Arduino focus control for DC AND stepper motors?

[michaelmorris]

My current imaging rig includes an 8" SCT + 66mm apo + an 80mm apo.  Both refractors have Skywatcher 'Autofocuser'  focus motors - this is serving me fine at the moment.  The SCT has a Meade zero shift focuser on the back.  This is basically a Crayford focuser with a built-in DC motor.

I am hopefully soon to upgrade from a DSLR to a CCD  and I can see a day that approaching when I'm going to look to invoke computer-controlled automated focussing routines.  From all the reading I've done this is really only practicable when using stepper motors rather than the  DC motors I currently have.

My plan would be to slowly replace the current focus motors with Arduino-based stepper motors.  As I can't afford to do this all in one go, I thought that my first step could be to get to grips with Arduino-based systems by replacing my present HitecAstro DC focuser controller with the myDCFocuser Arduino-based system.

 https://sourceforge.net/projects/mydcfocuserrelativedcfocuser/   

Once I've got the hang of this, I would then add a stepper motor controller to the Arduino and replace my two Skywatcher 'Autofocuser'  focus motors with stepper motors.  

This would mean using the same Ardiuno to run the DC motor on the Meade focuser and the stepper motors on the refractors (obviously not all at the same time).   Is this possible, or would I need a separate Arduino for each focuser or each type of focuser?

Replacement of the Meade focuser on the SCT with a stepper motor-based system would come later.

[SkyBound]

This company www.pegasusastro.com build and sell a focus motor controller that at the flick of a switch will control both a high res stepper and a DC focus motor, and its superb as I have one, but it also shows that it can be done, I was going to build the one you are talking about, but then came across this company, and so I got in touch, and they were and are so helpful and built one bespoke for my needs, I can't recommend them highly enough.....

but there off the shelf one will do exactly as you require if you decide not to build...

[Dr_Ju_ju]

The Arduino on its own cannot drive anyform of motor, that's why the 'Arduino' part is usually made up from an Arduino Nano plus a motor driver module e.g. DRV8825, and some other components e.g. power connector etc...

 I mount mine in a custom 'black box' and can move it between various OTA's\Motors, so to answer your question, build the right one and you can re-deploy as required..

[michaelmorris]

12 minutes ago, Dr_Ju_ju said:

The Arduino on its own cannot drive anyform of motor, that's why the 'Arduino' part is usually made up from an Arduino Nano plus a motor driver module e.g. DRV8825, and some other components e.g. power connector etc...

 I mount mine in a custom 'black box' and can move it between various OTA's\Motors, so to answer your question, build the right one and you can re-deploy as required..

Thanks

[John78]

So I think this is already effectively supported with @tekkydave 's project, if you use a L293D driver it will drive your DC's for now and can drive the steppers in the future, it's not a great device for driving a stepper so you'd probably switch to a DRV8825 pretty quickly - but fundamentally it will work.

You might need to change the code to adapt it for DC driving (i.e. changing the pulse length rather than sending multiple pulses such your motor's move) other than that I suspect you will then have a ASCOM compliant DC focuser.

 

[michaelmorris]

29 minutes ago, SkyBound said:

This company www.pegasusastro.com build and sell a focus motor controller that at the flick of a switch will control both a high res stepper and a DC focus motor, and its superb as I have one, but it also shows that it can be done, I was going to build the one you are talking about, but then came across this company, and so I got in touch, and they were and are so helpful and built one bespoke for my needs, I can't recommend them highly enough.....

but there off the shelf one will do exactly as you require if you decide not to build...

That Pegasus controller looks to be pretty much what I'm looking for.  However, I do have two reservations.

1 - The Price.  Whilst it is around £100 cheaper that most of the alternatives I've found so far, £270 is still MUCH more than what I guess an Arduino-based system would cost.  (On that note, how much would an Arduino-based controller cost to put together?)

2 - The connections.  I would have to build and additional converter to allow the 3 different focus motor types to connect to it.

 

 

[Davey-T]

I built T'Daves version and all the bits came to around £12.00 from memory.

Dave

[John78]

My focuser cost me :-

 

£3.39 arduino nano

£2.00 DRV8825

 

I already have stepper motors for free and veroboard etc... in my project box, so you can create one for easily under a tenner.

[Dr_Ju_ju]

As stated elsewhere the most expensive part is the stepper, I use these http://www.ebay.co.uk/itm/27-1-Planetary-Gearbox-Nema-17-Stepper-Motor-1-68A-DIY-CNC-Robot-3D-Printer-/121683241474?hash=item1c54e2ea02, for approx £35, together with boxes\components\mounting parts etc. the complete package can be done for £50-£60.....

[SkyBound]

1 hour ago, michaelmorris said:

That Pegasus controller looks to be pretty much what I'm looking for.  However, I do have two reservations.

1 - The Price.  Whilst it is around £100 cheaper that most of the alternatives I've found so far, £270 is still MUCH more than what I guess an Arduino-based system would cost.  (On that note, how much would an Arduino-based controller cost to put together?)

2 - The connections.  I would have to build and additional converter to allow the 3 different focus motor types to connect to it.

 

 

Yes I think if you have the know how it will be far cheaper to build one, no doubt about that, but I have yet to see an arduino version that will control both stepper and DC motor from the same port down the same cable with the flick of a switch, but I may be wrong, also the software with the Pegasus is very good, you can run two at a time from within the same instance of software, there is an Ascom driver, the step modes are superb, and I had one made with the encoder focus knob, on a length of cable rather than on the top of the controller, for very little extra cost, there stepper motors are also superb and give around 6000 steps per Rev of the coarse focus on my little WO scope. I know they are not cheap, BUT they are the cheapest you can buy....! Especially with the included functions.

the connector is a standard robofocus Pinout connector....and the same cable can be used to connect to stepper motors with that pinout and a DC motor....

the encoder control knob on the controller is superb and it moves the focuser as if you are turning the actual focuser, and by pushing it down it alters to a 10:1 speed, just like using the fine focus....really is a superb design, and not seen anything like it with the arduino projects......but at a higher cost I know...

Edited December 13, 2016 by SkyBound

[John78]

13 minutes ago, Dr_Ju_ju said:

As stated elsewhere the most expensive part is the stepper, I use these http://www.ebay.co.uk/itm/27-1-Planetary-Gearbox-Nema-17-Stepper-Motor-1-68A-DIY-CNC-Robot-3D-Printer-/121683241474?hash=item1c54e2ea02, for approx £35, together with boxes\components\mounting parts etc. the complete package can be done for £50-£60.....

I've seen that motor reported as a good candidate for a focuser in the other sourcforge focuser project, the problem I see it as is the torque of that thing is astronomic (3Nm continuous rated), you've only got to get it wrong once at that's the end of your focuser, it'll smash it to bits, that and it weighs like 500grams.  Its just massive massive overkill.

 

If you've got a light image train you could get away with over powering a 28BYJ-48, or use a 4 or 5:1 reduction with a toothed belt straight to a nema 17 stepper, a nema 14 with a gearbox would be a better motor.

[John78]

9 minutes ago, SkyBound said:

the encoder control knob on the controller is superb and it moves the focuser as if you are turning the actual focuser, and by pushing it down it alters to a 10:1 speed, just like using the fine focus....really is a superb design, and not seen anything like it with the arduino projects......but at a higher cost I know...

This does that...

https://sourceforge.net/projects/arduinoascomfocuserpro2diy/

You can either use 4 buttons coarse and fine back and fro, or a potentiometer and a switch to swap between the focus speeds.

[John78]

Word of caution with that project - you need 328 Nano's not the cheap 168's as it compiles way too big to fit on a 168...

[Davey-T]

Less than a fiver on EBay.

Dave

[John78]

I'd be absolutely flabbergasted if what's inside that Pegasus focuser isn't heavily based on ascom focuser project I linked with a L293D or fet equivalent driver and a few code tweaks to change the name of the device etc... and then laid out onto a real pcb.

Edited December 13, 2016 by John78

[SkyBound]

1 hour ago, John78 said:

I'd be absolutely flabbergasted if what's inside that Pegasus focuser isn't heavily based on ascom focuser project I linked with a L293D or fet equivalent driver and a few code tweaks to change the name of the device etc... and then laid out onto a real pcb.

I can assure you it is not...!!

[michaelmorris]

I've decided I'm going to start off with a simple DC motor only system to get me acquainted with Arduino first .  I've just ordered a bundle of bits on Ebay so that I can build a myDCfocuser system.   https://sourceforge.net/projects/mydcfocuserrelativedcfocuser/    .  This will then become part of a mini-hub system that includes 12v power distribution.

My plan is to get this up and running, then switch over to a stepper-motor based system when time and budget allows.  I'll keep you posted with progress.

 

[Dr_Ju_ju]

Good Luck, if you have any problems (especially if you aren't used to programming Arduino's) just shout....

[michaelmorris]

32 minutes ago, Dr_Ju_ju said:

Good Luck, if you have any problems (especially if you aren't used to programming Arduino's) just shout....

Get your ear plugs ready!

[redtail]

I use these motors on all the focusers i have built for friends.

[michaelmorris]

Okay, I've now ordered what I think is everything I need to make a basic test bench version of the myDCfocuser.

• Arduino Uno
• L9110S DC motor board
• assorted jump cables
• breadboard
• 4p4c socket (to connect to the Accufocuser motor)
• 9v battery connector (to power the Accufocuser motor)

Have I missed anything? (or probably more accurately - What have I missed?)

Edited December 17, 2016 by michaelmorris

[SteveBz]

I've just done the ST4 connection to my Enhanced Dual Drive with an Arduino using a project from Hackaday (https://hackaday.io/project/4386-arduino-st4-telescope-control). 

It works just by by-passing the buttons on the handset (ie the Arduino shorts the contacts on the button thus "pressing" them).  The LEDs are direction indicators.  Could focusing not work the same way?  Just by-pass the buttons, then you don't need any additional circuitry at all.  As there are still several pins unused on my Arduino nano, I thought I'd try the same thing on my focuser handset, drill a hole, insert grommet and cable, solder to contacts, add arduino.  Then it would be a combined focuser and navigation system.  Eventually adding other electrics like the dew-heater controller, fans, etc. onto a dashboard on my PC.

[Gina]

I've only used stepper motors.

[SteveBz]

2 hours ago, Gina said:

I've only used stepper motors.

Do you mean you haven't converted an existing electric focuser, you've built it from scratch?

[Gina]

Yes, all built from scratch.