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myFocuserPro2 stepper motor choice ( again - sorry !)


Astro-Geek
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My apologies for asking questions about this already well discussed subject..... 🙄

It's because of the multitude of sometimes conflicting info that is causing my poor old brain to not know which way to jump....

I've just finished making my myFocuserPro2 control box and I'm really pleased with it, (thanks for the heads-up on here that made me aware of it 👍).

I did read quite a bit of the online info before taking the plunge, but didn't have the patience to explore every avenue, (which would have taken months !)

So I therefore went with the "recommended" stepper motor, the Nema 17 with 27:1 ratio.

As I now find others have mentioned, it's serious "mega uber" overkill for most scopes and quite heavy too.

Not only that, but even when stepping "fast", it takes ages to complete one revolution,  good for precision, I realise, but surely the 27:1 is far too much, even with a direct coupling ?

I read somewhere on here that Gina said she used 28BYJ-48 steppers instead with no problems, and I'm amazed to find they're only £11.58 for FIVE from Amazon, including 5 ULN2003 Driver Boards.

This could fit in nicely with another ambition I have, and that is to have the stepper motors permanently fitted to my collection of scopes, each with its own physical mounting adaptation, so that I can switch the single myFocuserPro2 control box between them.

Does this sound feasible ?  Has anyone else tried it with multiple scopes ?

The only fly in the ointment is that my veroboard built control box has the DVR 8825 driver board (for the Nema17), so I'm guessing that I'd need to modify it to fit the ULN2003 driver board ?  Or could the 8825 run the 28BYJ-48 motors ?

Edited by Astro-Geek
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I use variants on these https://www.ebay.co.uk/itm/5-1-Planetary-Gearbox-High-Torque-Nema-17-Stepper-Motor-1-68A-DIY-CNC-3D-Printer/121683241475 from OMC for all my focusers, whether they be direct drive or belt driven. Being geared their torque is high and so hold position without slipping \ losing focus....

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It depends on the kit you are hanging off the focuser. I have used both the cheap 5v and the more expensive Nema 12,14,17 with gears as shown by Julian. All have worked well with my DSLR (Canon 100d so lighter than many I guess).

However (there always is) the "quality" of the 5v gears are not very high and I have one or 2 break (gears only) - possible me when I tried to move the focuser manually. Julians example gets high torque AND when the motor is off (which ,If I remember Roberts code, allow) then you can move your focuser manually if required.

Also ,IMO. with the more "main stream" steppers you can do Micro stepping without problems, are more accuate over repeated long moves and can move faster if required - e.g. DIY filter wheel.

You can run the little 5v from the drivers you mentioned (never done it myself) just google it - think it involved removing 1 wire. The beauty of DIY is you can find out for yourself.

1 hour ago, Astro-Geek said:

£11.58 for

Or even less if you are prepared to wait for China 🙂

Edited by stash_old
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1 hour ago, Astro-Geek said:

Not only that, but even when stepping "fast", it takes ages to complete one revolution,  good for precision, I realise, but surely the 27:1 is far too much, even with a direct coupling ?

I would tend to agree and so you dont need Microstepping with 27:1 gear set up IMO  - depending on what your focuser is.  But you may need to "play" with Robert options (which there are many - the man's over active LOL !) to see if you can speed up the movements or even drop him a line he is very open to questions.

 I dont use Roberts exact code any more (just his protocol - 01 mean "this" etc) as I use Accelstepper library which IMO give better control of Speed,Acceleration and is simpler (needed for my brain) to use.

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Thanks for the very rapid replies everyone.

21 minutes ago, stash_old said:

.....options (which there are many - the man's over active LOL !)...........

Yes indeed, the Guy has amazing attention to detail, and has covered so many aspects of his invention.

 

33 minutes ago, stash_old said:

.......You can run the little 5v from the drivers you mentioned (never done it myself) just google it - think it involved removing 1 wire. ......

That would be a really good option for me, I wouldn't need to alter my nice and neat control box (even if I say so myself 🤓), and yet I might be able to configure it to drive Nema 17's and 28BYJ-48 steppers, so that I can use the most appropriate "strength" motor for each scope/focuser mechanism.

Failing that, (and conscious of your comment about the 5v gears), I may settle for sticking with Nema 17's in geared and ungeared variations (or maybe the Nema 14 that Bottletop mentioned..... )

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I've tried the cheap stepper\drivers & found they soon wear out & quickly introduce slop, and for me, they were more problematical to mount (yes I have printed brackets), but for the Nema's its easier to use Allu 40x40 angle \ bar and ensure you have a firm fixture that doesn't bind on anything else.

As with everything you pays your money, and takes your choice...

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I've taken the plunge (again), and bought another Nema 17, an ungeared one this time, just to try it out.

I was surprised to find it on Amazon for just over £11, complete with the right angle bracket, inc Prime delivery.

My Nema 17 with 27:1 gearbox but minus the bracket was £32. ( I really should look round more before buying things !)

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I have built three MyFocuser units for each of my three scopes and use Nema 17 stepper motors, one being a 27:1 geared unit and is directly affixed to my WO Star 1:1 focuser control side. It easily holds my filter wheel, OAG, Lodestarx2 and Atik 383 without slippage. I would never fit the geared Nema 17 to the 10:1 micro focus side of a focuser, any mishaps and the torque of the Nema 27:1 motor would seriously damage the fine gearing of the micro focuser. My other two focusers are driven via toothed belts.

Steve

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On 15/09/2019 at 11:36, sloz1664 said:

....... I would never fit the geared Nema 17 to the 10:1 micro focus side of a focuser, any mishaps and the torque of the Nema 27:1 motor would seriously damage the fine gearing of the micro focuser............

Yes, I can well imagine that.  I'm sure the torque of the 17 with the 27:1 gearbox could move the telescope if it was on wheels !

I've taken good heed of Robert's warnings about maximum travel and stop settings.

Almost all of my scopes have Crayford type friction focuser mechanisms though, so I won't have to worry about stripping any rack teeth. I have them adjusted just right so that they can slip if the meet an end stop.

The ungeared Nema 17 arrived yesterday and it looks well suited to my needs.  It can still move in tiny increments with 1/4 and 1/8 stepping, and does complete revolutions on full steps much more quickly than the 27:1 gearbox model.

I'm now busy making up a quick release attachment bracket for my SCT crayford two speed focuser.  It sits quite neatly in place of the left hand knob and still leaves the dual speed end available for manual.  I fitted a 4mm thumbscrew into the flexible coupling so that I can quickly engage and disengage the motor.

I'll put some pictures on here when it's finished.

It will then give me motorised remote focussing on my Skymax 180 Mak and my Celestron C8 SCT, (two for the price of one !)

I'll then sort out some sort of bracket for the focusers on my Newtonians.

Edited by Astro-Geek
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I used the PG-5 27:1- wanted the extra torque to ensure there wasn't any slip.

I could be wrong but I think it gives you more steps in the CFZ too, there were a few motor choices which I had to steer clear of because of this. Worth calculating with your scope as you may need that extra gearing (or tweak your microstepping)

It's been a while since I played with it and to be honest was never quite satisfied with how I built mine so will be going for the ZWO option instead :D

 

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I have to say I'm really satisfied with my attempt at building Robert's opensource focuser.

The only mistake I made was trying to fit it in too small a project box  (100 x 50 x 68mm). It was just big enough for the PCB and LCD display and switches/sockets, but the connecting leads were something of a tangle.  I then bought the next size up, (158 x 90 x 60mm ).  This has turned out much neater with tider wiring.  It's a waterproof box with a transparent lid, so it saved cutting any holes to see the lcd display.

The ability to use it stand-alone, via the push buttons combined with the very comprehensive remote control computer apps puts it way above even very expensive ready-made focusers.  I haven't even explored the auto-focusing options yet, which I understand it can do.

I'm now busy making the adapters to fix the Nema 17 steppers to my various scopes.  The one I'm fitting to my Crayford SCT will enable its use on my Mak and my SCT, and  my Skywatcher 200pds newtonian's focuser is next.

I've now found that the ungeared Nema 17's can be bought very cheaply, so I'll be fitting one to each of my scopes, rather than trying to build an adapter that can be switched between them. They can each simply plug into my single MyFocuserPro2 control box.  (They're all friction focusers too, so no racks to worry about setting safety limits etc.

I'm currently trying to discover which is the lightest/smallest ungeared Nema 17 that I can use that has enough torque so that I can keep the weight down.

My latest ungeared one is a 2 amp     1.8 degree step angle (200 steps/rev.)    64 oz.in (45Ncm).

Even without gears, it can turn the focuser in much smaller increments than possible by hand when using fractional stepping.

Does anyone on here use lower power direct drive Nema 17's ?

I'm tempted by these ones on Amazon, with the same stepping increments but .4 amp 26Ncm motors:

https://www.amazon.co.uk/ECO-WORTHY-Torque-Stepper-Motors-26Ncm/dp/B01N0DM6YW/ref=pd_rhf_dp_p_img_1?_encoding=UTF8&psc=1&refRID=7YE5Z1C2FKZG0F2ER92D

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Hi hi,

I actually use Nema 17 PG27 on the myFocuserPro2 focuser (on F5 newtonian+ASI1600+EFW) and yes, -  with direct coupling. 

What can I say... 100% OVERKILL.

PG5 probably is a sweet spot for heavy rigs and etc...

I chose PG27, as I was afraid and could not find info which motor will fit my rig, plus, I will probably use it for my future F2 system and it will fit perfectly.

Anyway, it does it's job perfectly! 

Slow? - I would disagree. Mine is on full steps and performs as expected.

Edited by RolandKol
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Thanks for the alternative opinion, I guess my comment about the 27:1 seeming very slow was based purely on just watching the shaft turn, rather than using it in earnest to focus a 'scope.  😀

I'd still very much value anyone's personal experience of the various torque/amperage Nema 17 motors, and also the 5:1 and 27:1 gearboxes.

I think I'd better be cautious (for a change 🤓), and take advantage of the useful fact that they all have exactly the same faceplate size and fixing centres, so that I can try my present un-geared and 27:1 variants.

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Interesting read.  Once I have finished building Robert's dew controllers I shall be looking at making some of these.

I like the idea of having a box with a clear lid so the display is protected from the damp but still visible.  I was going to 3d print my boxes, but perhaps I need to rethink, or make a lid that I can fit a clear window into.

James

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1 hour ago, Astro-Geek said:

Thanks for the alternative opinion, I guess my comment about the 27:1 seeming very slow was based purely on just watching the shaft turn, rather than using it in earnest to focus a 'scope.  😀

Can confirm that the 27:1 gearbox will do full travel on my TS65 in about 5-6 seconds if pushed to. I think it was a fluke moving it that fast though, I actually prefer slower movement as it seems smoother, less vibration etc.

What swung the decision for me was the holding torque. Being able to power the motor down and not have any slip, whereas the standard NEMA17s would slip slightly unless powered. This meant that a) less power was being used and b) the motor kept cool which was important for me as was using a 3D printed bracket.

Try turning the shaft of the 27:1 by hand and its VERY difficult, whereas without the gearbox its fairly easy. Thats effectively what your imaging gear is trying to do everytime you point up and power down the coils.

That being said, my mounting application looked dreadful and will be switching it out for a ZWO EAF soon hopefully :D The PG27 is heavy and gave me real issues balancing my tiny scope.

 

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2 hours ago, JamesF said:

Interesting read.  Once I have finished building Robert's dew controllers I shall be looking at making some of these.

I like the idea of having a box with a clear lid so the display is protected from the damp but still visible.  I was going to 3d print my boxes, but perhaps I need to rethink, or make a lid that I can fit a clear window into.

James

You won't look back James. They are really great focusers. I have been running mine for over 3 years.

Steve

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I'm already wearing a groove in the observatory floor from walking between the warm room and piers to adjust the focusing :)  I'm looking forward to not having to do that.  Dew control had to come first though.

James

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4 hours ago, JamesF said:

Interesting read.  Once I have finished building Robert's dew controllers I shall be looking at making some of these.

I like the idea of having a box with a clear lid so the display is protected from the damp but still visible.  I was going to 3d print my boxes, but perhaps I need to rethink, or make a lid that I can fit a clear window into.

James

Instead of a single box, I use two boxes, one with the main controller board, and a second, that houses the display and in-out buttons, with an RJ45 lead\connectors joining the two boxes.

This arrangement allows me to have multiple controllers, but a single 'manual-control' box, that can moved around as required.

 

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I am using the  Nema 17 PG27 on a myFocuserPro2 that I built, there are speed options in the setup ( slow, medium or fast) that allow you to speed up the motor. Once connected go to settings, Motor speed, and select the speed you require. I was quite supprised at how fast it can go! I have always prefered the overkill option, but I dont think this motor/gearbox combination is too bulky.

Jason.

IMG_0815.jpg

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2 hours ago, JAS said:

I am using the  Nema 17 PG27 on a myFocuserPro2 that I built, there are speed options in the setup ( slow, medium or fast) that allow you to speed up the motor. Once connected go to settings, Motor speed, and select the speed you require. I was quite supprised at how fast it can go! I have always prefered the overkill option, but I dont think this motor/gearbox combination is too bulky.

Jason.

IMG_0815.jpg

Hmmm, how do you balance your frac with such a motor placing?

PG27 is quite heavy, something around 400g as I recall... Plus I do see your guider/finder scope shoe on the same side...

(I am with Newt at the moment, just thinking about future options and etc.)

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2 hours ago, RolandKol said:

Hmmm, how do you balance your frac with such a motor placing?

PG27 is quite heavy, something around 400g as I recall... Plus I do see your guider/finder scope shoe on the same side...

(I am with Newt at the moment, just thinking about future options and etc.)

I have not had any balance issues with this setup, the motor is reasonably central. When you consider all of the other kit bolted on 400grams is not a huge deal, especially when you consider that the scope is 4kg.

I don't keep the finder on the scope, I was using it last night for alignment.

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Nice bracket @JAS Is it homemade? My mounting for the PG was too large and bulky and pushed the motor out too far causing some balancing difficulties.

Something like this could make me reconsider keeping MFP2 instead of getting the ZWO EAF (and save £200)

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