Balancing LX200 in RA

[yuklop]

Hi everyone,

I sometimes wonder if I’m not going a bit barmy!

I have a lx200 12” on a wedge. I understand balance is important and I can achieve perfect balance in dec. There are many guides, and it’s a straight forward matter to sort out. Most of the guides then say at the horizontal position release the RA clutch and see how the arms want to move - then balance.

No problems so far. 
The bit I haven’t seen explained is, as soon as the forks are rotated about RA the balance is lost. Whichever arm is high wants to drop. It very much wants to return to the level position. I can fix this by adding weight to whichever arm is low. But it would require a different amount of weight for each RA position.

Is this normal behaviour? Is there a sensible fix since it must be best that the scope to be balanced however it is pointing.

I can only imagine this is because there is a load of weight at the top of the forks, I.e motor assembly on one side and balance on the other. But if that’s the case why isn’t it mentioned in the guides on balancing!?

[Davey-T]

What balance system are you using, you need what's called a 3D system so you can rotate weight horizontally'

Dave

https://www.telescopehouse.com/accessories/meade-lx/seperate-weight-set-for-rail-systems.html

Edited October 22, 2020 by Davey-T

[yuklop]

I have a homemade balance system. I had to use my gym weights for something!

I can add to the underside of the scope or either fork arm. Shouldn't that be able to mimik a 3d system?

Do you rotate the 3d system depending on where the scope is pointing? Or once set should it be fine at any orientation?

Thanks

[Davey-T]

19 minutes ago, yuklop said:

Do you rotate the 3d system depending on where the scope is pointing? Or once set should it be fine at any orientation?

Usually modify balance depending where I'm imaging so the dec guiding corrections are in one direction.

Also got a threaded weight to alter balance as I've got a lot of weight on top.

Dave

[yuklop]

As an update to this, after a load of mucking around I learned that I can balance perfect in Dec or in RA but not in both.

I can move the counter weights far forward on the rail and the RA balance is perfect. Problem is then the scope is very front heavy. Attempts to correct this, either with extra weight or moving the guidescope back ruin the RA balance again.

At the moment I have a compromise setup with the Dec balanced OK at the most common observing declinations and the RA balance pretty good. Still has a tendency to want to return to forks level, but not so much I am worried about the motors.

I am still stumped as all the guides and even books just say, point tube up and add correct counter weight, point tube level and move that weight forward to back. This is perfect dec balance. Then simply add a little weight to the light fork arm. Then you have perfect balance.

Which you don't. I am beginning to think it may not be possible to achieve the fabled perfect balance with a wedge mounted fork and some accessories added. Has anyone done it?

[Davey-T]

You need to be able to offset the weight 

Dave

[yuklop]

Hi Dave,

I tried that too. Made my own 3d balance system where I could offset the counter weight. Didn't help me. What I could do with that is use it to balance at any specific RA. But not for all RA. So with the DEC perfectly balance the RA balance shifts depending on where the scope is pointing and would need to be rebalanced for every RA. This is a pest, so I went with the compromise balance option.

[Davey-T]

I find mine works ok with a bit of off balance so East heavy and guiding in only one dec direction, this is why I have that weight on a threaded rod to fine tune the dec so PHD  only corrects in one direction.

I watch the read out and move that weight so it keeps nudging in one direction.

I've got a 4 inch refractor piggy backed on mine so need a lot of counter weight on the bottom.

Dave

[michael8554]

11 hours ago, yuklop said:

I am still stumped as all the guides and even books just say, point tube up and add correct counter weight, point tube level and move that weight forward to back.

That's where you're going wrong.

Tube HORIZONTAL, move weight along rail until balanced.

Then tube VERTICAL, move weight out, away from rail, until balanced.

Repeat as necessary to fine-tune, but it will always be a compromise.

I have Dec backlash, so I balance so that the front of the tube wants to very slowly fall, taking up the backlash.

Then set a slight PA error southwards, PHD2 will only pulse north to correct the small PA error, but leave Dec guiding on Auto just in case !

Michael

[yuklop]

Hi Davey and Michael,

Michael, I don't think it matters whether I start horizontal or vertical. I can get perfect balance in DEC quite easily. But then RA balance is way out and it wants to re-centre. So its not a case of one RA arm being heavier than the other.

 

Davey, does your scope with the 4'' frac on the back balance well for all areas of the sky... i.e. could you point it anywhere and let go and have it stay there if you hadn't made it deliberately front heavy?

[Davey-T]

5 minutes ago, yuklop said:

Davey, does your scope with the 4'' frac on the back balance well for all areas of the sky... i.e. could you point it anywhere and let go and have it stay there if you hadn't made it deliberately front heavy?

No I tune the balancing depending where I'm imaging, I have to remove some weight at low dec' but it's not too fussy as long as it's east heavy and only doing small dec' corrections in one direction.

Dave