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Suggestion for how to solve radial out-of-balance

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#1 Nessus359

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Posted 17 December 2012 - 09:34 PM

I am looking for suggestions on how to achieve radial balance, or near radial balance for my GEM. My mount is fairly tolerant of imbalances.
I can get balance both horizontal and vertical for the default position of my rotator, but the system goes out of balance when the rotator is positioned at more than +/- 45degs off the zero position.
My imaging train is not symmetric about the optical access which is probably leading to the imbalance as the rotator is positioned. Other than adding weight at the camera/CFW/rotator to make the train symmetric, does anyone have any suggestions or have solved this problem before?
I want to avoid adding weight that the rotator will have to deal with.

#2 tomcody

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Posted 18 December 2012 - 01:26 AM

Some CFW's allow you to turn them 180 deg to change the balance.
Rex

#3 Phil Sherman

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Posted 18 December 2012 - 11:03 AM

If your sccope is mounted in rings, you should be able to balance everything out.

Balance your scope on the DEC axis with it horizontal as you normally do. Rotate the tube till it's vertical and rebalance it by rotating it in the rings. You'll need to keep it from slipping down the rings while you're doing this.

If your scope attaches with a dovetail that's mounted to the scope tube, you can modify a counterweight to counteract this. Drill and tap a hole in the edge of the counterweight and insert a threaded rod into it. Get a small weight and position it with nuts to offset the imbalance on the scope side. You might have to add an additional lockscrew to keep the main counterweight from rotating on the counterweight shaft once the offset weight is attached. Make sure that the counterweight clears your tripod legs in all positions of the mount.

Phil

Phil

#4 Nessus359

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Posted 18 December 2012 - 11:13 AM

Phil - The scope is mounted with rings so rotating to find balance will work while vertical. However this is for one position of the rotator, when it is repositioned, say by 90 degs, vertical balance is lost. It might be possible to rotate the tube to a position that the unbalance is minimal for all positions of the rotator.

Paramount MX - ATRC10 with Parallax rings mounted to Versa Plate, with addtional Versa Plate on top of the rings.
Imaging train is TCFSi focuser, Pxyis Rotator, SBIG AO8, CFW 10 and ST8-XME. The asymetry of the CFW10 seems to be the issue.

#5 tomcody

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Posted 18 December 2012 - 01:01 PM

I think you can rotate the AO8 180 deg, see the old SBIG website and look under products for the AO8 (there are some install drawings there that show the AO8 rotated on a CFW8/9), should work for the CFW10 also. Weather it will be enough? don't know. Also you could go to a CFW9 and save about 1 lb.That and rotating the AO8 should be close to a balanced condition.
Rex

#6 Nessus359

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Posted 18 December 2012 - 01:48 PM

I am probably going to end up replacing the SBIG CFW10 with a Optec IFW; that will remove it from the part of the image train that is rotating.

#7 Phil Sherman

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Posted 18 December 2012 - 11:27 PM

If you have multiple things attached to the scope's tube, you should be able to get it fairly well balanced. Changing the position of the rotator shouldn't significantly change the balance obtained by rotating the tube. It should change the horizontal balance a little bit if the camera/rotator's center of mass isn't coincident with the axis of rotation.

Another imaging trick is to start off with the camera pointed towards the center of the mount. This decreases the moment arm of the camera and should allow a little less counterweight. Rotating the OTA from this position will require moving the counterweight away from the mount a little bit from its position when the camera faces the mount but it'll still be closer to the mount than if the camera is on the side of the OTA that faces away from the mount.

Phil

#8 Tom and Beth

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Posted 18 December 2012 - 11:43 PM

Phil - The scope is mounted with rings so rotating to find balance will work while vertical. However this is for one position of the rotator, when it is repositioned, say by 90 degs, vertical balance is lost. It might be possible to rotate the tube to a position that the unbalance is minimal for all positions of the rotator.

Paramount MX - ATRC10 with Parallax rings mounted to Versa Plate, with addtional Versa Plate on top of the rings.
Imaging train is TCFSi focuser, Pxyis Rotator, SBIG AO8, CFW 10 and ST8-XME. The asymetry of the CFW10 seems to be the issue.


Have you tryed using weight directly opposite the focuser? Instead of dead weight you could mount an electronic finder: A videocam with a 50MM SLR lens, for example.

#9 Nessus359

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Posted 18 December 2012 - 11:53 PM

Adding weight at the right point to counter the asymmetry of the CFW10 might be the solution. Looks like I need to get out the calculator to compute the optimal position.






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