Noob Question concerning dec. backlash in EQ8-R Pro

[AstroAndy]

Hi Folks

Although I've been at AP for a while (even if my images don't always show it, ), I've come across this value using the guiding assistant concerning dec. backlash as my calibration and guiding left much to be desired yesterday (today?) night. Erm, this is a bad value, right? The mount, an EQ8 pro, is new, and has performed flawlessly until the last 2 nights.

What I would like to know, how does backlash develop (mount is handled with conscientiousness)?

Can I offset this with slight imbalance in dec., or do I have to open up the mount to tighten the gear mesh?

Strangely, guiding settled down after awhile, and I could get some decent subs; also, the calibration review looked ok, actually, so I wonder about this backlash issue.

Regs.

Andy

[michael8554]

 

EQ8 owner will hopefully say whether that figure is average, or needs adjusting, or sending back !

With good PA (3.8arcmins is fine), the mount will hardly need any Dec guiding.

So look which way the Dec is drifting at 3.8arcmins, balance to keep Dec on that side of the line, and maybe increase the MinMo a bit from recommended, to keep your Dec guide error about the same as your best RA error.

Equals round stars.

[david_taurus83]

Thats unacceptable for a mount in that price bracket. It's supposed to be Skywatchers observatory class mount. My CEM25 has 'only' 1370ms of Dec backlash.

[callisto]

I could be wrong, but I'm sure 'Gina' has this mount

[AstroAndy]

Thanks for the replies...@ Michael, that's kind of what I did, strangely enough, the guiding evened out after awhile, but it's the second time I get that msg (the first time, it didn't even move the guide star North in calibration).

@David, thanks for the input, I'll have to check that out, and@ Callisto, maybe Gina will find her way to this post, lol.

Andy

[michael8554]

41 minutes ago, AstroAndy said:

the first time, it didn't even move the guide star North in calibration

The mount's Dec is working, but has 3 seconds of backlash.

SOP before Cal is to pulse north until the star moves a lot, to remove any Dec Backlash.

Probably In your case PHD2 made lots of north Cal moves, but no north movement was detected, because it was only taking up backlash.

Michael

 

[AstroAndy]

Hi Michael

I usually do a West and North movement before calibration, don't know whether I forgot that time, it seems to be looking more and more likely that I have to tighten the gear mesh, which I don't like to do (2 left hands).

I've done a similar operation successfully on an EQ5, however, being loath to fiddle with 2mm Allen wrenches, I'm still informing myself as the first few times there seemed to be no perceptible backlash present. Even w/out the North movement, backlash was cleared relatively quickly, and calibration went beautifully in abt. 12 steps, that is why I was wondering how backlash develops (which it shouldn't after such a short time), or whether it was somehow already present but "hidden" when I bought the mount (orientation of scope and weights?, although my setup is well-balanced). However, orientation shouldn't be a problem when calibrating at Meridian and CE

Needless to say, for that price, I shouldn't have to be monkeying around with adjusting the insides of a mount after only a few months, 3s seems quite a lot of backlash.

[michael8554]

After a few sessions everything on the mount will have loosened up, like the old-fashioned car engine "running in".

Michael

[AstroAndy]

Maybe Volvo should make mounts then, I got the old 2001 battlecoach years ago, nary a service done to it (not proud of it), and she still performs now as she did then, maybe a bit worse on gas (although that could be due to using it to stay warm at my dark site). 😂

[david_taurus83]

16 hours ago, callisto said:

I could be wrong, but I'm sure 'Gina' has this mount

I think Gina has the older model. The newer stuff seems to have the 'Pro' badge

[AstroAndy]

Way this is developing, unless I find out it's not the mounts fault, I'd have a thing or 2 to say about the "Pro badge". 😂

[david_taurus83]

To be fair, my AZEQ6 'Pro' was bang on out of the box but after 6 months or so use I had to adjust both axis for backlash. Is there a guide for adjusting the EQ8? It shouldn't be hard to do.

[AstroAndy]

Hi David

Of course, there is ( https://wolfcreek.space/wp-content/uploads/2020/03/Adjusting-the-Declination-Axis-Backlash-Orion.pdf ), however, those who wrote it saying it's not too different from the new EQ8 didn't take me into account. 😂

There are people who just look at a screw, and it jumps into it's socket. Me, I look at it, and it jumps right out of it. I am not a mechanical wizard, and have 2 left hands. I suppose if I end up having to do it, I can (few hours, maybe, lol). I'm the type who needs a diagram drawn for a 2 year old , and when I see things like ...is hard to get to, had to grind down a 2mm Allen wrench, I run for the hills. Isn't there a rule which says once you open up the mount to fix something yourself, you void the warranty?

So now, I'm looking at clutch-gear interplay, hoping to avoid the adjustment.

[martin_h]

I have the older EQ8 and it had a shed load of Dec backlash out of the box, I adjusted it out myself and have had to do it twice more since, but, touch wood it's been fine since then

[tonyowens_uk]

There is a special interest group on Google for EQ8 mounts here: https://groups.io/g/SkywatcherEQ8/topics

Backlash adjustment instruction and help are available. All worm gear drive mounts that dont have antibacklash gears have significant backlash (for an imager). Either adjust it yourself or get your dealer to do it. Its perfectly normal.

[AstroAndy]

Ah, Tony, that's good to know...I've read somewhere on a website 😉 😂 that tightening the clutch in different ways may have an effect, and as I seem to get different values on different days, that's what I'll try first.

[tonyowens_uk]

Andy that isnt a great approach. The badly designed clutches on EQ8's do affect backlash on Dec (as well as cause image shift) on opening and closing them. But the effect is not predictable or controllable or desirable.

Overlaid on this, is a seasonal variation in backlash due to differential thermal expansion of the mount components and varying ambient temperature. The mount is tight or binding in winter, whiel backlash grows in summer.

If you are an imager, my advice would be not to waste your time messing around with a half-assed response, and either make the adjustment yourself or find someone qualified to do so. 

[skybadger]

I have a similar problem emerging on my eq8. I'll be removing the backlash through worm adjustment but could do with advice on how to ensure even friction through the whole revolution, unless it's just to run fast unclutched for a couple of revs and maybe watch the current.

[newbie alert]

With a eq8 do you have to take anything apart to adjust the worm.. surely it's the same as eq6,  celestron.. just loosen the 4 bolts for the worm housing and adjust the worm with a Allen key.. unless it's a different setup??

[AstroAndy]

Nominally, the actual process is not that hard, but it's fiddly, and fiddly is my enemy, lol.

[tonyowens_uk]

9 hours ago, skybadger said:

I have a similar problem emerging on my eq8. I'll be removing the backlash through worm adjustment but could do with advice on how to ensure even friction through the whole revolution, unless it's just to run fast unclutched for a couple of revs and maybe watch the current.

Hi Mike. Loved your account of the 12" Cass/RC build on your site BTW!

The EQ8 is awkward as its neither fish nor fowl. The underlying mechanical precision and structural stiffness is superior enough to encourage seeing-limited imaging, but the omission of anti-backlash worm gear meshing and extensive use of thermally-reactive aluminium components (shafts, structure, worm wheels) frustrates being able to set a stable mesh clearance as ambient temperature changes. On top of that, many have run-out issues of the Dec worm wheel relative to the Dec worm, caused by tolerance stack effects.

Consequently, it isnt possible to establish stable meshing friction around the Dec axis, never mind stable backlash. If run-out doesnt get you, temperature changes will! The best that can be done without surgery is to clamp the Dec clutch as lightly as possible, and set the worm meshing clearance at the 'tightest' position angle around the axis, judged empirically. The surgical fix is to replace the standard Dec gearing with an antibacklash one, which is very effective, and replace the standard clutch with a modified design. But this isnt particularly cheap. 

[Stuart1971]

I have been reading this thread with interest, as I have an EQ8 mount and have both adjusted the backlash and replaced the bad DEC clutch, and I have to say it’s much much better, but as @tonyowens_uk as said, it’s pretty much impossible to get rid of all backlash due to the “not so good” machining of the worm wheels on these mounts. They are not perfectly round, and so your best bet is, in the cold of winter, find the tightest point on the worm wheel rotation and adjust it at that point...this is what I did, and it took some trial and error, and a good guide was watching the amp meter on my power supply, as under normal load slewing the DEC was showing a 2 amp draw, as soon as it started to get tight this went up to 3.5 Amps, before it started binding, so I was looking for a point where it was a nice steady 2 Amps all the way round, I found the tightest point, and then with a long dovetail in the clamp as a lever, I rocked the end of it to see how much play there was....and adjusted as needed, and then run a cycle or two around and checked again,  but as I said, it’s impossible to get rid of it all.

My worm has no real noticeable backlash around half of the worm cycle and a small amount on the other half, this shows how out of true the worm wheels are and hence why the only way to solve is with spring loaded worm...

Stuart