Wanted: 1 RPM motor...<<<FOUND!

[asimov]

A 1 RPM motor. It could be any voltage I guess....EXCEPT 240V thanks..
Even if it's variable speed, as long it can get down to 1 rpm.

[mick pinner]

l doubt you would ever get a voltage supply that low, you certainly won't get a motor to turn that slowly with a standard armature.

[asimov]

Perhaps a geared servo motor is what I'm looking for then. Sorry if I was un-clear.
I should probably also add that it's intended use is to drive a big home-built EQ mount...I have built the gear box that will allow the use of a 1 RPM motor of SOME description....I'll leave it up to the electrically minded experts as to what KIND of motor is needed I guess..

[Sausageman]

What about a stepper motor, They can be driven down to almost any speed you want, although at such a low speed they may jump a bit.

Mike

[asimov]

Yes Mike....A stepper would be good.....I have an EQ5 mount with dual drives on it.[synta] & their steppers..I even pulled the DEC motor off & mounted it tempoarily on my big EQ & it drove it without a problem...The only trouble is it doesn't rotate at 1 rpm....it rotates a lot SLOWER than that, therefore a stepper using a crystal controlled frequency oscillater to keep a perfect frequency for the timing/rotation of the motors is perhaps the way to go... The best design would be something similar where it would also keep track of the motor speed and feed it back to the electronics where it would then also adjust its own frequency to compensate for any variations....

[asimov]

I've been trying to motorize this scope for 2 years now, & it's really getting on my nerves. I just cant seem to be able to do it, for various reasons....I may just give up & sell the ****** thing!

[asimov]

Anyone want a 12.5" reflector with Parks optics sitting on a EQ mount UN-DRIVEN!?

[Astroman]

For free? :P

j/k

[mch62]

Your going to need reductions to drive the mount weather servo or steeper.
What are you driving a friction drive or worm gears drive?
What ratios are you using?
Check out this site and the links on driving a scope.

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

You don't need to have go-to but there is lots of info on basic motor drives from the MB site and suppiers of motors gears ect .

I use the servo controller and pittman motors on my large fork mount with 2200:1 total reduction and these motors can drive up to a 40"scope.
The steeper set up is cheaper and in kit form but the servo is more versatile when used on bigger scopes.

friction drives are the cheapest drive to use and offer a lot of benifits over worm wheel drives but have to be designed carefully to avoid slippage.

In driving a mount you have lots of variables to consider as far as tracking and correction of Ra drive rates ratios ect ect.
It's not just a case of wacking a motor on and hope for the best .
Mark



Mark


Mark.

[Starkler]

Oatley electronics sell a 1rpm 24ac motor designed for 60hz ac as used in the US.
You would just need to build a drive circuit to generate 60Hz to make it 1 rpm.

http://www.oatleyelectronics.com/kits/k038.html

[asimov]

My gearing is using a home built double-curved bolt drive. It consists of two 1/4” x 20 threaded rods bent along a curved section of steel with a radius of 11.43”. Turning against these rods is a 1/4” x 20 section of rod that serves as drive worm gear. It is designed to use a one r.p.m. motor. The design was adapted form articles in the January (p.26) and July (p.100) 1989 issues of Sky & Telescope.......So I'm not just 'wacking on a motor' & hoping for the best.

[see photo's of my setup]

[Sausageman]

I have found a web site for stepper motors.
http://www.eio.com/jasstep.htm#intro
It may give you some ideas about controlling the speed, I haven't read it all though.
From what I have read, they are every where in the computer world.

Mike

[RAJAH235]

The 'Oatley' site has a link, (download instructions), to the drive circuit which shows that the circuit runs off 12 volts DC, & is speed adjustable. BUT, it's only suitable to drive the 24 volt AC motor.
Did you have any luck with the stepper motor/driver, links at 'Silicon Chip'? Most are speed adjustable via a pot. :D L.
ps. Does the driven threaded rod have a support bearing at the far end? Looks a bit flexible!
pps. My camera tracker is a 'curved rod' type. A 1/4" threaded rod was used, & all I drive it with, is a modified servo with a system of pulleys to give me 1 rpm. It has more than enough torque for this app. Not sure about driving a big t'scope tho!
http://i2.photobucket.com/albums/y7/RAJAH235/IMG0002.jpg

[asimov]

The set up in the pic was just a quick experiment really. The end of the threaded rod was held temporarily in place by a strong rubber 'O' ring to the radial arm. There's a pretty long story to all the different setups I've tried on this. The best result I got, was from a 240V microwave turn-table motor, that did 7.55 RMP. I then made a gear-reducer from bronze gears to reduce it to 1 RPM....It tracked beautifully..The only problem being, I was getting vibration from the motor at medium to high magnification, rendering the system useless for astro-photography..I spent hours isolating the motor with rubber mount etc etc. & I got it within reason. I think it would still work, but I think I need to beef the mount up more to create some more 'mass' to dampen out the harmonic vibration..I'm getting closer to achieving the desired results though.

Sorry Mike & co. if this is turning into an 'equipment discussion' :)

[FNQ_View]

Looking at your design, you may be able to use a 200 step per revolution stepper motor using differential switching. this should give 800 steps for the revolution. When this is combined with the ratios of your worm drive it should be smooth enough drive system. All of this would still require a motor which can cope with the load required of it, and a control circuit to drive the stepper. How much torque is required to rotate the drive?

In case your wondering - I'm an office equipment technician. I have a large box of stepper motors salvaged from scrap equipment.

[asimov]

Hi Mick. I dont actually know how much torque is involved. But the little stepper off an EQ5 mount drove it no problems. Considering It is designed to push around a 150mm F/8 refractor around which weighs in at what...17-20 lbs? {plus counter weights etc} It pushed my 160lb OTA/counter weight assembly. Put it this way, with one finger it is EASIER to push the big scope than it is to push the refractor on the EQ5.. This is due to the big diameter bearing I have on the RA shaft. Your box of steppers sounds promising.

Do you know about controllers etc? As stated, it needs to do 1 RPM. I'm definately interested in what you have to say, Thanks.

[RAJAH235]

Asimov, See attached circuit. You just need the stepper motor & suitable power supply. Can be comp. controlled or stand alone with hand controller. :D L.

[asimov]

:eyepop: Your a good man Laurie!!:thumbsup: thankyou.

[asimov]

Mick. Would it be as easy as using one of your biggest stepper motors with Laurie's circuit above?

[RAJAH235]

John, You need to know the voltage/current required & then choose the switching FETs to suit the motor/power required. Will chase up the article for further info. :D L.
ps. Found the issue. It's May 2002 Silicon Chip.(www.siliconchip.com.au)
pps. Found this update/modified circuit for a 4 wire stepper motor.


This thread may need to be moved. L.

[asimov]

I just finished stripping out an electric type-writer, it had 5 steppers in it, the biggest one being 6V dc 1.2A 1.8 deg/step = 200 steps per 1 rotation. (6 wires) Seems to be a nice chunky heavy duty motor. As I state...I'm basically brain-dead in this area...would this motor be of any use to me Laurie? I would gladly pay you to make me a hand-controller etc etc L ........IF this would be a suitable motor. How much would you charge me.....(IF you wanted to make it)
PM me.

[FNQ_View]

In my salvage box, underneath the first surface mirrors, lenses, optical slide rails etc, I have stepper motors. All are six wire 1.8 degree per step. ratings vary from 4.2v 1.5A, 8.4V 1A, 9V 0.96A. Mounting holes are @ 48mm Centres, square pattern. Body size 56mm Diameter. Depth 58mm.

[FNQ_View]

The dimensions given are from the 4.2 Volt motor. Others are similar.