Even more guiding problems

[dyfiastro]

Good evening everyone

I have been fighting to try and get my guiding better, I am beginning to wonder if there is a bigger issue here.

I knew that my polar alignment was not great so have just invested in a polemaster.
This week I have set about having another go at getting it sorted now I should be getting decent polar alignemnt but I am really having issues now.

I was up till 4AM this morning trying to get it working but still no luck. Here are two sets of graphs from last night

If anyone can give me any insight as to what may be happening it would be great. I have tried just about every combination of setting including setting it back to PHD2s standard.

The mount is a HEQ5 Pro with a belt drive mod.
The scope is balanced and the 9x50 is attached to the top using a dovetail and pipe clamps to prevent movement.
I have even followed the astrobaby guide to try and make sure there is no movement in the mount (no performed a full stripdown however as I was informed it has not long been done).

I am really getting to the point of breaking now, any help would be great

 

 

[Tiny Small]

Can you post an image of the entire bottom half of the PHD screen so we can see the settings etc.

In the first image above, it looks like the dec axis is suffering from a fair bit of backlash and stiction. The backlash is evidenced by repeated south pulses with nothing happening and the stiction by the sudden jump south as the built up energy overcomes the resistance. I would be taking a look at lubrication and worm spacing.

Although backlash shouldn't be an issue with RA, there are clearly issues there. Perhaps the aggressiveness and hysteresis are a little too high.

Are you balanced in 3 axes or 2? 

[geordie85]

Is your mount over loaded? Have you entered the correct information for your guide scope? How many steps does it take to calibrate? Have you got the boxed ticked for it to remember the last calibration? If yes to my last question you'll need to hold down the shift key to force a new calibration 

[Thalestris24]

Hi

I have an heq5 with the belt mod which I installed myself. I did have some trouble with it initially and, as I recall, had to firm up the tension - definitely worth a check. I also found that it needed balancing quite accurately in all 3 axes with no 'east heavy'. I believe the Synscan handset facilitates an accurate PA (I only have the Syntrek but use the PHD2 drift align tool). I'd recommend you run the Guiding Assistant and post the results. Also use PHDLab on your log file and post the results please. Of course, with the belt mod there's no backlash with the motor gear drives but you can still have problems with the worm drives. Seeing conditions, clouds and wind can obviously also have a negative effect. The large RA deflections look short and sharp but appear to recover straightaway but it's hard to tell what's causing them. You probably want to lower your RA aggression setting. What PHD2 exposure setting? How was your calibration? You need a good PA to get a good calibration. Guide star snr? No cables trailing? Focus tube etc. nice and tight? Just some ideas. I know guiding problems can be hard to pin down (I've had my own share!) but do persevere!

Louise

[Dave S]

If the dec axis driving that much then the polar alignment is a good way out.  A correctly aligned mount shouldn't need to drive it's motors in the Dec axis.

As Tiny small correctly states there is backlash usually is in the RA axis and this can be compensated by balancing the scope east or west heavy to ensure the motors gears are always pushing.

This quote from another thread explains this better than I can.

Dave...

On 17/10/2012 at 13:52, martin_h said:

Ok, when using an EQ type mount the telescope will (genraly) be on one side of the mount and the weights on the other. If you stand behind the mount (on the south side looking north) the scope will rotate in an arc up and over the mount if you are imaging in the east. ie. the scope will start in the east and follow the target across the sky to the west. So it is best to make the side that is rising heavy so as to keep the gears in mesh. Imagine that the scope is being pulled up and you pull down on a bit on it, it will keep the gears tight against each other. So, when the scope is rising move the weights towards the scope a bit to unbalance it towards the scope, if the weights are rising move the weights down the shaft to make that side heavy.

 

[Thalestris24]

Just now, Dave S said:

If the dec axis driving that much then the polar alignment is a good way out.  A correctly aligned mount shouldn't need to drive it's motors in the Dec axis.

As Tiny small correctly states there is backlash usually is in the RA axis and this can be compensated by balancing the scope east or west heavy to ensure the motors gears are always pushing.

This quote from another thread explains this better than I can.

Dave...

 

Hi Dave

The OP has a belt drive fitted - just thought I'd mention

Louise

[Dave S]

Yes I just spotted that. Whoops!!

Forget everything I said. Doh!!

 

Dave...

[Thalestris24]

Just now, Dave S said:

Yes I just spotted that. Whoops!!

Forget everything I said. Doh!!

 

Dave...

Still true about the DEC drive and PA

[dyfiastro]

Thanks for the replies everyone.

The scope is balanced on 2 axis as per the video I followed when I first started on the astronomy shed youtube channel.
Over the last few nights I have tried all kinds of settings to see if anything would work however I did not screenshot all of them and got rid of some of the logs.

Here are the graphs with more info as requested along with their calibrations.
My guide scope is a 9x50 set to 175mm as was stated after plate solving a test image from it. Exposures are on the first one are at 1.5s and the second 3s.
I normally create a new calibration at the start of each session but just to double check I actually calibrated at the begin of each separate  run in different areas of the sky to double check and make sure it was correct.

Is it worth putting a little bit of play back in to each axis using the little grub screws?
I did test it to make sure the motors turned fine but maybe its just a little to tight to be able to move with very small pulses?

Any thoughts would be great

and thanks again

[Thalestris24]

Hi

The Dec axis could be a little tight... Maybe also the RA... Those worm adjustment grub screws are very tricky to get just right and they only need a tiny adjustment. They are a pain! Don't forget to loosen the worm carrier before adjusting and retighten it after! Or... It could be to do with the belt tension. The Guiding Assistant will tell you how the mount is performing without guiding i.e. in particular the DEC and RA drift. The drift align tool will show you visually whether there is a lot of unexpected drift. You absolutely do need to balance vertically as well. As I mentioned, the belt drive is more sensitive to any slight imbalance. As Dave pointed out, with very good PA, DEC shouldn't need driving at all - in a perfect world! In practice DEC does need some driving but it's possible to arrange the PA error such that you only need to guide DEC in one direction but it can be that the seeing conditions can result in still needing to guide on auto (especially here in Glasgow!). By the way, I take it that your tripod is placed on a firm base? Anyway, hope you can sort it.

Louise

[Owmuchonomy]

All good advice above. Your trace tells me that your PA is a long way out. You can use the PHD 2 drift alignment tool to sort that but do a PA first with Synscan to get it close.  Secondly, Assuming your belt tension is correct I would conclude there is a lot of worm backlash in your Dec axis. It could be sticky but I doubt it and I would tune out your backlash first. The belt drive in mine helped a lot but it still needed tuning.  Do all that, nail your PA then worry about your RA axis issues if you still have any. Just make sure you don't have any cables snagging anywhere.

[dyfiastro]

Thanks again for the replies.

I there is that much of an issue with my PA still then I would be surprised, the main reason I got a postmaster.

I will take another look at the mount this afternoon

[Thalestris24]

Hi

A couple of pics showing your scope and everything on the heq5 might be useful. Also, what are your subs like - an example would be good.

Louise

[dyfiastro]

I have spent this afternoon adjusting the mount again. There is now a little bit of play in each axis but the the belt seems to turn easier. I have also rebalance the scope again but everything was the same. Here are a few photos of the setup and the balance with the clutches released.

I will leave as it is now and see what the results are the next clear night.

[Thalestris24]

Hi

Looks ok - hope the tweaks help!

Louise

[dyfiastro]

Well I had another chance last night to see if there was any improvement and it's still the same.

I actually striped everything down yesterday afternoon and regressed everything as well. I am either doing some wrong here or there is a bigger problem at play.

I doubled checked my PA last night and seemed fine according to the postmaster software.

[Thalestris24]

Hi

Did you run the Guiding Assistant? Output? How does the mount perform unguided?

Louise

[Thalestris24]

ps what are your individual subs like - that's the acid test! I just posted on another thread in the software forum (Peje's thread) about the size of guiding errors I get!

Louise

[dyfiastro]

Its been very hit and miss over the last few months due to having problems looking through the pole scope and having to drift align each setup.
The interesting thing there is some nights it would go great and others it would seem that I could not get it to align at all.
Things got a to a point a few weeks ago that I realised I was spending more time aligning than imaging so after reading the great feedback on the polemaster I went ahead and ordered one.

I managed to get a single night of decent subs using the polemaster and after that everything decided to start misbehaving.

The Dec axis is currently now sitting in bits on the workbench and I will give everything a good clean and service and see how it goes form there.
 

[dyfiastro]

Well finished stripping down the mount this evening and it really was in a state, two different types of grease and one that felt more like glue.

I did however find this whilst stripping the ra worn down, good job I ordered new bearings.

Will be putting it back together tomorrow so if anyone has any advise and setting the worms etc

Thanks in advance

[Waldemar]

Well... that explains a lot, doesn't it...Use ptfe grease like superlube or FIN grease, not lithium grease and get good bearrings like SKF. That will make a huge difference.

[libraryman]

Good advise all above ....but....don't discount your local seeing, I was imaging last night and early evening was dreadful......it wasn't until after 2am that the atmosphere calmed.....I went from 0.9 rms to 0.5 rms without touching a thing!

my guide graph was cabbage until it improved!

 

Ray

[dyfiastro]

Thanks again

The grease I was intending to use is Comma NLGI2 which states the following
" Suitable for chassis, wheel bearings, hubs, universal joints and electric motor bearings.
Good temperature tolerance - stable in hot conditions but still flows when cold. "

would this be acceptable to use?

[Waldemar]

Nothing beats PTFE

The grease you are mentioning is based on Lithium, a more or less old fashioned lubricant, cheap but not by far as effective as ptfe (teflon)
I think your precious equipment deserves the best lubricant available: PTFE based grease 

 

Super Lube® is a patented, multi-purpose synthetic lubricant, containing SYNCOLON® (PTFE) particles held in suspension. Super Lube® lasts longer and outperforms conventional petroleum-based greases. Super Lube® Grease is an exceptionally pure lubricant, because it is synthetic. This gives Super Lube® very stable and predictable chemical properties.

 

Super Lube® Grease with SYNCOLON® (PTFE) contains Polytetrafluoroethylene(PTFE) which is one of the most slippery surfaces (lowest coefficient of friction) known to man. The SYNCOLON® (PTFE) particles in Super Lube® fill surface irregularities of mating parts and are compacted to form a smooth, lubricated surface.

 

SYNCOLON® (PTFE) provides improved anti-wear properties, is waterproof, not washed away by acids or alkalis, and resists temperatures to 750°F. The SYNCOLON® (PTFE) particles in Super Lube's unique patented formula are held in constant suspension ensuring they will always be evenly applied to the lubricated surface.

[goose35]

I had these guiding issues with my exos mount. The graph was all over the place, espesialy in DEC. i stripped the dec and regreased this improved matters but still not a good graph overall. I started to think "this mount is un guidable"

It wasnt till i discovered PHD 2 and its drift align feature. This was when i discovered how far out my polar scope was even though it was aligned as per many "how to's" in the mount. after running with PHD 2 i have since had my 2 best images ever "pacman and the bubble in my gallery*. Round stars (apart from the bubble as i tried my old astromaster) and a good graph. I left it for an hours worth of 2 min subs and was still guiding within +- 1.5" on the graph

 

As for grease i used ptfe bicycle grease from halfords. As mentioned above its very silky and water resistant.