Stepper Motor System / Advice

[netwolf]

Brett, you should take a look at the Sitech system I mentioned above, I know i do harp on about it in multiple threads but it really is developing into a bees knees system. The Ascom driver now includes Platesolving system, a Mount Modeling system, all this in the Ascom driver itself. Most other systems relly on external software for this intelegence.
http://www.siderealtechnology.com/
Its reltively inexpesnive esepcially if as you say you can get your hands on Servo motors through work. Or you get them of ebay.

Dont get me wrong the Stepper systems are very good for what they do, and yours sound like its quiet a work horse. But what are you going to use to drive it? Do you have some plan in mind for this? I am not sure if there are any generic programs that you can use, but you may have to write your own. I would like to see something like this develop here, becuase there are many dob users out there that want an affordable local solution that can be made from of the shelf parts.

There are a few Stepper systems out there in Europe that are quiet good also. Like the LittleFoot and BigFoot http://littlefoot.rajiva.de/
The MicroGigga system, this is available via Telescope and Astronomy in SA. http://www.micgiga.com/
The FS2, etc etc.

All of these perform well based on user reports.

Regards
Fahim

[Bassnut (Fred)]

Bojan, I agree with you that an Astromount is not in a hurry, so no need for a powerfull, fast servo. But I have found the holding torque and acceleration of a stepper problematic on a system with high inertia. One of the reasons for useing a stepper is its often not necessary to use a tacho or encoder feed back, just count the motor pulses, so cheaper, but electromagnetic slipping in that case (even a bit,without an encoder) leads to rapid loss of position accurracy, or oscillation with an encoder. As with Barrys experience, I think steppers are a bit of a dead end these days, and not much cheaper than servos. Mount motors do so little work generally, that bushes are unlikely to wear out for many years. A servo will always give better performance.

Im not saying you are dead wrong Bojan, am interested in futher thoughts from you on this.

[bojan]

Fred,
Steppers can not slip a bit.. they can only miss a whole step. And when this starts to happen, motor stalls completely, so the user is made aware of it immediatelly. The reason is mechanical overload (very rare), or too high driving frequency (very often) - thus low torque due to coil inductance which does not allow current to ramp up sufficiently.
But all this can be dealt with by proper (and not expensive) design of the motor driver, with appropriate parameters (low enough max speed, high enough driving current/power supply voltage etc). Also, as you said, encoders on the stepper shaft can be used, so missing pulses can be accounted for and corrected as necessary. This however adds to a cost of the system (and with servos, they have to be there).
As to moving heavy telescopes, there is no reason why appropriate acceleration should not be used. And Bartel's program supports it, the practical ratio of speeds is around 1:10 and it is of course configurable. The only problem with this particular software is, slewing is done in half-step mode, so at lower speeds motors are a bit loud (every step is audible). However, this software is supplied with source so someone who knows how to do it, can change it as necessary.
As I ponted out before, I am using this system for years on my dob and it is good enough for visual on star parties and allows for finding difficult objects by short jumps from easier and brighter objects.
Usually I do not need to reset coordinates for the whole evening, which means there is no significant mechanical slippage present. Of course, if I deliberately jump to and from between two far away objects, probably there will be some noticeable slippage, but I never had the urge to test my mount to such extent.. I rather spend this time observing :-)
True, there are better systems.. Ferrrari versus Toyoyta argument was presented on this forum countless of times.
And I am sure there are people on this forum and elsewhere who prefer Ferrari (and perhaps some of them can afford it) over Toyota (or Datsun 180B) but I am not one of them. For me it is important that with my mount I can do what I want it to do, and this is more or less so.
I see no reason to spend k$ for something that may be better, but what will almost never be used (other that need to posses something exceptional and valuable). Being a technical mind and engineer by profession, I always prefer to be practical and extract maximum value from what I already have (or from what I can afford to have).

Anyway.. each one of us is different..

[richardo (Rich)]

Brett,
if you are wanting a Bartels system already built and ready for you to mount,
I still have mine for sale....
See ad..
http://www.iceinspace.com.au/forum/s...ad.php?t=44874

These motors have heaps of tork...
Sounds like you'll get some help from Bojan which wil be good... to get you up and running.

Can sell it without lap top for $380.00...


PM to let me know if your keen..

Rich

[Rod]

I can't add much to the technical discussion here but thought it might be useful to let you know I can run my Bartels stepper system comfortably at 3 degrees per second when slewing. In fact I can run azimuth at 4 degrees per second. The alt drive won't go that fast - I assume slight imabalances in the tube prevent that as well as a slightly finer gear resolution. I use large expoxy worm gears so they are very cheap and work well visually.

I am used to running the system at 2 degrees per second for slews and find that more than adequate. Adding flywheels recently increased the speed. Slewing is much quieter than the commercial SCT systems I have seen. Steppers are noisy when tracking and I find that annoying but the noise can be reduced substantially by using plastic mounting bolts etc.

Thought I would add this for sake of completeness when discussing / comparing the Bartels drive.

Rod.

[Spanrz (Brett)]

You know, lots of good valid points. Something I have taken on board.
And gladly accept your views.

Rich, thanks for the offer, but I think I've committed myself now.

Bojan, the concept is to be diversified. Meaning, not only track stars, but also Satellites, Space Shuttles, ISS and a challenge to possibly track other airborne stuff (i.e For a bit of fun, Jet Planes).
It wasn't designed to track so fast that it's like a radar dish whizzing by. It's the variance of speeds with steady motion.

Now I looked at all possibilities, but the cost factor put me off (Netwolf, I did consider Sidereal a while ago). Not only that, the function (IMHO) of speed varience was limited (locked). Shoot me down, if I'm wrong??
It was designed to track stars, with a very low error rate.
With Argo and (we'll say) a Servocat or to the likes of a high end GOTO, the $$$$ vs Functionality just didn't gel with what I envisaged/dreamed of.
I wanted to push the envelope, than just tracking stars. Blame NASA, hehe. I have just got the want to track the ISS and the Shuttle.

What your views are on stepper systems Bojan and the issue about steppers at low speed are an issue which I took great recommendation to (your views). That was one of my concerns and I teetered to a Servo System.
I have read entireless threads on Mel's system and agree wholeheartedly on what you guys think of "If it works, leave it alone" or "stick to what's best".
I grew up with DOS, win 3.1, win95, win98, win2000, win xp and now vista. I am accustomed to changes with the software (and the sometimes lack of tech support/redundancy when all else fails), but IMHO, it's time to get a project in today's world.
I had made myself sucumb to making a system from scratch, you know, on the cheap (what some of your views are), keep it basic and all, but the effort that I have already put in wasn't giving me results on how I wanted it to be.
I just got tired of trying to find something that was "proven" but wanted a view on todays world that used today's technology, like using a USB port, not parallel or serial (etc)
Yes, as you guys have voiced good opinions about what is best, I haven't forgot that.

Now what I bought, cost $600. Gave me a power supply, parallel board, 2 drivers and 2 motors.
I have had a play around with it the last few days. Have an issue with the PC talking through to the Parallel board and making that tell the drivers what to do.
I can connect to the driver itself through the serial port/cable and program and test off that. That works fine.

Though, I've got a case of "IKEA" at the moment. Got it all together, but the instructions say confusing stuff.
The Software for all the talking is working, but not correctly. The board instructions are very very basic, I know I got the board on and functioning, but the software to drive the board isn't moving the drivers.
I've done as the instructions say, but nothing moves. It's a trial and error. I've been told to have a crack at VisBasic, if all else fails.
It's just that I don't know (I can't see it - the signals), that where the communication is failing (i.e signals at the board but no further, the board is faulty, the software is setup wrong, cable wired incorrectly etc etc.).

It will be something stupid I haven't setup yet. Plenty of settings to get through.

But it does work and to show, I have got the speed down again, to a point where it still makes no noise or vibration.
I must make a point, that "all" stepper systems I have seen thus far, whether on youtube or what some of the IIS users have got or experienced, do make noises, vibrates and jitters quite a lot at this level of speed. And IMHO, they use older technology.
But what I have achieved (to show myself), that at slow speeds that it shows no signs of vibration (resonance) and noise. Even no jitter.
And heaps of torque.
I've had this system a lot slower than the link/vid below with outstanding results, but forgot to take a vid of it. I had it turning about 1 rev a minute, with no vibration / noise / jitter.
It has settings in the software for the driver, to adjust for that. (phasing etc etc)

http://www.youtube.com/watch?v=TYTS4-YgaXw

It's one of the reasons why I bought it. As the non digital driver models could not perform at this level. I was shown with the same model motor on both devices and the digital one blew the other one away.
Now, I'm only assuming (voice your opinions if you want), that most models of what Mel's system or most other people use on a stepper control systems, use the non digital driver one with older tech.


The problem is, there is hardly anyone here or around the world, that have tried to use the Digital driver for a Stepper system for a Telsecope.
Someone (1 person in the states) has tried it and also gave absolute rave reviews on how it's handles the steppers.

Me think's, I'm a guinea pig

[MrB (Simon)]

I'm a little unsure what you mean by digital/non-digital stepper drivers?
Could you elaborate please?

[kinetic (Steve)]

I made the Datsun 180B from the ground up too
I cannot comment on the pros and cons of the servo system
as I have no experience of it.
Feedback on Mel's site about the Servo system is very positive.

I couldn't add anything more about the stepper system except
maybe about positional feedback and stepper stalls during slews.

If the system has been designed and refined well, as Bojan refers
to in his post, the slews can ramp up in speed, slew at a linear
rate and ramp down....all without a stall or problem due to inertial
load. On my system the slew is about 2 degrees per second.
But I hardly ever use it...it's mainly push-to locally or a correction
using the ASCOM interface in microsteps.

Also, positional feedback can be made to be quite accurate.
And quite cheaply too. 4000+ count rotary encoders can be a few
hundred dollars each US.
Or you can rip apart a cheap serial mouse and use the photo
interrupters out of it. Your imagination is your only limitation as
to the practical implementation.
Here I recently upgraded my positional accuracy on the homemade
GEM to be 8500 counts per 360 degrees on DEC and 25,000 counts per 360
deg on the RA. All using cheap recycled bits and pieces.
FWIW

regards,

Steve

[Spanrz (Brett)]

Originally Posted by MrB

I'm a little unsure what you mean by digital/non-digital stepper drivers?
Could you elaborate please?

Digital :
http://www.americanmotiontech.com/pr...ries/DM556.htm

Analogue :
http://www.americanmotiontech.com/pr...eries/M542.htm

Look the same, but perform way different.

The Digital is promoted "as Servo like".

The analogue talks a lot about "the driven motors can run with smaller noise, lower heating, smoother movement and have better performances at higher speed"
Which tells me, they still have a choppy jittery feel at low speeds, but better than most on the market.

Steve, loving your (Datsun 180B) project -(worm gear stuff).
Engineering greatness!

My head (mind) is somewhat in the Datsun 180B, but my heart is in the Ferrari. I have the hands to design to build that 180B, but my heart won't let me...haha.
The Datsun 180B will be in the gearing and mounting.

[netwolf]

In essence I think the diffrence is that a DSP microprocessor is used on the controller to provide intelegent microstepping over a larger variance in speed. Things like natural resonance are automatically calculated and dampning is provided. Also there is more microstep options available than on a standard analalogue controller, in which the microsteps available are pre-defined.

I think however you will still need to program code to drive it for Alt/Az tracking. Genrally the software provided is for testing and demo use. There is probably some basic code out there that you can use for some intial simple tracking programs and build on that. In essence you are going to need something like Mel's software Scope for dos or Scope II for windows. Or even simplar to a AScom driver like what Dan has developed for his Sitech controller. I am not sure of the full capability of your controller, but you might be able to program it to do just basic slew and track without need for computer, and use the computer to provide extra control for Goto, alignment, pointing etc.

You may also consider something Like Labview to create your computer interface. Labview alows you to create realtime instruments on your computer that you can then interconnect with external controllers to provide a total control system.

[MrB (Simon)]

Thanks guys, was just a little confused as all stepper drivers are essentially digital.

[Spanrz (Brett)]

An update.
It's taken a bit of time to get used to all of this system.

I used a CNC software called Mach3 to drive the motors.
After many hours, attempts, trial and error and plenty of coffee, I got the parallel port to talk to the drivers. I think I had the steps/settings a bit messed up.
Still a few adjustments on the drivers, but it is now a fully functional 2 x stepper control system.
The motors have a huge amount of torque, but as some of you have said about steppers, there can be an issue of dropped steps.
I've had that issue, but because there are so many types of settings, you can accomodate for that.
Wrong step setting/amperage/phase on this system, does produce drop steps and no/reduced torque, but with a bit of paitence, it all comes together.

Vid of what it can do now.
http://www.youtube.com/watch?v=bex-VJLsgeM

Now, it's just making a G-code up, to track.
Going to see if I can control a g-code as slow as I can with no jitter/dropped steps. Less gearwork, less backlash.

Then comes the fun part of mounting and geartrain system.

[rajiva]

Hi Fahim,

Originally Posted by netwolf

There are a few Stepper systems out there in Europe that are quiet good also. Like the LittleFoot and BigFoot http://littlefoot.rajiva.de/

yes, but the BigFoot Project was replaced by the new LittleFoot Elegance Photo Controller. The LFE Photo is also a self construction project but available as ready made controller (~450 Euro) over several companys as well.

CS
Rajiva

[MrB (Simon)]

Hi rajiva, welcome to IIS

Thanks for the link. Looks like a great little unit, very well thought-out.
I particularly like the heater for the LCD panel! A very nice touch.

[rajiva]

Hi Simon,

Originally Posted by MrB

welcome to IIS

thanks.

Looks like a great little unit, very well thought-out.

Yes, we put a lot knowledge in this controller. The LittleFoot story is now running for many years and the community around the project is growing and growing.

I particularly like the heater for the LCD panel! A very nice touch.

We put the heater in as with very low temperatures the LCD gets slow. The temperature is measured by a NTC that is connected to the ADC of the MCU. The MCU is triggering the heater depending on the temperature.

We also put a lot features in the controller that we see outside as extra equipment. EPEC is a similar feature as the Meade Telescope Drive Master, the SkyAgent is something like Celestrons SkyScout but useing our huge object database, the Robofocus controller is just that and so on. I like the idea to just have one small box that includes as much as possible.

At the moment we are trying to get the stand alone autoguider running which uses the build in video controller. I do not know where we end up with this project in the future.

CS
Rajiva

[MrB (Simon)]

Originally Posted by rajiva

...
We put the heater in as with very low temperatures the LCD gets slow.
...

Hehe, I discovered this problem when I visited Germany mid-winter, my mobile phone screen was un-readable most of the time!
Australians don't normaly have this problem

[rajiva]

Hi Simon,

Originally Posted by MrB

Hehe, I discovered this problem when I visited Germany mid-winter, my mobile phone screen was un-readable most of the time!

yes, LCDs do not like the cold, me neither.

CS
Rajiva

[Spanrz (Brett)]

Bit of an update.
Been a slow progression here, namely costs and priorites got the better of me.



Since the last update the following has happened :

• I spiked the breakout board a couple of weeks ago, with one of the loose motor wires (doh!) And it still worked, but one motor would turn only one way. I figured I spiked the IC. Just re-purchased another board, no worries now... Motor wires are taped up
• Bought a USB to Parallel adapter, on the onus that I would try to atleast attempt a connection to the controller. Nada, tried so many ways of drivers and all, I gave up as there is virtually no software or extremely hard to find someone who makes a type of usb to parallel port connection, so you can talk to the controller. These devices are "strictly" Printer only. I did read on IIS about the issues, but had to make it clear to myself that it could or couldn't be done. (It cannot be done)
• Looked at various ways of getting a parallel port connection using the new laptop. Found that you can buy an "expresscard" to use with the late laptops that can be built with parallel port connection.
• This option is the "only" and best alternative, than to buy an older Laptop PC with a dedicated printer port.
• Finally found a expresscard with a printer port, however this was an arduous procedure. No one stocked them. Went to about 7 stores (DSE, Jaycar, Officeworks, HN, etc etc). You could buy a Serial Port version, but not the Printer Port one.
• The only way was to purchase an expresscard via Ebay. That is, a PCI-E version, not the USB one. Had to buy it from China (Taiwan) for $59 AUD, including airmail shipping.

So far, as everything was a guess that it would work, has now come to a point that everything does infact work.

I now have succesfully tested a late model laptop, fitted with an expresscard (PCI-e) parallel port connected to a cnc breakout board (controller) that supplies two drivers and motors with a function to work.

Because there is such a finite control, I still haven't figured out the stepping yet, as it works so finitely, it's so hard to see it work.

I am still awaiting the delivery of my worm gear set from HES (Smallparts in QLD), it's due in around a week or so. But just realised, I have a package at the Post Office waiting for me. It might be the gears, or it might be some AC/DC tix.

Anyways, i'm just so relieved that now I can get somewhere with this stepper system with the newish laptop.

The hardest part now, is setting up the software (configs). I had it working really well on the Desktop ages ago, but wiped all my settings due to windows being corrupt and reloading it.
So now, I have to "trial and error" things to get what I used to have.

[Spanrz (Brett)]

Just got the gears in the mail. Happy with what I got.

Now comes the engineering of the brackets and the fitment of it all.
Not going to rush this part.

Glad I got the parallel port yesterday.

Here's the gear pics.

http://farm3.static.flickr.com/2576/...c8a3736692.jpg

http://farm3.static.flickr.com/2573/...895da330c7.jpg

http://farm3.static.flickr.com/2787/...fc696221_o.jpg

[bojan]

That looks good.
Good luck with the rest :-)