Gearing battery free electric focusser?

[Demonperformer]

Battery Free Electric Focuser

I am still giving thought to making one of these and wondered if some sort of resistor between the two servos would result in a 'gearing' effect, so for example one turn on the control servo would only turn the one attached to the focuser half (or one-tenth) of a turn, thus making it easier to achieve precise focus.

Does anyone with any electronics knowledge have any thoughts on this? And if it would work, how would I go about determining the best value resistor to buy?

Thanks.

[Reggie]

I would look at adding a larger diameter knob to your 'control' servo, much easier way to achieve better precision

[cabby]

I made one a couple of weeks ago and it works well. Turning the the knob on the control servo at different speeds allows for precise focusing. In the end I actually went ahead and built the electric one (bored over xmas!!) and focusing is now very precise. I'm hoping to give it a try out this weekend if the cloud stays away.

[theodore]

Hi,

A resistor might gear the second motor - but it would just give it much less power, which you don't want. I tried experiments with stepper motors from a printer, which you can similarly drive off each other, you can use different step-per-turn motors to get the gearing effect and gain power.

Theo

[Reggie]

For servos it's incredibly simple to make a controller using a '555' timer a couple of resistors, a couple of caps and a pot. SERVO TESTER Circuit

That is just one example, there are many many more on the interwebz.

[Demonperformer]

Thanks for your replies.

@theodore - I thought there had to be a catch.

@reggie - now that is an idea. So if I had a control wheel that was 10x the circumference of the one on the focuser servo, then I could get 10x more accurate focussing? Definitely a possibility.

[Reggie]

Demonperformer, yup, that's about the principle of it, not sure what the exact maths is for it