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A Low Cost RA Stepper for Small Telescopes


AstroTux

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After a succesful first light last night, I think it is time to let this project into the wild!!

It is based around an ATmega8A microcontroller and features an LCD and three control buttons, and handles two unipolar stepper motors, one for the RA motion of the 'scope and the other as an electronic focuser. The code is written in C so should be portable to Arduino systems, PIC micros, etc.

This is my attempt to provide an extremely low-cost but precise solution to replace the RA motor drives found on small telescopes ( such as my AstroMaster 130 ). It may be of interest to others building barn-door trackers, or looking for a solution on larger telescpes. It is not my intention to provide a replacement for the more sophisticated computer controlled GOTO systems, but simply to improve on the cheap stuff sold for smaller telescopes and I hope you find it interesting.

If you want to know more, I have attached two files to this post. One is the README file that contains all the details of the project including pictures, etc. so that you can see what I have done. The other is a complete .ZIP file containing the code and circuit diagrams as well.

If you have any comments, please feel free to let me and others know. You can always PM me if you would like further details.

I think I've said enough, so here goes...........

RA Controller README.pdf

RA Controller Documentation.zip

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Sounds interesting, thanks!

I've recently purchased some stepper motors to make up a few remote focus units for my small telescopes but the motor drive for my Celestron Astromaster 130 fascinates me. I can put a different scope on my EQ3 pro GOTOG mount and put the celestron back on it's own with a motor drive.

5 small scopes (70, 80, 90, 102mm refractors, 130 reflector) and only one good mount....

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Sounds interesting, thanks!

I've recently purchased some stepper motors to make up a few remote focus units for my small telescopes but the motor drive for my Celestron Astromaster 130 fascinates me. I can put a different scope on my EQ3 pro GOTOG mount and put the celestron back on it's own with a motor drive.

5 small scopes (70, 80, 90, 102mm refractors, 130 reflector) and only one good mount....

Well I hope it can be of some use. All I've got to do now is find a precise way of achieving polar alignment with the EQ3 mount and stop it wobbling about :grin: !!

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It's good to see the knowledge being openly shared with the community :)

Many thanks :grin: . As an avid user of Linux and a lot of 'open software', I'd be hypocrytical not to.....

At least if you see someone offering a similar 'product' elsewhere you know where it came from, its free and you can point others to it. I sometimes wonder how many of those offering LX modded SPC900s on that well known auction site have actually donated to the charities Steve wanted them to?

To be honest, I've solved my little problem which was not difficult and the point of forums is to share information.

Again, many thanks and end of little rant..... :smiley:

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Sounds like an extremely interesting project AstroTux, and one I'm very keen to learn more about... I too have a 130eq and RAW drive and find it stupidly difficult to get accurate enough to match the sidereel rate. Would it be possible to modify the code somehow and control the Celestron RA motor somehow, or would I need to strip it down to bare parts and use the existing gears and stepper motor for this project?

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Would it be possible to modify the code somehow and control the Celestron RA motor somehow, or would I need to strip it down to bare parts and use the existing gears and stepper motor for this project?

I looked at this option, but unfortunately the motor in the Celestron drive is a 'bog-standard' electric motor and can only be controlled by an analogue current, unless you wish to add some form of motor speed sensor which becomes more complex than just building a new system.

The reason for using a stepper motor is the abilty to control it at the correct speed. The gearbox of the standard motor is quite good, but you would have to ensure that you have some way of connecting to it ( it features a small drive gear from a small motor shaft ) and you would also have to work out the gear ratios accordingly.

It is not difficult to take the motor apart so that you can see what I am talking about, simply remove the cover then unscrew the two screws holding the motor to the bracket and the drive gear will slide out with the motor. If and when you do this then you will be able to make your own decision.

regards

AstroTux

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Just wanted to thank you for the trouble you have gone too in bringing this to the masses.

The entire package has been so well presented in detail and it was an absolute pleasure reading through the information.

I was reading through and realised I have all the items listed, identical to what you listed in the guide (except printer stepper motors, I don't want to trash my good printer) including the 28-BYJ-48 stepper motors. It shouldn't cost any more in financial outlay for me to attempt to recreate this project.

Again, Thank you very much!

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I was reading through and realised I have all the items listed, identical to what you listed in the guide (except printer stepper motors, I don't want to trash my good printer) including the 28-BYJ-48 stepper motors. It shouldn't cost any more in financial outlay for me to attempt to recreate this project.

I wish you luck.

A quick point about the stepper motors - I noticed that the 28-BYJ-48 5V did not have much torque. If you have the 12V version you may have a better chance of success. It is also worth trying to drive the gearbox using a worm gear to reduce the torque required..

It should also be pointed out that many modern printers do not use stepper motors anymore, but use synchronous motors instead. If you are looking for other stepper motors if the 28-BYJ-48 does not do the job, then it may be worth trying to find a really old ink-jet printer from about 7 or more years ago. You can probably pick one up for a snip at a carboot, garage sale, etc.

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I actually have a few old inkjet printers laying around. I tend to strip out my old stuff before I scrap it.

I studied electronics for many years but have forgotten too much now. I did manage to spark an interest in electronics in my son who also loves programming and since getting my EQ3 pro GOTO mount with Synscan, I have gotten my son interested in astronomy too (only needed a computer drive), so what I can't do my son does for me (I struggle to learn programming but my son can't cook...(I'm a single dad)) so it balances out.

I was thinking of using the 28-BY-***** to drive another worm gear, not driving direct from the included gearbox. They are only the 5V steppers but if I do it that way, driving a separate worm gear from the attached gearbox I'll have to recalculate speeds and ratios.

I mainly purchased 4 of the 28-BY-***** steppers for remote focus applications as I have 5 small scopes which I am going to take to a friends dark sky regional house and invite a few others out to enjoy the viewing once the weather warms a little. Early spring at my place still sees night temps drop below zero C

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I was thinking of using the 28-BY-***** to drive another worm gear, not driving direct from the included gearbox. They are only the 5V steppers but if I do it that way, driving a separate worm gear from the attached gearbox I'll have to recalculate speeds and ratios.

Sounds like a good idea as the higher gear ratios will lessen the torque requirement from the motor.

When I was testing out some of my theories about gearboxes, timing, etc. I used the ATmega8A circuitry as a test device. This was done by attaching a black circle of card with a white stripe painted/ stuck on it to the shaft of the motor and then using a photoreflector ( the RPR220 is a good choice ) attached to the INT0 pin of the ATmega. By writing small routines I was able to count the number of steps required to turn the shaft of the motor, or to measure the exact time it took to turn the shaft once, and output this information of the LCD.

If this helps I may be able to find the code for these routines and send them on to you. At one point I was thinking of leaving this code in the project so that the device could calibrate itself, but thought that this might confuse matters so removed it.

By the way, don't worry too much about being able to programme - I started out life as an electronics engineer ( mainly analogue ) but after many years in the IT industry had forgotten most of what I had learned in college too. I learnt C in my spare time ( it's really not that difficult ) and now find that most of my 'little projects' are centred around microcontrollers. When you learn what you can do with them, they won't leave you alone :grin: !!

All the best.

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By the way, don't worry too much about being able to programme - I started out life as an electronics engineer ( mainly analogue )

Me too, only my qualifications are only at a tertiary level, not university. Problem is I spent my working life in mechanical and not using electronics much at all. I have forgotten so much it's embarrassing and upsetting considering the hours/years I put in studying after work.

I'd appreciate the code, Thanks!

My son could most likely write it for me but he's working on quite a few projects at the moment.

We have a dead Arduino Uno (good PIC chip), a working Uno and a Mega, along with heaven knows what stuff laying around to play with. With Summer coming in Aus soon and hopefully, some clear skies (last year was a total wash out) I'm keen to get my scopes, web cams and camera out. The remote focus is my first priority but since I only have 2 driven mounts (one's a Tasco 240V drive, not very accurate) I want to get some better equipment rolling along.

Everyone who knows me keep trying to tell me I'd be good at programming, I learned basic (many moons ago) but never progressed beyond that point. I specialise in hardware and leave software to the experts.

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I'd appreciate the code,

OK Leo.A, I'll try and dig it out, but it may take a couple of days. I have too many computers lying around with too much stuff on them :grin: !! Would you like me to PM it to you, or would you just like it posted?

BTW, just had a thought about C. If you google 'C in 24 Hours' there is a .PDF download available of the book. I don't know how legal this is, but the book has been around for quite a while and is very useful. I have a copy as a .CHM file, but don't think I should post it.

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In the ol' days I used a single stepper driver chip (1020?) with a R-C controlled 555 chip timer for the pulses. This gave a compact drive pcb for say a 1 rpm output. Ideal for barndoor mounts etc.

This there still a similar driver chip available today??

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In the ol' days I used a single stepper driver chip (1020?) with a R-C controlled 555 chip timer for the pulses. This gave a compact drive pcb for say a 1 rpm output. Ideal for barndoor mounts etc.

This there still a similar driver chip available today??

Do you mean the HCTL 2020 quadrature driver? If so these are still available but are quite pricey. There are a number of other chips around that may still do this job, but I'm afraid I don't know which. Maybe someone else could shed some light here......

IMHO a microcontroller using Darlington arrays would be cheaper, more controllable and could be built on a compact PCB, but that's just my bias speaking :grin: .

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For those who would like to test the motor and gearbox combination, I am attaching a .ZIP file that contains the code to do this. This is a simple routine that starts the stepper motor moving and then counts how many steps it takes to turn the output shaft once. It willl average the count over many rotations if required - such as for the 28BJY-48 motors,

To do this some form of motion detector is required such as a black cardboard circle with a white stripe on it attached to the output, and a photoreflector to detect when the stripe appears.

I will post the code to time events with another system soon.

Wishing you luck..............

Step Counter Code.zip

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Just a quick toe in the water here, I am thinking of redesigning the main board for this project and was wondering if anyone else would want one?

I would be willing to make a small number available on a non-profit basis for around £6 plus postage, if the demand was sufficient ( obviously not too sufficient or I would have to start a factory :grin: ). These would comprise the ATmega8A, the LCD, Darlington arrays, the voltage regulator and a 10-pin programming header ready to accept the cable from a USBasp programmer or similar. They would also be programmed with my code to start with. If the board without the LCD was required, then the cost would be around £2.25p plus postage.

What you would still need to do to complete this project would be to source the stepper motors, the keypad keys and the gearbox, put it all together, and then programme the device to your specific requirements, using the code above as a template.

Obviously I can only supply these if you accept full responsibility for your actions with the device as I am not a manufacturer trying to sell a product. I simply want to help anybody who wants to try their hand at this project.

If any of you are interested please let me know by PM ( private message ) or through this topic.

Please note that as I will soon be off to scarper up some hills in Snowdonia for a while, the lead time on these would be about 4 weeks.

All the best.........

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Thanks for the code!

The offer for the premade boards is quite generous and if I didn't have all the gear laying around here I'd jump at the opportunity (with extra to cover postage to Australia of course).

I'm sure other members will benefit greatly from the time you have put into this project, thanks again for sharing the information.

Leo

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Just thought you might like to see some of the results from this project taken two nights ago. They are not going to set the world of astrophotography alight, but it tends to show that things are moving in the right direction:-

post-17616-0-69440100-1349106374_thumb.j

Sadr taken as 32, 8 sec subs

post-17616-0-85204700-1349106432_thumb.j

An area near Sadr taken as 8, 32 sec subs.

post-17616-0-21431000-1349106479_thumb.j

Tycho taken as an 800 frame .avi

All taken with an LX modded SPC900 webcam.

Please excuse the processing ( after all these are just a test :smiley: ), and yes the focus was not perfect.

Whilst the stars near Sadr do appear somewhat egg shaped, this is probably because I cannot achieve perfect polar alignment at the moment. I live right in the centre of Reading and my next door neighbours have kindly ignored the young sycamore tree growing directly North of the only place I can put my 'scope :mad: . I'll have to wait until the leaves fall before I can get a really good fix!!

I know that some will say that for deep sky astrophotgraphy and for using an LX modded webcam you need a really good mount, etc., but I like the challenge of being able to do things for a lot less money. When this is added to the appalling light polution that I have to struggle with then an expensive setup is not really feasible. When I move to a dark sky area then I will look at upgrading, but for now.......

The main things that have pleased me about this test are that:

1. The old motor would never have allowed me to get anything other than star trails with a 30 second exposure.

2. The .avi of Tycho would have wandered all over the shop in the past leading to alignment problems in registax.

I think that this is showing that with care some reasonable ( but nowhere near the best ) shots can be taken with a modest setup, a webcam and an accurate RA motor.

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looking good Alan, i'm hoping to push the little drive unit a bit further and try it with my piggy-backed DSLR doing2-3minute subs, currently with the Celestron RA Drive Unit i can't even manage 60 seconds tracked accurately due to the battery fluctuations!

regards polar alignment, you shouldn't need Polaris to do it if you have clear south & east views. If you've got these, then you can try Drift Alignment. it's a bit more hassle, but worth the effort for good subs!

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