RA drive induced vibrations.

[Alien_Photons]

Recently I changed my observing location at home to avoid a conifer at the end of our garden. Right now the top of which is in the way given the time in the evening I am most like to be observing Jupiter. In fact the thing is a nuisance full stop. To retain a good polar alignment I normally put two of the tripod legs up against the brickwork in a low wall. Last week having noticed that there was some vertical drift in Jupiter from this new location I decided to tweak this out over the evening using the azimuth adjustment to refine north. All very run of the mill.

So during the adjustment of the azimuth Jupiter pans across the field of view, then using the hand controller to pan Jupiter back I noticed that while engaging the 1.5x RA drive that Jupiter became noticeably sharper. As soon as I stopped it blurred (you know where this is going don’t you). If I turned OFF the RA drive and let Jupiter drift it becomes sharp again. You can imagine my surprise and confusion.

This is obviously associated with the drive/handset and is a high frequency induced vibration. I’ve been reading up on the net about it. Right now I intend to try two things changing the power supply to a battery and loading the balance to the west side of the mount so the RA acts as a brake to see if I can remove/smooth this effect. I will also try my WO 80FD which is heavier than the FC100 to see if I get the same effect either way a comparison.

I have noticed in recent years that the DEC drive has become erratic in its movement and I suspected the hand controller a Vixen DD3.  As a result of swapping the RA DEC leads around I belived the RA was working fine. I am not ruling the hand controller out but I can't check or compare it with another.

It’s not as bad as a problem to live with as its sounds as panning across and letting Jupiter drift is no hardship.

Anyone else had similar experience and did you find a solution?

Regards Kevin.

[Les Ewan]

HI Kevin,

I have the same trouble with my 1990's TAL Siberia 6"Newt. This thing is a sturdy piece of kit using old Soviet style tractor engineering with a cast-iron pier.It has a internal motor drive.One night while observing the Epsilon Lyrae system I noticed that the binaries were much more difficult with the motor running and when I switch it off they became clear again.I only noticed this effect after a couple of years  so I must have being putting up with sub standard views off and on during that time and putting it down to bad seeing.Its a pity as its the only fault I can find with a other wise great well made and robust  telescope.

Les.

[Alien_Photons]

Les.

I wonder if I have not noticed this since issues with the RA when I became aware of the problem with the DEC. Its easily mistaken for poor seeing and not something I would have thought to look for. I always do a quick star test but now I need to check for this effect as well.

Did you find a solution for this problem? 

[Les Ewan]

Kevin,

No I haven't tried to fix it as the drive is internal. I suppose if I was more savvy in such things I could replace the resin cogwheels and bearings with metal ones and the such but its only a problem where high powers are involved and anyway the mount also has easy to use  manual RA control wheels.The Siberia is not now my main scope,most of my work over the last 15years is carried out with my Helios 200 Newt fitted with  Skywatcher drives.

All the best Les.

[SteveA]

It may be worth trying to damp the vibration by using some kind of material between the scope and the telescope cradle. My Skywatcher tube rings have a self adhesive rubber tape on the surface of the tube rings, principally I guess to prevent the OTA slipping in the rings, but would also also acts to damp any low level vibration. It's an interesting observation though and I dare say it will set a few people off on checking this out themselves...me included

Steve

[Alien_Photons]

It might be that things are to rigid having made efforts to reduce vibrations over the years. There seems to be plenty of reference to this type of problem that I have found on the web. Trying my other older scope which is a different weight and length will highlight if the problem is associated with an unlucky resonating issue. Which would be easy to change with balance or as you suggest material between the scope and rings. 

[Alien_Photons]

Well last night  I tried more and less counter balance, a longer rail to mount the scope rings on and balancing and un balancing the ra and dec axis. Little or no difference. The little is actually worth making a note of given it was an improvement. This was more counter balance closer to the axel with the mount east side heavy. (Inertia, moment and play) but because of play in the ra axis this made centring a bit messy with the ra drive.

None of which stopped me watching an Io transit of Jupiter by turning of the drives and letting the view drift.

I have a lot of play in both axels particularly the dec so I am going to strip, clean and rebuild the head. The last time I stripped this head must be six years ago. So it might or might not help. But it doesn't cost anything and it will be in better shape afterwards.

I have to finish painting the living room first.

[Alien_Photons]

Good news boys and girls. Yesterday I took all the slack out of the DEC axel and worm gear being as it clearly had some. Possibly over tightened the big ring on the end given the resistance now felt in it. But all the vibrations have gone. Right now nice and steady views of jupiter at x180.

A mount is a mechanical creature and needs a bit of attention from time to time. I guess the summer is a good time to service my mount. I will be stripping mine soon enough.