Unbalanced Dob

[Gort]

Hi Guys,

My recently purchased Guan Sheng GS-680 seems to be unbalanced on its mount. When the scope gets to about 25-30 degrees of the zenith then it starts to slowly go to its vertical position. Hope I am making sense.

I spoke to Andrews over the phone (I am in Melb) and they have sold 100's of this model and haven't heard of any balancing issues. Given that I am in Melbourne and they are in Sydney I told them that I would photograph/film the set-up and email it to them to assist.

I think I installed the mount as per instruction. Also, the springs don't seem to make any difference.

Anyone here had such a problem ?

Appreciate any advice if possible.

Many Thanks.

[Spanrz]

I have the later version of the GSO (Bintel 302). The GSO with the springs is the earlier design. The version with the handles that turn is the later design.
The difference between the 2 is the design of the brake/pivot. WHich they made the turning handles, to better optimise the smoothness of the altitude operation.

Do you have a slider for your pivots? If so, you will need to adjust the slider by a few mm here or there.
I had to play around for an hour or so, to get mine the way I wanted it.

In your case, it sounds like you have it set for a heavy eyepiece. If you have a barlow and a 2" EP, that should balance it.
But it sounds like the pivot needs to be moved a few mm back towards the mirror. So the front end of the tube should be outwards by a few mm.

You can see by the pic, that what is circled is the adjuster for the altitude firmness. Tightening up might help just a bit. You have to comprimise a bit, due to the different weight of EP's. It surprised me that most times I went for the Wide Field EP (2") with barlows, it was very well balanced., take that away put a 1.25" EP in with an adapter ring, and the scope would teeter a bit.
It's all an experiment what works best.

See how you go.

[rmcpb]

This is where a large speaker magnet with a felt cover works really well. Just slide it up and down your tube to maintain the balance as necessary. A very common and old "trick" to handle one of the weaknesses of the dob design with small bearings.

[bmitchell82]

this is where i must admit, the sw excels in, i have no balancing issues, just tighten up the handle a bit more and it stays! ahhhhhh. i guess the next step is to whack it up on a eq6 hehehehe

[Gort]

Thanks guys for your replies. I appreciate them.

Brett thanks for posting the pic as well. I can't change the pivot on my scope,but the idea of the wider ep and barlow sounds good. Alternatively I can try the magnet trick mentioned by Rob.

Cheers and thanks Again.