diy electric focuser

[starship trooper]

Hi there,

I am looking to make my own electric focuser but would like to be able to control it from my pc how would I do this ?i am going to use a servo that I have laying about ,is there any body out there that has done this and has already done a write up on it.

All help appreciated cheers dazz

[The Sailor]

ST, you can buy USB servo controllers and with software can control how they work. Have been doing this for a couple of years now but it s only a small hobby, an offshoot from my RC days .

Jim

[RogerTheDodger]

ooh I didn't know about them... and SK Pang sell them quite cheaply

[themos]

Look here for ideas, design ,code

sgl_observatory_automation : SGL Observatory Automation

I used stepper motor instead of servo. I started with a just a mechanical switch arrangement that gave me manual jog control and then added an ASCOM Focuser driver by putting an Arduino microcontroller in to do the switching as commanded by the PC.

[Gina]

I'm thinking of using a DC motor and gearbox :- Multi Ratio Motorgearboxes : Motors Gearboxes : Maplin

Not quite decided on the computer interface. I have a USB interface board which I may use :- USB Experiment Interface Board : ExperimentProgrammer Kits : Maplin

OTOH I might use the 1-wire network that I'm developing with my home grown weather station.

[starship trooper]

all good info cheers i shall have a look thanks again

[Tom How]

I did a great deal of investigation into focuser motors several years ago and decided that this range of products

RS Components | Electronic and Electrical Components

was the most suitable. The large reduction offered gave the required resolution on my crayford style focuser. I have two or three of these now for focusing SLRs as well as the main scope.

Of course, you need to know how to run a stepper motor, but that is another story!

If anybody is interested

Homemade DIY focuser for telescope with computer control.

I seem to remember that the 1:150 stepper motor with a 5mm shaft gave a resolution of about 0.002mm in focuser travel - about the kind of resolution you need to focuser at F5

NB The motor/gearbos survives the element extremely well. Over 5 years and still working!

[themos]

2 microns of step is probably overdoing it at f/5

There's a formula for the "critical focus zone"

Useful Formulae

For f/5, it gives 62 microns. For f/8, 159 microns.

A step size of 15 microns would be enough to sample the CFZ adequately.

[pete_l]

ST, you can buy USB servo controllers and with software can control how they work.

Ordinary servos only have a travel of about 270° or so. However, if you take them apart, remove the controlling potentiometer and the end-stops you can turn them into reasonably powerful slow-rotating motors.

You have to change the way the control software works, but if you're into a bit of fiddlin' it can be a neat solution.

[Tom How]

I failed optics at university!

Maths aside, empirically it seems to work well.

I seem to recall l I used the 50:1 reduction set when I did a timing belt drive SLR lens focuser.

[Gina]

Thanks on the focus accuracy information, very useful

[starship trooper]

i am looking at using a stepper motor and a arduino board but am wondering if anybody can tell me what i actually need to get to do the project.

Any help is appreciated thanks

[themos]

Arduino - StepperUnipolar

has everything you need to get the motor to turn.