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tekkydave

Arduino Ascom focuser Mark2

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3 hours ago, dyfiastro said:

Thanks this is something I was not sure about.
The motor is labels the same as the one in the link and as per the parts list but I have a feeling there is a variation here somewhere.
I went ahead and changed the ascom motor steps from 8 down to 4 and I can confirm that it now take just over 3000 to reach full throw.

I intend getting the 12v version of this motor as the 5v does not seem to have enough torque and struggles, I will see how it compares once it comes.
 

The motors are the same, just the rated supply voltage changes. I got some 12 volt units to put in place of the 5 volt, and I found there is a noticeable torque increase.

I'm driving my Crayford focuser on the 11:1 shaft. And it works very well so far. (Although I'm using a refractor, so my focuser has considerably more travel than a reflector) My "Sweet Spot" on my focuser is around the 400mm area (out of 740mm). I ran my focuser from 0 (fully in), out to the end of the scale. It amounts to 23,400 or so steps. My sweet spot is ~12,500. (Or close to the focusers mid-point.)

Some points to note here are:

1. When changing over to a 12 V source, the 12 V goes to the +/- of the motor drive board. (ULN2003)

2. Eliminate the 9 V input to the Nano, and let your USB power the Nano.

By doing this, you have only the USB, the 4 leads 7,8,9,10 from the Nano to the ULN2003, the 12 V in to the ULN 2003, and the 5 lead motor harness. The biggest advantage is using the already present USB 5 V for the Nano, and same 12 V already present on the mount for running the mount, CCD cooling, or powered USB hub. And it eliminates any motor load on the USB side of things.

The DS18B20 temperature probe will be powered by same USB voltage present in the Nano board.

Lastly, the nano clones I am using don't have the pins soldered in. So what I've done is to solder in only the four wires jumping to the ULN2003. (7,8,9,10 to N1,N2,N3,N4) That makes the Nano a lot easier to place in a project enclosure with everything else.

 

Edited by SonnyE
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When I built the first version it had 8 steps. Later I changed the code to allow values from 1 upwards. The default value is 8 for backward compatibility but you can change it to any value that suits your hardware.

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7 minutes ago, tekkydave said:

When I built the first version it had 8 steps. Later I changed the code to allow values from 1 upwards. The default value is 8 for backward compatibility but you can change it to any value that suits your hardware.

I'm not sure, but I think I'm using the default value. What I can say is it works great for my focuser. I can "tweak" my focus by single steps when I'm close to nervana, and get right at my best shot.

One question Dave: Does the temperature probe do any focusing compensation? Or is it just for temperature indication?

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The temperature probe only measures the temperature. Any compensation is usually done by the Ascom client program, although there are probably exceptions to that.

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Thanks everyone.
The 12v motor is on order along with a few connectors etc... to build the final version.
I did in fact decide to power the nano from the usb and will be having a 12v connection going directly to the motor controller.
My nano is already soldered and at least for now I will build on a small breadboard, this will also give me an easier option to add the temperature sensor or bluetooth at a later time if required.

I went ahead and changed to default value down to 4 and will wait and see how that does it with the new motor, if it looks like its need more then I can always reduce it further again.

Thanks again

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Thought I would post a photo of the finished project. I have tried this twice now and works great.58e6983b091fd_IMG_20170329_1956341.thumb.jpg.83223da911a0ce28fa4cf884a5dd51e1.jpg

The main unit and electrics are housed in a small project box near the guide scope on a dovetail bar and attached with Velcro.

I did have one small issue when trying to use the new version 64bit of fire capture however

58e699c39c6bc_fovusererror.thumb.jpg.1c98d21d6366762a409efa7161112ec9.jpg

is this something that can easily be fixed by your or would it mean major re-write?
If it comes to it I will downgrade to the 32bit version if needed

Thanks again

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Are you mounting the stepper motor onto the tube rings somehow?

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44 minutes ago, frugal said:

Are you mounting the stepper motor onto the tube rings somehow?

yes I made a bracket that is thin enough on onside to slip between the tube and the rings but secure enough not to move once the rings are bolted down.

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Interesting. I have all of the parts for mine, except for the Nano itself which is on a very slow boat from china ;)

 

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1 hour ago, frugal said:

Interesting. I have all of the parts for mine, except for the Nano itself which is on a very slow boat from china ;)

 

The bracket I used was a standard "L" Bracket. I enlarged one of the holes and ground down on side to fit under the ring a little easier.
My Nano I got from amazon for £4.50

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11 hours ago, dyfiastro said:

Thought I would post a photo of the finished project. I have tried this twice now and works great.58e6983b091fd_IMG_20170329_1956341.thumb.jpg.83223da911a0ce28fa4cf884a5dd51e1.jpg

The main unit and electrics are housed in a small project box near the guide scope on a dovetail bar and attached with Velcro.

I did have one small issue when trying to use the new version 64bit of fire capture however

58e699c39c6bc_fovusererror.thumb.jpg.1c98d21d6366762a409efa7161112ec9.jpg

is this something that can easily be fixed by your or would it mean major re-write?
If it comes to it I will downgrade to the 32bit version if needed

Thanks again

Not sure. I'll investigate when I get a spare minute :)

 

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The last bit turned up today. So I am having a play with the various bits before trying to remember how to use a soldering iron (I think I last picked one up 30 years ago doing DT at school). Just connecting the Nano to the stepper motor board and then the 12v power supply to the stepper motor board I can successfully get the motor to turn. Now to figure out how to wire it all up onto the veroboard.

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Fail the first: I was experimenting to check that I could at least get an the Nano to turn the motor. All connected up with Dupont connectors. Turns out that if you connect a 9V battery to the motor controller board the wrong way round nothing happens; if you connect a 12v power supply the wrong way round there is a pop, a fizz and then the magic smoke escapes from the motor controller... This is why I bought a 5 pack

Fail the second: I figured I should practice soldering components onto the vero board as I have not held a soldering iron since I was 13. Turns out that the soldering iron I inherited from my dad doesn't heat all the way to the tip properly, so I was trying to use the side of the tip about 1/4" back from the tip. Not really going to work. Amazon Prime to the rescue, new soldering iron and a heat proof mat should be here tomorrow (so I can put the chopping board back in the kitchen)

Fail the third: Figured that I should have a look at Dave's schematic and figure out where the voltage regulator fits in so that I can power the 12v stepper motor without blowing up the cheap Nano clone. Turns out that I had forgotten to add the capacitors to the shopping list in order to smooth out the DC voltage on either side of the regulator. Turns out that you can't buy two capacitors on Amazon Prime ;)

Did I mention it has been 30 years since I last did any kind of electronics...

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just like 30 years ago - just get a can of magic smoke and refill the controller ...........

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Attempt 2 seems to have gone a lot better. I have a very basic board soldered together (no Bluetooth, and everything apart from the motor powered from the USB). Dave's Focus test software works flawlessly and it picks up both the temperature and the focuser position.

Now I just need to figure out how to attach it all to the box and how to mount it to the scope.

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Some days I shouldn't be allowed string, let alone expensive mechanical devices like telescopes...

Got everything neatly (well sort of neatly) packaged into the little box I got for it. Connected it up to the PC and the power, all still works. Time to mount it on the scope. Decided as the scope sits on it's dovetail when it is not in use that I would attach the box to the top of the tube rings using the camera mounting point. All good so far.

I decided that the least invasive method to connect to the focus knob was a belt drive. I have read in the instructions with Rob Browns focuser that you should never use the fine focus knob for the belt drive as the constant tension on the knob causes it to fail. So I thought "4096 steps per revolution I shall drive from the coarse focuser". First thought was to put some of the belt on the knob to make a large gear out of it. Of course when you put a 2mm pitch belt around the focus knob you get a 2 and a bit mm pitch gear, so the belt kept slipping over it.

Next idea was to attach one of the 16 tooth pulleys that came with the belt directly to the centre rod of the focuser. So following the instructions on a You Tube video of how to fit an autofocuser to an ED80 I disassemble the focuser and try. Of course the pulley has a 5mm bore and the rod is only 4mm in diameter, plus if I do that then the rod is not fully supported at both ends so it wont work anyway.

Third idea. Drill out the end of the focus knob and put in a bit of 5mm rod, then attach the pulley to that. Ok, that seems to work. However when I put it all back together and fit the belt, it won't turn the focus knob. The commands are getting to the motor, and I can see one side of the belt getting tighter and one side getting slacker, but the knob is not turning round.

Plus to cap it all off, something I have done has disconnected the fine focus knob. It now goes around the same speed as the coarse knob if I turn the coarse knob; and it just turns freely with no effect on the focus if I turn the fine one.

So now I not only don't have electric focusing, I now don't even have fine focusing ;(

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6 hours ago, frugal said:

Of course the pulley has a 5mm bore and the rod is only 4mm in diameter, plus if I do that then the rod is not fully supported at both ends so it wont work anyway.

I did it that way, just use some 5mm OD 0.5mm wall brass tube to make up the diameter. You'll need to drill through the tube so the grub screws tighten on the focuser shaft. Works great.

Edited by richyrich_one

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I decided that as I still had all of the bits for the focuser I must have just not tighten something up in the correct way. So today I went out and disassembled the focuser and put it back together again. Fine focuser now works. The coarse focus knob is quite stiff to turn which I do not think was helping the poor little motor last night. I looked at various high end expensive electric focusers, and even the Baader Steeltrack focuser uses a belt from the motor pulley to the fine focuser knob; so I have decided to ignore the American's advice and just do what most other people have been doing and drive the whole thing from the fine focus knob.

The electronics box is mounted to a surplus piece of 1.5mm steel that was part of a router fence and had the advantage of being bent at 90 degrees so it would not sag. The steel support is then bolted to the end of the guide bar. The steel support had two slots cut in it so that I can adjust the tension by sliding the whole lot up and down the guide bar by about an inch if needed. The belt was made up from a length of GT2 belt that was cut to size and superglued together on a diagonal. and yes that really is a strip of Elastoplast you can see providing some extra strength to the joint.

The red electrical tap is covering up a couple of mounting holes for the motor that I cut in the wrong place. The black tape is attaching the thermometer to the side of the unit (I figured it should be outside the box to get the best reading).

Using Dave's focus tester I need to do movements of about 250 to be able to detect any movement in the drawtube, so the accuracy should be super fine. The next step is to wait until there is a clear night and have a go on some stars with SGPro.

IMG_20170414_150027.thumb.jpg.911bee8f8bf50b82275913086c4b4159.jpg

00002IMG_00002_BURST20170414150035_COVER.thumb.jpg.cf527ca0cb2ae4319cb93d0d85ca9ff2.jpg

 

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1 hour ago, frugal said:

I decided that as I still had all of the bits for the focuser I must have just not tighten something up in the correct way. So today I went out and disassembled the focuser and put it back together again. Fine focuser now works. The coarse focus knob is quite stiff to turn which I do not think was helping the poor little motor last night. I looked at various high end expensive electric focusers, and even the Baader Steeltrack focuser uses a belt from the motor pulley to the fine focuser knob; so I have decided to ignore the American's advice and just do what most other people have been doing and drive the whole thing from the fine focus knob.

The electronics box is mounted to a surplus piece of 1.5mm steel that was part of a router fence and had the advantage of being bent at 90 degrees so it would not sag. The steel support is then bolted to the end of the guide bar. The steel support had two slots cut in it so that I can adjust the tension by sliding the whole lot up and down the guide bar by about an inch if needed. The belt was made up from a length of GT2 belt that was cut to size and superglued together on a diagonal. and yes that really is a strip of Elastoplast you can see providing some extra strength to the joint.

The red electrical tap is covering up a couple of mounting holes for the motor that I cut in the wrong place. The black tape is attaching the thermometer to the side of the unit (I figured it should be outside the box to get the best reading).

Using Dave's focus tester I need to do movements of about 250 to be able to detect any movement in the drawtube, so the accuracy should be super fine. The next step is to wait until there is a clear night and have a go on some stars with SGPro.

IMG_20170414_150027.thumb.jpg.911bee8f8bf50b82275913086c4b4159.jpg

00002IMG_00002_BURST20170414150035_COVER.thumb.jpg.cf527ca0cb2ae4319cb93d0d85ca9ff2.jpg

 

Glad you got there in the end. You are using pretty much the same setup as I am in regards to the skywatcher focuser.
I found the same thing when I changed my motor but also came across a small issue when using APT.

For some reason I could not go past 10,000 steps in APT which using the standard code was not enough to be able to rack the focuser all the way in or out.
I ended up changing the ascom focuser steps section in the code to 19 instead of 8, this brought it down to just below 10,000 and solved the problem.
If you are only going to use the bundled software then it will not be an issue but if you end up with problem then this may be the solution and is still fine enough for critical focusing.

Edited by dyfiastro

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7 minutes ago, dyfiastro said:

Glad you got there in the end. You are using pretty much the same setup as I am in regards to the skywatcher focuser.
I found the same thing when I changed my motor but also came across a small issue when using APT.

For some reason I could not go past 10,000 steps in APT which using the standard code was not enough to be able to rack the focuser all the way in or out.
I ended up changing the ascom focuser steps section in the code to 19 instead of 8, this brought it down to just below 10,000 and solved the problem.
If you are only going to use the bundled software then it will not be an issue but if you end up with problem then this may be the solution and is still fine enough for critical focusing.

I am going to be using Sequence Generator Pro which assumes you have it in focus to begin with. You tell it how many steps to take and how big each step should be and then it takes a photo at each step and works out which one is most in focus. So if I say take 7 images at 250 steps apart, it will rack out by 750 steps and then take a photo and then rack back in again 250 steps at a time until it is at 750 steps the other side of the starting position, then it works out a curse and moves to the lowest point of the curve. So so long as I declare an initial position high enough it should be fine.

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On ‎14‎/‎04‎/‎2017 at 17:24, frugal said:

I am going to be using Sequence Generator Pro which assumes you have it in focus to begin with. You tell it how many steps to take and how big each step should be and then it takes a photo at each step and works out which one is most in focus. So if I say take 7 images at 250 steps apart, it will rack out by 750 steps and then take a photo and then rack back in again 250 steps at a time until it is at 750 steps the other side of the starting position, then it works out a curse and moves to the lowest point of the curve. So so long as I declare an initial position high enough it should be fine.

did you get it working with SGP? I'm now highly tempted to use the arduino I was given a while ago to add motor focus to my WO66.  I've got a moonlite on the 120ED, but not willing to shell out for another 'real' focuser...

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Am alos going to use this with SGP, but need to get it fixed up to my new focuser once that is fitted.  Should be good as the fine knob has similar notches so the belt will fit over.

Did notice a weird one the last time I used it.  Using the AF control software I was not ablke to go into negative numbers on the steps.  If I set initial position to 0 then is fine going upwards but any commands to go lower than 0 and there is no movement.  Is no biggie as just set initial position to 2500 or something and then have full movement control

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1 hour ago, jimboozle said:

did you get it working with SGP? I'm now highly tempted to use the arduino I was given a while ago to add motor focus to my WO66.  I've got a moonlite on the 120ED, but not willing to shell out for another 'real' focuser...

Unfortunately my mounting technique caused some problems. It made the scope far too camera heavy, and the mounting box also clipped the altitude adjustment bolt. So I have had to take it off again until I can come up with a new mounting approach

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2 hours ago, Shelster1973 said:

Am alos going to use this with SGP, but need to get it fixed up to my new focuser once that is fitted.  Should be good as the fine knob has similar notches so the belt will fit over.

Did notice a weird one the last time I used it.  Using the AF control software I was not ablke to go into negative numbers on the steps.  If I set initial position to 0 then is fine going upwards but any commands to go lower than 0 and there is no movement.  Is no biggie as just set initial position to 2500 or something and then have full movement control

An absolute position focused can never go negative - what does it mean to be further in than "all the way in" (i.e. at zero) ?

You really should start fully wound in, and then track out to focus under software control, so that it knows your real position, not just some arbitrary starting point, as would be the case with a "relative position only" focuser...

 

Clear skies,

 Carl

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On 04/05/2017 at 13:13, celkins said:

An absolute position focused can never go negative - what does it mean to be further in than "all the way in" (i.e. at zero) ?

You really should start fully wound in, and then track out to focus under software control, so that it knows your real position, not just some arbitrary starting point, as would be the case with a "relative position only" focuser...

 

Clear skies,

 Carl

Sorry to come in half way through the conversation.

1) Should it also "park" at the end of the session?

2) I'm playing with the idea of doing an automatic "refocus" in between each guided exposure to allow for small changes in seeing and assuming each "perfect" exposure is not exactly identical allowing me to take the best, say 20% of exposures to stack afterwards.  This would mean that after the first focus, subsequent ones would need to be relative.

3) Are you using Std Dev (ie contrast),  FWHM or  Half Flux Diameter to autofocus?  Or even something else.

Steve

PS I probably need to sit down and read through this whole thread :)

 

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