noob project, cool idea, need help...


i bought a lens thinking it would be compatible with the zoom button on my camcorder, unfortunately it isn't :( ...

i've been looking at building an servo motor to control the zoom function, this will be better for me because i'll be able to place the control stick/trigger exactly where i need it on my camera rig.

i have a few of specifications however...

-it will need to be as quiet as possible (for obvious recording reasons).
-it needs to be variable speeds.
-able to ease in and out of zoom smoothly/seamlessly.
-the control needs to be operatable by my thumb alone, a left/right thumb-stick or seasaw peddle would be ideal.

i've drawn up a very basic schematic of my idea-

(the control stick will go on the handle of the poleroid chest stabilizer, shown below)

a servo tester was suggested for the controller. it needs to be a thumbstick/sea-saw peddle which will allow me to operate with smoothness and precision. like the libec controller shown above.

not sure, but perhaps something like this?-

as for the motor, somebody said i would need a continuous rotation servo... suggestions? must be quiet and able to ease in and out smoothly. i don't know where to begin choosing continuous rotation motors so a few suggestions would be greatly appreciated... please provide links also.

please help me, let me know what your approach would be.


regal johnston...
Looks interesting, I have one suggestion. Get rid of the belt drive in favor of a simple wheel drive. Use a rubber wheel where the pressure of the wheel against the focus part of the lens. A drive belt would be hard to keep in place as it might walk itself off the area it needs to be on. You would not have that problem with a rubber wheel that just presses up against the focus on the lens.

If you are still working on this let me know and I will gladly help the best I can.

Take a regular servo and remove the bottom plate. De-solder the circuit board from the motor. Now you have a DC motor running through step-down gearing to the output shaft. Extend those wires outside the case. Replace the bottom cover and remove the top cover. Find the gear with the travel-limiting pin. Usually the biggest gear in the stack. Use a small saw to remove that pin. Put it all back together.

Servos take 4~6 volts. Running any more through the motor might cause damage.

Anyway, at that point, you'd have a fine-control, gear-reduced motor.

Use a 555 PWM controller to drive the whole thing. Maybe get creative and use a POT to control the speed of rotation.

Is there an easy way to reverse the PWM signal though? Maybe connecting dual timers with one reversed and diodes to stop feedback?