Uneven mechanical resistance dec axis DDM60Pro

[w0mbat]

Hi all,

I took delivery of my DDM60 Pro about two months ago and have only recently finished my observatory so I could finally put the mount on the pier.

I have noticed something about the mount which concerns me. If I gently rotate the RA axis by hand, the motion is beautifully smooth and even. However, when rotating the dec axis the resistance to turning varies quite a lot as though something is causing friction more at some positions than others, I wondered if the plastic locking/rotation limit post was not free in its hole so I removed the top plate and undid the screws holding on the plate which contains the hub etc. I was then able to check the freedom of the plastic post and was easily able to rotate it in its hole thus establishing that it was not jammed. I was not willing to investigate futher so I reassembled the top plates.

What do other owners think? It seems to me that varying rotational resistance in the dec axis will require varying amounts of power for a given angular movement.

Before I complain to ASA through my ASA agent I would like some opinions from other owners.

Thank you,

Ian

[RamaSpaceShip]

Hi Ian,

 

With my DDM85, I had initially the same feeling. Examining it carefully showed that the braking screw was tightened. Loosing it resolved the problem.

May-be it's also the case for your DDM60.

 

Regards.

 

Bernard

Edited June 25, 2013 by RamaSpaceShip

[w0mbat]

Thanks Bernard, but I have already checked this and have even removed the screw completely. Also I have checked that the plastic plug that the lock screw presses on is not itself jammed.

Ian

[GeorgeCarey]

Hello Ian,

Is that with the telescope loaded on the mount? The DEC axis always seems a bit stiff in places when the mount is unloaded.

My mount has just come back fron ASA after a bearing problem. Even with new DEC bearings there is still some stiffness unloaded, but with my scope which weighs 20 kg in place it seems very smooth.

Maybe ASA can give a comment as to what we should expect?

 

George

[w0mbat]

Hi George,

The variation in resistance is most evident with the mount unloaded. To ease my learning curve I have sofar only had a fairly light carbon fibre refractor on the mount, around 6.5 Kg with diagonal and eyepiece while my N10 astrograph waits patiently in the house. When manually balancing this scope I can still feel the varying resistance in the dec axis. Having had a lot of mechanical experience, it feels to me like a bearing which has excessive preload similar to a wheel bearing on a vehicle which has been over tightened.

I also was hoping for a comment from ASA. The prospect of returning a mount from Australia to Austria is not very appealing!

Thanks George.

Ian

[w0mbat]

Hello again George and others,

I have been in contact with ASA through my ASA agent. I very quickly received an email from Martin Puchner of ASA. I have been reassured by what Martin has said. I will quote some of his email:-

 

It is not unusual that your DE axis does not feel consistent while moving by hand.

There are 2 factors that cause this:

1. There are a lot of cables within the axes that interfere smooth movement. Because of the way they are installed, they have much more influence in DE than in RA.
2. Magnetic effects caused by remanence of the motors

 

I can’t exclude that there is a problem with your mount, because I can’t feel the inconsistency. But probably it is not a problem of quality check but only a thing that is caused by the way it is designed. The motors are able to handle this easily.

 

So I am happy for now. I have said I will contact them again if further issues arise when the mount is more heavily loaded.

I have interpreted "magnetic effects caused by remanence of the motors" to mean that there is some residual magnetisation in motor components which can result in the perception of regular "tight spots" as the axis is rotated by hand. This is what I experience.

I hope this reassures you too George.

Regards

Ian

[destrehandave]

Good Day, Gentlemen

 

It is now about 6 months since this original post.

 

May I ask the other participants if the problem is resolved?

 

Is the resolution basically just to not worry about this?

 

I was wondering if the cables were taking a beating, if they are the reason for the additional drag.

 

Thanks

Edited January 27, 2014 by destrehandave

[Gerald]

Hello,

 

To put it straigth - cables had never influence at tracking or slewing.   Do you already own a mount with any problem?

 

with best regards

 

Gerald

[Waldemar]

Hi,

 

Maybe it is sixth months since your original post because nobody has any problems and there was nothing to solve?

 

I never encountered any mechanical problem and do not expect one either.

The mechanical quality is absurdly high I think.

I can hear the cables move inside the mount, but that is because the mount is so incredibly silent

The only thing I am not font of about my DDM60Pro is the tip/tilt system for azimuth, but that is very personal.

To solve that I made a simple azimuthal adjustment system from 25 and 40 mm. bamboo plywood 250 mm circles on top of my pier.

Works great! Of course I will change it for anodized aluminum when I can and/or need to. 

I would love to have an original ASA replacement for this like the adjustment system on the DDM85... ?? ASA Gentlemen??

 

Best regards, Waldemar