I think my mount has a problem

[emyliano2000]

Hi guys. I dont know what's going on but I think my mount has a problem. 

My guiding is always quite good  (0.8" RMS) up to the meridian an flip. After the flip the DEC is starting to go crazy. 

I polar aligned, I don't know how many times, I balanced the scope the best I could but still nothing. 

Any idea what it might be by looking at my phd2 graph? 

1st image is before the flip and second is after the flip. 

The mount is a hypertuned eq6 that was done 2 and a half years ago. 

Emil

[michael8554]

Hi Emil

I can't see the guide pulses so it's impossible to know what PHD2 is doing - tick the Corrections box. 

Possibly your balance is too good, so the mount is wobbling by itself between the Dec Backlash limits. 

By the way, look at the Star HFD readings in your two screen grabs. 

The first one is 5.81 which is poor, because the star profile has a flat top instead of a point - did you let PHD2 select the star, or did you up the exposure to 3 secs afterwards?

After the flip it's 2.11 which is excellent, so what changed? 

Michael 

 

[vlaiv]

It looks like RA is acting pretty much the same. There is a small difference between the two - first one is 0.73", second one is 0.86" but second one is probably closer to truth since in pre meridian flip - you had saturated guide star which lowers centroid precision.

But DEC is acting funny post flip - and I think you have DEC backlash. I also think that you have disbalance in DEC that was working against PA error and hence minimized the backlash (similarly like you should make your mount east heavy to minimize RA backlash) but once you switched side of meridian - now disbalance started working with PA since it changed orientation and DEC backlash now started to show.

[emyliano2000]

I'll tick the correction bix on my next clear night. 

I noticed the star was saturated and I changed it after I took the photo. I usually let them run on their own and go to bed so I have to let PHD choose the guidestar. 

I was thinking it might be backlash but this only started recently. When I had it on the pier, the total RMS was 1" on bad nights and 0.5" - 0.6" on very good nights. 

I recently moved and now the mount is sitting on the tripod. It was good at the beginning but about a month ago it all started. 

I would make the mount east heavy but letting it run on its own because of my work commitments, after the flip it will be west heavy. That's why I try to balance it as good as I can. 

[newbie alert]

Is it belt modded Emil?

Don't shoot me down lads but thought that if it's belt modded it don't need to be east heavy as there's no gear teeth to be engaged?

[emyliano2000]

1 minute ago, newbie alert said:

Is it belt modded Emil?

Don't shoot me down lads but thought that if it's belt modded it don't need to be east heavy as there's no gear teeth to be engaged?

It is belt modded, yes. I checked the balance again and on RA is very good in all positions but in DEC in some positions, the cables are pulling down  the camera end. I adjusted it a bit more and it is a bit better but still not good enough. 

[1parsec]

On 06/03/2020 at 20:29, newbie alert said:

Is it belt modded Emil?

Don't shoot me down lads but thought that if it's belt modded it don't need to be east heavy as there's no gear teeth to be engaged?

The worm wheel gear may still have a bit of backlash that needs a slight East imbalance even with a belt conversion fitted. 
 

 

[jed2i]

Disable Dec guiding and see where it drifts (north or south) then enable Dec guiding but just in one direction, opposite of the drift.

That will solve your problem.