Arduino Ascom focuser Mark2

[Mav359]

I used that one simply because it was the one in the documentation of the SGL focuser when i first did this for my SCT. They need a bit more room but they have a longer shaft and they deffo have more power, the torque at higher speeds moves the focuser assembly if its not secured.  Works with the easy stepper board

The other thing i like was that it number of steps in a revolution is quite high and it has very smooth motions at the right speeds. From one end of my focuser to the other on my SCT took 331350 steps :-) 

The only downside is at the moment i can't use Dave's aurdino sketch because it doesn't currently work with the Easy Driver and i don't know how to mod it. Its still ASCOM compliant on the older sketch and works with all the 3rd party software.

[blackdragon72]

I'm,afraid not. The AAF2 project was my first foray into ASCOM.

I managed to get my two channel focuser driver up. It is (including visual studio project) available here:

https://sourceforge.net/projects/arduinodualchannelascomfocuser/?source=navbar

It uses one Arduino Nano to control two focusers. The protocol is based on Moonlite, and the main difference is that TempComp is handled by Arduino, not the driver (which I believe Moonlite does).

I have not tested it fully since I have only one telescope, on which one channel focuser works fine.

You should be able to connect the focuser via Moonlite driver directly, but my driver supports more commands than Moonlite so it wont talk to Moonlite focuser (it could be done by removing those additional commands).

[redtail]

Do you mean you want an indication of some sort in the FocusAAF2 program so you can tell if the focuser is moving when you can't see it.

I have added a link to the Wiki section of the SF site http://sourceforge.net/p/arduinoascomfocuser/wiki/To-Do%20List/ to keep track of any requests - I've added yours to it.

Hi has anyone managed to get the program to show the focuser movement.I noticed golyo73 has it showing movement in APT.Thanks

[redtail]

If i wish to use a bipolar 4 wire stepper what changes would i have to make?

[Astroboffin]

Don't forget the advantage in the pulley system. Mine is 4:1, so 1 revolution of the coarse focus knob = 256 steps. You could easily make it 5:1, 320 steps.

When I made mine I had doubts on whether the motor's steps were fine enough but it was so cheap I figured it would be worth a go and maybe upgrade later. As it turns out it is more than adequate, I doubt that the movement would be quantifiable if it was much finer.

Hi all,

Fantastic thread, just wanted to quote on this

I understand that with the Gears and pulleys you will get very fine focus, but if, as I want to, you have a direct to shaft connection, then one Rev of the motor is one Rev of the focus shaft, so with the motor mentioned and used throughout this thread that's only 64 steps, as opposed to 256 with a 4:1 pulley system.

So is 64 steps enough, or is there a different motor I could use, as I have to have a direct connection ?

Regards

AB

[richyrich_one]

I've gone for a direct connection, using the 10:1 shaft on my focuser and that works a treat! I think direct to the normal rate shaft would not be fine enough IMHO. 

Hope that helps. 

[Astroboffin]

I have installed all the software from sourceforge, and all worked perfectly first time, with no issues at all, trying my windows 8.1 laptop next.

Still sorting out which steppers to buy, I think as all my kit is run from a purpose built 12 power hub, I may go for the 12v version of the motor used at the start of this thread.

I realise it is only a 64 step motor as I mentioned earlier, but I notice now that you can alter the sketch from 8 steps per instruction to anything down to 1 so does that mean that it in theory becomes a 256 step motor if I reduce to 4 as shown here in my screenshot.

It will be fitted straight onto my focus shaft I will not be using the 10:1 knob, failing this, would a better motor with more steps be needed, and if so which one, as I don't want to alter any of the provided code, well I couldn't if I wanted too......lol

So I just want to connect a motor and it works straight away, so is the sketch and code purely written for the motor used at the start of this thread or will it work with any available stepper motor

Edited July 8, 2015 by Astroboffin

[Astroboffin]

I've gone for a direct connection, using the 10:1 shaft on my focuser and that works a treat! I think direct to the normal rate shaft would not be fine enough IMHO. 

Hope that helps.

That is my worry

I have a standard skywatcher DC motor fitted ATM on the rough focus shaft, (direct drive) of my William Optics ZS66, and can get very good fine focus with that using the Hitecastro DC focuser controller using the DC motor step routine built into it.

So how much better would this 64 step, stepper motor be, apart from the obvious of incremental steps and being able to move back to exact position.

The other thing is that I am going to go for the 12v version of the stepper mother used here by the OP.

Am I right in assuming that on a 66mm f4.8 scope focus is not quite as critical for wide field deep sky imaging, as it will be for planetary imaging on my f10 8" SCT, this is the one I want the stepper motor for, as I am getting a new Crayford focuser on the back.

Regards

AB

[richyrich_one]

That is my worry

I have a standard skywatcher DC motor fitted ATM on the rough focus shaft, (direct drive) of my William Optics ZS66, and can get very good fine focus with that using the Hitecastro DC focuser controller using the DC motor step routine built into it.

So how much better would this 64 step, stepper motor be, apart from the obvious of incremental steps and being able to move back to exact position.

The other thing is that I am going to go for the 12v version of the stepper mother used here by the OP.

Am I right in assuming that on a 66mm f4.8 scope focus is not quite as critical for wide field deep sky imaging, as it will be for planetary imaging on my f10 8" SCT, this is the one I want the stepper motor for, as I am getting a new Crayford focuser on the back.

Regards

AB

I have no experience of the Skywatcher motor but as you, I also suspect that it woud provide finer if not as precise control as the stepper.

The 12v motor will provide more torque and this "mod" seemed like the logical choice given that pretty much everything else astro wise is 12v, except the 5v stuff

As far as I know focal length has nothing to do with focus, it will be the same what ever the scope...I stand waiting to be corrected on this.

You may well be right on the MOTOR_STEPS_PER_DRIVER_STEP value, I have not tried altering this value.

If it does do what you hope, from what I can gather on the web the motor has about 512 steps per shaft revolution. So if you change it to 4 from 8 it will be 128 steps(512/4=128)

As with most things try it and see what happens, some of the best discoveries have been found that way.

[Astroboffin]

I have no experience of the Skywatcher motor but as you, I also suspect that it woud provide finer if not as precise control as the stepper.

The 12v motor will provide more torque and this "mod" seemed like the logical choice given that pretty much everything else astro wise is 12v, except the 5v stuff

As far as I know focal length has nothing to do with focus, it will be the same what ever the scope...I stand waiting to be corrected on this.

You may well be right on the MOTOR_STEPS_PER_DRIVER_STEP value, I have not tried altering this value.

If it does do what you hope, from what I can gather on the web the motor has about 512 steps per shaft revolution. So if you change it to 4 from 8 it will be 128 steps(512/4=128)

As with most things try it and see what happens, some of the best discoveries have been found that way.

Yes agree with most of that, but not sure about the bit to do,with the steps on the mentioned stepper motor, it is reported to be a 64 step motor, not 512, as it says that in the write up on these motors each step is about 5.3 degrees, so 64x5.3= 360 approx one full revolution.

By lowering that number from 8 to 4 I thought they became, 1/4 steps so in effect the actual steps get smaller but more of them, so 64x4 =256 steps per revolution, as each step moves about 1.3 degrees........

That was my understanding but maybe the OP can step in and explain.....as we seem to have completely opposite answers to this one....lol

Thanks anyway

AB

[Dave_D]

i used this one and it works a treat. 

http://www.ebay.co.uk/itm/12V-4-phase-5-wire-Stepper-Motor-Gear-Motor-28BYJ-48-12V-for-DIY-Project-XN-/271475220977?pt=LH_DefaultDomain_3&hash=item3f352f21f1

[tekkydave]

The MOTOR_STEPS_PER_DRIVER_STEP value is how many 1/2 steps the motor takes for each step (Position property) from the Ascom driver. I originally had the motor cycle through all combinations of the motor pins to simplify the programming which gave multiple motor steps per driver step. I realised this could be made finer by just making it step once per driver step so I changed the sketch to accommodate that. The MOTOR_STEPS_PER_DRIVER_STEP value is set to 8 by default to mimic the original behaviour but it can be changed to whatever suits you. Remember - the motor always does 1/2 - steps but they are always the same size.

I think some of the steppers on ebay like the one I used have internal gearing from 64 to 512 steps per revolution - check the datasheets carefully. Hope that helps.

Edited July 9, 2015 by tekkydave

[NEM]

Am I right in assuming that on a 66mm f4.8 scope focus is not quite as critical for wide field deep sky imaging, as it will be for planetary imaging on my f10 8" SCT, this is the one I want the stepper motor for, as I am getting a new Crayford focuser on the back.

If I'm reading the info on this  http://www.astropix.com/HTML/I_ASTROP/FOCUS/DEFS.HTM  page correctly, I think the depth of focus changes as the square of the F number.  So an f10 scope is more forgiving than an f4.8.

Noel

[richyrich_one]

i used this one and it works a treat. 

http://www.ebay.co.uk/itm/12V-4-phase-5-wire-Stepper-Motor-Gear-Motor-28BYJ-48-12V-for-DIY-Project-XN-/271475220977?pt=LH_DefaultDomain_3&hash=item3f352f21f1

Ditto

[richyrich_one]

If I'm reading the info on this  http://www.astropix.com/HTML/I_ASTROP/FOCUS/DEFS.HTM  page correctly, I think the depth of focus changes as the square of the F number.  So an f10 scope is more forgiving than an f4.8.

Noel

Nice explanation... I can sit down now 

[Astroboffin]

Nice explanation... I can sit down now 

If I'm reading the info on this  http://www.astropix.com/HTML/I_ASTROP/FOCUS/DEFS.HTM  page correctly, I think the depth of focus changes as the square of the F number.  So an f10 scope is more forgiving than an f4.8.

Noel

I think that is the other way round, f4.8 is more forgiving than f10, as f10 is far More magnified, than f4.8, the field of view is much smaller.

Well that's my understanding anyway

AB

[Astroboffin]

The MOTOR_STEPS_PER_DRIVER_STEP value is how many 1/2 steps the motor takes for each step (Position property) from the Ascom driver. I originally had the motor cycle through all combinations of the motor pins to simplify the programming which gave multiple motor steps per driver step. I realised this could be made finer by just making it step once per driver step so I changed the sketch to accommodate that. The MOTOR_STEPS_PER_DRIVER_STEP value is set to 8 by default to mimic the original behaviour but it can be changed to whatever suits you. Remember - the motor always does 1/2 - steps but they are always the same size.

I think some of the steppers on ebay like the one I used have internal gearing from 64 to 512 steps per revolution - check the datasheets carefully. Hope that helps.

This is the spec sheet for the motor I have found, and the others I have seen 12v and 5v are the same apart form voltage, 64 step, 5.625 degrees per step, so 64 x 5.625 = 360 degrees.

Can't find any with 515 steps,

So with your method of being able to reduce that figure from 8 to 1 does that then give me 512 steps, per shaft Rev, assuming there is no internal gearing

[NEM]

I think that is the other way round, f4.8 is more forgiving than f10, as f10 is far More magnified, than f4.8, the field of view is much smaller.

Well that's my understanding anyway

AB

I think it's to do with slower scopes (higher f numbers) having a less divergent light cone, so the focal plane can move more before blurring becomes noticable.  Here's another website http://starizona.com/acb/ccd/advtheoryfoc.aspx giving the same type of analysis.

[richyrich_one]

I think it's to do with slower scopes (higher f numbers) having a less divergent light cone, so the focal plane can move more before blurring becomes noticable.  Here's another website http://starizona.com/acb/ccd/advtheoryfoc.aspx giving the same type of analysis.

That's how I understand it (now)

Makes interesting reading, thanks for posting the link.

[Astroboffin]

That's how I understand it (now)

Makes interesting reading, thanks for posting the link.

Yes very interesting, but I stand by what I said before, I still think you have it the wrong way round, if you take a wide field image with the small 66mm f4.8 scope you can get away with it a tad out of focus without it damaging the image too badly.

But in contrast if you use an 2000mm f10 scope and image Jupiter for instance, focus is absolutely critical for a half decent image.

And I think on the site that was linked it says that but in a very very scientific way, which is very hard to decipher.

The in focus area of the f4.8 scope is much smaller due to the large field of view, whereas the f10 scope has a much bigger in focus area because of the much smaller FOV, so consequently much more critical as much more noticeable......

So let's here from others......on this

AB

[Astroboffin]

Ok, so I have figured out this stepper motor issue with the steps, the motor I am getting is the 12v, 64 step with a 1/64 gear inside, version of the one the OP used, which means that it gives 64x64 = 4096 steps, but as in the sketch the motor moves 8 steps per driver step, that means 4096\8 = 512 steps per Rev, so I will leave set at 8.

But I can see the motor the OP used was a 32 step with 1/16 reduction gear, which gives 32x16= 512 steps, but for that motor to get the full 512 steps the MOTOR_STEPS_PER_DRIVER _STEP would need to be set at 1

Well it makes sense to me now anyway, but worth knowing if you are looking at buying one of these motors, as they all look the same on eBay, but they are not.

:)

AB

[tekkydave]

Ok, so I have figured out this stepper motor issue with the steps, the motor I am getting is the 12v, 64 step with a 1/64 gear inside, version of the one the OP used, which means that it gives 64x64 = 4096 steps, but as in the sketch the motor moves 8 steps per driver step, that means 4096\8 = 512 steps per Rev, so I will leave set at 8.

But I can see the motor the OP used was a 32 step with 1/16 reduction gear, which gives 32x16= 512 steps, but for that motor to get the full 512 steps the MOTOR_STEPS_PER_DRIVER _STEP would need to be set at 1

Well it makes sense to me now anyway, but worth knowing if you are looking at buying one of these motors, as they all look the same on eBay, but they are not.

:)

AB

The sketch does half-steps too as it alternatively energises both coils in between the single coils. If you look at the sketch there is an array of values you should be able to see how it works. Plus I have it geared down further by the belt & pulleys I use. The main thing is this is not a completed design and I like the idea of people experimenting with it and and adapting it for their own needs. Post some pics when you have it working

[Astroboffin]

The sketch does half-steps too as it alternatively energises both coils in between the single coils. If you look at the sketch there is an array of values you should be able to see how it works. Plus I have it geared down further by the belt & pulleys I use. The main thing is this is not a completed design and I like the idea of people experimenting with it and and adapting it for their own needs. Post some pics when you have it working

I will do, as I have all the bits arriving over the next week, so the fun will start, although by the sounds of it, I have done what can be a awkward bit and got all the software installed and up and running, but using my Arduino Uno ATM.

I am going for a design that see just the motor on the focuser and the rest of the electrics and control boards will be in a project box on my mount about a metre away, so I will need to extend the 5 core motor cable, and am thinking of using a Cat5 cable with sockets

On the box either end to connect all together.

AB

[redtail]

I went with this one simply because id use them before and it worked so i just went again. They also do a bracket for it which i bought to use as a template

https://www.coolcomponents.co.uk/stepper-motor-with-cable.html

I have made another focuser with one of these steppers http://www.mclennan.co.uk/product/p542-geared-stepper-motorthey are available from rs components and are very very strong.In fact you would be pushed to to stop it.same software and driver board as the original set up.The stepper is the exactly the same stepper used in the lakeside focuser but works a lot faster than the lakeside.This maybe due to the arduino.well chuffed

Edited July 11, 2015 by redtail

[redtail]

Wow these mcclellan steppers are power houses