Arduino focus control for DC AND stepper motors?

[michaelmorris]

On 18/01/2017 at 17:48, brown_rb said:

Yes 10k pots, any will do.

http://www.ebay.com/itm/2Pcs-10K-OHM-Linear-Taper-Rotary-Potentiometer-B10K-Pot-Knob-XH2-54-Wire-Cable-/191941882370

 

I've got some pots, but accidentally ordered ones with switches (Doh!). I assume I just ignore the two pins at the back of the pot and just use the front three.  Is this correct?

Playing with the system, they don't seem to make a vast difference to the motor speed, it varies between almost stationary and slow.  The movement of the focuser motor is a bit jerky with the pots connected.   Would getting pots without a switch give a me greater number of degrees of rotation and would this give a greater range of speeds?

Thanks

 

Edited January 20, 2017 by michaelmorris

[michaelmorris]

On 20/01/2017 at 20:12, michaelmorris said:

I've got some pots, but accidentally ordered ones with switches (Doh!). I assume I just ignore the two pins at the back of the pot and just use the front three.  Is this correct?

Playing with the system, they don't seem to make a vast difference to the motor speed, it varies between almost stationary and slow.  The movement of the focuser motor is a bit jerky with the pots connected.   Would getting pots without a switch give a me greater number of degrees of rotation and would this give a greater range of speeds?

Okay, wiring fault spotted.  All now working as I would hope.

[michaelmorris]

I've been mucking about with 'Fritzing' electrical design software ( http://fritzing.org/home/ ) to try to get my head around how I'm going to wire this all up.  

I've by no means mastered the software (I can find half the components I need), but I've put in some proxies and notes where I can't find what I'm after.  Once the final components have arrived, my mate Dave has 'volunteered' to help with soldering it all up.

 

Edited January 22, 2017 by michaelmorris
incorrect picture

[SkyBound]

1 hour ago, michaelmorris said:

I've been mucking about with 'Fritzing' electrical design software ( http://fritzing.org/home/ ) to try to get my head around how I'm going to wire this all up.  

I've by no means mastered the software (I can find half the components I need), but I've put in some proxies and notes where I can't find what I'm after.  Once the final components have arrived, my mate Dave has 'volunteered' to help with soldering it all up.

 

So you went with the 6p6c cable I suggested above then...good choice..  will make it much lighter

[SteveBz]

Hi Guys,

I've been watching this thread with great interest.  I have an Arduino "Goto" for want of a better word and I was thinking of adding a focusser based on this thread to my set up.  So I do have a SkyWatcher focuser attached to a celestron C8-N with a belt and a sort of home-made coupling.  It could be better but it works fine.  My main issue is the slack/wobble in my focusser.  I imagine all new telescopes start with some slack and you find a way of removing it, otherwise automating it with an Arduino is a bit superfluous.  How have you managed to deal with the slack?

Regards

Steve.

[Davey-T]

Most commercial motor focusers have a backlash setting that you can set.

Dave

[SteveBz]

4 hours ago, Davey-T said:

Most commercial motor focusers have a backlash setting that you can set.

Dave

It has a screw you can tighten, but it just stiffens the whole mechanism and doesn't wholely cure it.

It seems to me I need to go down one of those astronomy-shed style solutions: ie take it apart and re-line it with PTFE.

I don't really want to do that and I wondered if you guys have done this?

Regards

Steve.

[Robd]

If you intend using arduino based do as I did, I based mine on TekkyDave's, elsewhere on here.

I added functions to PC and arduino code to allow setting of backlash compensation. This is then applied within the arduino logic every time movement direction is changed. I think I ended up with a 100 step correction. 

Edited January 25, 2017 by Robd

[SteveBz]

2 hours ago, Robd said:

If you intend using arduino based do as I did, I based mine on TekkyDave's, elsewhere on here.

I added functions to PC and arduino code to allow setting of backlash compensation. This is then applied within the arduino logic every time movement direction is changed. I think I ended up with a 100 step correction. 

Oh, wow.  Does it not matter however bad the backlash is?  You just put in a correcting factor?  I've seen TekkyDave's thread before.  I'll look it up.  I just recall it being very ... very ... longggggg.

Amazing.  I'll look it up

Regards

Steve. 

[Robd]

In principle that's correct, you can allow for any amount of backlash. Of course you would want to eliminate as much as possible mechanically. 

Once set there should be no need to change unless drive belt stretches or you take off for any reason. 

[michaelmorris]

The hand box for the focuser is now starting to take shape and I'm now looking at the final configuration of the housing for the Arduino, power supply and motor driver board.

The plan it to use the focus controller to operate either the the Meade Zero-image shift  focuser on the back of the C9.25 or the Skywatcher Accufocuser on the refractor.   The Meade focuser uses a mini jack whilst the Skywatcher uses an RJ11 plug.  But how to wire this up?  I presume the simplest way would be to simply wire the sockets for both focusers into the same pair of terminals.

However, this creates a problem. I would like to be able to leave both focusers plugged in all the time. But, if I do this, sending a signal will surely operate both focusers simultaneously.  So what I really need is a simple selector switch that diverts the signal to one of the two sockets. Does his sound logical?

If this is a viable solution, is this the sort of switch I should be getting?

http://www.maplin.co.uk/p/10a-toggle-switch-spdt-b-jk28f

Thanks

Edited January 29, 2017 by michaelmorris

[SkyBound]

1 hour ago, michaelmorris said:

The hand box for the focuser is now starting to take shape and I'm now looking at the final configuration of the housing for the Arduino, power supply and motor driver board.

The plan it to use the focus controller to operate either the the Meade Zero-image shift  focuser on the back of the C9.25 or the Skywatcher Accufocuser on the refractor.   The Meade focuser uses a mini jack whilst the Skywatcher uses an RJ11 plug.  But how to wire this up?  I presume the simplest way would be to simply wire the sockets for both focusers into the same pair of terminals.

However, this creates a problem. I would like to be able to leave both focusers plugged in all the time. But, if I do this, sending a signal will surely operate both focusers simultaneously.  So what I really need is a simple selector switch that diverts the signal to one of the two sockets. Does his sound logical?

If this is a viable solution, is this the sort of switch I should be getting?

http://www.maplin.co.uk/p/10a-toggle-switch-spdt-b-jk28f

Thanks

I had the same issue and built a switch box like you describe, it worked well, so don't see any issues there...obviously a more complicated way would be to have it switch via software.... ? Not something I could do...

[michaelmorris]

1 hour ago, SkyBound said:

I had the same issue and built a switch box like you describe, it worked well, so don't see any issues there...obviously a more complicated way would be to have it switch via software.... ? Not something I could do...

Thanks. I can see no need at present for a switching via software.  Eventually, I hope to convert all the focusers to stepper motor-based systems as part of a more automated set up.  Because I plan to have a dual imaging rig, at that stage software-based switching would be desirable, but that is probably a year or two down the line.

Edited January 29, 2017 by michaelmorris

[Robd]

Hmm just managed to repost.

I used the arduino and adafruit driver for mine. The latter will drive two steppers. My plan was to use one for the guide scope and the other for the imaging scope. It all worked fine switching between the two motors via software. 

Unfortunately one driver no longer works - think I blew something up on the board. 

Fortunately the other side still works and the guide scope doesn't need re-focusing very often. 

Edited January 29, 2017 by Robd
Double post

[michaelmorris]

The new box of tricks has just passed its final testing and will hopefully soon be wired up to my new scope set up.

 

[michaelmorris]

All now (hopefully) finally tested and wired up.  I'm pleased as a really really pleased thing with it.  It means I now have just two wires coming off the mount head - 1 x 12v power and 1 x USB.

 

A billion thanks to my friend Dave Lloyd for all his help.

 

[Vox45]

I already have a SkyWatcher Auto Focuser and the HitecAstro DC focuser control in hand but I'd like to switch to a stepper motor... This thread got me thinking.

Would it be possible to replace the DC motor in the Skywatcher enclosure so I can use the brackets, RJ11 connector and cable ? I could open up the Hitecastro controler case and fit in the arduino (?) This would look better than making my own bracket and case ... I guess this is just a question of form factor for the motor and size of the arduino board... Anyone knows the type of motor used in the SkyWatcher Auto Focuser and if there is an equivalent size in the stepper motor world ?

Edited October 27, 2017 by Vox45

[jmel]

Hey everyone - I came across this thread via a search on the ol' 

I just built one of these: http://www.scopefocus.info/arduino-focuser-2

I'm looking at building a different unit, that I saw here: https://www.cloudynights.com/topic/594658-pnp-focus-the-simplest-ever-arduino-focus-controller/

I'm just struggling with one last bit - how to attach to the scope itself. I have a 5mm to 8mm coupler for the shaft of the focuser, but it seems the best way to attach would be some sort of flange to the focuser housing. I have an at65edq with a feather light focuser (rack and pinion). 

 

I figured since so many here are building similar devices - they might have some thoughts about attachment...

[Dr_Ju_ju]

If you have access to a 3D printer, then there are a few designs on Thingiverse, e.g. https://www.thingiverse.com/thing:1260785 or https://www.thingiverse.com/thing:1406126 which can be adapted to suit most directly and or belted coupled motors....

[jmel]

6 hours ago, Dr_Ju_ju said:

If you have access to a 3D printer, then there are a few designs on Thingiverse, e.g. https://www.thingiverse.com/thing:1260785 or https://www.thingiverse.com/thing:1406126 which can be adapted to suit most directly and or belted coupled motors....

Thanks - although I don't have access to a 3d printer (the urge to buy grows greater each week...), I figure I can use an online service to get it printed. The 1406126 thing looks best in my case (I didn't want to fuss with belts). I didn't know if there was a specific bracket for a nema 17 and at65edq... I was really looking for a flange style mount, but this might work.

My only fear is that if I use a plastic bracket, that it will break... Now, I can see one advantage there though. If for some reason the stepper motor binds up on the focuser, the path of least resistance breaks first; the bracket; rather than the focuser. 

I plan to use the nema 17 in half step or quarter step mode to reduce the torque a bit. Going to test that out this week.

 

EDIT: something like this, but with a smaller bell end to fit the focuser housing on the feather touch: https://www.thingiverse.com/thing:2720575

Edited February 5, 2018 by jmel

[pavolg]

On 06/01/2017 at 16:25, michaelmorris said:

It works!!! 

 

Next I need to order the buttons for manual control , sort out a 9v power supply and put it all in a case. 

Hi,
I plan to make a similar Arduino focuser using my DC motor from SkyWatcher motor focuser. I don't need any buttons etc. I can't see from the video how it's connected motor driver to RJ11 socket and also to Arduino. Could someone help me?

 

[SteveBz]

3 hours ago, pavolg said:

Hi,
I plan to make a similar Arduino focuser using my DC motor from SkyWatcher motor focuser. I don't need any buttons etc. I can't see from the video how it's connected motor driver to RJ11 socket and also to Arduino. Could someone help me?

 

I did exactly that and it works perfectly.  You can even do your own auto focus routine.

You can easily slide the black cover off to check, but as I recall there are only 2 connections wired in parallel.I'll check properly later.

Just make sure it's all tight or it won't work well using AF.

Good luck.

Steve.

 

[SteveBz]

3 hours ago, pavolg said:

Hi,
I plan to make a similar Arduino focuser using my DC motor from SkyWatcher motor focuser. I don't need any buttons etc. I can't see from the video how it's connected motor driver to RJ11 socket and also to Arduino. Could someone help me?

 

Here's some photos and a video. The yellow cable tie is so I can see it remotely through a webcam. Actually it looks as though the connections are antiparallel. I hope you can make out the colours through the RJ11 plug.

Hope that helps.

Steve

 

[pavolg]

Steve, thank you for your answer.

I also made some investigation. The black (1st) and red (2nd) cables are connected together and the same for green (3rd) and yellow (4th) (see photo). I drew a scheme of planned Arduino focuser. Is something wrong on it? I'm only waiting for a package with the motor driver. I hope that the focuser will be completed in a month.

Edited June 24, 2020 by pavolg

[SteveBz]

Hi Pavolg,

It looks fine.  What is the board attached to D4, is it some sort of weather sensor?  I didn't use the driver board you are using, just an opto-coupler chip with four gates, two in the positive direction and two in the negative, but otherwise pretty much the same.  I also added a manual over-ride (a switch for direction and a cheap PWM board for speed) so that I can still focus manually when I am outside.  My only real comment is that you don't show the double connection at the motor.  It's quite important that you get it right, otherwise you can burn out your driver board.  The motor will be fine with 12v.  I have 2 speeds, 90% PWM and 10% PWM, and in fact I mostly use 10% on the micro control knob, so in fact its 1% normal speed and I love my focusing.  Really tight.

Good luck.

Steve.

Edited June 25, 2020 by SteveBz