HEQ5 polar alignment routine inconsistency

[Apharov]

Recently I have experienced a problem with my HEQ5 handset polar alignment routine: my initial alignment through scope is reasonably accurate, say within 3-10 arc minutes as reported by the first subsequent 3-star alignment. When doing the first handset polar alignment after this the handset demands huge corrections to polar alignment, which results in errors of tens of arc minutes or even a degree as reported after the second 3-star aligment. Subsequent polar align - 3-star align pairs then sometimes improve and sometimes worsen the PA.

This is obviously a big problem, since the polar alignment routine doesn't consistently improve the polar alignment. One thing that may be related is that the 3-star alignment slew locations are not very accurate even after the first one. Especially the third star is typically at the edge of the wide eyepiece or off the sensor with a camera.

A contributing factor may be that my setup is somewhat unbalanced in RA, as the counterweights are not quite enough for the 200PDS. On my first night out I however got the polar alignment routine working reasonably nicely, so imbalance is unlikely to be the sole cause. One other unusual thing with the mount is that on one side the RA axis rotates less freely than on the other.

Any ideas on what the problem is or questions for clarification would be most welcome!

[Lonestar70]

Hi Apharov,

What version firmware does your handset have installed... there were some errors in the first versions of the polar alignment routines which have been corrected in the latest V3.35 version.

If yours is the earlier version you should update it from here: -

http://ca.skywatcher.com/_english/05_service/01_download.php?ccid=8

You need to download the handset firmware update and the installer (both free) and follow the installation instructions to the letter (also downloadable from the same page).

The issue you have with the RA rotation could be caused by the grease Synta use in the bearings... take the scope off and just fit a dovetail bar in the mount head... loosen off the RA clutch and spin the RA round by hand for a good few rotations... this will distribute the grease more evenly in the bearings... lock the RA clutch again (in the home position) and re-mount the scope... hopefully this will resolve the problem... if not, then you will probably need to dismantle the RA shaft to clean and re-grease the bearings with white lithium grease.

There is an excellent tutorial/guide for doing this by Astro Baby... who is a member on this forum.

http://www.astro-baby.com/heq5-rebuild/heq5-m1.htm

Hope this helps.

Best regards.

Sandy.

[Owmuchonomy]

As post 2 check you have 3.35. If you are getting the issue with this version of firmware then I suggest the following. Through trial and error I found that the Synscan PA routine works best if you do the initial star alignment with 2 stars. The 3 star routine appears to be designed to map the sky for GoTo and counter any cone error. Perform the 2 star routine using both stars on the same side of the meridian as you intend to view/image using the RA/dec parameters described in the manual. Then run the PA routine using one of the 2 stars you used for the initial alignment. Repeat this 2 star alignment followed by the PA alignment until your Mel/maz error drops to 30" or below. It usually takes me 2 or 3 cycles.

[jambouk]

What scope are you using?

Are you using two or three star alignments?

Are you staying on one side of the meridian or flipping across it?

Do you have much cone error?

Do you have much backlash?

I think the above will impact on how accurately it works.

Jd

[Apharov]

Thanks for the replies! Here are some answers for the questions:

The handset is ver. 3.35. Thanks for the grease distribution tip!

I've been using 3-star alignment exclusively, but I'll be sure to try 2-star alignments next time as described by Owmuchonomy.

My scope is the SW 200PDS. I've tried staying on one side and flipping, no huge difference there. I probably have some cone error, I haven't analyzed or attempted to fix that. It appears to me that the SW dovetail doesn't sit exactly the same into the mount head every time, and it's possible to tighten the bolts solidly while having almost 1mm empty space between the dovetail and the mount head bottom. I've been checking that the scope sits tightly on the mount though.

I have a small amount of backlash in RA and significant amount in DEC. When aligning stars I've followed the manual suggestion to always finish the move by presses of the up and right buttons, which should eliminate the effect of backlash.

[jambouk]

It was suggested to me to just use a two star alignment routine when doing this, and pick two stars on the same side of the meridian. I tried this a few weeks ago with arcturus and deneb (deneb was pretty low in the north east). It seemed to work much better than my previous attempts.

The other thing i was finding (previous attempts and last attempt) is that it is impossible most of the time to get the star to centre in the fov when adjusting either the elevation or azimuth; it is just a case of each time making a very small adjustment to move the target star a little towards the very centre of the fov. I think it would be better to make smaller adjustments and do the whole routine an extra few times.

Are you using a reticle eye piece? If not this could also be contributing to your variation in results. I use a 12mm reticle ep which gives me a magnification of 233x and a fov of 12 arcminutes so i can be pretty sure the object is truly centred in my fov.

If you have a lot of relatively easily fixable cone error, i'd try and resolve that, if not for this routine, just to make your goto more accurate (though you have a much shorter focal length than me so it may not have as large an impact on your goto as my cone error had on mine).

Jd

[jambouk]

Are you able to quantify the amount of backlash you have? Again there was a good link somewhere on here where by you point the scope on a fixed object on the horizon, then select the slowest slew rate, turn tracking off (do this first), then not the coordinates on the handset, then slowly slew away, and initially the coordinates will change as the worm is moving but the scope won't move as the mechanism hasn't meshed together. As soon as scope starts to move and the object moves off the centre of the fov note the new coordinates. Subtract one set of coordinates from the other and that is the amount of backlash (roughly). You'd need to find the link to do it properly though.

Various online tutorials about adjusting for backlash are easy to follow but it takes some time to do; i used the astro baby tutorial. Not something to tinker with if you are not the least mechanically minded.

Jd

[dph1nm]

I had this problem, not sure with which firmware version though. Aligment (which was pretty OK to begin with) ended up miles (degrees!) away from where the polar scope suggested it should be, after several iterations with the handset. Had to do a complete power off and restart from home to get it to re-align reasonably correctly. Now I never try more than one iteration. I still get different offsets depending on which stars I use for the aligment though, so it is clearly not an exact science (the telescope is on a permanent obseravtory mount by the way).

NigelM

[Owmuchonomy]

I hope you can sort it. For me it made a huge difference using the 2 star routine I describe above. If as someone says above the first try is miles out I find this is because I haven't levelled the base well enough. Two nights ago I implanted tile feet into my lawn to add stability. I also used a new bubble level instead of my iPhone app. I did the 2 star alignment and PA twice only and got 8" error. That's very very good for me!

[Apharov]

Thanks for all the replies.

I'll try to analyse and fix the cone error the next chance I get and see if it makes a difference. I've been using the camera live view through BYE, so that should be very accurate for centering the bright stars. Fixing the backlash might also be on the agenda at some point, I've no problem with dabbling with various mechanisms.

I also might try controlling the mount from a computer for comparison. Dph1nm's experience seems to indicate that there might be something wrong with the handset software.

[Thalestris24]

Hi

This might be of interest especially for those who are in a particularly northern latitude.

A quote from the Astrotortilla support page talking about inconsistent PA results (by the Finnish Astrotortilla authors):

"I have noticed a bit of inconsistent results when shooting "too low" near the horizon, this may be in part due to atmospheric refraction or some other issue. Most consistent results have come from around 45 deg altitude. One additional source is often the mount, at least with the Synta HEQ5 and EQ6 mounts the factory altitude screws are not stable, they give a fair bit of flexure, visible also when measured with drift align. For our astronomy club EQ6 mounts we've added an additional altitude "claw" and switched to proper steel bolts."

https://www.flickr.com/photos/mickut/7713113644/in/set-72157630904452262/

This caught my eye as I'm at nearly 56 deg (not as north as Finland, fortunately!) and have suspicions about my own Heq5 PA stability. I'll be getting a pedestal mount soon so will use the opportunity to have a look at the alt adjustment mechanism and see whether there is much wear. I've only had the mount since just before Christmas and I upgraded the latitude bolts. Dunno what I could do about any problems myself though :-|. I'm envious of the Advanced VX alt adjustment mechanism (purely based on photos of it).

Cheers

Louise

[Apharov]

That's a really good point, Louise. When adjusting Alt I've also noticed that turning the more extended bolt has less effect on alt than turning the shorter bolt, which means the more extended bolt must be bending and/or sliding on the claw. Given that my setup is insufficiently balanced it probably creates some flexure.

I've seen Alt claw mods for EQ6, but would anyone know if a similar exists for HEQ5? Swapping to bolts alone might not help much if the bolt end slips on the claw.

[Thalestris24]

Hi

As far as I know the heq5 is basically the same, just a bit smaller. Maybe it would be possible to somehow just fix some extra metal to the existing claw. Perhaps just making a sort of lip which would prevent slippage might do. What is your latitude? The guys above mention 60 deg - Helsinki? If you are further north I imagine the problem would be worse.

My mount is in a semi-permanent position and is more or less polar aligned at the moment so I don't want to tamper with it until I have to (when the pedestal arrives). Unfortunately I don't have metal engineering skills or facilities, or tools even. I might try just Aralditing a piece of steel to the existing claw. Not sure even where I could get a suitable piece of metal from. If anyone has any ideas or suggestions, I'd be grateful.

Cheers

Louise

[Baffa]

As already been mentioned here, 2-star alignments works best. Altitude adjustment can 'slip', mine did until I got Gunnars alt fix, works like a charm!

Also, one thing that improved my goto's quite alot was reducing the backlash, I simple followed Astrobabys walkthroughs how to adjust it. I had quite some backlash in my dec axis.

[Tinker1947]

If your power LED flickers when slewing check the voltage it better to be nearer to 14 volts than below 12 volts......

[Thalestris24]

As already been mentioned here, 2-star alignments works best. Altitude adjustment can 'slip', mine did until I got Gunnars alt fix, works like a charm!

Also, one thing that improved my goto's quite alot was reducing the backlash, I simple followed Astrobabys walkthroughs how to adjust it. I had quite some backlash in my dec axis.

Hi

I came across this - just what I had in mind! It refers to Gunnar

http://darrenjehan.me.uk/blog/skywatcher-eq6-altitude-mod/

Trouble is I don't have the wherewithal to do it It will probably have to be an epoxy job...

I'll take a photo of whatever wear I might find when the pedestal arrives - hopefully later this week. Being not so far north it may not be as bad as that suffered by some Scandinavians. But I've always had suspicions about the alt adjustment stability. I think if I  get a second mount it will be the Advanced VX..

Cheers

Louise

[Baffa]

Hi

I came across this - just what I had in mind! It refers to Gunnar

http://darrenjehan.me.uk/blog/skywatcher-eq6-altitude-mod/

Trouble is I don't have the wherewithal to do it It will probably have to be an epoxy job...

I'll take a photo of whatever wear I might find when the pedestal arrives - hopefully later this week. Being not so far north it may not be as bad as that suffered by some Scandinavians. But I've always had suspicions about the alt adjustment stability. I think if I  get a second mount it will be the Advanced VX..

Cheers

Louise

Yes, that's the mod! Actually, the hardest part was to remove the alt scale and NEQ6 logo without breaking them. Everything else was just some measuring, drilling and tapping and I'm almost completly incompetent when it comes to tools.

[Thalestris24]

Yes, that's the mod! Actually, the hardest part was to remove the alt scale and NEQ6 logo without breaking them. Everything else was just some measuring, drilling and tapping and I'm almost completly incompetent when it comes to tools.

I don't even have a drill

Louise

[Owmuchonomy]

As already been mentioned here, 2-star alignments works best. Altitude adjustment can 'slip', mine did until I got Gunnars alt fix, works like a charm!

Also, one thing that improved my goto's quite alot was reducing the backlash, I simple followed Astrobabys walkthroughs how to adjust it. I had quite some backlash in my dec axis.

Yes, this is very good advice.  I service my mount and do backlash play adjustment twice a year. A rainy day sort of thing.  Astrobaby's instructions are pretty good and can be adapted for your own situation.  I also found that the dec axis bearings were too tight.  Don't be afraid to knock them off by a quarter turn. This adjustment alone greatly improved by PHD guiding graph.  It also confirmed it wasn't my PA that was at fault!