from injection throttle position sensor, matched the desired position, IF NOT, CUT IGNITION!
2)throttle pedal switch and choke closed switch - If foot off throttle, then choke closed switch should also be sensed, if its not within 0.0x seconds, then again CUT IGNITION!
3)are inputs within expected range - i.e. - if the sensor on the throttle pedal fails - make the system fail safe!
etc, etc, etc.
A fully programmable/mapable throttle will allow different drivers to have different setups. Or a softer setup for road use as opposed to track use. Or how about a limit on available throttle for letting 'novice' drivers 'have a go'?
The options go on and on and I know some would/will consider this sacrilege but each to their own I say. We get pleasure in devising / developing the car for mainly track work - who knows - we might even fit it one day!!
best wishes
ps - one final thought - fit a receiver and a power servo rack and you've got one hell of a radio controlled car!! - anyone fancy a ride??
[ February 28, 2003: Message edited by: Paul Thompson ]