Star discovery clutch adjustment

[Slightly Brown]

I'm just adding to an earlier thread, instigated by Bezzi on September the 7th last year, on the the subject of the Star Discovery mount's clutches.
Thought I'd start a new discussion, given the 4 months between then and now, and since I have some findings on the subject.

Like Bezzi,  I too noticed a "lack of ooomph" on the mechanical side of motor driven slewing (rather than voltage related issues, which was also mentioned)
Unlike Bezzi's issue, which I seem to recall started after just a few days !  my issues came to light after nearly a year of use.

To be fair, it was probably getting progressively worse for some time, but wasn't until the scope stopped mid slew to a 2nd star during an alignment procedure, I finally realised there was a real problem.
To be clear we are talking about the Star discovery & 6" Newt package, which, should be absolutely fine, since it is sold as a package, and since the tube itself is a slightly lighter weight version of other 6" Newts. (No tube rings Etc.). Therefore we shouldn't need to consider exceeding the mount's carrying capacity with use "as the manufacturer intended".

I use mine with a small CCD video camera, which is less weight than a chunky "expensive" eyepiece, although I do have an ali bracket attached to the base of the head, carrying the Synscan handset and a DVR.  Even so, we're well under the mount's 5 kg "limit".

 

 

Having had the scope actually stop mid slew (but with motors still running fine) it did make me think that perhaps, both axis were "looser than I remember" them being initially.  Certainly manually moving the scope tube really did seem "freer and easier" that when I first acquired the beast.
So I tried an Azimuth slew, with the handset at default slew rate, and physically tried to stop the tubes movement.  It took no force at all to stop the tube - the torque/power to the head was truly pathetic.  We're in "couldn't pull the skin off a rice pudding" territory here.

Whipping the top cover off for a looksee I found two clutches on the Azimuth axis.  Hadn't particularly expected that, but thinking about it, yes you do need two.
I'm please to say they are nicely engineered, "dry" multi plate affairs - but how on earth do you adjust them !.
Some one on the original post way back in September mentioned a "good manual" - of course I got a 404 page for my trouble clicking the link, and having Googled around I can't find anything that goes as deep as "under the bonnet" clutch adjustment.  So if any one know of different - let us know !.

Actually adjustment isn't really a problem but what would be useful is some guide to "output torque" as I can see, over tight clutches having a long term implication on the motor's plastic gear train.

However, it turns out (on the Azimuth axis),  the top clutch is effectively the "motor to head (Azimuth rotation) power [removed word] torque control".  
While the bottom clutch does effectively the same as the hand control does on the Altitude axis.

Both clutches have an adjuster plate at the top of a chain of other "motion" plates, that slip n grip accordingly.  The top adjuster plate rides on a thread on the main shaft, so that (viewed from the top of the main shaft) "screwing in" (clockwise) drives the adjuster closer to the little gaggle of motion plates, increasing friction, and therefore "output" power.
You have to release 2 tiny Allen grub screws in the top adjuster plate boss (opposite the spanner flats) which lock the plate in it's final adjusted position.
Interestingly on BOTH the top and bottom clutch, only one of these locking screws were remotely tight.  
That in itself could account for everything !
Then, after manufacturing a spanner the right size, and slim enough to get into the rather tight access, I gave the top clutch's adjuster a tiny (% of a turn) clockwise, and re tightened both lock screws.

Powering up the Synscan I tried a handset driven slew, and was greeted by 2 notable things:

1) It took a whole load more effort to stop the tube and make the clutch "let go" - far more like I remember it being when it was new.
2) Since the slew motors start "instantly" and don't "ramp up" to speed (always thought it was a shame they didn't ramp up - far less stressy on the drive train) there was a visible shudder from the tube. Partly due of course to the lighter weight tube to mount connection having rather a lot of movement and "bounce", specially when suddenly being asked to quickly change state from stationary to moving.

I'm not a great fan of things like that though, as, in my little brain,  it always translates to mechanical stress somewhere else.  Backing off the the clutch adjustment a tiny weeny bit rewarded me with, still plenty of force needed to stop the tube mid slew, but a far, far less aggressive start to the slewing motion.

Clearly, there's a delicate balance between over stressing the drive train, while having sensible slewing forces.
But the next time I'm delving in there (I'm sure there will be a next time !) I'll actually hook up a spring balance to the "open" end of the tube, and get a real measure of the force involved.  By then it will have done some hours, so I can also see if theres any tell tale signs of premature wear and of course check that the adjuster plate locking grub screws are still tight !.  It's not beyond the realms of possibility that they just work themselves "un tight" over time and motion.

It's also "not beyond the realms" that after an initial run-in period they simply do need adjusting.  We see this requirement in other mechanics day in and day out.  It's also possible that the initial factory setting could be quite variable … depending on who does it, and whether there's an "R" in the month or not !.

Of course all this might amount to nothing (apart from severe embarrassment on my part), if on the second night out I strip the motor worm gear !!!.  But I really don't think that will happen !! …

[happy-kat]

Do you have any pictures of the internals please?

[Slightly Brown]

Afternoon Happy-kat ...

No I don't, but I've just taken some !!!

Having made the adjustments I can say the GOTO is way more accurate, so I reckon the clutch/s were iffy to start with or "on the move" due to lack of grip on the locking grub screws.

Having tried and tweaked a few times now, I've worked out that the bottom Az clutch should be just tight enough to alleviate any mechanical "slap" if you take hold of the mount's body and try to move it from side to side.  Then, the top clutch needs to be tight enough to guarantee 100% slip free motion when doing a real life slew, complete with the tube.  At some point I'll get a spring balance to measure the kind of forces that are working for me !!.

With the top clutch reasonably tight, and the bottom clutch just doing enough to maintain the main shaft's stability, your mostly "feeling"  resistance due to the top clutch, when moving the scope tube by hand, and, just the slightest "too much" on the bottom clutch makes manual movement "stiff & sticky".

With almost no resistance from the bottom clutch, manual movement of Az axis, is incredibly smooth, with no initial "tight spot" to overcome - really nice !

I've now also done the same to the Alt clutch.  Much easier, it's just under the hand wheel.  Again, I found "not entirely tight" locking grub screws !!!.   Tightened the clutch a little (rotating the adjuster plate clockwise) and now it's like it was when it was new - tighten the hand wheel and the tube position pretty well locks, useful if your not motor driven tracking / slewing or re positioning the tripod and don't want the tube flapping around !

 

[cv01jw]

Resurrecting an old topic here, but just wanted to say thanks for this.  I noticed last night that even with the hand wheel tightened I could rotate the mount with minimal effort, so I think getting inside and checking / adjusting the clutches is a job for this evening.  This thread will help enormously.

[bendiddley]

Hi. I'm trying to adjust the bottom clutch on my star discovery as I've got some manual rotation slop going on on the azimuth axis. I see you 'manufactured' your own spanner, can you tell me what you used or how you manufactured one as my spanner is too thick to go into the space? Cheers.

[bendiddley]

Also here's a link to my post about the problem I'm having if you're interested...

https://stargazerslounge.com/topic/323361-skywatcher-star-discovery-azimuth-slop/?tab=comments#comment-3524353

Hoping your fix might help with this.

Edited October 6, 2018 by bendiddley

[prusling]

Hi, I'm also keen to learn what flat spanner sizes are needed as my closest for the bottom nut (31.5mm - 1.25") is slightly too large - digital calipers show about 29mm? The top nut is harder to get to with the calipers but looks to be about 23mm?

Nevertheless I think I managed to get some traction to tighten the bottom nut but the mount seems to manually move as easily as before (far too easily!). Though now the hand control won't move the head at all despite the gears turning.  Maybe I adjusted the wrong one...?  Thanks for any help.

[prusling]

Some progress here - I bought a Bahco 9029T adjustable wrench with thin jaws (not cheap at £21.50 from Amazon prime but I tend to regard tools as investments that I'll probably use for other purposes). It fits the lower spanner flat fine and it seems to fit the upper one too though I haven't adjusted that yet.

I had previously managed to tighten the lower clutch as tight as it would go but the mount still seemed to move too easily in azimuth and it would not now slew.  I have now backed the lower clutch off and the mount slews fine though it now moves manually even more easily - maybe I just need to be more careful (it's freedom find anyway).

My other main issue was that it wasn't tracking well.  I now need to see whether the looser lower clutch has removed any stiction to the main drive that could have caused this.

I'd very much appreciate hearing other's experiences with these mounts - does yours move manually very easily in azimuth, does it track well, what could I do with the upper clutch to improve things?

I was close to ditching it in favour of an Az GTi but it seems to be fundamentally a very-well built mount (much better than the old Az Goto) and is still on sale in conjunction with the wifi adaptor (which I have) for £289 so I feel it's worth persisting with!

[prusling]

A quick update - after the previous post I checked the upper Az clutch and indeed it was not tight enough.  After tightening it to a (hopefully) appropriate level, that also had the effect of increasing the resistance to manual movement. Need clear skies to test it out but I'm feeling very hopeful!

Many thanks to the OP for posting this thread and to happy-kat for pointing me to other related threads - this has hopefully saved me from having to buy a replacement.

[bendiddley]

1 hour ago, prusling said:

A quick update - after the previous post I checked the upper Az clutch and indeed it was not tight enough. After tightening it to a (hopefully) appropriate level, that also had the effect of increasing the resistance to manual movement. Need clear skies to test it out but I'm feeling very hopeful!

Many thanks to the OP for posting this thread and to happy-kat for pointing me to other related threads - this has hopefully saved me from having to buy a replacement.

Glad to hear you've got yours working. Did you have any issues with play in the azimuth and is that solved now? With mine if you go to rotate in azimuth by hand when the mount is stationery you can rock it back and forth slightly, did you have this problem at all? Thanks for sharing the spanner you used, I'll give that a go.

[happy-kat]

It's good to see you've made progress on resolving your issues. I'm quite lucky the baby Virtuoso mount has both clutch adjustments external and they can be totally loose too too tight all by a spin off a large nut wheel.

[prusling]

Hi bendiddley, yes I too have a small amount of manual play in Az - I expect (or rather hope!) it is normal backlash which would be managed by always finishing with up and right movements. I've not had a chance to check it out in the field yet - maybe Monday evening if the forecast holds here.

I've tweaked the Alt as well, now - dead easy!  Hope that's not misplaced confidence...!

I'd still like to do a more 'scientific' adjustment of the clutches with a spring balance and recommended settings if Slightly Brown was ever able to determine these?

Hi happy-kat, I too had a Virtuoso for a while with a 90mm Mak on it and they are excellent mounts.

Thanks again, all

[bendiddley]

1 minute ago, prusling said:

Hi bendiddley, yes I too have a small amount of manual play in Az - I expect (or rather hope!) it is normal backlash which would be managed by always finishing with up and right movements. I've not had a chance to check it out in the field yet - maybe Monday evening if the forecast holds here.

I've tweaked the Alt as well, now - dead easy! Hope that's not misplaced confidence...!

I'd still like to do a more 'scientific' adjustment of the clutches with a spring balance and recommended settings if Slightly Brown was ever able to determine these?

Hi happy-kat, I too had a Virtuoso for a while with a 90mm Mak on it and they are excellent mounts.

Thanks again, all

So playing with the clutches didn't solve it? That's the only reason I want to adjust them, to try and get rid of the manual movement in azimuth. It's annoying because if you've found your target, one nudge and its moved position.

[happy-kat]

At least with the beauty of freedom find you can re select the target to goto it.

[prusling]

bendiddley: I had two issues - poor tracking and it being too easy to move the mount by hand in Az (freedom find helps but it was a pain to have to reselect the target often).  I may have solved both these issues by the adjustments as both Az and Alt drive clutches were slack. I thought you may have been referring to a slight amount of play before real movement occurs in Az which could be backlash - this may be tweakable but I suspect it would require gear adjustment which I'm not happy to do myself.  It may well be 'within design specifications' anyway!

[bendiddley]

26 minutes ago, prusling said:

bendiddley: I had two issues - poor tracking and it being too easy to move the mount by hand in Az (freedom find helps but it was a pain to have to reselect the target often). I may have solved both these issues by the adjustments as both Az and Alt drive clutches were slack. I thought you may have been referring to a slight amount of play before real movement occurs in Az which could be backlash - this may be tweakable but I suspect it would require gear adjustment which I'm not happy to do myself. It may well be 'within design specifications' anyway!

Yes my problem is a slight amount of play before real movement in az. See attached video which shows the problem. So is this backlash then? And if so, you think it requires gear adjustment?

[prusling]

Yes, that is exactly like mine now.  I believe there is always backlash in any mount with cogs meshing against each other (belts help) - if not, then there would be other problems. I may be wrong though...!  In any event that is not the reason why I needed to adjust mine.  If you don't have issues tracking or with too-easy manual movement then I think you have a good one in my experience!

[bendiddley]

I don't have any other problems as far as I'm aware, just the backlash. Seems to be quite prominent though. I've just checked my celestron 6se and there is a tiny amount with that but there seems to be excessive amounts with the star discovery.

[bendiddley]

Guys. Do you know if there is any way of knowing if the play I'm getting is caused by backlash?

[prusling]

A brief update - post-adjustment the tracking is still not great but probably better than before. Gotos are OK and the mount is less prone to accidental manual movements although as noted there is a fair bit of play before real movement. Will persist with it for now, but underwhelmed...

[seacommander]

Thanks Slightly Brown for the article and photos. They gave me confidence to proceed and explore the internals of my Star Discovery mount. My mount suffered from the opposite problem to yours in that there was no way that hand slewing was possible in order to use the convenience of Freedom Find.  I initially loosened off the bottom nut as you described but to no avail. Incidentally it was quite loose to start with. Adjusting the top nut did the trick. I then returned my attention to the bottom assembly - this presumably had been made adjustable for a reason. After whipping off the base (3 x cap head screws) that screws to the tripod I came to the conclusion that the bottom adjustment is just to slightly pre-load the large caged roller bearing that supports the whole head and enables it to turn so smoothly. Care is needed to ensure that the pre-loading is not so great that it causes the head to bind due to any slight machining irregularities. The Widescreen Centre in Cambridgeshire managed to obtain a short video from Optical Vision, who are the UK importers for Sky Watcher products, of factory clutch adjustment . The mount in the demo (only azimuth) is set up for hand slewing by only adjusting the top nut. Thanks again for the photos and description of your adjustments.

Edited November 13, 2018 by seacommander

[prusling]

On 12/10/2018 at 15:26, bendiddley said:

Yes my problem is a slight amount of play before real movement in az. See attached video which shows the problem. So is this backlash then? And if so, you think it requires gear adjustment?

IMG_7036.MOV

Resurrecting an old thread, I rarely use my Star Discovery but tonight I thought I'd have one more go at dialling out the 'backlash' in Az.  I've found the cause and fixed it so I thought I'd pass it on to anyone who may be suffering with this.

It's not backlash after all!  The Az drive assembly is held in position by two pairs of screws on either side (one pair is shown on the left of Slightly Brown's first photo above) and I noticed that the movement I had was because these were not fully bearing on the assembly and so were allowing it to move a little from side to side.  I carefully tightened these down evenly on both sides using a flat head screwdriver and that eliminated the movement completely.  I notice that there is a similar setup on the Alt drive assembly but I had no movement there.

I've tested this in the house and the motors seem to operate fine.  When it's clear I'll test it outside and report any issues.  Hopefully this will improve performance significantly - I hope so as these mounts are well engineered and streets ahead of the old Az Goto.  They seem to have ended up as an under-utilised stop-gap between that and the Az Gti but with a wifi adaptor they are equally competent.

Edited July 19, 2019 by prusling
typo

[bendiddley]

Thanks for sharing this. I'm sure this will be welcome news for anyone else who has a similar problem.

[speako]

Hi all,

I have owned this telescope just over a week and already my Azimuth axis is loose and wobbly. I have tried to fiddle with the locking nuts but the Allen key is just spinning inside the hole, however on the top clutch the same Allen key is able to tighten the locking nut. Im struggling to see the 'great engineering' people keep referring to (this post is 5 years old and SkyWatcher have clearly done nothing to address it). Luckily, with the fact that I've had it for just over a week it's still under warranty. However if you happen to be considering buying this telescope then just avoid it at all cost. I've never spent so much money on something that feels so cheap. I've never been so underwhelmed and disappointed at making a big purchase.

If you did unfortunately happen to buy this piece of plastic my advice would be to forget the 'freedom find' feature. The mount was rock solid until I decided to spend one night manually slewing it, this has somehow caused the clutches to become loose and now there's an inch of play side to side when wobbling the Azimuth axis. In one night the mount aged 5 years. 

With hindsight I would have never have bought this scope but I'm stuck with it now and just hoping the next mount was put together properly. 

Sorry for my negative post, but the only reason I found this website was due to having to google how to fix my brand new mount.

Hoping this post at least saves another person from sinking 600 euros into this junk.

Best regards,

Ryan

 

[Zermelo]

It's a pity you have had a negative experience with this mount, which has performed well for others on this forum, including me.

Is there a reason you can't return it? If it's only a week old, and it's not fit for purpose.