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Buddy piggybacking Sky-Watcher Esprit 80mm in his CPC 1100; is this pushing the CPC 'too far'?

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#1 SimonIRE

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Posted 09 June 2019 - 11:08 AM

Dear All,

 

A colleague of mine at work has the same scope as myself - a CPC 1100 (I ultimately bought mine on his recommendation as well as advice here and I am very happy). He recently bought a Sky-Watcher Esprit 80mm and mounted it on top of this CPC. 

 

Simply for my own knowledge, is this possible in terms of weight and balance? This system would in principle capture wide field viewers that escape the 11 inch scope so it seems attractive. I am curious to know from others who have piggybacked refractors on their SCTs if it "works" in terms of ergonomics and the load limits of the "mother" scope. Is 80mm doable? I see mixed views on this and from pictures posted, people seem to mount all manner of extra kit on this scope. 

 

Thanks, 

 

Simon



#2 Don W

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Posted 09 June 2019 - 12:19 PM

Should work very well.


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#3 carolinaskies

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Posted 09 June 2019 - 12:27 PM

Very doable and reasonable on the 11". 
The 80mm short refractors can be mounted via accessory bars.  Doing so though will require adding a weight system to the bottom of the scope to counterbalance the top weight. 

Most of these mounts can handle 15-20lbs extra weight properly balanced.  That's the key, proper balance.  


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#4 Migwan

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Posted 09 June 2019 - 06:22 PM

Ditto on counterbalance weight.  I started out 2 years ago with a ST80, then ED80 and presently an ST120.   I am using 7lb, which is equal to the weight of the ST120 OTA without the diagonal or EP.  Mine is mounted near 2 o'clock position, so not as top heavy as 12 o'clock mount.    Weight needed can also be reduced by extending it.    Enjoy.  jd



#5 punk35

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Posted 10 June 2019 - 04:35 PM

Does anyone have a link to the appropriate counterweight system needed for a C11?

I’m also considering putting a small refractor or the AT102ED on top of mine. It sure would be nice to have a setup like that. 

Thanks

 

Wade.



#6 Migwan

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Posted 10 June 2019 - 06:55 PM

If you extend the weight out away from your tube, this might just do it.   Otherwise, you might have to add a bit more weight than it comes with, but it certainly would get you going in the right direction.  Link

 

Good luck

jd



#7 punk35

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Posted 11 June 2019 - 06:31 PM

Thanks jd.



#8 TxStars

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Posted 11 June 2019 - 11:53 PM

You might also look at the ADM series of adapters.

https://www.admaccessories.com/



#9 Don W

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Posted 12 June 2019 - 10:41 AM

Here's mine with a Celestron version of the Short Tube 80:

 

DSCN0008.JPG

 

And with a TV 85 Refractor:

 

 

 

 

Attached Thumbnails

  • DSCN0009 (2).JPG

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#10 punk35

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Posted 12 June 2019 - 02:35 PM

Thanks folks. 

 

Don, no counterweight needed for scopes that small? 



#11 Don W

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Posted 12 June 2019 - 07:41 PM

The motors will handle it, but it would be best to put some weight on the bottom.


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#12 twjs

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Posted 13 June 2019 - 09:50 AM

The motors will handle it, but it would be best to put some weight on the bottom.

For those of us who are somewhat dense...is that due to the small refract creating an unbalanced torque moment?



#13 carolinaskies

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Posted 13 June 2019 - 10:12 AM

For those of us who are somewhat dense...is that due to the small refract creating an unbalanced torque moment?

For the Declination axis getting the balance to where it has minimal extra force for/against the backlash adjustment is important.  Too much and the backlash can't be reduced by the mount electronics. To little and the backlash loses adjustment value.  Especially for guiding and periodic error .  If you have too much weight either direction then in auto-guiding unnecessary adjustments can blow out the guiding values. 

Remember too, if on a wedge too much out of balance weight will cause more wear on the RA worm gear/mesh, overtime this stresses even the motors if the imbalance is high. 

Finally, consider the OTA facing higher than 60 degrees.  The top-weight of the refractor is spread across the ota, mostly being forward of the centerpoint of the Declination. Any weight to counter-balance this needs to be far back enough on the ota to put the weight behind that centerpoint.   If you ever took physics remember the drawing of force lines?  Essentially we want the lines of force near equal. 



#14 Don W

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Posted 13 June 2019 - 01:23 PM

All well and good, but the altitude motors on the Nexstar GPS and CPC mounts are strong enough to handle a little extra weight. Of course, that's just my opinion. But I've been doing it for nearly 20 years with no problems.

 

That said, if I were imaging, I would probably balance things out.



#15 punk35

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Posted 13 June 2019 - 02:23 PM

Don, I noticed both your refractors are mounted almost exactly over the top of the forks. Did you just find the balance point of them and then put that point over the arms? That would make sense to me..



#16 Don W

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Posted 13 June 2019 - 03:06 PM

Not really. I was just taking pictures and switching out the refractors. The TV85 is probably back a bit far and might interfere with the C11's eyepiece.


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#17 MikeBOKC

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Posted Yesterday, 07:56 AM

https://www.cloudyni...r-gpscpc-setup/

 

Scroll through this lengthy thread and you will see lots of examples of folks mounting various refractors atop CPC scopes.



#18 Migwan

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Posted Yesterday, 07:32 PM

I bought my CPC used and mounted a ST80 on it.  When I switched to a heavier ED80 I noticed about 2" of play in the Alt.   When I opened it up I found that the thrust spring on the motor assembly was already tightened to the max.  This is how I resolved.  Link

I also counter weighted, have ever since and can't recommend not doing so.  

 

I misstated the weight of the current ST120.  It comes in at 8.4lb.  I am using 7 lbs. of weight and have perfect balance from horizon to zenith.   I am mounted to the side, so I am not as top-heavy as most.   jd

 

 

 

 

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  • weights_resized.jpg


#19 Procyon

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Posted Today, 11:40 AM

Here's mine with a Celestron version of the Short Tube 80:

DSCN0008.JPG

And with a TV 85 Refractor:

Hey Don, I have a small light 70mm Celestron Travelscope, and rings as well from Scopetronix. Do you know which parts I'd need to buy to attach it to the bar like you have it?

Edited by Procyon, Today, 11:42 AM.


#20 Don W

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Posted Today, 01:57 PM

I use a Vixen size dovetail bar. You would then need something like an ADM dovetail that slides onto the bar and attach the rings to that.

 

https://www.highpoin...mUaAvmGEALw_wcB




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