10" dob, stepper motor for focus and movement

[davidpretorius]

I am going to be updating my attempts to use stepper motors to follow elusiver and drive my focuser. I am also attempting to drive my alt/az movement for tracking, field rotation etc

• Stepper motor controller thru the usb port http://www.ar.com.au/~softmark/page44.html has been ordered.
• 2 x 12 volt 1.8 degree stepper motors to be bought probabley RS components with 6 leads.
• 1 x 12 volt bipolar 4 lead.
• Gear reducer (60:1) and roller driver (with reduction 40:1) to give reduction of 2400:1 or 1/4 arc second per microstep
• Bearings for the dob base will be bought from a hardware store tomorrow

http://www.bbastrodesigns.com/cot/ch...ring_ideas.jpg

• References for alt / az conversions to ra / dec:
  • http://www.stjarnhimlen.se/comp/tutorial.html
  • http://www.asahi-net.or.jp/~zs3t-tk/
• Reference for field rotation: http://www.stargazing.net/yizen/fieldrotation.html

Hopefully end result along these lines
Altitude:
http://www.bbastrodesigns.com/cot/rollerdrivealt.jpg

Azimuth:
http://www.bbastrodesigns.com/cot/rollerdriveaz.jpg

reference: http://www.bbastrodesigns.com/cot/mechanic.html

[davidpretorius]

From http://www.bbastrodesigns.com/cot/mechanic.html, apparently these are sourced from the local hardware store

http://www.bbastrodesigns.com/cot/ch...ring_ideas.jpg

Anyone ever seen any??

Also the roller drives seen here closest to the dob base, has anyone seen these anywhere before, google not much help

http://www.bbastrodesigns.com/cot/rollerdriveaz.jpg

[elusiver]

i know that RS have the top ones. Not too sure about the bottom. there's SOOO much stuff in the RS catalogue.. its the size of a phonebook! .. but they'd probably have everything u'd need dave. even though they're not the cheapest.

el

[davidpretorius]

thanks mate, i am getting excited about your focuser.

i have worked out in .net how to connect to webcam image thru code, ie bypassing the default imaging software. with a little research, would an automatic focuser, ie software driven from the images and your focuser be worth the exercise

[asimov (John)]

:d .

[davidpretorius]

freddy kruger's telescope!, good idea or fine focussing, have you tried your motors on your eq mount yet?

[asimov (John)]

No Dave, currently baby-sitting 3 kids...no time.

[ballaratdragons (Ken)]

Dave, the 2nd items are just mounted bearings. Take a pic to a bearing shop and they will show you hundreds of sizes & varieties.

[cristian abarca]

Who or what is RS

Regards Cristian

[davidpretorius]

radio spares http://rsaustralia.com my impression is that they are what d1ck smith used to be like in the old days!

[davidpretorius]

rs looks good

http://img-asia.electrocomponents.co...C311269-01.jpg
about $13

http://img-asia.electrocomponents.co...E749935-02.jpg

about $90 for 500mm if i am going to be driving the external circumference of the dob mount
http://img-asia.electrocomponents.co...C440420-01.jpg
cost $77 and a 100:1 gear reducer
http://img-asia.electrocomponents.co...C718852-01.jpg
$168

need to get to 2400:1 , so need 24:1 somewhere else along the way

[Astroman (Andrew Wall)]

That gearing, are you going to use worm on it or another gear? the thread size will change as you bend it around the scope so you will have to be careful when selecting a mateing gear for it, otherwise it may slip and strip gears.. Another way is to mould your own gears using Selleys KneadIT. It's fiddly but works to some degree.

[elusiver]

dave you can also try farnell.. theyre like rs.

el

[asimov (John)]

Nylon all-thread: 2 lengths side by side, bent along the radius. Anothe piece attached to your motor shaft, laying in between the 2 on the radius...

[davidpretorius]

I have been racking my brain working out whether to go with thread around radius as others have mentioned (asimov most recently) or with the setup pictured down the bottom of this post.

So I thought why not ask Mel Bartels who seems to be a demi god in this area. So here it is.............

Thanks Mel,<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o:p></o:p>

<o:p></o:p>

I really appreciate your quick response.<o:p></o:p>

<o:p></o:p>

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<o:p></o:p>

I think I know where I was getting confused. I was thinking the whole piece of equipment after the reducer was termed a roller drive that had special gear reduction. It was only after thinking for a while that it hit me that the diameter of the shaft versus the diameter of the wood circle is what gives you the extra 24:1 reduction.<o:p></o:p>

<o:p></o:p>

Yes all I need is: a stepper, a 100:1 reducer, two pedestal bearings a shaft.<o:p></o:p>

<o:p></o:p>

Thanks again for your advice and your great website!!!<o:p></o:p>

<o:p></o:p>

David Pretorius<o:p></o:p>

<o:p></o:p>

-----Original Message-----
From: Mel Bartels [mailto:<?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-comffice:smarttags" /><st1ersonName w:st="on">mbartels@bbastrodesigns.c om</st1ersonName>]
Sent: Sunday, 14 August 2005 12:31 PM
To: <st1ersonName w:st="on">david pretorius</st1ersonName>
Subject: Re: Hi from <st1:country-region w:st="on"><st1:place w:st="on">australia</st1:place></st1:country-region>

<o:p></o:p>

Hi David<o:p></o:p>

<o:p></o:p>

I don't know of anyone selling roller drives. People just build them. Have <o:p></o:p>

a machinest make a 1/2 inch diameter shaft a few inches long and then let <o:p></o:p>

that drive a wood circle rimmed with aluminum.<o:p></o:p>

<o:p></o:p>

Mel

[Wombat_In_Space (Darren)]

Hi Dave found this company today well looking for stepper motors for another project they might be worth having a look at they sell steppers and encoders. and lots of other fun stuff.

http://www.erntec.net/

[davidpretorius]

thanks darren, just picked up 3 free 12V stepper motor from the old 5 1/4 disk drives from a local computer who owed me a favour. i will have a look at your site as well.

i am going to be stubborn and resist the need for encoders. i want to be able to think that my software and engineering skills do not need a feeback system?

wait and see i think.

are you coming to snake valley?

[elusiver]

did u see the steppers with built in encoders in the RS catalogue??? awesome.. but mighty expensive from memory.


el

[davidpretorius]

only been looking at the net version. have you had much to do with microstepping??

bartels mentions starting with 7.5 deg and then microstepping in lots of tenths???

[davidpretorius]

Hi all, have bought some "LEMCOL" bearings @ $12 ea for the base and acquired 3 x old 5 1/4" disk drives for the stepper motors. Also purchase the beer to get myself drunk enough to post a pic.

15 minutes later, three destroyed drives and 3 x 1.8 degree stepper motors.

hopefully just saved myself $230. please note, that if this all works, and if anyone wants stepper motors, lay your hands on as many 5 1/4" disk drives. the old ones!!!