DIY Motor Focuser

aokman · #1 05-04-2010, 01:53 PM

Hey guys, well after many days of stuffing around with many test circuits i finally managed to finish my motorised focuser

It incorporates a Japan Servo 0.6deg 3 Phase 1.5A stepper...

I set the unit up with a regulated 555 driver supplying from 6hz to 133hz with a full 50% duty cycle up to 100hz. I could increase it more but i went for accuracy instead.

So far ive set the controller up with switches for:
frequency>forward>backward>halfstep A>halfstep B> full stepping>motor lock

The halfstep is great for precise movements and low vibration with full stepping supplying massive torque at the cost of more vibration and the motor lock is great for locking the position of the motor and whatever is attached to it...

So far ive been very impressed with it and im glad i went with silicone cords as they are amazing at staying untangled

i cant wait to get the order through for my FLT-132 so i can mount it up

Just curious what you guys have come up with for your scopes as this one was certainly a challenge

bmitchell82 (Brendan) · #2 05-04-2010, 07:03 PM

That is some great DIY work, i am currently trying to sort out the same thing but with USB drivers to connect it to the PC for Auto focus.

My crude but workable way was a reostat resistor with a dpdt switch and a RC servo motor modified for continuous drive. very crude, and works (just).

Are you able to give some more detailed instructions drawings?

aokman · #3 05-04-2010, 07:16 PM

certainly can, ill post it up when i get home

most of the smarts is done by a dedicated 3 phase stepper driver but ill show you how i integrated it

a normal stepper isn't that hard usually but 3 phase can be quite a challenge. I am however working on parallel port controlled ones at the moment aswell with smaller steppers. Though this one could be easily controlled also through a PC.

aokman · #4 05-04-2010, 10:28 PM

Ok heres a quick drawing of the circuit

Basically the unit is controlled by a 24v source which is shunted through a 7805 5v regulator for the 555 timer and driver logic. In theory the unit can run on anything between 12 and 24v easily as long as enough current is supplied via the power supply.

Once the 555 timer gets its power the dischaging capacitor and trimmer/supply resistor make up the timing for the clock signal that is fed to the input of the driver chip. The signal is fine tuned from 6hz to 133hz using the trimming resistor starting at 50% duty cycle. I can change this range using the capacitor and resistors. If you google 555 timers you will find many amazing things they can be used for

Once the clock is fed into the driver it has what it needs to step the motor however it requires a grounded ENABLE to conduct to the outputs. If ENABLE is grounded without a CLOCK signal the motor will lock and hold position. To reverse direction of normal operation the DRIVE connection is shorted to ground.

Full step / Half Step modes can be enabled by switching each to ground

Overall it is a very flexible driver capable of being run off a PC no worries as all it basically needs is a clock signal and a few other grounds.

I was lucky to have a dedicated driver for the motor as 3 Phase motors are a bit more difficult to use due to the windings needing either + - or open to function properly.

aokman · #5 08-04-2010, 04:43 PM

on another note im going to start work on a some computer controlled steppers and see how far i can go

I managed to salvage these bad boys today from work

also grabbed driver boards for them...

bmitchell82 (Brendan) · #6 09-04-2010, 03:47 AM

christ almighty!

I will be watching with vigor!

bojan · #7 09-04-2010, 10:00 AM

Quote:

Originally Posted by aokman

on another note im going to start work on a some computer controlled steppers and see how far i can go

I managed to salvage these bad boys today from work

also grabbed driver boards for them...

What company do you work for, mate?
Do they need RF engineers with 30y experience?? I am keen to join

aokman · #8 11-04-2010, 12:20 PM

Quote:

Originally Posted by bojan

What company do you work for, mate?
Do they need RF engineers with 30y experience?? I am keen to join

i work in the printing industry fixing office machines through to production printing machines

not sure if that sort of thing interests you though

im a very electrical / mechanical sort of person

bojan · #9 11-04-2010, 12:28 PM

No worries mate, it was kind of a joke

(I work in RF R&D and I am very happy where I am at the moment)
But I really like those beauties

alistairsam · #10 28-08-2010, 02:32 AM

hi i just finished testing a a focusser prototype with a servo and a microcontroller with very simple code.
standard rc servo modified for continous rotation.
but since the modification (replacing the pot with two fixed resistors) does'nt alter speed, and you don't have much control of speed by varying pulsewidth, is it better to use steppers for motorized focussers?
came across a thread here where someone used a servo but can't find it.
moreover, i found it very noisy with the plastic gears.
i read that for variable speed, you have to modify the servo control circuitry to adjust feedback.

is it possible to slow down servo's like steppers microstepping? that would reduce reduction needed for the focusser.

bmitchell82 (Brendan) · #11 28-08-2010, 02:49 PM

hey mate im currently prototyping a ardunio mega + Stepper motors. all is going well at the moment and i have the drivers so i can integrate it with MaximDl or any other auto focus program. ill keep you upto date with the progress.

alistairsam · #12 30-08-2010, 03:33 PM

Hi Brendan,

are these drivers from Arduino? is it ascom compatible or compliant, and if so can it be used as ra and dec drive from planetarium software?

bmitchell82 (Brendan) · #13 31-08-2010, 11:42 AM

its not a driver for RA and Dec it is drivers for a motor focuser. back forward temp ect ect and it is written in ascom compliant code

Its not from arduino though its made by a dude that wanted auto focusing via PC

aokman · #14 17-10-2010, 09:15 PM

well i thought i better do the final update lol, i put this aside for some other projects but finally got it finished as im going to need it for the feathertouch...

I had to make some modifications with cooling by adding a 40mm delta fan and exhaust ventilation and also increasing heatsink size for the driver to stop it overheating. Now i can hold the motor in full locked mode indefinitely without overheating the driver

http://www.epicphotos.com.au/MVI_7852.m4v