bad tracking mount. Should I just shoot images of polaris?

[realflow100]

My tracking mount is so bad i haven't been able to get it to behave in any way shape or form. the tracking is so inconsistent and jerky its unusable past 50mm focal length. Way too much periodic error. it shows up in just a few seconds at 420mm
and even at 50mm it shows up slightly in a 15 second exposure image.
I have quadruply confirmed its not the polar alignment. I recorded images over period of 30 minutes and converted it ito a video and played it back. and the image is jerking up and down almost on a scale of half a second to 2-5 seconds. (the teeth of the gears as they each come into contact with one another
And on a slightly slower scale at 5-30 seconds. (one of the gears is out of round so I have a periodic error on top of periodic error on top of more periodic error)
Then on a slower scale of several minutes (the actual worm gear period)

Its so far beyond unusable at 400mm. I have played with the worm gear tension adjustment for hours and never being satisfied with the resulting performance. I have tried everything possible adjustment.
It works ok at very wide angle like 18-20mm several minutes of exposure can be gotten easily.

All I can really get pictures of with my telescope are polaris. because periodic error effect is greatly reduced there. but its not very exciting.

[OzEclipse]

My tracking mount is so bad i haven't been able to get it to behave in any way shape or form. the tracking is so inconsistent and jerky its unusable past 50mm focal length. Way too much periodic error. it shows up in just a few seconds at 420mm
and even at 50mm it shows up slightly in a 15 second exposure image.
I have quadruply confirmed its not the polar alignment. I recorded images over period of 30 minutes and converted it ito a video and played it back. and the image is jerking up and down almost on a scale of half a second to 2-5 seconds. (the teeth of the gears as they each come into contact with one another
And on a slightly slower scale at 5-30 seconds. (one of the gears is out of round so I have a periodic error on top of periodic error on top of more periodic error)
Then on a slower scale of several minutes (the actual worm gear period)

Its so far beyond unusable at 400mm. I have played with the worm gear tension adjustment for hours and never being satisfied with the resulting performance. I have tried everything possible adjustment.
It works ok at very wide angle like 18-20mm several minutes of exposure can be gotten easily.

All I can really get pictures of with my telescope are polaris. because periodic error effect is greatly reduced there. but its not very exciting.

If it's really bad, you could try to lap it? This involves putting a polishing compound onto the worm and running the worm at speed with an electric drill. If it works, this might polish off all or some of the rough spots responsible for the short period stuff leaving you with the PE from the full worm rotation which can be removed with guiding or PEC.

Joe

[Graeme1858]

My tracking mount is so bad i haven't been able to get it to behave in any way shape or form.

Sorry to hear that RF. I can understand your frustration, my mount sat in the garage for 9 months and now it's behaving in a similar way to how you describe. It slews ok but it fails to respond accurately to low power guiding nudges. I have contacted the supplier, who has contacted Celestron, to see what I can do about it or to advise someone who can strip it down and sort it out. I'll keep you posted.

If it's really bad, you could try to lap it? This involves putting a polishing compound onto the worm and running the worm at speed with an electric drill. If it works, this might polish off all or some of the rough spots responsible for the short period stuff leaving you with the PE from the full worm rotation which can be removed with guiding or PEC.

I have tried loosening the clutches and running the motors with the covers off to see if there is anything obvious visually. I did hear grit in the cogs on one occasion but there was nothing to see. My next step was to attempt to clean up the grease and cogs as best I can and to re-apply some clean grease. And I have lots of spare time to do it as I'm retired now!

Right, I'm off to put telescope lapping into Youtube to see what I get, cheers for that Joe.

Graeme

[Juno16]

Joe’s recommendations @OzEclipse are spot on. Sounds like short period error.
Polishing the gear teeth ss he describes works very well.
Have you tried adjusting the gear mesh? Too tight will bind the gears and too loose will create backlash.
Also, try looking on YouTube for ways to reduce friction on your axis (both). Sometimes loosening a friction nut can reduce axis friction (and stiction).
Lastly, do some research on adjusting the worm gear. Or, at least remove its drive gear and see if it rotates freely in each direction ( be sure to test its whole range of rotation).
Not sure what you’re mount is, but you are probably not the only one that has has this problem and there are probably helpful videos on YouTube that can help.

Graeme’s recommendation on greasing is very helpful. @Graeme1858. Just a small amount will go a long way.

Sounds like your mount is mostly unusable at this point. Hopefully you can have some success with it.

Good luck!

[OzEclipse]

My tracking mount is so bad i haven't been able to get it to behave in any way shape or form.

Sorry to hear that RF. I can understand your frustration, my mount sat in the garage for 9 months and now it's behaving in a similar way to how you describe. It slews ok but it fails to respond accurately to low power guiding nudges. I have contacted the supplier, who has contacted Celestron, to see what I can do about it or to advise someone who can strip it down and sort it out. I'll keep you posted.

If it's really bad, you could try to lap it? This involves putting a polishing compound onto the worm and running the worm at speed with an electric drill. If it works, this might polish off all or some of the rough spots responsible for the short period stuff leaving you with the PE from the full worm rotation which can be removed with guiding or PEC.

I have tried loosening the clutches and running the motors with the covers off to see if there is anything obvious visually. I did hear grit in the cogs on one occasion but there was nothing to see. My next step was to attempt to clean up the grease and cogs as best I can and to re-apply some clean grease. And I have lots of spare time to do it as I'm retired now!

Right, I'm off to put telescope lapping into Youtube to see what I get, cheers for that Joe.

Graeme

Graeme,
If you put telescope lapping you'll probably get links about mirror polishing. The lap is a layer of pitch laid over the tool that polishes the mirror froma. ground glass to a mirror finish.

Try searching "how+to+lap+a+worm+gear"

https://www.google.com/search?q=how+to+ ... e&ie=UTF-8

This is old school technique. I wouldn't suggest it except that the performance is so bad it can only improve. But definitely clean off and replace all grease and get rid of any grit and test first before doing any lapping.

cheers

Joe

[SkyHiker]

What mount do you have? Please add it to your signature.

Also, periodic error of about 5" is what a good mount will get you, for a less than good mount it could be 15" but usually an autoguider will take care of it. Do you use an autoguider?

If not, have you attempted adaptive PEC? PEC is a cumbersome procedure, but adaptive PEC is just clicking a check mark. Ekos has it, I believe PHD2 as well. It should take a few cycles for it to tune in.

If you get a chance, take a PHD2 log with the RA and DEC controls disabled, and adaptive PEC too. That is the best way for us to help finding out what is wrong with the mechanics.

[Solsearcher]

@OzEclipse Joe's lapping idea is a good one and will remove any rough spots in the gear train . Lapping compound comes in various 'grits" so choose a fine one . The most important part will be to make sure you flush out all of the compound once you are finished and replace with fresh clean grease . If you leave the compound in there it will find it's way into the bearings and create a new issue .
I am a retired machinist and have used lapping compounds in a variety of ways .
@Graeme1858 Congratulations on your retirement !!! You are going to love it , it's the best job I have ever had !!

[yobbo89]

try swaping out the worm gear bearings,they seem very sensitive to dirt and moister and dirty bearings can give a perodic error as the drive does a full rotation it rolls over dirt/debre , i use abec -7 skatboard bearings , but you may want to check out your bearing sizes on your mount before you shop for them.

[realflow100]

its a star adventurer 2i pro mount
No its not the worm gear at all. I have watched it in motion while turning and I can see the middle spur gear in the 3 stages is COMPLETELY OUT OF ROUND. Nothing will fix that.
No amount of polishing or cleaning or anything. other than replacing the gear entirely.
The shaft part of that middle stage spur gear is not only offset slightly from the middle. its SLANTED with a lot of play in it.
As it is theres no way to minimize the gear backlash because that gear will cause binding if you get the backlash too small. So theres always some gear backlash and it causes ai jerk every time one of the gear teeth come into contact with another gear tooth.
Its just complete trash with poor QC.
THe free-spinning gear with no grubscrew is the one in question.
Its the spur gears fault. its extremely bad.
Ive checked all the things and theres no adjustments too tight or too loose. The spur gears are just completely trash. I have tried adding new grease to try to smooth it out or push the old grease out and it had no effect.

The best option for this cheap mount is to throw it away and buy a better one at this point. its not worth the time effort and mess of trying to fix or improve it. Or only use it for very wide angle lenses such as 18-24mm.

No amount of guiding will fix it either as the error is way too short jerky and extreme. I get short trails in half a second to 2 seconds exposures if I look really closely on the image.
So guiding is out of the question too.

[Graeme1858]

Sounds bad RF.

I just searched for star adventurer 2i pro mount and discovered that Skywatcher sell their mounts without the tripod whereas Celestron only sell their mounts with a tripod. If I replace my CGX, I have to buy a new mount and tripod too, which I don't need for £2,600. The new EQ6-R PRO Synscan without a tripod is £1,500. You might have just saved me £1,100! Cheers for that.

Could you post some images of your faulty spur gears?

Graeme

[realflow100]

I dont have it apart right now but theres some articles about the mount where they take it apart and you can see all the gears inside.
Theres a spur gear train that drives the worm gear from the main motor gearbox. and those spur gears are the real culprit and root of the problem.
The worm gear is ok and has a worm period of many minutes which could be guided out easily.
but the spur gears are absolutely trash and have extremely bad QC (or none at all) and causes lots of problems.

[SkyHiker]

its a star adventurer 2i pro mount

This review shows some nice wide field imaging. The author also showed images with a periodic error of +- 20" saying that this was one of the better ones. What you describe is a lot worse.

No its not the worm gear at all. I have watched it in motion while turning and I can see the middle spur gear in the 3 stages is COMPLETELY OUT OF ROUND. Nothing will fix that.
No amount of polishing or cleaning or anything. other than replacing the gear entirely.
The shaft part of that middle stage spur gear is not only offset slightly from the middle. its SLANTED with a lot of play in it.
As it is theres no way to minimize the gear backlash because that gear will cause binding if you get the backlash too small. So theres always some gear backlash and it causes ai jerk every time one of the gear teeth come into contact with another gear tooth.
Its just complete trash with poor QC.
THe free-spinning gear with no grubscrew is the one in question.
Its the spur gears fault. its extremely bad.

The good news is that you know exactly what is wrong. If you bought it new, I would call SkyWatcher. It sounds like a clear manufacturing defect. It's too expensive to just let it go and can be a nice piece of gear to have if it works.

[realflow100]

Shipping it back is not worth it. The effort and time is just not worth it.
I ordered it through amazon so its long past return window and I'm just going to discard it and save up and get something better.

I'm so annoyed because the very first night it worked ok for the first set of images. Then after that it went all downhill and NEVER worked that good ever again. I was able to manage at least 10 second exposures and got sharp stars in most frames and even got a decent pic of m13.

Now It won't even manage 1-5 second exposures with nearly all images having visible trails

[OzEclipse]

That's a pity but if you have the receipt, it was new, and Amazon or not, it is less than the warranty period you should be able to send it to SW for warranty repair. They should only need to replace that gear.

I have a garden variety Star Adventurer astro pack and mine is quite good.

You are correct that QC is poor and it's a matter of luck.

I have done up to 4 minute unguided exposures with a 135mm lens with mine but my friend @scribbly has an average(?) one and mostly limits himself to using a 70mm lens and up to 2 mins if I recall correctly. Phil may jump in and correct me on this.

Good luck
Joe

[realflow100]

Ive got either an 50mm F1.8 stm lens or a 420mm F6 telescope
The mount is at least several years old now.

[Juno16]

Someone might have already mentioned it, but have you checked the gear grub screws to make sure one isn't slipping?
I think that you have already done that because you mentioned that the spur gear didn't have a grub screw. Must be glued. Could it be loose? That would be a great find!
I'm sure that there is some sort of Locktite that would work to re-glue it.

The strange thing is that the mount worked well for a time. Unless the spur is loose, I wouldn't think that it's performance would just all of a sudden go south.

[realflow100]

Its a free-spinning gear it is not screwed onto a shaft. it just free-spins on a shaft None of the gears are slipping I watched it closely while running. the worm gear rotates always and none of the gears are slipping at all
The middle spur gear just freely spins on a shaft. because its in the middle of a 3-gear train from gearbox to worm gear it just spins from the other gears driving it.
but that is what it is

[scribbly]

That's a pity but if you have the receipt, it was new, and Amazon or not, it is less than the warranty period you should be able to send it to SW for warranty repair. They should only need to replace that gear.

I have a garden variety Star Adventurer astro pack and mine is quite good.

SW-SA-test run-M8-M20 copy.jpg

You are correct that QC is poor and it's a matter of luck.

I have done up to 4 minute unguided exposures with a 135mm lens with mine but my friend @scribbly has an average(?) one and mostly limits himself to using a 70mm lens and up to 2 mins if I recall correctly. Phil may jump in and correct me on this.

Good luck
Joe

I have successfully used mine with 135mm for 30sec when new (3+years ago) but tend to only use it for wide field (usually 14mm but up to 70mm) , which it is good for several mins. My experience with my 300mm lens was very poor at quite short exposures.

My recollection is that PE can be up to 50 arcsecs peak-peak, though this appear not to be RF's problem so I can't help.

Though don't "chuck" it out if you are planning to image the eclipse in 2024; it might be fine for tracking the sun and images are typically less than 4 seconds. Others with more experience might "chip in" but would think that you could test it to see if the errors affect images of this length by imaging the moon at night? I successfully used my Star Adventurer (v1) with 300mm lens aboard to image the recent eclipse at Exmouth.

Cheers, Phil

[realflow100]

I don't have a solar filter for the eclipse right now.
Maybe I'll think about getting one eventually.

For the moon or planets with short exposures and tracking its fine at 420mm no problem.