ollypenrice

I'm not known for being the voice of reason, but here goes. The EQ8 is a mass produced unit, not a hand built Mega expensive unit. In any mass production run there is a failure rate, which will be balanced against the cost of decreasing the failure rate. Now whilst, from a PR point of view, sending a poor mount to a guy that is well known in the community and that will use the mount in a commercial environment, was a bad move, it probably reflects the nature of the selling model (stack 'em high....).

Unless these mounts start failing all over the place, then, probably, these should be dealt with in the normal way that any failure of a mass produced item would be dealt with-replace the unit.

Its regrettable (especially from a PR point of view) and it is extremely annoying to be on the receiving end of it. I'm sure that FLO will sort the job out.

This is fair, Id say. However, the consumer has a role in determining the cost of the failure rate. Make it too easy for the manufacturers and the failure rate cost goes down and the failure rate goes up... 

Olly

Im unsure where to go with all this concidering that Ive not had first light with this mount, My plan for a while is to load this mount up and have all my eggs in one basket, I checked the full rotation of the dec and there is loosness at one part and none in the opposite which indicates the same issue other have with their mounts.  There is also some play in the RA.  I had a quick look through the manual last night and there seems to be a backlash compensation option on the hand controler, also Im sure my guiding software AA5 has a backlash compensation option too?  Should I bite the bullet and contact the deal and send it back or carry on till first light .  Problem is I send this back I have no mount.

Firstly I'd read the SW answer on Dark Matter's CN thread and see if you agree with my interpretation in the post above.. http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=6269957&page=0&view=collapsed&sb=5&o=all&fpart=1&vc=&PHPSESSID=  Although they haven't replied to my emails yet, this is a farily open answer and is informative.

Can you use Dec backlash compensation to resolve the issue? Yes and No;

Yes, you can inform AA5 of the delay in response and it will try to allow for this.

Yes, if you have a deliberate polar misalignment you can disable guiding in one direction. This will stop the guider tossing the scope back and forth across the backlash in a perpetual oscillation. I'm using this method on one mount here at the moment. It's a temporary fix till I adjust the worm. 

No, this fix won't work in the wind.

No, on the EQ8 the Dec backlash varies during the rotation so one backlash compensation value cannot be right throughout the rotation. It will need recalibrating during the run.

Olly

Steve, I was trying to give you a break over Christmas! No rush.

I also wanted (and still want) to do more homework. A SW reply to Dark Matter is remarkably open. It's at the bottom of this thread. http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=6269957&page=0&view=collapsed&sb=5&o=all&fpart=1&vc=&PHPSESSID=

My interpretation with only a little reading between the lines;

1) They have either failed to make, or cannot make, the centering of the Dec worm wheel accurately enough. The answer is to set mesh at the highest point and let the backlash do its worst at the lowest. If the offset is 'tiny' as they say in the thread then OK. Ours cannot be described as tiny, and it may be even worse than it seems, viz...

At the high point ours feels tight and the motor gets warm. If this is so then the worm will have to backed away from the wheel, making the Dec backlash even worse. I've asked how to measure amp draw on a different thread but if anyone sees this and can tell me, then great. This is to find out if, indeed, the mesh is too tight and likely to seize the drive as in Dark Matter's case.

2) They realize that they should have spring loaded the drives to allow for this. Expect a redesign at some point, maybe?

Olly

Well, at some point one loses interest. Whatever 'Skywatcher' or 'Synta' is, they don't understand QC. I'll stop there for now. If you buy an Astrophysics product the buck stops at Roland Christen. If you buy a TEC it stops at Yuri Petrunin. If you buy a Takahashi it doesn't stop if you don't speak japanese. You just have to rely on their QC. Buy their optics but not their mounts.

Interestingly, EQ8 discussion on the French forum is very much along the lines of, 'Hey, it's cheap, what do you expect?' That is why I don't buy things in France. There seems to be no culture of, 'You are selling it so it has to work. If it doesn't, take it back.' The EQ8 I just bought cost 3/5 of the price of the new car I bought seven years ago and which has delivered seven years of solid service with no signs of not delivering seven more. For goodness' sake, this is not a tripod with a head motorized in two directions, it is a car with a turbocharged, fuel injected engine, ABS brakes, airbags, electric windows, sound system, catalytic converter...

Olly

It would be interesting to know more about the relationship between 'Skywatcher' in Canada (whoever they really are) and the factories in China who produce for them. I'm pretty sure that this is where the problem lies. I doubt that Skywatcher are delighted to have rubbish served up under their name but they don't seem to be very good at doing anything about it. The most cursory glance at the mount I received would have said, No. That is not right.

They cannot possibly be producing so many mounts that it would be impossible to check them properly. Let's say that the factories who churn out the stuff just want to see it gone and get paid. That is probably a safe bet. (I do know someone importing from Chinese factories in a different field.) The key thing is, Why are they not checked? Skywatcher stuff is drop shipped. In general the dealers don't see it. So who the hell does see it? Do Skywatcher have people on the ground in China checking it or have they just signed a specification contract with a factory and counted on them to meet it? If this is the case they need a major change in management policy. If it isn't the case, why is QC so absurdly unsatisfactory?

Speak to us Skywatcher. I'll document my unreplied emails after the Christmas period because, fair enough, it is Christmas.

I'm very upset for FLO because for some time I have sincerely wanted to give them a good sized order and it has backfired. Not their fault. Most upsetting. From my own point of view I have enough good mounts to satisfy my immediate guests so it isn't a crisis and I don't intend to pretend that it is. It's just a disappointment.

Olly

At shorter FLs I can live with 2 seconds. My Tak mount defaults to 1.9 though I wish it were better. It certainly should be better. It is easy to find backlash in RA because the C/W shaft is so long that it will move a lot at the bottom for what is a small amount at the worm and wheel. If you feel only a tiny bit at the bottom of the shaft ne panic pas, Captain Mannering.

When setting up the guiding on the Mesu I set the Dec backlash to zero because that's what it is. Makes you think.

Olly

Just to chuck my results in Olly ... mine is now finally set up and I can report there's no backlash in DEC and I've checked this every 15deg all the way round the axis, no feel of movement and hand controller does not report any movement either

That's great. Just as it should be. 

Olly

Galaxies, apart from a few, need focal length. You can consider using a shorter focal length and smaller pixels, I suppose.

Trouble is, long focal lengths/high pixel resolution require pecision guiding. This won't come out of a box. It is much easier to start with a short focal length, really. If you did so you could spend a very long time enjoying M51, M33, and M101. Any one those is worth fifty hours of imaging time. (Actually I do mean it! I worked on an M31 collaboration with over fifty hours of data.)

I'm with Steve and Sara. I'd look at the specific scope, not the generic type. Sara was lucky to find a Pentax but a TV85 should come up fairly frequently. With the TV flattener I'd be happy with that. Most of my scopes are bought second hand. Takahashi FSQ106N for around £2K. (Cosmetically fair, otherwise bang on.) TEC140 for under £3.8K. (Literally as new.)

As Steve says, there is something about that ED80 lens... 

Olly

Hi Olly

I can't see any reference in the manual. If it was an anti-cable wrap thing then it wouldn't sent the axis off in the same direction surely?

Not a clue!

Olly

You need to check it at various points along the rotation.

one thing that I noticed with mine is that if you do a couple of full 360 slews in DEC the handset reports "Slew limits exceeded" and then rotates the DEC through another 360⁰. I have no idea what thats all about?

There may be some internal cabling that mustn't get wound round too many times! Or maybe the encoders get confused of you exceed a full turn.

Olly

Discernible. 

Olly

The level of Dec backlash on mine is small enough that on tracking rate 2 and pressing the button on the hand control it takes a couple of seconds to start moving the scope. So, in the scheme of things not huge. Actually no worse than my old CGEM mount.

Having said that, when I first set it up, before moving onto the correct pier adapter, I could see no decker able backlash.

I suspect this will just be a matter of where on the wheel you were.

I wouldn't leave the blanking plugs out. It is vital to keep a worm drive clean. (On the iEQ45 the drives are visible from the outside. That cannot be good.) I would just put a drop of Loctite on the plugs. They will come out OK but won't fall in.

Olly

Thanks Olly.  I did try the very same method you mention above last night, I would detect the slightest of movement in th dec, at first I thought the dovetail plate was not sitting in the saddle correctly,  The movement is ever so slight - I can just detect it by hand and sound I cant see it by eye? does this sound right ??

This sounds as if it might be OK to me. The thing is, is it consistent all the way round? If it is you can adjust the tension of the mesh should you find you need to. I'm guessing you have the version with the three blanked off holes on the Dec worm housing? These seem to have been introduced to facilitate this. Don't screw the blanking plugs all the way in, ever. They can drop right inside.

Olly

Having bought my mount 2 weeks ago and stil not had first light due to the weather this thread is making me very nervous indeed and I dont need that. How obvious is the backlash? Are we talking you can rock the mount and see the backlash clearly or is the issue during guiding?  Can anyone confirm the best way of testing ?   Wound not mind seeing some positive reviews  - think I will read Gina's thread agin ;-)

Mark

Gina's seems fine and yours might also be fine, Mark.

The backlash is very obvious in my case. Just put a dovetail in the saddle plate. Let it overhang a bit on one side and feel that side. Simply wiggle the dovetail side to side in the direction of Dec rotation. On the slack side there is clear 'wiggle' in my case and when you think in terms of sub pixel guiding that means a lot. Then drive the Dec round a quarter rotation and try again. Better, worse, different? And another quarter, and so on. The Dec backlash should be at the limit of detection with your fingers. No more. I can make mine rattle. Note that you must drive the dec axis round on the motors, not move the puck on the clutches.

I'm guilty of recording two seized Dec drives when they turned out to be the same one on different forums. My apologies for that.

Olly

It's getting worse. Peoples' Dec motors are now seizing up. http://stargazerslounge.com/topic/202845-eq8-dec-binding-or-total-failure/

As I said on the thread to which I'm linking here, I noticed a remarkable heat build up in my Dec motor after some slewing without any load or C/W bar in place.

For me that spells curtains.

Olly

Hi Olly, too bad it's mechanical issue. An non-concentric wheel would explain why we didn't feel the backlash equally in every position... More EQ8 owners should have this. I'll ask my Australian friend that also has an EQ8.

Cheers,

Jeffrey

Cheers, Jeffrey. You're right. Several other people with the same issue have appeared on the net, unfortunately.

Olly

Just an idea!! find the tight spot on the dec axis then loosen the clutch and rotate the saddle into the polar position arrow up, relock the clutch and test for backlash, is it exists rotate the saddle back to the tight spot location and re-tighten the clutch, test for backlash..is backlash still zero?

Yes?

Undo clutch rotate saddle again to polar and  test again..if backlash is there it is either Ra or a clutch issue? possibly not an out of round worm wheel?

comments/ critique  welcome

Ray

The clutches lock the puck to the worm wheel. If I move the puck via the clutches the amount of play doesn't change; It only changes if the worm wheel is driven round to the other side.

Olly

Hi Olly,

I powered up the mount, entered the date and time as normal and unparked. I then went to Utility Func. >Show Position. You can select RA/DEC, Alt/Az or Axis 1 & 2 readouts by pressing the selection arrows (not the 4-way directional arrows). I slewed to various points around the DEC axis and watched the readout as I pushed and pulled on the dovetail. This will also show if the movement is in RA or DEC. Obviously, this method is pretty crude and is only as accurate as the resolution of the encoders, but it does give a way of measuring the backlash.

Rgds

Steve J

Good idea. I'll try that. I was forgetting the encoders.

Olly

I made a large number of worm and wormwheel sets before retirement, concentricity was paramount and each set was tested for mesh and smoothness. You can't adjust out eccentricity with a rigidly fixed worm assembly, you could get away with a small amount with either a spring loaded or rubber mounted unit. Unfortunately you can no more judge the performance of a gear set than that of optics just by looking at them. I hope it's not the dec/ra  shafts that are running eccentric.

Thanks Peter. This has been mooted in Australia and speculatively linked to the delay in the initial production run. I don't have a view on that, given no known evidence.

Olly

Ive had a play with mine (seeing that there's near constant cloud and rain hhere there's little else to do!). Am pleased to report that mine seems to be OK. With a 15" dovetail in the saddle (all overhang to one side) there is a tiny amount of backlash that can be felt. I'm talking about way less than 0.5mm as measured at the end of the dovetail. This is consistant right through the DEC rotation. Using the handest to measure the backlash it comes in at roughly 1-1.5 arc minute. I don't have enough experience to deem this acceptable or not. It feels OK to me, but what says you?

How did you do this measurement with the handset? I can see how to do with a guidescope calibration. If you let me know I'll give it a go. 

Olly

I find it hard to picture what is wrong when a worm gear has uneven "tightness".  The only thing that comes to mind is that the worm wheel is not centered, as Olly suggests. How the heck do you fix that???

/per

In my opinion you won't be able to. Either the wheel isn't centred or it isn't round. Or both. Ruddy nuisance. It would be so much easier for everyone if Skywatcher spent a couple of quid on QC and saved us and themselves an incredible amount of wasted time.

Ray has a point about repeatability. I'll also give the drives some run time to see if anything changes.

Olly

OK, the bad news.  After a lot of net research I've found out how to adjust the mesh of the worms. However...

Stage one is to rotate the dec drive a little at a time using the motors and to feel the amount of backlash at each point. The purpose of this is to determine the tightest point of mesh between worm and wheel before tightening the mesh any further. 

Stage two is no longer relevant in my case because on one half of the wheel's rotation the mesh is tight (no backlash) and on the other half it is very slack. (Lots of backlash.) Even if I felt like trying it there would be no point in adjusting the mesh because the problem, presumably, is that the wheel is not concentric with the Dec axis. I found an Australian owner who has precisely this problem and was in contact with Tasco who seemed to be trying to fob him off with a software fix. This has to be a waste of time because the problem is mechanical. Adjusting the dec guiding response speed is not the way to sort it. The way to sort it is to have a concentric (or round) worm wheel.

Oh dear, oh dear. Not very happy.

The most basic QC would have spotted this, especially since they obviously know to look out for it. (Hence the modification to the dec motor housing to assist in mesh adjustment.) Unless I've completely misread the symptoms I suppose the mount will be going back.

Olly

I now have a copy. Many thanks to Ray for that. The process is quite complex but later mounts have three large access screws to reduce the complexity of the adjustment. If you have these access holes for the Dec adjustment (the one that really matters) it will be easier. At the end of the PDF there's mention of a verison of the document covering the version with the access holes. I don't know where to find this version of the instructions.  Be aware that the allen bolts blanking the holes are actually just grub screws and if screwed inwards will fall into the worm housing. Why no heads on these blanking bolts? No idea.

Olly

Olly, that thing has low resolution absolute encoders! What happened to your principles? It is even suitable for automation! (sorry, shouldn't use that word)

/per

The modern world is creeping up on me. I've even started replacing some of my wooden lenses with glass ones...

Olly

OK, regarding the Dec backlash I've sent off enquiries to OVL and SW. The issue seems to be well established on the net and there's a PDF document discussing a fix to the clutches which I still haven't successfully downloaded, but I'm hoping to get there!

Olly