A Low Cost RA Stepper for Small Telescopes

[Merlin66]

In NSW yes, being a member of a recognised astronomical society allows you to store and use laser pointers. Unfortunately other states don't allow this and you need to apply for a special permit. Currently $180 for three years.

[Leo.A]

I'm in NSW and have removed the capacity for an internal battery, having hard wired the device internally with wires running out ready for my yet to be made power tank. I have a separate voltage regulator to supply the required 3 volts and it will be a somewhat permanent mount on one of my scopes with the ability to swap it over with tools.

I live nowhere near a city (Lithgow NSW) and there are no direct commercial flights over my area. My only concern will be not using it when the military do night training in their blackhawks over the area (twice in the last 6 years, the weapons factory is in the town).

We also get emergency choppers coming to the hospital which is close but I know better than to try and interfere with that, it was nearly me in one a year ago (close call yet my doctor never told me exactly what was wrong, only that I'm very luckyy to still be here, it was close).

I really miss the edit feature, especially with my lack of typing skills!

[Oser]

I recently bought a telescope and started looking towards the sky. Its a skywatcher 150P on an EQ3-2 mount. After a couple of nights observing I started thinking about making my own tracking/goto system and my internet research lead me to this thread!

First of all great work AstroTux! Your documentation was really well laid out and a pleasure to read. I imagine it will be quite a help to any work i'm able to do.

The idea I had is slightly different to yours Astro. I'm hoping to have GoTo functionality and my plan is to use a Raspberry Pi as the brains of ther operation. I'm assuming I could download a list of stellar coordinates and once I align the scope to a known target, let the Pi know what its looking at and from there it would know how to navigate to any object in the database. If I make any progress, I'll be sure to let you guys know. I also may have a question or two which you might be able to help me with AstroTux, if it wouldn't be any trouble

At the minute I'm wondering about the motor. I read in your PDF that the arduino one didn't have enough torgue for the RA axis. I was wondering if you knew the torgue requirements? Then I'd be able to get a motor from RS or somewhere like that. Also did the shaft coupler connect the motor to the scope without any problems?

Thanks if you're able to offer any help. If you've any questions regarding my project feel free to ask. I've yet to start it though and am in the preliminary planning stage

Kind Regards,

Matt

[AstroTux]

At the minute I'm wondering about the motor. I read in your PDF that the arduino one didn't have enough torgue for the RA axis.

The stepper motor needs to have enough torque to overcome any latent friction in the mount's RA axis. There are plenty available that can do the trick for not a lot of money, such as this one http://www.ebay.co.u...=item35beb45f6c but the design would have to be changed slightly to make this one work as it is a bipolar motor. This motor would work best with an L298N driver chip instead of the Darlington arrays in my original design although the same code could be used.

Another way to increase the torque from a motor is to driver it in 2-2 step mode ( i.e. two coils energized at any given time ) but this will increase the current demand.

I have recently been modifying my original design to handle micro-stepping and this uses 2-2 driving as standard with the micro-stepping waveforms overlaid on top of this using pulse width modulation - unfortunately I am away from home at the moment but when I return I will post the details here and can probably assist you more.

As far as your idea of the Raspberry Pi is concerned, I am quite sure that with some work the code on my motor system could be given a USB interface and a control protocol written and you could then use the Pi to run software such as Kstars and use the INDI interface to control the mount.

If you wish to talk more about these ideas please feel free to PM me, but it will probably be next week before I can get around to replying.

All the best,

Alan

[Oser]

Thanks for the info!

I'm currently in my 3rd year of an electronics engineering degree, although embarrasingly i've never really created any projects outside the degree (I don't even own a soldering iron yet!). I was expecting to write it all from scratch but it's encouraging to see the sucess you've had and if any code transfers over, all the better . If i get something usefull out of it, I can also share what I've created.

I'm pleased to hear that I could use a stepper motor that isn't too expensive, I was looking on the likes of RS at 500 mili NM stepper motors and they were in the £40-50 area. From looking at the Pi it has a bank of Gerneral purpose IO pins that support a manner of protocols such as SPI and I2C which I was thinking of using to drive the motors. As a learning exercise I might design a PCB for the motor drivers, and link it to the Pi using the GPIO pins.

Thanks again for your help, and I may take you up on the PM offer . I'm not in any great hurry to have this done, I'm doing it as a side project mainly P.S I'm thinking of putting a version of Arch linux on the Pi. Thought I'd mention as I see your avatar is the Tux.

Kind Regards,

Matt

[AstroTux]

P.S I'm thinking of putting a version of Arch linux on the Pi. Thought I'd mention as I see your avatar is the Tux.

Yup!!! I do everything with Linux. Gave up on Windoze about 6 years ago......

Alan

[Joseki]

Hi Alan, as you know I'm hoping to have a go at this soon. However I'm rather tempted by the development boards on ebay as a shortcut for me in making the hardware. Basically what looks good to me is to get

1) Atmega32 dev board: http://www.ebay.co.uk/itm/ATMEL-Minimum-Development-Board-Core-System-Shield-Board-Atmega32-Mega32-AVR-/281012534396?_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D14838%26meid%3D6571139761985401882%26pid%3D100005%26prg%3D1048%26rk%3D2%26sd%3D170579115769%26

which includes a 16MHz crystal (not sure the quality, but it could always be replaced later), USB port (+ JTAG and ISP interfaces etc). (GBP 6.61)

2) Darlington array development board ILN2003 http://www.ebay.co.uk/itm/New-Stepper-motor-drive-board-UL2003-test-board-4-Phase-Discount-Free-sale-/261087521046?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3cca076916

(GBP 1.40)

3) HD44780 LCD - same as yours. - GBP 5 ish

Other than worrying about volts and amps, taking the push switches off the board (or adding extra ones to the IO pins perhaps) and adding fuses, as far as I understand this should be pretty easy to plug together (?) with only minor soldering required.

I'm planning to use it with one of these stepper motors for an equatorial platform.

http://uk.rs-online.com/web/p/stepper-motors/0440458/

It's a unipolar stepper motor. (which I got cheap from Astroboot)

Anyway, I'll probably order the parts later next month and start playing but I thought I'd post my plan here in case it's useful (or a really bad idea). I hope that's not being too lazy. Any comments gratefully received - none demanded!

John

[Joseki]

Oh and if you want to pay twice the price for the Atmega32 dev board, to get it from a UK seller (also on ebay), or rather if you want to see a nice photo with the different parts written on, this is the ebay link for you:

http://www.ebay.co.uk/itm/New-Minimum-Development-Board-Core-System-Shield-Board-for-Atmega32-Mega32-AVR-/221147885074?pt=UK_Computing_Other_Computing_Networking&hash=item337d70ee12

[AstroTux]

Joseki,

most of what you have outlined looks good, but I'd be carefull with the stepper motor and driver chips. The motor you are looking at is 20ohms per phase which means that the LN2003 would max out at around 12V ( 600ma x 20ohm ). Driving these chips near their maximum would generate a lot of heat and shorten their expected lifetime.

The thing to be aware of with stepper motors is that they are current based devices ie. it is the current in the coils that creates the magnetic flux that gives the motor its torque. If you reduce the drive voltage, you reduce the current, stress and heat but also reduce the torque.

I think you will find that the control side of things is rather easy using the ATmega board, so I would concentrate most on the motor, gearing and drivers. You should find that a smaller motor can be used using the correct gearing, especially if the output from the motor drives a worm gear as this reduces the 'back torque' of driving gears directly meaning the motor has less to do.

Another couple of driver chips you may wish to look at are the L293D and the L298. Both are H-bridge devices and can be used to drive both unipolar and bipolar stepper motors ( as well as DC motors ). I recently purchased 5 L293Ds for around £3-4 from fleabay and they are used extensively in astronomical equipment. A Hitec DC focuser I recently looked at used one controlled by a PIC18F2550 microcontroller. I am using L298s in a trial barn door mount controller that I am developing and managed to get 10 for around £8. They could benefit you in the amount of current they can handle and their flexibilty. Interfacing them does not require any great changes in the code.

I'll be posting more soon on the barn door controller and some updates to the main code of the RA stepper motor controller, both of which use micro-stepping, but am currently looking at how to integrate a USB stack into my devices so that they can be controlled by a PC.

Hope this all helps,

Alan

[Joseki]

Thanks for taking the time to explain this stuff to me Alan, I appreciate it. There are some L298N and L293d (L298 have heat sinks, 293's don't it seems) modules for sale on ebay that I'll investigate - I'd got it into my head that they (L298N's) were just for bipolar motors (I haven't bought anything other than the motor yet). I'd prefer to use one of those if I can rather than get another, smaller motor. I was planning on using direct drive rather than worm gears for the equatorial table, since the manual reset will be easier.

As an aside - I'll be very interested to read about your USB driver project when its done. I wouldn't want to have to have a PC plugged in to the dob base but I did read a bit about stepperbee+ as one possibility (and I know one day I'll want a eq3-2 or eq5 mount to play with).

[AstroTux]

There are some L298N and L293d (L298 have heat sinks, 293's don't it seems) modules for sale on ebay that I'll investigate

If you get the L298s they can be bought without heatsinks in the vertical version, I might have 1 or 2 left if you want them. If they are used well you do not need a heatsink.

The L293Ds do not have heatsinks but the PCB should be designed so that there is enough copper to act as a heatsink.

The main thing to bare in mind is that you probably want your device to operate from a 12V supply. Most folks want to be able to power from a 12V battery rather than a PSU, as this entails leads and a mains supply. This limits the torque available from most motors, hence my reason for the need for gearing.

Another thing to realise is that unipolar motors can be driven just using a Darlington pulling one end of the coil to ground, but they need a positive supply to provide the current. If you use H-bridges these are slightly more expensive ( hence the reason why I did not use them in the original design ) but they can be used with unipolar motors by just leaving the positive supply connection disconnected. This is in addition to being able to work with bipolar and DC motors. Most unipolar motors are wound the same as bipolar motors but with the centre-taps exposed to enable unipolar operation, hence the ability to use the same driver with all three types of motor.

hope this helps a bit more,

Alan

[Joseki]

Thankyou again! Yes I think I'd need a 12v battery rather than a PSU. The Mega32 board has a voltage regulator on board but at the moment I get the impression that running it through a dedicated buck converter board (also pretty cheap on ebay) would be more efficient and generate less heat - then use that to power the Mega32 and the driver IC, but use the 12v to drive the motor (looks pretty easy to do with the L298N boards)- I plan on reading up on this properly but the wikipedia article on buck converters made them sound good .

If it seems I'm making things complicated by wanting to bolt together pre-made boards it's partly because I don't have the setup to do make my own PCBs (not even a laser printer; and stripboard always seemed too fragile and made the layout too messy for me), so if it ends up being a one-off experience then ebay boards are very cost effective. Thanks also for the offer of the the L298Ns that's very generous, but as I can't make the boards I wouldn't be able to make use of them.

[chrisp9au]

Hi AstroTux,

Another new member from Australia, just 70km up the road from Merlin.

It was this thread and your downloaded files that brought me to Stargazers Lounge.

I'll PM you to see if you're still making up boards for members.

Cheers

Chris

[Gina]

I'm thinking this could be a very useful approach for a mount for camera plus SLR lens.  A lightweight mount is all that's required and something like an HEQ5 is "using a sledgehammer to crack a nut".  As many here know I have an interest in widefield (ish) imaging using the old (and quite cheap second hand) film SLR lenses of yesteryear.  I'm also experimenting with converting DSLRs to mono for narrow band imaging.  All this could lead to a very economical astro imaging system for those with good DIY skills but limited funds.  IMV you can generally achieve things relatively easily if you have tons of money to throw at it - I find it much more fun trying to achieve good results on a shoestring

[Gina]

I have the Celestron AstroMaster 130 scope with it's mount and tripod plus the little DC motor drive.  I made an improved drive some years ago but still using a DC motor.

Making a cheap mount for AP with camera lenses has been something on my mind for some time now as yet another DIY project for the future.  I would like a separate widefield setup with it's own mount and this is one way of getting that.  Admittedly, I hadn't thought of useing the old AstroMaster mount but that would certainly be one solution.  I'll start a thread of my own rather than hog this one.

[c3po]

Not one for dredging up old threads normally but thought I'd post my thoughts on this little beasty of a mod for the Astromaster 130eq stepper driver designed by Alan here.

I'd bought the bits well over a couple of years ago from Alan, and a few extra items from a robotics retailer online, including a small plastic project box to house the finished article. Sadly, life got the better of me and I had very little slate time fire anything outside of work, so the parts were consigned to the depths of my man cave, until very recently.

So with a bit of free time on my hands thanks to the Xmas holidays I took on the challenge.... Here's what I ended up with.

Sent from my GT-I9305 using Tapatalk

[Joseki]

Looking good - I'm still meaning to get round to finishing my copy.  I've got a development board and all the bits, but I need to get round to debugging it (I had issues getting it to work in Atmel Studio and ended up replacing all the LED libraries and calls with the latest ones, plus I'm adapting it a bit to use on an equatorial platform at the same time .. i.e. messing everything up- the display won't refresh, probably very minor ). Um so thanks for posting, it's very motivating

[nagarajan]

Not one for dredging up old threads normally but thought I'd post my thoughts on this little beasty of a mod for the Astromaster 130eq stepper driver designed by Alan here.

I'd bought the bits well over a couple of years ago from Alan, and a few extra items from a robotics retailer online, including a small plastic project box to house the finished article. Sadly, life got the better of me and I had very little slate time fire anything outside of work, so the parts were consigned to the depths of my man cave, until very recently.

So with a bit of free time on my hands thanks to the Xmas holidays I took on the challenge.... Here's what I ended up with.

uploadfromtaptalk1390406952291.jpg

uploadfromtaptalk1390406979244.jpg

uploadfromtaptalk1390407146406.jpg

Sent from my GT-I9305 using Tapatalk

Hi Can you share the design. Did you make any changes in the circuit or coding from the original one from AstroTux. I want to make one for my scope but have no knowledge in electronics. at best I can do some soldering. The wounderfull amnual suggest that it ws not the final design. Will be happy if I can get a complete list of componets and the final codes. I am not able to open RA Control V1.10.sch file. what format is that?... Help me please

[AstroTux]

Hi Can you share the design. Did you make any changes in the circuit or coding from the original one from AstroTux. I want to make one for my scope but have no knowledge in electronics. at best I can do some soldering. The wounderfull amnual suggest that it ws not the final design. Will be happy if I can get a complete list of componets and the final codes. I am not able to open RA Control V1.10.sch file. what format is that?... Help me please

Hi Nagarajan,

the .sch file is an Eagle CAD circuit schematic. You should also find a .brd file which is the corresponding PCB layout file. Both can be opened simultaneously with the Eagle CAD Lite application. This is a free version of Eagle CAD and can be obtained for Windows, Linux or MAC using this link - http://www.cadsoftusa.com/download-eagle/?language=en . When you install it it will ask for a license, but at this stage you can tell it to run the 'Lite' version, which has some size limitations compared to the full version but is sufficient to show these files and is fully featured.

The design has changed a bit over time, but this really just affects the code and is centred around providing micro-stepping of the motor rather than full-stepping as originally shown. There is one minor alteration for the LCD dimming circuit but this is documented in other files that I have placed in this post.

I have to admit that I have been a bit lax in putting the new documentation up but it is on my 'to do' list. Unfortunately other things keep getting in the way....... :grin:

hope this helps,

Alan

[c3po]

Hi Can you share the design. Did you make any changes in the circuit or coding from the original one from AstroTux. I want to make one for my scope but have no knowledge in electronics. at best I can do some soldering. The wounderfull amnual suggest that it ws not the final design. Will be happy if I can get a complete list of componets and the final codes. I am not able to open RA Control V1.10.sch file. what format is that?... Help me please

I used the original PCB as supplied by AstroTux for my project, and updated the code to include micro stepping and brightness controls from files supplied recently by AstroTux via email.

The only extra components needed for my unit were the project box, a selection of gears and shafts to match, push button switches (3 of), solder tags (not mandatory but makes things easier) and, finally, the stepper motor. The motor is the crucial item, it MUST be Unipolar, run from a 12v source and must have enough torque to move the scope on the mount - read the documentation and the rest of this thread for ideas on which one to get.

[nagarajan]

Thanks for the prompt response. I have started to learn how to burn codes in to a chip. once I complete it let me start assembling the board.

[nagarajan]

I recently bought a telescope and started looking towards the sky. Its a skywatcher 150P on an EQ3-2 mount. After a couple of nights observing I started thinking about making my own tracking/goto system and my internet research lead me to this thread!

First of all great work AstroTux! Your documentation was really well laid out and a pleasure to read. I imagine it will be quite a help to any work i'm able to do.

The idea I had is slightly different to yours Astro. I'm hoping to have GoTo functionality and my plan is to use a Raspberry Pi as the brains of ther operation. I'm assuming I could download a list of stellar coordinates and once I align the scope to a known target, let the Pi know what its looking at and from there it would know how to navigate to any object in the database. If I make any progress, I'll be sure to let you guys know. I also may have a question or two which you might be able to help me with AstroTux, if it wouldn't be any trouble

At the minute I'm wondering about the motor. I read in your PDF that the arduino one didn't have enough torgue for the RA axis. I was wondering if you knew the torgue requirements? Then I'd be able to get a motor from RS or somewhere like that. Also did the shaft coupler connect the motor to the scope without any problems?

Thanks if you're able to offer any help. If you've any questions regarding my project feel free to ask. I've yet to start it though and am in the preliminary planning stage

Kind Regards,

Matt

Hi,

    I found this link who is doing similar project. hope this is usefull.

Microcontroller based Telescope Driver IV

http://martin-cibulski.de/atm/mount_controller_4/

[nagarajan]

Hi Nagarajan,

the .sch file is an Eagle CAD circuit schematic. You should also find a .brd file which is the corresponding PCB layout file. Both can be opened simultaneously with the Eagle CAD Lite application. This is a free version of Eagle CAD and can be obtained for Windows, Linux or MAC using this link - http://www.cadsoftusa.com/download-eagle/?language=en . When you install it it will ask for a license, but at this stage you can tell it to run the 'Lite' version, which has some size limitations compared to the full version but is sufficient to show these files and is fully featured.

The design has changed a bit over time, but this really just affects the code and is centred around providing micro-stepping of the motor rather than full-stepping as originally shown. There is one minor alteration for the LCD dimming circuit but this is documented in other files that I have placed in this post.

I have to admit that I have been a bit lax in putting the new documentation up but it is on my 'to do' list. Unfortunately other things keep getting in the way....... :grin:

hope this helps,

Alan

Awaiting eagerly for the final documentation  .  Once I did it(Using your brain) I want to share the design with everyone  in astronomical club in my home town. they will be delighted.  

Thanks

Nagarajan

[AstroTux]

OK folks. I think I've finally managed to complete the documentation for this project :grin: .

As some of you already know I've been playing around with it and added some new stuff including:

1. Micro-Stepping of the stepper motor
2. The ability to slew the motor by small amounts East and West
3. A brightness control for the LCD
4. The ability to use either a Darlington array to handle a unipolar motor or an L293(D) or L298 driver chip to handle either a unipolar or bipolar motor

I have also taken it a lot further for my own use by adding USB support and writing code under Linux using GTK and libusb to control the device from my PC. However I have decided against releasing this as I have far too many other things to do at the moment, and sometimes life just seems too short :evil: .

I am attaching a .zip file that contains the new code as V1.31 and also contains a long and explanatory .pdf outlining the changes and my reasoning behind them.

RAController V1-31.zip

Anyway, I think that's all, and this will probably be the last post I make on this topic as I want to move on to other things. However if you have any questions please feel free to PM me after you have read and re-read all the information here.

hope this helps,

Alan

[nagarajan]

OK folks. I think I've finally managed to complete the documentation for this project :grin: .

As some of you already know I've been playing around with it and added some new stuff including:

1. Micro-Stepping of the stepper motor
2. The ability to slew the motor by small amounts East and West
3. A brightness control for the LCD
4. The ability to use either a Darlington array to handle a unipolar motor or an L293(D) or L298 driver chip to handle either a unipolar or bipolar motor

I have also taken it a lot further for my own use by adding USB support and writing code under Linux using GTK and libusb to control the device from my PC. However I have decided against releasing this as I have far too many other things to do at the moment, and sometimes life just seems too short :evil: .

I am attaching a .zip file that contains the new code as V1.31 and also contains a long and explanatory .pdf outlining the changes and my reasoning behind them.

RAController V1-31.zip

Anyway, I think that's all, and this will probably be the last post I make on this topic as I want to move on to other things. However if you have any questions please feel free to PM me after you have read and re-read all the information here.

hope this helps,

Alan

Thanks Astro. I was egerly waiting for this. may god bless you for serving the dum people.