10" dob, stepper motor for focus and movement

[davidpretorius]

hi mate, if you have any 7.5 degree steppers or even better 1.8 degree steppers with say a 5mm shaft, then i feel that they could prove quite popular if el and i are successful with the focusser and the tracking.

http://img-asia.electrocomponents.co...C440420-01.jpg or http://img-asia.electrocomponents.co...C332947-02.jpg

doesn't really matter!

I am ok at the moment as I have three from the disk drives, but anyone else may have need of them at some stage, they are upwards of $70 new!

[asimov (John)]

Yep. The one in the first pic I have for my EQ mount (still yet to be tested) See the pic for the steppers I have.

[davidpretorius]

i am writing some software to drive from the computer. what stepper motor drivers are you suing for the eq???

[asimov (John)]

"step-syn" DC 6V 1.2A 1.8 deg/step. (sanyo denki co.)

[davidpretorius]

do you want me try any code to drive from the laptop. assuming i get it right for mine?

[asimov (John)]

I'm going to use the controller built for me as seen in this pic. Only problem is, it takes big chunky steps so my concern is these steps will be seen in the EP rendering the system useless! Have'nt counted the actual steps per revolution as yet. Would it be possible to make it take less steps per revolution to counter act this potential problem? It has been suggested I need a .9 deg/step motor to solve it.I'm brain dead in this area...& it KILLS me! (ain't tried it yet so it's all hypothetical at the moment!)

[asimov (John)]

Sorry, forgot to answer your question...No, was not planning on using a computer to run it..

[davidpretorius]

by applying the power to motor in what is full step mode, then the magnetic fields cause the motor to step full step (in your case 1.8 degrees). if you however power up the magnets differently, you can get 1/2 step mode ie in your case, .9 degrees.

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micro stepping is where you send sine and cosine waves and get smaller fractions of your full step.

[netwolf]

Dave, here is another Dave who has done something similar to what you want to do.

http://www.mindspring.com/~davebevel/altaz/altaz.html

[mch62 (Mark)]

Davidpretorius , Just another site for small parts.

http://www.minibearings.com.au/cgi-b...l?alpha=G=post

I have Mels servo system on my EQ fork mount with friction roller drives .

Mark

[davidpretorius]

Thanks Mark for the link

, any comments on your system, good / bad, can be improved, worth the money.

Any pics?

Thanks again

[mch62 (Mark)]

Will be able to tell you more in a few weeks.
Am just getting the SS drive rollers mounted on the base at the moment.
Have used 30v Pittman motors running at 12v with RS 25:1 reducers.
The main 650mmRA disc is steel with SS rim and the DEC is 19mm ply with SS rim.
Have set up the soft ware and run the servos unmounted and all appears to function , but setting up the paremeters and interfacing with the Sky 6 will be the test.
From the manual there is vertually every conceviable mount and drive error controll and function that is needed for any mount type from Alt AZ (DOB) to EQ and some I have never herd of.

As to weather it's worth the money , well it sure beats buying a very large mount.
There are lots and lots of people using Mels gear and commercial varients of it and he is the Guru of Amature scope making and have found him and Dan Grey to be very helpfull .
I take it you have visited the Yahoo group Scope drive?

[davidpretorius]

i had read thru mel's site a fair bit and followed links etc. The yahoo group, i assume you have to join?

[elusiver]

thats a MIGHTY FORK MOUNT! awesome!

el

[davidpretorius]

yes, it is rather large. i was aboout to ask why 30V pittman motors, and then i clicked on the piccy

[mch62 (Mark)]

They were the new surplus units Mel had at the time if you bought the complete kit.
He now has 19v new surplus Pittmans but basicaly any servo will do , just a matter of paremeter change and total reductions.
The servo system has and will drive a 40"Dob with the included pittman motors..
As far as running at 12v that's all the voltage that is required in most cases to give a resonable slew speed with accuracy.
You can use 24v if you need more slew speed but for my scope I should get 6deg/sec with 1/4 arc sec tic size at 12v.

David i have been lurking around the Scope drive site for a couple of years now .
You do have to join but there is heaps of info there and any problems you may encounter will surely have been delt with before.
It took me 12 months of intense study to finally take the plunge and make a mount
Not every bodies cup of tea making a mount and getting it to drive accuratly for imaging.

[mch62 (Mark)]

Elusiver,I am interested in the focuser drive your working on for my new focuser unit.
Am I correct in that it runs on your XP system?
What sort of reduction are you using with the steeper?
This is the focuser (pic Clement focuser ), I know it's weird looking but lots of advantages over the standard Crayfords.

It requires 10 turns of the knob / inch of draw tube travel and has 3" of travel.
There is a Robo Focus kit to fit but there quite a few $ and am hoping the Jay car kit will do.

[davidpretorius]

this guy directly coupled it

http://www.philip.davis.dsl.pipex.com/focusser.htm

quote
"The full range of the focus tube, from one end to the other, is in the order of 500 steps so focusing can be quickly achieved using the larger steps first followed by the smaller step and finally the smallest step.

Since the distance travelled by the focuser, from end to end, is around 60mm this means that each step of the motor is equivalent to 0.12mm. I could have wired the stepper driver to allow 400 steps per revolution which would have halved this figure to 0.06mm per step!"

i am very interested in how accurate this focusing has to be? ie is .06mm too coarse?

[mch62 (Mark)]

It will depend on the focal ratio as to how precise it needs to be for imaging but here is a link dealing with the just what your saying.
It's a large file and only the first page is relevant but he is saying that for his f4 astrograph his deep of focus is .0015"
It will be less at f5 .

That works out if i am correct at 0.038mm??



http://www.clementfocuser.com/images...Clementrev.pdf

[davidpretorius]

thanks will have a read.