Balance/Regidity - or avoiding mount collisions?

[ian_bird]

I have two contradictory problems here.

First off - I want to keep my imaging train as far away from the mount as I can - to avoid collisions. So I set my rig as far forwards in the saddle as I can. This means I have to mount my guide scope pretty far back to get DEC balance. Which means its flapping around at the long end of the top losmandy plate. (Ignore the nose weight - it's fine tuning).

I think that if I mounted the guide scope so it was bolted down between the tube rings it would be a bit more rigid. And the overall balance would be better (closer to the RA axis).

But if I do that the rig will be nose heavy - so I would have to move it back in the saddle to compensate - which would bring it closer to a mount collision.

So - which is the better option?

PS - Thanks Olly - as usual - your "simple solutions" like "just bolt it down on to the top plate and forget all those funky but useless gizmos" has worked a treat. Much appreciated. Just wish it did not take me so long to understand what you are telling me!

Cheers

Ian

Right way up! Yeah!

[ian_bird]

Rigidity. Doh!

[ian_bird]

Should perhaps mention - where the rig is in the saddle at the moment - I can go way past the meridian before I ever get near a mount collision.

Yes - I know I need a pier. But SWMBO etc.... Not an option. Sigh!

Pip Pip

[ian_bird]

PS - the image train goes from the OTA to a Starligtht Instruments focuser which goes directly to another 72mm Tak, which goes to yet another 72mm Tak into an SX AO, which is directly attached to an OAG bolted to the filter wheel which has an SX H18 bolted to the back of the filter wheel.

Not a 2" nose piece in sight!

The field flattener is carried within the Tak to Tak adapter and is square on to the rest of it.

The SX bits were collimated by SX. (Thanks Terry).

So pretty rigid you would think.

Nope. Looks like Warp Speed in the bottom left of my images!

Go figure!

Ian

[ollypenrice]

I know the problem from our TEC140. Pushing it up the saddle plate is a bonus. So far as I can see your only options are;

- to use a long, stiff rail to carry the guidescope firmly but right at the back or

- to swich to a weight saving finder guider mounted right at the back on the normal finder shoe and 'spend' the weight saving on a nose weight or

- to switch to an OAG and again spend the saving on a nose weight.

However, SWMO presumably only disallows permanent piers? There is no reason you couldn't make a pier like the Astrophysics one ( http://www.astro-physics.com/index.htm?products/accessories/mounting_acc/piers ) which is really a special case of a tripod. It is, in effect, a nearly flat tripod with a pier rising from it. I've made one like that and they work fine. I dare say somebody already makes them. There is also the possibility of using a riser between the top of the tripod and the mount. This slightly 'pier-ifies' the standard tripod and gives more time before the dreaded flip. SW list these risers for the EQs. You could see if Celestron do likewise.

Note that the clever thing about the AP is the use of an oversized main tube to give rigidity and low weight. This is the thinking behind modern cycle frames as well. Also the stays are in tension, not compression, using turnbuckles. (Bicycles again; the spoked wheel...) Crafty.

Olly

[ian_bird]

Thanks Olly

Will have a look at the Astrophysics mount. Might be a good excuse to brush up on my welding skills (which used to be pretty good BTW).

Cheers

Ian