Turn dial to generate pulses
I'm building a pan/tilt unit. I plan to have a 200 step motor attached to a 20:1 worm gear, (the latter is needed so it will 'lock' in place, and not be solely reliant on the motor's holding torque.. So in order for the output shaft to turn 180 degrees needs the worm gear to turn 10 times. In turn the motor must do 10 revs, which would need 2000 pulse steps.
It's the pulse generation that's proving difficult. Whilst a 555 timer could generate pulses, I want it to be 'mechanical' For example, if I turn the knob 90 degrees, I want to create 1000 pulses, (45 degrees creates 500 pulses) and so on, so the knob matches the physical position of the camera. If I turn the knob 180 degrees in 1 second ... the motor will turn 180 degrees in 1 sec. If I turn the knob slowly, pulses will be generated slowly, and the camera/motor will turn slowly.
My idea at present is some sort of optical encoder ... but that would need 4000 divisions on the wheel!! Or - a 1024ppr wheel with a 1:4 step up gearing ... but such encoders are several hunderd Pounds!! And I would need two of them!!
I have software that will allow me to print an encoder wheel, but resolution will have to be 'course' since it will use an LED / transistor, so I suspect around 64 divs.
I purchased a RC servo, wondering if I could remove the motor, and turn the output shaft by hand. Couldn't be done.
I've also considered 'planatary gears' in reverse to 'step up' the revs ... but I cannot locate any 'hobbyist' versions other than the Tamayia type.
Also briefly looked at RC servos, but having done the maths, it would be impractical to get the output to move (say) 0.1 degrees as the motor would only move about 1/4 of a rev and have no torque!! (One option may be to make it continuos rev, and place a feedback pot externally.but again, moving 0.1 degree around a pot would create minimal feedback) Incidentally, 0.1 degrees is the stepper resolution 180 degrees / 2000 steps
Anyone any ideas? Bearing in mind that the speed of the pulse train is dependant on how fast the control (pot) is turned, and also matches physical camera position. Encoders are preferred option as it's then possible to electronically guage which way the motor is turning.
If electronic, here is (sort of) what the circuit would need to compute. (Sample and hold?) Moved from 0 to 45 degrees in one second. That degree of movement needs 500 pulses, thus need to generate a pulse width to get 500 pulses in 1 second timescale. ** This is just to give an example. The actual sampling rate would be much faster. If it was a 'slow' 1/10th second, in the above example it would check every 4.5 degrees, and generate 50 pulses in that time scale.