Inconsistent results with Balance function

[w0mbat]

Hi all,

I am having a frustrating time with the balance function in Autoslew 5.1.1.6

I am trying to balance my N10 on my DDM60Pro. I can achieve good balance using the balance function with the red lines aligned. The problem is if I then slew the telescope to another position and then back again to the original balance position, Autoslew then says it is out of balance! On the 1.5A full scale graph, the red lines are now anything up to 200 or 300mA apart. This happens on both axes though Dec seems worse.

Is this normal behaviour? Has anyone else balanced in a particular position, moved the telescope, moved it back to the balance position and then checked the balance again? I cannot see the point of being able to make such measurements if the results are not repeatable and consistent.

Or is something wrong?

Thank you

Ian

[nakbrooks]

It is very sensitive so, obvious point, but I assume nothing is moving? For example, I have a rotator and had to balance the camera and filter wheel assembly separately because they were off-centre. Once I did get everything balanced (which took some time as you have to do it at a wide selection of pointing angles) I got very good repeatability.

 

This is with a Cassegrain, not a Newtonian, but the principle is the same.

[GeorgeCarey]

I suspect this is normal. Maybe it is due to the cabling that goes through the mount? If I balance with the counterweight bar horizontal and East and then slew to the West, it is not balanced. This is with the scope horizontal, so offset filter wheels and so on should not make a difference.

However, I get good performance from the mount, with no position errors, so this slight imbalance is not a problem.

[nakbrooks]

Agreed, although I think Ian was saying that he gets different results when he slews back to the original position. I wouldn't have thought that should be the case unless something is moving.

[w0mbat]

Thanks Nigel and George.

My current setup is very simple....3" corrector, camera adapter, Canon 60Da DSLR. I have secured all cables. So I don't think movement is a problem. Yes I am saying I get different results when I slew back to the original position at which the balance was done.

I had wondered about the cables through the mount.....sometimes I think I can hear them moving when slewing.

Sounds like I should assume the balance is OK and see how it goes.

[RamaSpaceShip]

Hi Ian,

 

I agree with Nigel. You probably have something moving.

I had a similar problem with my DDM85. It was due to the fact that when doing the dec balance with the main mirror on the north, the screws of the dovetail are below the tube and tightening them correctly is difficult because you have to go against the weight of the OTA. This caused a small movement of the OTA when moving, thus changing the balance. Now, I do the balance with the dovetail screws on top, and I tighten them with a key, not only with the hand.

 

My guess is that you have a similar issue, and you should check to find which screw is not tightened enough.

 

Best regards.

 

Bernard

Edited September 12, 2013 by RamaSpaceShip

[w0mbat]

Hi again,

A few days ago I realised I would have to fix some design errors with my pier by adding an extension on top of it. So today I started to disassemble the telescope and mount in preparation for that.

This has led me to solve the inconsistent balance issue. You guys were absolutely right......something was moving, in fact the whole OTA. Some time ago I had removed the telescope mounting plate. I replaced it and the four screws but had somehow forgotten to retighten them! So the mounting plate was free to move about under the screw heads allowing the whole OTA to move around several mm. No wonder it was hard to balance!

Thanks again,

Ian

[nakbrooks]

Glad you sorted it.

 

In the words of Sherlock Holmes: "If you eliminate the impossible, whatever remains, however improbable, must be the solution".