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Help with attaching a Pegasus motor focuser

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#1 StuartT

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Posted 22 September 2021 - 06:22 AM

I just got a Pegasus Universal Motor focuser and I am trying to attach it to my SW Esprit.

 

But when the adapter is pushed all the way over the focuser shaft, the screw holes don't match up. If I slide it further out until the screw holes match up, then the adapter is not gripping very much of the shaft.

 

What do I do?

 

 

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#2 BobT

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Posted 22 September 2021 - 07:35 AM

Stuart,

 

I have had the Pegasus FocusCube2 (Universal) on my SW Esprit 120 for several years.  I cannot answer your question directly since I did not use their coupler to attach the focuser, I used a flexible stepper motor coupler which, if memory serves me, I bought on Amazon.  That said, is it possible you can gain any grasp on the focuser side by reducing the coupler overlap on the telescope side?  

 

Here's another tip for you:  once you attach the Pegasus, you will not be able to rotate the telescope focuser manually to access the grub screws for tightening (or for manual focusing).  You will have to run the focuser from the Pegasus software or use their optional hand controller.  I chose to purchase the hand controller, really nice accessory if your doing any visual observing with the scope and don't want to be attached to a computer.  For astrophotography I have used both SGP and NINA to control the Pegasus via the ASCOM driver, both work very well once you get the autofocus parameters adjusted correctly.

 

Clear skies,

 

BobT


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#3 rhaskins

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Posted 22 September 2021 - 07:50 AM

Can you flip the L bracket? Also at Pegasus there is a support forum. Pegasus responds fairly quickly to any issues posted there. One final thing, I went to MoonLite and got one of their couplers from their focus motor for a Pegasus focus motor so I could de-couple when I wanted to manually focus. It worked well but I had to drill it out to match the pegasus focus motor shaft and my Stellarvue focuser shaft. And, since things keep occurring to me, there is a coupling kit sold by Pegasus that has different sized couplers. IDK if that would help.

 

Rick


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#4 3snows

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Posted 22 September 2021 - 07:50 AM

My Pegasus focuser came without the bag of couplers.  Fortunately they are easy to find on Amazon.  Search for xmm flexible coupler.  Perhaps you can find a longer coupler that will make it work.  I use one I found on Amazom.  You will need the shaft size for both the Pegasus unit and your focuser.  Email Pegasus, they can tell you the shaft size.  Mine was 5mm but I have an older model.


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#5 StuartT

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Posted 22 September 2021 - 07:51 AM

Many thanks BobT. In fact this one is not the FocusCube, just the regular motor focuser, but the issue is the same. I shall loosen the grub screws again and slide the coupler along a little towards the focuser as you suggest. This will 'share' the lack of overlap between the scope's shaft and motor's shaft.
 

Stuart,
 
I have had the Pegasus FocusCube2 (Universal) on my SW Esprit 120 for several years.  I cannot answer your question directly since I did not use their coupler to attach the focuser, I used a flexible stepper motor coupler which, if memory serves me, I bought on Amazon.  That said, is it possible you can gain any grasp on the focuser side by reducing the coupler overlap on the telescope side?


Thanks Rick. I'm not really getting much support from Pegasus, but you guys are always super helpful!
 

Pegasus responds fairly quickly to any issues posted there.

 
Useful to know! Thanks

Fortunately they are easy to find on Amazon.  Search for xmm flexible coupler.


Edited by StuartT, 22 September 2021 - 08:23 AM.


#6 daveco2

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Posted 22 September 2021 - 08:54 AM

Choose where you want the holes to be in the bracket, file away or cut away the bracket at those positions, and use large washers (or a plate) to bolt through.  Brackets are made to be modified.

 

I usually make my own brackets from angle aluminum from the local hardware store rather than deal with brackets that never seem to fit.


Edited by daveco2, 22 September 2021 - 08:59 AM.

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#7 StuartT

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Posted 22 September 2021 - 09:33 AM

is it possible you can gain any grasp on the focuser side by reducing the coupler overlap on the telescope side?  
 
BobT

 Ok, I tried this, but to no avail. Problem is once I slide the coupler a mm or two off the scope's focuser shaft, the grub screw hole in the focuser housing no longer matches up, so I can't tighten it up again.
 

Fortunately they are easy to find on Amazon.  Search for xmm flexible coupler.  Perhaps you can find a longer coupler that will make it work.

 Sadly I can't find any 5mm to 5mm coupler that is any different in length to the one I have (25mm)
 

Choose where you want the holes to be in the bracket, file away or cut away the bracket at those positions, and use large washers (or a plate) to bolt through.  Brackets are made to be modified.
 
I usually make my own brackets from angle aluminum from the local hardware store rather than deal with brackets that never seem to fit.

Thanks. Many of you guys seem to be much more practically skilled and tooled up than I am. I don't have that kind of skill or tools unfortunately, so I have to rely on what I am sent by suppliers.

 

Anyway, the result is probably ok, there is only a 4mm or so separation between coupler and focus motor. Hopefully that will still allow enough overlap with the shaft to get it to work

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#8 OldManSky

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Posted 22 September 2021 - 10:16 AM

Stuart, test it of course, but...that's probably fine.

I have 2mm spacing per side on my coupler (ZWO EAF on Esprit 100).  No issues whatsoever.

You actually don't want them too close -- with temp changes they can "scrape" a bit!


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#9 rhaskins

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Posted 22 September 2021 - 03:55 PM

I knew I recognized that setup - I just sold my Focus Motor. If I understand you correctly you have 4mm between the end of the coupler to the face of the bracket? That should not be any issue. The salient issue is to have good, full contact with the set/grub screws on the shaft. There is no real loading on that shaft from the stepper motor but good contact is reassuring.

 

And, yes, it is helpful to have end-cutting bits and various other machine tools to help make things work :). but I draw the line - no milling machine.

 

Rick


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#10 StuartT

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Posted 23 September 2021 - 05:49 AM

Thanks everyone. I tried my new focus motor out last night (for once I had a clear sky on the same day some new equipment arrived!!)

 

The guys at NINA were super helpful in helping me set all the backlash parameters in NINA, but there still seems to be a flat part on my focus curve. They think this may be slippage, rather than backlash. I think this means the grub screws are not tight enough?

 

Ideas? Does it matter?

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Edited by StuartT, 23 September 2021 - 05:50 AM.


#11 rhaskins

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Posted 23 September 2021 - 06:32 AM

Some thoughts - are you at the limit of travel? Where it binds? Have you been able to reproduce this same result a few times? Is there any reversing so backlash becomes a big issue? I agree it is weird that the curve looks so good and then goes flat. It can be that the set screw/grub screw is not tight enough. Can you run it inside and observe slippage? Like hold the focus know and see if the motor still moves?

 

Rick


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#12 OldManSky

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Posted 23 September 2021 - 09:39 AM

I don't think that's slippage, if it were you'd have an issue on every focus point, not just the first one.  That appears to be classic (and typical) backlash.

Use the "Overshoot" method of backlash compensation (Options-Autofocus in NINA), and add another 120 steps to whatever value you have for the backlash there now, and that should take care of it.

Make sure you only have the backlash set in ONE of the two boxes (IN or OUT) there, the other should be 0.  Then the Overshoot method will work fine.


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#13 StuartT

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Posted 23 September 2021 - 04:53 PM

Some thoughts - are you at the limit of travel? Where it binds? Have you been able to reproduce this same result a few times? Is there any reversing so backlash becomes a big issue? I agree it is weird that the curve looks so good and then goes flat. It can be that the set screw/grub screw is not tight enough. Can you run it inside and observe slippage? Like hold the focus know and see if the motor still moves?

 

Rick

 

 

I don't think that's slippage, if it were you'd have an issue on every focus point, not just the first one.  That appears to be classic (and typical) backlash.

Use the "Overshoot" method of backlash compensation (Options-Autofocus in NINA), and add another 120 steps to whatever value you have for the backlash there now, and that should take care of it.

Make sure you only have the backlash set in ONE of the two boxes (IN or OUT) there, the other should be 0.  Then the Overshoot method will work fine.

Thanks both. I have been trying all kinds of options and showing the NINA creator each time and he can't seem to figure it out either. Here is my latest focus curve (and I have backlash IN=0, OUT=800, overshoot method, step size 120).

 

Who knows what the problem is! But if any of you can solve it I will buy you a pint (several). As it stands, I'll have to revert to the good old Bhatinov mask!

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#14 rhaskins

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Posted 23 September 2021 - 05:29 PM

Crap! I don't think I will get that pint. 

 

My suggestion is to contact Pegasus.

 

Rick


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#15 OldManSky

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Posted 23 September 2021 - 06:29 PM

Crap! I don't think I will get that pint. 

 

My suggestion is to contact Pegasus.

 

Rick

Yeah maybe not me either!

Although, the second curve does look more like slippage. Did you get at least one of the hold down nuts in the coupler on the “flat” part of both the motor and focuser shafts?


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#16 StuartT

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Posted 24 September 2021 - 03:34 AM

Yeah maybe not me either!

Although, the second curve does look more like slippage. Did you get at least one of the hold down nuts in the coupler on the “flat” part of both the motor and focuser shafts?

I think I'm going to have to start over with the fitting. I thought I'd done it right, but clearly there is some kind of mechanical issue here.


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