Stepper Motor System / Advice

[Spanrz (Brett)]

I have got the itch to get a setup for controlling the Az/Alt of the 12" by the stepper motors.
I've read here, there and everywhere about all the systems but still a little dazed at what system will do me, an off the shelf system or a custom built setup.

I have a plan / project to make a system up, but need some advice on my methods of my madness. The plan isn't defined, but I am not at all concerned if it takes a few months to figure out.

Now, I am very noob-ish, to these systems, though I am electronically minded to make a system, but this is what I want to do :

• Have a stepper motor / control system to guide on DSO's / Planets etc, you know, the normal stuff.
• Also want to have the ability to speed up or slow down both axis's (er or is it axi ?? ), as I want to have the ability to follow a satellite or other feature that goes slower / faster than sideral time. (e.g follow the ISS or shuttle in orbit or eventually show the shuttle's entry to earth's atmosphere)

Watched a few vids on youtube too, just to get an idea as well.
Stepper motor system - http://www.youtube.com/watch?v=DYG8SlrwGHM
Moon guiding - http://www.youtube.com/watch?v=k-O5H2drEsw )

Now please correct my noobishness, but is this what I might need?

2 x stepper motors, a variable controller (either controlled standalone or by PC), wiring, gearing system (or a method to drive the mount), batteries.

Do I need a PC / Laptop (as I already have both)? Will the PC / Laptop take away the complexity of making a variable box on it's own or is it better to use both in conjunction?

Now the variable controller, I want the adaptibilty to switch between sidereal time to whatever speed I choose.
Like using 2 potentiometers and stuff.

Now if all else fails, and I choose to throw it all away, that I might choose an Argo Navis or similar system.
Is the Argo system encoder a motor? Or just a digitial sensor (where you still have to move the mount manually?)
I'm just confused at exactly what the argo navis system is. (automatic or manual)

Thanks.

[Barrykgerdes]

Hi

Stepper motors are usually limited in what they can do. They don't have the speed range of the more common electric motors with encoders. If you make the steps small enough for smooth tracking the slew speed will probably not be fast enough for satellites although they can be quite precise in their positioning.

There was a stepper motor drive system quite popular 12 years ago called the DOB 11 driver system or Roboscope. Used for driving Dobsonian mounts I believe they are still available but quite expensive. I had one and did a lot of experimenting with it until I got a LX200 which was far superior in its control.

I wrote a program in Qbasic to drive it complete with goto, two star alignment and catalogues of ngc, IC an Messier objects and a selection of stars for alignment. The method of imparting drive to the axes was by belts or friction drive and was suseptible to slipping. I also had a version of this program that used to drive stepper motors salvaged from old hard MFM drives. I found one variety that would accept up to 3000 half-steps/sec from a stepper drive PC board kit from Silicon Chip. Incidently the steppers that came with the DOB 11 ran at up to 5000 half-steps/sec.

I am not very familiar with the Argo Narvis system but If you put decent ball or roller bearings with some preload on all the rotating sections and a positive method of drive by toothed belts or gears I think it will turn out more practical and cheaper in the long run.

On my web site there is some old files of the work I did years ago in beefing up a Dobsonian Mount and fitting of a DOB 11

Barry
www.geocities.com/barrykgerdes

PS. By the way the plural of axis is axes

[bojan]

Have a look at Mel Bartel's system (100% freeware if you know how to solder).
I build it and it works perfectly - Goto, Push-to (with encoder from mouse or better ones, with David Ek box - also freeware in principle), data base with objects.. you name it.
http://www.bbastrodesigns.com/BBAstr...ted_Telescopes

We live close it seems so we can even arrange a demo :-)

[Rod]

Hi Barry,

Are you aware of Mel Bartels stepper drive system? You can find details here:

http://www.bbastrodesigns.com/BBAstr...ted_Telescopes

I built the stepper drive for my 12 inch dob and it works well, although I am still ironing out some issues with goto. You can get excellent tracking, goto and slew speeds are usually between 1.5 and 3 degrees per second. You do need an old laptop for this system but the software is free and there is a very good yahoo group that can assist you. Mel is very active in his support of those who build his system.

A friend did the electronics for mine and I made all the mechanical parts. I just made moulded epoxy gears for the reduction system. They work very well visually.

Hope that helps,

Rod.

[bojan]

BTW, it seems the interest for gathering in Melbourne is again on (well, one person for now :-)
http://www.iceinspace.com.au/forum/s...t=26200&page=4
So, perhaps, this may also be the opportunity to meet and have a look :-)
Rod, are there any plans for gathering at place near you in 3 weeks ?

[Rod]

Hi Bojan,

I am sure we could arrange to catch up at the Briars (in Mount Martha) on Friday Feb 27. On the 28th is the Messier star party which the ASV is holding at Heathcote. You would be welcome to meet up there too - great skies but more traveling. It would be a good chance to look at a lot of scopes too.

Rod.

[Barrykgerdes]

Originally Posted by Rod

Hi Barry,

Are you aware of Mel Bartels stepper drive system? You can find details here:

http://www.bbastrodesigns.com/BBAstr...ted_Telescopes

I built the stepper drive for my 12 inch dob and it works well, although I am still ironing out some issues with goto. You can get excellent tracking, goto and slew speeds are usually between 1.5 and 3 degrees per second. You do need an old laptop for this system but the software is free and there is a very good yahoo group that can assist you. Mel is very active in his support of those who build his system.

A friend did the electronics for mine and I made all the mechanical parts. I just made moulded epoxy gears for the reduction system. They work very well visually.

Hope that helps,

Rod.

I had a quick look at that site and the method appears to be very similar to what I did in 1994. My main difference was that my stepper drives used a computer program to drive discrete components rather than those special chips. My budget was a lot less than the prices listed. Driving the steppers is a function of the sequence of how you excite the fields and was done via the printer port with two four bit words.

This needs a faster computer than the old PC I was using as the control loop was quite large. Later With 386 and 486 computers speed was no problem.

The program to drive the DOB 11 originally only sent commands to the controller at one per second which at high resolutions made the scope move up a stair case. I developed a method of sending commands every 100ms which was a great improvement.

I used parts from the junk box and salvaged stepper motors. I went through lots of motors looking for the ones that could drive the fastest and at one half step for each second of rotation I managed to get the fastest slew to just under 1 degree/second.

I wrote my own software and the source is free to anyone who wants it although it is written oin Qbasic and is a bit archaic by modern standards.

My main problem was getting suitable mechanics to drive the scope. I experimented with all sorts of devices using parts mainly salvaged from old computers and printers.

I spent many months refining software and mechanics but before I got everything fully working. I had a loan repaid and bought a LX200 10" classic. The stepper drive system and 8" Dob was given to my daughter.

The system worked OK from a laptop although at the time the only hand controller I had was via the games port which left a lot to be desired in speed of operation.

I occasionally get the old test board and motors out and hook it up to the computer and do dummy alignments and gotos. The motors look good slewing and tracking. Oh did I say how I tracked. I re-calculated all the coords every 100ms in the program loop at sidereal rate and sent them to the motors.

It was a lot of fun but I prefer my LX200 these days.

Barry

[Spanrz (Brett)]

Thanks for the replies. Wow.

Barry, thanks for the advice. I've programmed in Basic a little myself on the C64, but it's been a long time between drinks.
Hehe, I was being a bit jovial with the plural meaning of "axis", I just thought it sounded well, calling it "Axi".

Bojan and Rod, That link is fantastic. (Mel Bartel's). Now why didn't I just search on Mel.

I just needed to quell my curiosity, just in case I was going to make an idea that was simple, but in practice, got a little too complex for my liking.
Again, the idea, is sort of to do what Nasa does when they film the shuttle going up (how they track the shuttle in the middle of the view). I know how complex that can get, so I'm trying not to aim too high in a build aspect.

I'll have a good read over that link. Great starting point. Thanks.

[gary]

Originally Posted by Spanrz

Now if all else fails, and I choose to throw it all away, that I might choose an Argo Navis or similar system.
Is the Argo system encoder a motor? Or just a digitial sensor (where you still have to move the mount manually?)
I'm just confused at exactly what the argo navis system is. (automatic or manual)

Hi Brett,

Gary Kopff from Wildcard Innovations here.

On its own, Argo Navis does not directly drive stepper or servo motors.

Instead, it interfaces to a pair of devices known as optical encoders which
are fitted to each axis of the mount.

As the mount rotates, the encoders provide a stream of electrical pulses
to the Argo Navis unit such that it can keep track of the position of the mount.

In order to use Argo Navis, you align on any two objects you know, typically
a couple of bright stars. Argo Navis then can keep track of where you
are pointing in the actual sky. In typical use, one then dials up an object
from the in-built catalog of objects and the Argo Navis display shows you
the amount in degrees by which you need to push the scope in both axes in
order to acquire the target. The display updates in real-time as you move the
scope so that when the numbers read 'zero' you can look through the eyepiece
and there is your object.

So, in a nutshell, one can use Argo Navis in conjunction with a pair of encoders
and then manually push the scope, using what John Dobson would refer to
as 'yoghurt power'. Some refer to this mode of operation as PUSHTO.

Having said that, Argo Navis can interface to a couple of the popular third
party servo motor solutions on the market, namely the ServoCAT by
StellarCAT in Arizona and the Sidereal Technology (Sitech) controller by Dan Gray in Oregon.
The Sitech Controller is the one on the left-hand column of the cited web page -
http://www.bbastrodesigns.com/BBAstr...ted_Telescopes

Keep in mind that the Sidereal Technology controller, despite some confusion
out there, *is not* what is referred to as the 'Mel Bartel's system', which is the
one that appears in the right-hand column of the aforementioned web page.
It just happens that BBAstroDesigns Inc, which is a company owned and
operated by Mel in the United States, is a dealer for the Sidereal
Technology controller as well.

Sidereal Technology's own web site is at -
http://www.siderealtechnology.com/

These days, the better commercial telescope control systems employ servo motors
rather than stepper motors owing to the considerable advantages servos
have, including a higher dynamic torque range.

The older Bartel's system is a stepper-motor based system.

When interfaced to either the ServoCAT or Sidereal Technology controller,
Argo Navis performs all the object offset and tracking rate calculations on
their behalf. Simply dial up an object on the Argo Navis and then press the
GOTO button on the motor controller hand-pad and you have full slew and
track capability.

Keep in mind that on an Alt/Az mount, when tracking, both axes
are moving simultaneously and the tracking rates are continually changing as
you track the object.

An example of a Sidereal Technology controller used in conjunction with the
Argo Navis is the SpicaEyes scope by Tom Osypowski of Equatorial
Platforms. See http://www.equatorialplatforms.com/s...lipstream.html

An example of a ServoCAT controller used in conjunction with the
Argo Navis are many of the scopes coming out of Obsession in Wisconsin
where both are optional accessories.
See http://www.obsessiontelescopes.com/a...ies/index.html

SDM Telescopes in Victoria also routinely install Argo Navis and ServoCAT
systems on their range of premium Dobs.
See http://www.sdmtelescopes.com.au/

The ServoCAT tends to be optimized for scopes in the 14" to 48"+ class and
its price/performance point tends to reflect this and I note you currently
have a 12" Bintel Dob.

Argo Navis itself is deployed on all ranges of apertures and mounts and
there are many users with 12" Bintel Dobs. The unit is completely standalone,
doesn't need a PC or laptop operate, will run off a set of AA batteries so it
is easy to throw in the car, drive to a dark sky site and begin observing.

We provide full assistance to many ATM'ers and see units deployed
on all sorts of mounts, from the conventional to the exotic.
For example see http://www.wildcard-innovations.com....NO460_argo.jpg

Argo Navis is designed and manufactured in Sydney and has been a U.S.
Sky & Telescope Hot Product.

Hope this answers your question.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au

[bojan]

Brett,
Argo Navis is much too expensive for what it does.
If you have any DIY skills, you should seriously consider Mel's free software, as it will give you the same functionality but for much less money.
Also, as time goes by, you can add necessary mechanical parts + stepper drivers (they are not specialized in any way, it is a design using discrete components) to have full-blown Goto system (including field rotation, focus control etc), something not possible with AN only (which is a good system, but it has its limitations, one of them being a price range, as mentioned before).

And, I am sure Mel Bartels solution will give you much more satisfaction - after all, this is DIY area of the forum.
Being a freeware, you can even write your own routines if you want, as the source code is made available under the public license, and contributions are actually encouraged.

EDIT:
Another alternative to AN is David Ek's box: a small interface between optical encoders and computer (via RS232) which can be interfaced with your favorite planetarium software via ASCOM platform.
Again, free if you know how to use soldering iron.

Link to David's website is below:
http://digicircles.eksfiles.net/software.php

[Spanrz (Brett)]

Gary,
That's the info I was after (and the detail of it). I just found it hard to get a definition of what the Argo was. Thank you.

Bojan, yeah pretty handy with the soldering iron. I am a Diesel Fitter by trade, which is now becoming more of an Auto Elec job. So, well into electronics.
The interesting this is, I know of a system with encoders (PWM sensor) coupled with a driver box and a small ECM, but it's used in a hydraulics circuit to slow the hydraulics down with precise movements. It's quite a Japanese system, built and made in Japan, had to read Japanese manuals to figure out how it works. Problem is, I can't just figure an easy way to implement it as it will need to be modified quite a fair bit. Frustrating, that the infrastructure is there, it's just not easy to install. So that idea is out.

I even got thinking about using wiper motor units, or planetary drives for the mechanical motor parts.
I just have to think what is best for what I want to do.
Lots to think about, but my curiosity is a lot better now. Thanks.

[bojan]

Brett,
The encoders you are mentioning are not suitable for telescopes.
Telescopes are using incremental encoders (or rarely, absolute - but they are VERY exepsive compared to incremental ones), which is not PWM sensor.
Incremental encoder outputs a certain number of pulses per full revolution of shaft. and it has two channels (signal is delayed by 90°), so the processor can determine the direction of motion, and can account for position/direction of where telescope is pointed at.

To (quickly) track satellites and that sort of stuff with telescope, most likely steppers are not the right answer (they will be too slow), you need a fast servo mechanism, and you will not find this sort of thing used for astronomical telescopes very often, as we are here more concerned with positional accuracy and smooth tracking without periodic errors and much less concerned with speed.

Perhaps you should look into military surplus for something to implement here for your project?
In the past I was working with Marconi artillery radars (from WWII), they were using powerful servos to drive radar antennas very quickly, as they needed to track aeroplanes and calculate the parameters for aiming guns.
Maybe something similar can be found somewhere on some military crap yard..
Also, so called RAWIN receivers (used for tracking balloons with meteorological sondes, again in US artillery units), they also had suitable servos.
Anyway, good luck with your project.. :-)

[netwolf]

Well this brings back memories of my journey from dob to goto telescopes.

Most of the usual options have been covered of here but there is one that has been left out. Many people have retrofitted a Meade Autostar system to there Dob and various other mounts. This is commonly refered to as a "roboscope". There is a yahoo group called roboscope where people discuss such conversions.
http://tech.groups.yahoo.com/group/roboscope/

This is a good site with various conversions done.
http://bedair.org/ScopeStuff.html

I am actually using the Siderealtech Controller with Losmandy Servo motors on my G-11 mount. Dan Grays system is very robust and Dan actively participates with users why the yahoo group.
http://tech.groups.yahoo.com/group/sitechservo/

The Mel Bartel system can be built if you have the skill from ground up relatively cheaply. Mel also has yahoo group through which he interacts with the user base and is quiet responsive and very helpfull.
http://tech.groups.yahoo.com/group/scope-drive/

Another good resources for kits for either Mels Stepper system or Dan's Servo system is
http://gototelescopes.com

Gary's AN system while expensive comes with awesome support. And Garry is always available on the phone and willing to talk and help you with anything astronomy related. I have the AN and will be using it with my Siderealtech system to give me a portable system without the need for laptop.

Plenty of options out there. And also plenty of great people to meet along the journey, that perhaps is the best of all things.

Regards
Fahim

[Barrykgerdes]

Originally Posted by bojan

Brett,
The encoders you are mentioning are not suitable for telescopes.
Telescopes are using incremental encoders (or rarely, absolute - but they are VERY exepsive compared to incremental ones), which is not PWM sensor.
Incremental encoder outputs a certain number of pulses per full revolution of shaft. and it has two channels (signal is delayed by 90°), so the processor can determine the direction of motion, and can account for position/direction of where telescope is pointed at.

To (quickly) track satellites and that sort of stuff with telescope, most likely steppers are not the right answer (they will be too slow), you need a fast servo mechanism, and you will not find this sort of thing used for astronomical telescopes very often, as we are here more concerned with positional accuracy and smooth tracking without periodic errors and much less concerned with speed.

Perhaps you should look into military surplus for something to implement here for your project?
In the past I was working with Marconi artillery radars (from WWII), they were using powerful servos to drive radar antennas very quickly, as they needed to track aeroplanes and calculate the parameters for aiming guns.
Maybe something similar can be found somewhere on some military crap yard..
Also, so called RAWIN receivers (used for tracking balloons with meteorological sondes, again in US artillery units), they also had suitable servos.
Anyway, good luck with your project.. :-)

Not something like a 262 by any chance.

Barry

[Spanrz (Brett)]

Update.
Well I have put myself to shame (to a degree). I spent a bit of money.
I have now a stepper control system that can be computer controlled (like a CNC machine can)

After many hours of contemplating, pulling apart a dead fax machine for it's steppers, reading IIS for stepper system ideas, countless hours watching youtube on concepts/designs, reading Mel Bartel's Website for ideas, researching and understanding what IC's do, decide what system do I need, designing and redesigning a circuit board for my needs, I thought it was all too much for what is supposed to be a simple system.

So, after many ummm's and arghs, took a venture down to Ocean Controls in Seaford (Melb) and asked what's on offer for my needs.
Figured that a system that closely matched a CNC design is exactly what I need.

So after my efforts, I bought 2 stepper motors (biploar), 2 microstepping drivers (digital ones), 1 parallel port breakout board (to connect the drivers to).
Ok, it cost a small fortune, but after seeing what it can do, I think this best suits my needs of different speeds of tracking stars to all satellites. (original concept).

I'll post up more details soon, with pics, but the drivers blew me away with the beautiful control at slow speeds, with low vibration from the motors.
The standard driver (assuming it's analog??) does not control well (vibration and jerkiness wise) at slow speeds with somewhat of a microstep, motor gets all noisy and vibrates a lot.

OK, so now I have to come up with the goods, so happy
Going to drive my wife nuts, but it's all about me, not her

http://farm4.static.flickr.com/3550/...38b24d01_b.jpg

[netwolf]

Brett, you might want to ask Mel Bartel if his DOS based stepper software can be made to work with your hardware. I would have thought Mel's hardware would be cheaper to buy rather than microstep controllers.

[Bassnut (Fred)]

Its great that your stepper motor set up produces the results you are after, and it suits low cost astro mounts in general. But very few true industrial CNCs use steppers, they are mostly servo drive, as do high performace astro mounts, just to prevent possible confusion.

[Spanrz (Brett)]

Netwolf, I was stuck bewteen a rock and a hard place about using DOS/Mel's system. It was just too old, for my liking. What works is great (Mel's System), but me being tech savy and all, I just couldn't bear with older technology.
Don't get me wrong, I did venture down this path, just I didn't feel comfortable being left in the 70's and 80's technology era.
The only bonus about this type is cost savings and basic funtionality.
The major issue I had with a stepper system, was of course the jitter at low speeds. Now seeing what a digital driver does vs the older drivers, there is no comparison to smoothness.
I was floored and stoked about how it performed over the older drivers.
Unfortunately my mind overtook my wallet and parted with a few hundred dollars as soon as I seen it. I was silly, hehe.

I found this website as a bit of relief about the decison of the Digital Driver.
http://www.cnczone.com/forums/showthread.php?t=82317
(I made a posting about some wiring, but it's all good now)

Bassnut, I did contemplate a servo drive, where I work, I can get servo drives and a few types of gearboxes (reductions). I looked at buying a premade system (ServoCat, ETC) and the cost was just not to my liking for my functionality.
For some reason, the servo method just didn't grow on me.

I've prepared a small vid, to show the stepper in it's first ever movements tonight. Ok, it's fast, but it's being controlled by preprogrammed software, that I have to get used to. Hehe.

http://www.youtube.com/watch?v=7fOY-9HJJ_g

I just have to setup the parameters now, that's the fun part.

[Barrykgerdes]

Hi

I have been reading back through the posts on this topic and have read some interesting findings. However my experimenting with dob driving using friction drives and stepper motors always gave poor results due to slippage and poor speed ratios for the stepper motors. I could not find any steppers easily salvaged that would spin under computer control faster than 3000 steps/sec.

The only really satisfactory method is a servo system based on the feed back from an encoder rigidly fastened to the rotating axes of the telescope. I believe Gary's encoder system meets these requirements in the Argo Navis. Although I have not had the oportunity to test it, in the long run I believe the price would be well worth it.

I have given up playing with stepper motors as in the long term they are never going to be as good as a full servo system.

My next experiment will involve gear drives (or toothed belts) to the axes of my Lightbridge using the salvaged motors and encoders from a Meade Autostar system and use a 497 controller.

Barry

[bojan]

It all depend on do you REALLY need such fast slewing speeds.
What is the rush?
If you do something serious, it is of no importance (unless you want to check hundreds of objects over the night).
Just fiddling with the computer (inputting the coordinates etc) takes significant time and it is not very practical for occasions such star parties.. I found that star-hopping method is much better (of course, you need to know how to find a way among stars). In that case, Bartel's system tracks the object when it is already found (by star hopping or Go_To... or Push-To, via cheap encoders of course.. 7000 ticks per shaft rotation is enough).
Also, you need to consider the rotating momentum of the telescope.. no-one wants to swing it so fast that things are flying of in all directions in the night.

Stepper motors are OK for tracking and short jumps to objects that are not easily visible. They are also much more mechanically reliable (no brushes etc) and simpler to drive.
Slippage in the wheel system is not the problem, if the wheels are done right (brass or steel wheel on steel shaft for example.. and no grease of course), and if the pressure is sufficient.
Of course, wheels are just one way to do it.. I have seen Bartel's system done with worm gears, so any possibility of slippage is removed.
Also people are using timing belts. No slippage there.

"Old" computer technology is OK, it works and it is cheap. $50 for old computer (that will be used outside in the cold, dew, prone to fall in the mud in the dark from a table and so on) is justification enough, I would think.

I wish you guys all possible luck with Vista and such modern products, you will need every bit of it :-)