Just a quick post to show you the tracking setup I came up with to drive the 12.5" newt.
The radial arm is constructed out of galvanised sheet metal & tack welded together. It is 209mm long & attaches to the RA axis. There are 2 lengths of 1/4" X 20 TPI all-thread, curved to the radius of the arm & tacked in position. Attached to the 1.8 step motor shaft is a piece of the same all-thread. With this reduction, it is necessary to have the motor rotating exactly 1 RPM to track at the correct rate. The close up of arm & stepper is just a representation of the setup used..(a previous prototype that failed)
She's a rough set-up as you can see, but it works, & works good. Total cost was about 10 bucks for the all-thread. & my labour if you want to include that. The stepper & controller were free. Same for the battery, which was a 12V car battery from the local dump cut in half to make it 6V.
Asimov, I know you have been trhough a few iterations before geting it right. Given your intrest in Equatorial Mounts. Here is a link i came accross that may intrest you and the others. I have collected quiet a few designs in my umm research.
Hi wolfie, thanks for the links. I've seen them before. Just to give you an idea on how long I've been researching EQ mounts. Heres a pic of my 1st EQ made back in 1978.
I was 15 at the time. There was no such thing as a dob back then of course.
I'm quite happy with my mount though. Works fine. It was just my pig-headed notion of driving a big EQ mount for under a hundred bucks that I had 'trouble' with lol. Seeing I did it for less than 50, I'm stoked.
1978?? i wasn't even BORN!!! top work asi.. i'm sure u've posted before that u've been working on this project for a while.. so u must be happy? has she had first light yet? how long does it track for?
I can see myself building a dob soon, just to see what all the fuss is about! I ain't a 'rule follower' though....I'll come up with my own design
For under a hundred bucks driven?
G'day YOUNG FELLA! (EL) First light sunday night just gone. Tracks really well. Should be able to track for 5 hrs before re-setting. Yep! I'm definately happy. Been working on it for near on 2 yrs.
Well, I don't reckon it'll be much chop for long exposure stuff...all-thread straight off the shelf is not high precision stuff. = big periodical error. This stepper takes pretty coarse steps so even though I can't see the steps by eye even as high as 212X mag...I reckon it'll be seen in the camera. Need to make some all-thread in the lathe & micro-step the motor for that. Short time exposures should be ok though. Just have to test it better to see what it's capabilities are I guess..
After saying all THAT...I also thought that this drive setup had buckleys of driving it & not seeing the steps taken by the motor in the EP.....go fiqure.
There was no such thing as a dob back then of course.
I can see myself building a dob soon, just to see what all the fuss is about! I ain't a 'rule follower' though....I'll come up with my own design 
First light sunday night just gone. Tracks really well. Should be able to track for 5 hrs before re-setting. Yep! I'm definately happy.
