Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

3D Balance CEM60

  • Please log in to reply
11 replies to this topic

#1 Dynan

Dynan

    Gemini

  • *****
  • topic starter
  • Posts: 3121
  • Joined: 11 Mar 2018
  • Loc: NOLA

Posted 23 October 2019 - 03:28 AM

No matter where I put the counterweight the mount keeps moving to the west. (Unless I put the CW so low that it's definitely out  of balance. My scope setup doesn't have any significant weight off of centerline, so I'm perplexed as to why it's acting this way. I remember reading that off axis weight from finder, guide camera can effect the balance, calling for a 3D balance. I've seen (but can't seem to find) that there is a solution posted here, somewhere.

 

Can you link me? Or give instructions on adding the side bolt-on weight to the CW?

 

I'll be heading to 'the bolt store' tomorrow to get the necessary gear, by trial and error if necessary. (What size is the hole on the CEM CW? Looks like a 10 or 12 mm.)

 

Thanks, Cheers, and CS!



#2 gotak

gotak

    Vanguard

  • *****
  • Posts: 2082
  • Joined: 18 Sep 2016
  • Loc: Toronto, CA

Posted 23 October 2019 - 05:40 AM

I think it's a M12 bolt hole.

#3 Tapio

Tapio

    Vanguard

  • -----
  • Posts: 2185
  • Joined: 24 Sep 2006
  • Loc: Tampere, Finland

Posted 23 October 2019 - 06:35 AM

You mean it's drifting to west while tracking ?

What have you put there - C11 ?

Any images of the setup ?



#4 kathyastro

kathyastro

    Viking 1

  • *****
  • Posts: 899
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 23 October 2019 - 07:04 AM

Any off-axis weight will affect balance.  Finders are especially common culprits.  I recently moved my guide scope from the off-axis finder bracket to a dovetail rail on top of the scope, partly for rigidity and partly for balance.

 

To do a 3-D balance, start with the longitudinal declination balance.  That is pretty straightforward, and you have probably done it hundreds of times.  With the scope horizontal, move it forward and back in the rings or on the dovetail until it balances.

 

Then do the lateral balance.  Place the mount in the home position, scope pointing at the pole.  Disengage the gears and see which way it drops.  Since there is obviously excess weight on that side, look to see what is causing it: finder, focus motor, whatever.  Then loosen the mounting rings and rotate the OTA to put that weight closer to the centreline.  If it is a single off-axis load causing the problem, you will need to bring that load right onto the centreline.  If there are multiple off-axis loads, the balance position will have some to the left and some to the right.  Once you have rotated the OTA into balance, lock the rings.

 

Finally, proceed to the RA balance.  You do this last, because the previous steps may redistribute weight relative to the RA axis, which would need compensation.


  • B 26354 and Kegan128 like this

#5 Dynan

Dynan

    Gemini

  • *****
  • topic starter
  • Posts: 3121
  • Joined: 11 Mar 2018
  • Loc: NOLA

Posted 23 October 2019 - 07:48 AM

Thank you Kathy! It makes sense when you explain it that way...one axis at a time. The only things off center is the finder and the focus motor. Yesterday I went to an OAG, so I'll be able to remove the guide scope and put the finder in its place, not that I use the finder much anymore. But knowing me, if I remove it, I'll need it again. All will be on center, except for the Moonlite focus motor.

 

Thanks again.



#6 TOMDEY

TOMDEY

    Aurora

  • *****
  • Posts: 4938
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 23 October 2019 - 08:38 AM

Most scopes are terribly balanced... all need multi-axis balancing... which can be done off-line, in the daytime, in a couple of hours. Once you've achieved that, will rarely need to adjust anything again! It also takes a lot of the load off your drive trains. Nearly all damage and failures to mounts and drives is overloading and bad balance. PS: the only correct way to balance your scope is to trim the balance(s) with all clutches (each, in turn) entirely disengaged. Only after that, you then bias the two drives with appropriate small preloads... preferably magnetic or spring-loaded... independent of gravity. From what I've seen, in the field... only a couple percent of scopes (amateur and professional) are properly balanced. Same comment regarding optical alignments!    Tom



#7 Der_Pit

Der_Pit

    Viking 1

  • -----
  • Posts: 909
  • Joined: 07 Jul 2018
  • Loc: La Palma

Posted 23 October 2019 - 08:39 AM

Just keep in mind that placing side weights on the main CW for the CEM60 is futile.  The CWB doesn't rotate with a declination change, as it does for standard german equatorial mounts.  So you'd have to add the weight at the OTA.  

 

One thing worth to look at, too, is the orientation of the CWB.  Mine wasn't exactly 180⁰ opposite the scope, and that slight V made proper balancing really cumbersome.  But it's easy to adjust :)



#8 Tom K

Tom K

    Viking 1

  • *****
  • Posts: 654
  • Joined: 19 Jan 2010
  • Loc: Escondido, CA

Posted 23 October 2019 - 08:40 AM

Here is how I handlled that matter - a simple pipe hanger clamp from Home Depot and some washers.

Attached Thumbnails

  • IMG_1430.jpg

  • Dynan and OldManSky like this

#9 Dynan

Dynan

    Gemini

  • *****
  • topic starter
  • Posts: 3121
  • Joined: 11 Mar 2018
  • Loc: NOLA

Posted 24 October 2019 - 01:15 PM

With Kathy's advice and remembering I had seen Tom K's picture, the process turned out to be quite simple.

 

Balance East:

 

CEM BALANCE 1.jpg

 

Balance West:

 

CEM BALANCE 2.jpg

 

Final balance that allowed the scope to stay in ANY RA position:

 

CEM BALANCE 3.jpg

 

The weight was a little hard to estimate. But I realized that the by adjusting the angle of the additional weights off center of the CW shaft, it changed the effect on balance, as long as there was enough weight to overcome the 3D imbalance. Before the added CW weight, when I let the scope go it would slowly creep to the West Side of Pier. So I rotated the CW toward the East until all three axes were happy.

 

It certainly helped with my guiding...which I'm still learning. But it's much easier to learn with a balanced scope.

 

And, Gotak, you were correct... 12mm bolt worked.

 

Thanks to all for the input!


Edited by Dynan, 24 October 2019 - 01:41 PM.

  • Tom K, bmhjr and B 26354 like this

#10 Der_Pit

Der_Pit

    Viking 1

  • -----
  • Posts: 909
  • Joined: 07 Jul 2018
  • Loc: La Palma

Posted 25 October 2019 - 08:50 AM

Have you tried it with also DEC at random settings?


  • Dynan likes this

#11 Dynan

Dynan

    Gemini

  • *****
  • topic starter
  • Posts: 3121
  • Joined: 11 Mar 2018
  • Loc: NOLA

Posted 25 October 2019 - 09:04 AM

I buttoned up the pier because of the weather, but I was thinking along the same lines as you Der_Pit. Next time out I'll unlock both axes and try random positions. 



#12 Mil.Dave

Mil.Dave

    Lift Off

  • -----
  • Posts: 4
  • Joined: 01 Jul 2016
  • Loc: Hampshire, England

Posted 01 November 2019 - 08:15 AM

If I may add a few extra steps that will further aids obtaining a good 3-D balance on these mounts:

  1. Lock the RA axis in a horizontal position;
  2. Rotate the DEC axis to the vertical position with the camera down-most;
  3. Balance in this orientation to ensure no left or right bias with +/- 15° to 20° of vertical.

Now proceed to balance with the Dec and RA axes as mentioned previously, utilising the offset weight as required based on your equipment fit.

 

I've found that by employing this initial few steps the remainder of the balancing process is a lot quicker and easier.

For reference it's the same procedure recommended when using a side by side equipment setup, i.e. having a guide scope mounted beside rather than on the main scope.

 

I hope you find this helpful. Clear skies,

Dave


  • Tom K and Dynan like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics