Dec Backlash in EQ5 goto

[SteveBz]

Hi People,

I have quite severe backlash, such that guiding assistant just gives up.  It seems to be about 11 secs in total, the one time GA came back with anything, but it's about 3-4 secs if I measure it by hand.  Here's some guiding.  Actually, it's worse when I'm dithering.

So, I tried measuring the backlash with by counting and it's about 3-4 secs.  If I used PHD2 guiding assistant, mostly it fails, or it comes back with a very big number, like 11,350 msecs.

I tried entering this:

But then I got a see-saw mechanism, even when I dropped 8,000 to 3,000 it was the same.

I've taken the motor off just now and looked at the grub/hex-screw mechanisms.  One hex-screw was loose, so I tightened it to hand tight and let the grub-screw off an eighth of a turn.  I'll look again this evening.

I ran a three hour sequence of exposures on NGC6888 (with dither) and this is what I got on EVERY image.  Amazingly, they stacked nicely.

So last night I ran without dither and it was mostly OK.  What I want is full dither, but to do that I need to deal with the backlash.

Here's a photo of the motor and gears, most of the backlash seems to come from the top gear (ie the 12-tooth gear and its neighbour).  I guess the rest comes from the worm-gear:

Does anyone have any suggestions? There doesn't seem to be a belt-mod for the EQ5 as far as I can see.  Maybe there are better Dec backlash compensation settings I could use.

Thanks,

Steve.

[Budgie1]

I pulled my EQ5 motors and worm gears apart a few weeks ago to give everything a clean and re-grease, as I'd never done it and it had been in storage for 4 years.

I found quite a lot of backlash in the dec worm gear after I removed the motor. After cleaning all the old grease off and coating with new, I followed a couple of videos I found on Youtube which run through removing the backlash of the worm gears and installing the motor gears correctly. I had a quick look and this is one I used:

The grease I got from Rother Valley Optics and it's the green grease you need for the worm & motor gears.

Getting these set correctly should solve your problem, even though it's a bit daunting when you start pulling it all apart. I only did the minimum to clean & re-grease the mount, I didn't go for the full strip down and rebuild but it has made quite a difference and only took an evening to do.

Make sure to do a good search for other videos and watch the process all the way through before you start. If you're not happy doing it yourself then don't, it's not for everyone and you can cause excessive ware to the gears if it too tight. 

Edited September 13, 2020 by Budgie1
Spelling

[SteveBz]

7 minutes ago, Budgie1 said:

I pulled my EQ5 motors and worm gears apart a few weeks ago to give everything a clean and re-grease, as I'd never done it and it had been in storage for 4 years.

I found quite a lot of backlash in the dec worm gear after I removed the motor. After cleaning all the old grease off and coating with new, I followed a couple of videos I found on Youtube which run through removing the backlash of the worm gears and installing the motor gears correctly. I had a quick look and this is one I used:

The grease I got from Rother Valley Optics and it's the green grease you need for the worm & motor gears.

Getting these set correctly should solve your problem, even though it's a bit daunting when you start pulling it all apart. I only did the minimum to clean & re-grease the mount, I didn't go for the full strip down and rebuild but it has made quite a difference and only took an evening to do.

Make sure to do a good search for other videos and watch the process all the way through before you start. If you're not happy doing it yourself then don't, it's not for everyone and you can cause excessive ware to the gears if it too tight. 

Hi Budgie,

Thanks for this. I don't really want to strip it right down, but it maybe a good idea to take the worm off and make sure it's fitting snuggly.

Do you know how to set the phd2 backlash compensation?

I'll try tomorrow. Looks like we're in for a week of fine weather.

Tx

Steve.

[Budgie1]

Hi Steve,

If you start with the Dec axis, there's only a few screws & bolts involved.

You've already removed the cover from the motor, the motor housing is held on by a single bolt above the motor. Once this is off, you will see the two adjustment bolts and grub screw for the worn gear.

Before you start anything, check the backlash in the Dec worn gear but rotating the drive gear the motor connects back & forth and feel for any slack before the axis starts to move. If there is any slack, you may be able to take this out by simply tightening the grub screw by a quarter or half a turn. Keep rotating the drive gear back & forth as you do so and if it gets hard to turn then you've gone too far, likewise, if it goes slack then loosen the grub screw.

Have a watch through the video and see how he does it as you may need to loosen/tighten the two adjustment bolts as well as the grub screw and there are also two mounting bolts for the worm drive which may need to be loosened and then nipped up for the adjustment to be done properly.

It can take a bit of time to get it just right but it's worth the time and effort.

Also, on the motor there are two grub screws which hold the gear shaft into the motor body. Make sure these are tight as they can also contribute to the backlash it they're loose.

When re-mounting the motor, make sure the gears are meshed correctly and the top of the motor body is flat against the mounting bracket that the mounting bolt goes through. Put the bolt in and nip it up, then check for play in the gears and adjust if required before tightening the motor securing bolt fully. Then connect the power and try it out to make sure there is no grinding or other strange noises before you put the cover back on.

Unfortunately, I haven't tried the PHD2 backlash compensation tool as I only started using PHD2 after I re-greased the mount and I haven't had any issues since then.

[rnobleeddy]

I had a similar issue with my EQ5 which I've tried to resolve as well. I got one good session out of it but I'll wait for another before I declare success.

First question is probably what are you aiming for? I've had good quality 5 min exposures but I'll probably end up trying to make 3 minutes my standard. There's always going to be backlash, so focus on the imaging outcome you want rather than the backlash itself.

Generally my best guiding has been attained by having very accurate PA, whilst I've struggled if have poor PA and a lot of guiding is needed.

To try to make it better I have

 

- used sharpcap to get good PA. Best £10 you can spend imho!

- followed the worm gear tuning guide linked to above. Ensure the work gear shaft is tight against the bearings as well as the gear meshing

- the motor cogs can be adjusted by undoing the 3(?) Allen bolts. My RA motor had the two gears miles apart initially, but was easily adjusted

- follow the usual approach of intentionally unbalancing in one direction and/or aiming for a small PA offset and guiding in one direction only

[SteveBz]

2 hours ago, SteveBz said:

 

 

Hi Martin,

So I did lift off the motor and give the worm gear a little tighten, but I didn't go the whole hog and take off the worm covering.  I should do that tomorrow.  But if you look at this photo, the top cog contributes a lot to the slack.  If I run it back and forth, there is a real deal maybe of 3 or 4 secs.  Even if I fix the worm gear, that still leaves almost too much to handle from that top cog.  It seems to me that I need to get a belt-drive to overcome that alone - or use compensation.

What do you think?

Regards

Steve.

[SteveBz]

6 minutes ago, rnobleeddy said:

I had a similar issue with my EQ5 which I've tried to resolve as well. I got one good session out of it but I'll wait for another before I declare success.

First question is probably what are you aiming for? I've had good quality 5 min exposures but I'll probably end up trying to make 3 minutes my standard. There's always going to be backlash, so focus on the imaging outcome you want rather than the backlash itself.

Generally my best guiding has been attained by having very accurate PA, whilst I've struggled if have poor PA and a lot of guiding is needed.

To try to make it better I have

 

- used sharpcap to get good PA. Best £10 you can spend imho!

- followed the worm gear tuning guide linked to above. Ensure the work gear shaft is tight against the bearings as well as the gear meshing

- the motor cogs can be adjusted by undoing the 3(?) Allen bolts. My RA motor had the two gears miles apart initially, but was easily adjusted

- follow the usual approach of intentionally unbalancing in one direction and/or aiming for a small PA offset and guiding in one direction only

Yes, I've backed off from 5 mins to 3mins  as well but I haven't really got the unbalancing/small PA error thing working well.  Dithering hits everything.  Every time I dither, it takes much of the following exposure to settle.

Tx,

Steve.

[Budgie1]

As rnobleeddy said above:

8 minutes ago, rnobleeddy said:

- the motor cogs can be adjusted by undoing the 3(?) Allen bolts. My RA motor had the two gears miles apart initially, but was easily adjusted

 

If you look at the photo, there are three allen bolts on the front of the motor housing. Loosen these off and you can adjust the position of the small gear.

 

 

 

[SteveBz]

7 minutes ago, Budgie1 said:

If you look at the photo, there are three allen bolts on the front of the motor housing. Loosen these off and you can adjust the position of the small gear.

Oh, wow. I'm a gonna do it now!!!!!

I didn't see that. 😀

[SteveBz]

17 minutes ago, Budgie1 said:

If you look at the photo, there are three allen bolts on the front of the motor housing. Loosen these off and you can adjust the position of the small gear.

OK fantastic>  Done it.  I feel I've shaved about 1 sec off the top gear. But there is still 2-3 secs between the top and bottom gear.  How do I do the bottom one?

Can I have a belt-drive kit please?

S.

[SteveBz]

You can see I've put a blue cable tie on the bottom spindle. When I change direction I can count to three and it has just started moving, so I'm thinking 2.5secs.

[Budgie1]

2 minutes ago, SteveBz said:

OK fantastic>  Done it.  I feel I've shaved about 1 sec off the top gear. But there is still 2-3 secs between the top and bottom gear.  How do I do the bottom one?

Can I have a belt-drive kit please?

S.

Assuming you mean the top gear as the small motor gear and the bottom meaning the worm drive gear; you can loosen the motor mounting bolt and adjust the motor assembly double gears to the worm drive gear.

[Budgie1]

I would get some grease on those gears though and they look very dry.

If you have some lithium grease around, that would do until you can get the correct stuff.

[SteveBz]

4 minutes ago, Budgie1 said:

I would get some grease on those gears though and they look very dry.

If you have some lithium grease around, that would do until you can get the correct stuff.

It's a bit runny. I thought I had some motorbike chain lube but I can't find it.

[SteveBz]

11 minutes ago, Budgie1 said:

bottom meaning the worm drive gear

Bottom meaning the one with the blue cable tie.  I'll do as you suggest.

[SteveBz]

17 minutes ago, Budgie1 said:

you can loosen the motor mounting bolt and adjust the motor assembly double gears to the worm drive gear.

Done.  Seem to have got it down to about 1-2 secs.  Ie less than half the original.  I don't know what the worm still holds for me.  It's harder to test.  I'll try puting a marker on the OTA itself.

[Budgie1]

The only real way to test for worm gear backlash is to take the motor off and rotate the bottom gear back & forth and feel for when it catches on the large worm gear in the mount.

If there's backlash in there, you will feel it.

[Budgie1]

With the motor off, you're looking for the head of the mount (Dec Axis) to move as soon as you rotate the bottom gear in both directions.

If this doesn't happen and there's a lag before it starts moving, then you have backlash and need to adjust the worm gear.

[SteveBz]

OK, well I stuck a bit of fluorescent masking tape on it, so I could easily see when it moved.  I think the end-to-end delay between reversing the dec axis and it actually moving is less than 2 secs.  If that is true, then PHD2 will make recommendations when I do guiding assistant. 

Sadly you are far away in Fort William, otherwise I'd offer to buy you a beer.

I once went on a family holiday in Loch Etive and we got lost at Fort William!

I'll post here tomorrow with the results.

Many thanks to both of you and

Regards,

Steve.

[Budgie1]

No problems, Steve.

At least you know what and where to look if it's no better tonight.

Sadly, I have 8/8 cloud cover and my weather station is saying we've had 61mm of rain since midnight, making 85mm since yesterday afternoon, so I don't like my chances of doing any imaging tonight! 🥴

Clear Skies.

[SteveBz]

Hi Martin,

So it wasn't so good last night. So I stripped it right down to the worm gear:

And put it back together.  I think the worm is fine.  I played with it for about 20 mins until I felt it was OK.

I put the motor back on as tight as I could, but the central pulley still rocks as you can see here

I'll run it again tonight, but I think it's about the same as before, possibly a little worse.  As I recall it was about 1.5 secs measured yesterday, now its about 2.5 end to end.

Let's see.

I really think I need a belt-kit.  I've been researching it and there's a Polish guy on a website called astropolis (rather nicely) who seems to have made one.

In the meantime, I think it's workarounds.

What do you think?

Regards

Steve.

 

[Fraunhoffer]

.

Edited September 14, 2020 by Fraunhoffer
deleted

[SteveBz]

New backlash is 3445ms.  The lowest so far.

[Budgie1]

Hi Steve,

A clean and re-grease will help but I had a look at my Dec gears this evening to compare the movement in your video.

I still have some movement on mine but the main thing I noticed was the movement on your motor gear (the small one). Mine doesn't move at all, see below, how you tighten that I don't know as I've not stripped it down that far.

[SteveBz]

8 hours ago, Budgie1 said:

I still have some movement on mine but the main thing I noticed was the movement on your motor gear (the small one). Mine doesn't move at all, see below, how you tighten that I don't know as I've not stripped it down that far.

Hi Martin,

Yours moves less than mine, I can see that, but the top one doesn't move because the middle one doesn't reach it. The middle one wiggles without hitting the top one.  I think you can probably drop the motor a little.

Last night I took 70 3-minute shots of NGC6888 (Cyg) and only 20 were round.  And I dithered only in RA. 

I think I need a belt-mod.

Look at this guy talking in polish (thanks to google translate):

https://translate.google.com/translate?hl=en&sl=pl&tl=en&u=https%3A%2F%2Fastropolis.pl%2Ftopic%2F46999-eq5-belt-mod-atm%2F

and here it is in action:

Regards,

Steve