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HEQ5 Pro elongated stars. backlash adjustment broken?


Penguin
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Been trying to diagnose why I always get elongated stars (see attached crop of a sub from last night) and I think one possibility might be the backlash I have in the RA axis. I've been looking at videos on how to remove this but unfortunately the adjusters don't seem to work: it's as if the grub screw at the bottom of the mount is broken or there's a stripped thread inside or something: I can unscrew the grub fine but screwing it in, it never tightens, it goes in so far and then just keeps spinning. The screw itself looks ok to me (see picture). Can anyone diagnose what is going on here?

On the other hand, since I am just tracking and not guiding, surely backlash should not be too much of a problem? Maybe it's my alignment, although the mount is on a permanent pier and I spent a while getting the alignment right last year. I will double-check that tonight.

Any other thoughts?

 

L_6534_ISO800_180s__24C cropped.jpg

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  • Penguin changed the title to HEQ5 Pro elongated stars. backlash adjustment broken?

You are slightly slackening the worm housing Allen bolts then adjusting aren't you?

Otherwise they won't do anything...

Look up astrobaby's guide

If you give the shaft a wiggle you might see or feel the backlash

There's no point trying to adjust out something that isn't there

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OK, thanks guys. It was cloudy last night so I wasn't able to check the alignment. I can definitely feel backlash in RA but can't detect any in Dec.

I did realise something last night: yes I had watched Astrobaby's video and no, I had forgotten to loosen the locking nuts! Hope I haven't damaged anything there.

If it is periodic error then I assume guiding is the solution? Would doing the belt modification also help?

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1 hour ago, Penguin said:

If it is periodic error then I assume guiding is the solution? Would doing the belt modification also help?

Yes, best solution to periodic error is to guide.

Alternative that will lessen elongation in RA is to do PEC - periodic error correction. Belt mod usually also lessens the periodic error. Neither of the two eliminate it completely and are worth doing even if you plan on guiding as they help the guider by reducing the amount of corrections it needs to do.

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Thanks. Situation now though is that it is either binding or skipping and I can't adjust it! I think it is skipping as when I move east/west, or track, it gives me a regular clicking. I've turned it all off and I fear I will need to strip it down to find out why the lower grub is spinning so that I can then do the adjustment I originally intended. Not happy! I'll have to see if there is anyone in my local club who can lend me some expertise. Then I'll look into the belt mod and maybe PEC and guiding for the winter. 

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11 minutes ago, Penguin said:

Thanks. Situation now though is that it is either binding or skipping and I can't adjust it! I think it is skipping as when I move east/west, or track, it gives me a regular clicking. I've turned it all off and I fear I will need to strip it down to find out why the lower grub is spinning so that I can then do the adjustment I originally intended. Not happy! I'll have to see if there is anyone in my local club who can lend me some expertise. Then I'll look into the belt mod and maybe PEC and guiding for the winter. 

Might be worth checking your gear mesh first ,then look at the grubscrew , it positions the worm to mesh with the ring gear.. might pay not to use it as you might end up with lots of metal filings..

Is it a new mount?

Are you confident to take it apart?

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Sound like a strip down is the way to go - it really isn't that tricky if you follow Astrobaby's guide. you can then check that everything rotates nicely and is properly lubed. That grub screw sounds stripped which is a pain - in fact the screw looks OK so maybe the housing stripped which is worse. I dont think you absolutely need that to adjust it BTW, but certainly easier.

To get really good results you will need to guide though. And don't get obsessed about backlash! If you keep everything slightly "East heavy" you can have a fair degree of backlash and it wont matter.

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Thanks, all.

Yes, I am certainly not using it till I have it sorted out. I bought it second hand around 7 years ago. I am reasonably happy to strip it down using Astrobaby's guide but I'll wait to see if anyone from my club can help first. I also strongly suspect a stripped housing since, as you say, the grub screw looks ok.

Alistair.

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7 minutes ago, Penguin said:

I also strongly suspect a stripped housing since, as you say, the grub screw looks ok.

If it is the female thread in the housing that is stripped its not the end of the world.

3 options spring to mind

  1. Clean the hole thoroughly with acetone - then completely fill it it chemical metal - when it is fully cured retap the thread.
  2. Go up a size - ie M3 to M4 or M4 to M5 etc - simply retap the thread.
  3. Fit a helicoil - probably a engineers workshop job than a home task.

 

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39 minutes ago, Skipper Billy said:

If it is the female thread in the housing that is stripped its not the end of the world.

3 options spring to mind

  1. Clean the hole thoroughly with acetone - then completely fill it it chemical metal - when it is fully cured retap the thread.
  2. Go up a size - ie M3 to M4 or M4 to M5 etc - simply retap the thread.
  3. Fit a helicoil - probably a engineers workshop job than a home task.

 

One other option to add to David's:

If the grub screw screws into the casing to start with, maybe it's only the bottom of the thread that's stripped. If you can get a longer grub screw or a bolt with the same thread then this may allow you to make the adjustments to the backlash. This will use the thread at the top of the hole and there may be enough there to hold it.

A clean and running a tap down it wouldn't go amiss and a ultimately one of David's suggestions are far better for the long term.

These grub screws don't have to be done up tight, they're only for making the adjustments and should just be "nipped up", the three larger bolts hold the casing in place. ;)

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2 hours ago, Skipper Billy said:

If it is the female thread in the housing that is stripped its not the end of the world.

3 options spring to mind

  1. Clean the hole thoroughly with acetone - then completely fill it it chemical metal - when it is fully cured retap the thread.
  2. Go up a size - ie M3 to M4 or M4 to M5 etc - simply retap the thread.
  3. Fit a helicoil - probably a engineers workshop job than a home task.

 

I'd thought of number 2 and the option of a longer grub/bolt if there's enough thread left but the other options are new to me, thanks. When I do strip it down, what grease to I use when putting it together?

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If you are tracking and not guiding then I don't think backlash in RA should be a problem since it should always be driving in the same direction. I think it's usually suggested that you adjust the weights so that it is tending to keep the backlash out on RA. This will depend on which side you are working. You want the balance so it is in the same direction as the RA is driving to keep the gears always in contact.

I have the same mount and up till now I've only been tracking and not guiding. If I get elongated stars in a sub every now and then it's usually the wind. I had one problem where I had the tripod set up on an area of paving slabs and I found that if I shifted my weight the slab rocked slightly. It doesn't need much. 

I find over an hour with good PA there is practically no drift in RA but there is some in DEC.  That is to say if I take two exposures one hour apart and plate solve, the drift per minute in RA is negligible but you can still get PE over the worm cycle. I think the worm cycle time for the HEQ5 is about ten minutes. I find with one minute exposures there is very little elongation. You can see it if you magnify the image but it's not significant.  I don't use PEC at present. You don't say how long your exposure was or how long focal length your scope is. I think without guiding you will always get some elongation with long exposures and long focal length.

If the elongation is consistent between the subs then it's probably a systemic problem such as PE rather than say wind.

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  • 3 weeks later...

Thanks for all the suggestions guys and I was just on DarkFrameOptics site, looking at the belt modification which I thought I might as well do at the same time, when I saw their tuning service:

https://www.darkframeoptics.com/StellarDrive__5_Mount/p2013568_19207915.aspx

They'll collect it, strip it down, de-grease, replace worn bits and upgrade others, re-grease, add the belt drive modification, put it all back together, test and return it to me. Considering I bought it 2nd hand several years ago and have never serviced it, it might be worth the cost to have someone experienced give it the full works.

Any opinions?

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3 minutes ago, Penguin said:

Thanks for all the suggestions guys and I was just on DarkFrameOptics site, looking at the belt modification which I thought I might as well do at the same time, when I saw their tuning service:

https://www.darkframeoptics.com/StellarDrive__5_Mount/p2013568_19207915.aspx

They'll collect it, strip it down, de-grease, replace worn bits and upgrade others, re-grease, add the belt drive modification, put it all back together, test and return it to me. Considering I bought it 2nd hand several years ago and have never serviced it, it might be worth the cost to have someone experienced give it the full works.

Any opinions?

Not a bad idea to google that company and look at the numerous reviews on here of them before you do.

There are a number of guides out there on how to spruce up the mount...the belt mod isn't difficult either.

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3 hours ago, smashing said:

Not a bad idea to google that company and look at the numerous reviews on here of them before you do.

There are a number of guides out there on how to spruce up the mount...the belt mod isn't difficult either.

That sounds ominous! I'll try later this evening. Can anyone recommend other suppliers in case my googling puts me off?

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Just watched the walkthrough by Martin's Astrophotography and this does look eminently do-able. With the age and fact that it has not been serviced probably ever, I think it would be worth replacing the bearings, which will cost about £70, so with the belt mod that's around £200 in parts.

On the other hand he is also referencing DarkFrame Optics. They do seem to be the go-to guys for mount tuning so I am wondering if they just had an off period for a while. It's a quandry as there is also a lot to be said for the learning experience of doing it myself.

 

 

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So, I've stripped it all down (both axis) and degreased everything (except the bearings, I was going to replace them). The grease was thick, goopy and black. New grease is on order.

I have replacement bearings but I don't know what they should feel like: they seem if anything a little bit stiffer than the ones I have taken out. I took all the grease out of one of the old ones and it spins much more freely. Should I degrease and re-grease the new ones with the lithium grease once it arrives? Should the bearing s spin freely? I'd imagine that packed with grease they would have some resistance but I really don't know. can anyone advise?

 

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If the bearings are sealed (normally a black plastic type cover over where the ball bearings are) then there is no need to re-pack them. They are packed at the factory with the correct amount & type of grease for that bearing.

Unsealed bearings will need to be packed with grease and with these you can see the bearing carrier or the roller/needle bearings themselves.

A bearing should run smoothly, no notchiness as it rotates. When you come to replace them, you're likely to feel this notchiness in the small bearings which hold the worm drive. After you've taken the worm drive carrier off the mount, slowly rotate the spindle and see if you can feel it. 

There will be resistance from the grease in the new bearings when you rotate them, remember, these are designed to work under load so should work freely once installed. The old ones will rotate freely when the grease is removed but they will also be more likely to bind and seize due to lack of lubrication. At best there will be play in the bearing as it wears faster. ;)     

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