Skywatcher AZ GOTO alignment and accuracy

[DrRobin]

Hi,

Great let me know how you get on. I reckon when correctly set up and sorted these mounts can provide good accurate tracking. Mine is close to been sorted, but I want to do 3min exposures on DSO and I am not sure it is good enough yet.

I think the backlash will help, pity Skywatcher don't detail how to set this and also clutch nut setting. Once a few of us have set up our mounts and shared the knowledge then we will know what is best.

[mindburner]

hi

just had a quick go at backlash compensation. Not too successfuly i'm afraid. It didnt seem to make much of a difference. The backlash measured seemed to be about 2deg on the AZ. Keyed in 2 but still had backlash but the scope seemed to travel farther once I release the handset key. I could well have been doing something wrong as it was just a quick attempt at it.

The base drive is a bit sluggish I noticed, sort of labouring. It picks up after it's been moving for a while. The PSU is a good 10A 12v job so it's not that. I think I may have to seperat the base unit to see if there is a lubrication (or lack of). Sprayed some silicone on to the bearing from the side. Noticed bits of foam, may be to keep dirt etc away from the gears.

Just going to hunt for some Williams Optics bino viewers online. It's bad when there is no seeing as I spend too much time on kit websites oggoling at nice stuff.

[DrRobin]

Hi,

I found another thread on here about dob base bearings and the use of Ebony Star laminate and Teflon pads. Looks like this thread is relevant to you and possibly me as it talks about poor movement if your base is sluggish it suggest poor slip on the bearings.

Basically the recommendation is to replace the bearing material and improve the movement between the plates using turtle wax. The thread is http://stargazerslounge.com/discussions-scopes-whole-setups/117958-ebony-star-laminate-dobs.html

I am going to look in to this as soon as I get chance.

Good luck with the bino search. I am currently making a USB auto focus for mine, that's taking up all my spare time at the mo.

[mindburner]

That USB auto-focus sounds very nice. Interesting to see how that turns out. I have the skywatcher electric focuser, which does a good job. I am also trying a USB control to operate the onscreen menu of the SCB-4000 video camera I have to save touching the camera body.

I had a look through the posts re: bearings etc. Trying to find one with good pictures to get a feel for the way the base looks once it's separated. Most of the posts are for non motorised mounts. It looks like the motor and encoder should lift out once the 4 screws and clutch are removed. Something to definitely investigate though.

[DrRobin]

Hi,

The USB focuser is a design by Dave Trewren and is called SharpSky, Google it and you will find his website and also U tube videos of it in operation. Check out UKAI as well, he has a post on there. I had a motor focus on my last scope, never transferred it to the dob as I bought a 10:1 from Modern Astro and it was okay at the time. Now that I am doing more imaging, I need to be able to focus without touching the scope.

You need to be a bit handy with a soldering iron to make up the circuit, but I can say it works very well and Dave is very helpfull.

Regarding the bearings, I am going to take mine apart as soon as I get chance and of course I will photograph it and put some pics up. I am then going to work out how to improve it, but am going to start with the Alt as it is easier to get to and my scope has more problems with the Alt than the AZ, although I think they will be very similar.

Unfortunately, it's going to have to wait until the weekend, I am just too busy through the week and the light is no good either.

[mindburner]

great I will have a look at that,maybe something for when i'm off work over Christmas. I have done a bit of repair on vintage synthesizer keyboards so hopefully the circuit will be manageable.

As for the bearings, would like to get them apart myself but again time constraints. I have a 1 year old to keep me on my toes. I hopefully will get out to the shed maybe Thursday night though.

[DrRobin]

Alt bearing strip down

Okay so I found time to strip down the Alt bearing and clutch on my 10" Auto/Goto dob.

After removing the black cover we see the shaft encoder, shaft and friction/tension nut.

Removing the shaft encoder we get a better picture of the friction adjustment nut.

Removing the friction nut, the bearing and pressure plate is removed and the dovetail drive plate and gear drive plate is removed.

There is a caged roller bearing with a spring steel pressure plate which is used to apply pressure on the whole assembly.

The gear drive plate connects to the friction drive plate using a friction material. The gear drive plate is held against the dob side using three PTFE pads.

There should be grease on the gear drive plate and the three PTFE pads, as well as grease on the bearings, there shouldn't be any on the friction material between the dovetail plate and gear plate.

The same nut tightens the dovetail plate to the gear plate and also tightens the gear plate to the fixed side of the dob mount.

To provide good tracking I think you need high friction between the drive and dovetail plates and less friction between the whole assembly and the three PTFE pads. I also think you need smooth movement in the parts that are supposed to slip and no slip between the dovetail and drive plates.

This means that the dovetail and drive plates should offer high resistance for any given tension nut setting and the whole assembly should move smoothly for the same tension.

The first thing I noticed was that the grease was everywhere apart from where it should have been. There was lots round the centre of the shaft and very little on the three PTFE bearings or on the caged roller bearing.

My first try was to redistribute the grease to where it should have been before making any more radical changes.

I reckon I can now get a higher tension on the friction nut and the scope still moves very smoothly, whilst the drive and dovetail plates are held in higher tension and therefore less slip.

If this doesn't work then I am going to clean off all of the grease and find some better grease or apply a slip coating to the fixed side of the drive plate.

After that I might try a non slip surface to the dovetail side of the drive plate to improve the friction for lower tension settings.

I haven't had chance to take the AZ bearing apart, but suspect it is very similar.

Whilst I was at it, I also balanced my scope for the various set ups of cameras and eyepieces, this helps greatly as it allows for less load and hence less slip when moving in Alt. I tested it for smooth movement using an idea borrowed from this thread by taping my laser collimator to the finderscope and watching the movement with a long cable on a distant wall. Movement looked very smooth with no slip and no overshoot or backwards movement. It's looking clear for tonight so I will see how it works in practise later.

[mindburner]

hi DrRobin. Sorry I have not commented before now. Great write up on the Alt system there. I will take mine apart at the next opportunity and check it out.

I had a go at solving the very slow AZ rotation on my 300. The bearing consists of 2 metal plates with a plastic 'wagon wheel' type spacer with integrated mini rollers. Mine was covered in the skywatcher black grease and very sluggish. I cleaned the wheel up, polished it with car wax and used some quality bike litium grease on it and the plates.

The whole base rotates a LOT better now. The base also has a collar with 2 grub screws below the base which tightens the big toothed gear against the floor plate. I need to adjust this so I could still rotate the base by had but it didn't slip when motor driven. The top adjuster nut can also be tightened to get the desired tension of course. I attach some pics for interest.

pics

this is the grease I used

[DrRobin]

Hi Mindburner,

Nice strip down and some good pictures to go with the description. Thanks for posting your experience, I can see that your AZ problem is similar to my Alt problem, I think between us we are getting close to the solution, I.E. Strip the bearings down and replace the grease with some decent quality stuff, taking care to set the friction nut correctly.

My scope tracks really well in Alt now and AZ was always okay, but I have still to test it with a long exposure camera, so I think I will follow your procedure and photos and strip and rebuild the AZ as well.

Unfortunately, I have been so busy at work and with Xmas and birthdays coming up I just haven't had any time to do any more on my mount, but might get chance next weekend.

Let me know how your mont works in anger?

[mindburner]

hi

my approach was not very scientific as I was unsure of exactly how to adjust the collar thingy as to how much tension it should have. Too tight and the base would not turn very well by hand and too loose and the drive may slip. I will need to experiment with it to get a better understanding of the relationship between it and the tension nut/bearing on the other side of the shaft.

I also was unsure if I needed to re-align the encoder as it may have moved on removal. Maybe this won't matter as the software makes a fresh reading of it's position on powerup?

totally understand the pressures of the non astro stuff. I have lots of baby minding to do but it's great having the cabin I can escape to:)

cheers

Alan

[DrRobin]

Hi Alan,

You did an excellent job in stripping the AZ bearing down and documented what you did, that in my mind is very scientific.

After all science experiements are about having a look and recording what you see, of course a good old fiddle about helps to.

I think the friction nut is very much trial and error, try increasing the tension until the mount moves smoothly, but accurately and then leave it at that. The only problem with this approach is that it can take several sessions to get it right.

I am sure you are right about the encoder as well, it probably does get reset every time you power up. If you have any problems there is an option in the Synscan to realign the encoders, but I have never used it.

[mindburner]

thanks. I just need a good night to test it. Hopefully closer to Xmas, there will be some clear nights.

another link to pictures as I noticed the original link didn't work on my mac in work:

[SeedyF]

Alan/Robin,

I have been following this thread with great interest because I took delivery of a new 10" model in October. I posted on page 1 that the first try with the goto was a bit disappointing but I knew I needed some time to make sure I was not the problem (I'm never too hasty to rule that one out ). So using what great advice Robin has provided on testing and the odd luxury of time and clear weather together I've come to the conclusion it's not operator error! I'm confident with all the set up steps and I have built a platform with adjustable feet that ensures I have the scope absolutely level. So I think I am doing all I can.

Robin - I tried your daylight test of the motors by focussing on a distant tree. It had a really handy large knot where a branch had been removed which was an excellent focal point. I noted the position read out on the handset, slewed away by about 10 degrees and tried to return to the original position. In Alt I had no problem, it was out by tiny amounts that could easily be attributed to none too accurate final adjustments on my part. But in AZ the scope consistently overshot the original target. I was able to repeat the test several times and achieve the same results, when I centred the target the read out on the handset was just under 3 degrees below what it should be.

Next test - it was nice at the weekend so I just tried tracking. Sidereal rate on Jupiter with a 12mm eyepiece kept the planet in view for about 3 minutes starting with it centred. It drifted to the left and up in the eyepiece. When you consider the increase in magnification necessary to get a webcam image I would be lucky to get 10 seconds in view! So this is very disappointing.

And then last night I tried to star align - for the first time since my first weekend with the scope. I went through the standard routine at start up (and I am very confident I am putting all the right data in). I selected Brightest Star first and headed to Capella, slewing the scope with the handset. Finished the allignment with up and right key adjustments. Then selected Markab in Pegasus for the second star. At the time Markab was almost due West in the sky. The scope went sailing past it - roughly at the right sort of altitude - but ended up pointing North West when checked with a compas. So basically the scope slewed about 15 degrees too far. I tried again with approximately the same results.

I then started again and went for 2 star alignment and chose Aldebaran and Markab. The outcome was pretty much the same. The scope slewed a long way past the target 2nd star.

Just for good measure I selected park and the scope did it's thing and finished up pointed North East. It's clearly confused!

At this point it was getting too late on a week night to continue so I didn't do anything much to try to fine tune the tension. I ignored Alt adjustments completely and adjusted the AZ clutch screw a couple of times. When I tightened it the motor laboured so I guessed I went too tight. I loosened it again until the scope slewed smoothly and the motor didn't protest anymore. But I really had no idea how to judge the correct tension.

So far two things are bugging me;

1) How can I judge what tension to have in the clutch screw?

2) Do these symptoms suggest I need to re-align the encoders? I know I can just restore the factory settings if this does no good or makes things worse.

After messing about with testing I did some manual starhopping and have to say I was really pleased with views of the double stars and DSOs I selected. So I am really hoping I can get the goto/tracking issues sorted so I can start to really enjoy the scope

I'm reluctant to go anywhere near the strip downs you guys have been doing, I would expect a new scope to work without the need to do any of that, especially at over £900!!

All advice or speculation gratefully received

[DrRobin]

Hi Chris,

That is interesting that your mount overshoots, mine undershoots, which I think is due to slip. If it overshoots and remember the main encoder is on the end of the motor it actually sounds like the main encoder is not registering the movement correctly.

This might be just dust or muck or something else blocking the vanes or possibly a fault with the main encoder, it might be worth contacting the supplier if you don't want to strip it yourself?

I understand your reluctance to not mess about with a new scope/mount, mine is only about 8 months old and I was reluctant at first but decided to have a look anyway, the hassle of sending it back is more than I can bear, unless it's got a real problem, which I am not sure mine does/did have.

The last time I had a go at Jupiter with a camera and 5x Barlow, it tracked for around 3 minutes at a time before small manual adjustments were required. I reckon I am getting somewhere close. For about 30 mins Jupiter didn't move in the finderscope, still behind the cross hairs, it never did that before I started fiddling.

Let us know how you get on with the AZ movement?

[SeedyF]

Thanks to the weather it's been a while since I could do anything with the scope. Apart from the treacherous ice on my patio (even at only 7pm!) I've been out fiddling.

So I went through the standard set up and 2 star align. Then I selected M45 from the catalogue, it missed it by approx 20 degrees but that was just a guess. I slewed back to where the scope had been before selecting M45 and selected M45 again this time it missed by a further 10 degrees and when I repeated this sure enough it missed by a further 10 degrees. By this time I came to the conclusion that you were right Robin, the encoder isn't registering all the movement.

Cue my moment of common sense!! I set the scope up again from scratch and from the North position slewed it so that it pointed due south instead. Now my scope goes on a platform which is aligned to North and so I can easily see how far the scope has slewed without needing a compass. So although my test was only measured by eye it was accurate enough. When I I compared the position readout on the handset it said 136 degrees yet I had clearly slewed the scope through 180 degrees.

The altitude movement is great but something is clearly very wrong with the AZ movement. So back to the supplier I think for me.

[DrRobin]

Hi Chris,

Yes, it still looks like your encoder is under reading, leading to an overshoot if you use the GOTO. If is probably just muck in the encoder, a sticking encoder disk or possibly a badly aligned or faulty opto coupler on the encoder. At the end of the day if your scope is still under warranty, contacting the supplier is probably the best course of action.

When I started this thread I wanted to find out why my dob didn't track very well, both for visual observing but also for planets and DSO astrophotography. I think I now have my mount tracking well, I still need to strip and document the AZ bearing/drive, but I can get much better tracking on Jupiter than I ever had before.

Trouble is I have decided that even if I get it perfect I still have field rotation and would like to get in to Guiding to enable long exposures so have bitten the bullet and bought a HEQ5 and will then need a new scope (probably an 8") in Jan, to go on it. I intend to keep my Dob up until the point it no longer gets used and then will put it up for sale. I want to make sure my Dob is well sorted before selling it so would welcome any messages from other users of their experience and the solutions to fix the problems.

I would welcome any feedback from you if you get your problem with the encoder fixed and I still intend to do the strip down on the AZ bearing and post any results/recommendations, but I will not get anything done now until the other side of Xmas.

Looking forwards to an update when you get it fixed.

[SeedyF]

Robin,

This may only confuse the issue more but I decided to test the movement indoors. I set up as normal but obviously without star alignment. with the telescope pointing North. I then slewed it through 180 degrees, but this time the readout on the handset showed very close to 180 degrees, I slewed back to the starting position and the handset read very close to zero. I was able to repeat this several times. Strange that it was fine indoors.

I then left the telescope outside for an hour and repeated the test. This time after slewing the scope through 180 degrees the handset displayed the position as 161 degrees.

Now I might be jumping to conclusions but maybe the temperature is having an effect. Indoors at about +20C degrees the motor performed as it should. Outside where it was probably about +8C Tuesday night the fault emerged. It's interesting that on Sunday when the handset registered just 136 degrees when I moved the scope through 180 degrees it was approximately -2C. There may be a correlation between the temperature and the worsening performance.

I'm confident that power supply isn't an issue. I use a SkyWatcher 12V 17AH Power Tank and always keep it charged up, and I've been checking the power using the option in the Utility menu on the handset.

I've been in dialogue with Opticstar all week as they supplied the scope, I must say that they have been excellent. They concluded that something is wrong with the motor and arranged for the base to be collected by Fedex yesterday to be taken back to Optical Vision (main supplier) for a check up.

I'll keep you posted.

Now I have no scope, and two weeks off work starting today. Bummer

[DrRobin]

Hi,

Very interest that, so it is temperature related. Batteries perform worse at low temperature, but I don't think that is your problem either.

I am glad Opticstar and OVL are been helpful, but I doubt your problem is the motor and I still think it is the encoder on the end of the motor.

I suspect it is sticking, probably on the optical sensor and due to contraction/expansion it gets better or worse with temperature.

Temperature does also effect electronics if you have a faulty device. I have seen circuits work fine in the workshop only to fail constantly when the temperature is lowered or raised by 10 degrees, but I am sure OVL will get to the bottom of it or just replace the whole base motor assembly which is what you really want.

Real shame it's gone back over Xmas, especially as it will sit in their workshop whilst everyone is having their turkey and if we get any clear nights you could be out, but at least it will be fixed.

No observing for me either, I am away in sunnier parts of the world on holiday and didn't pack my ST80.

[mindburner]

hi DrRobin

I must say I have been a bit of a traitor and bought an EQ6 & meade 127 APO. Tracking is light years ahead of the dob. It's being a bit unfair to compair but I just got tired of trying to keep objects in view. The EQ keeps the objects on screen for ages, it's like the sky stopped moving. It's 2nd hand and has a few issues of it's own though.

I still will use the dob as the visual views are great but for video and imaging the eq will be better I think.

[DrRobin]

Hi,

You probably saw my post, I have bought an HEQ5 and am seriously considering a 200mm carbon fibre tube to go on it. Like you I intend to keep the dob, but once it doesn't get used I think it will be up for sale, so I don't think you are a traitor, just like me making a rational decision to maximise your viewing for what you want to do.

I reckon I will get about 10 - 12 good nights a year for DSOs, I don't want to waste half of them fiddling with the dob to make it track smoothly and work with a guide camera.

I always wanted to get more into DSO imaging and have decided that even if I get the dob right, and it is very close now, it will always be second best to an EQ mount.

I still like the idea of the Dobs and there is no reason why they won't make good scopes, certainly they are easier to assemble and disassemble if you don't have an observatory, but I want to get in to longer exposures and that means guiding and field rotation, both of which the dob just isn't going to be easy/possible with.

good luck with the EQ6, let me know if you have any problems as I am probably going to encounter them on the HEQ5.

[mindburner]

nice one! I don't feel so bad now:) Yes it seems to be a natural progression from dob ownership to EQ mount. I love the scope but really never quite got to like the mount.

I tried EQ mod for setting up and polar alignment and would highly recommend it. Having never used an EQ before, I managed to lock on to several objects (m42,m31, blue snowball) That was with a very dodgy, badly threaded polar scope. Get an EQ, you will never look back.

It was nice to go into the kitchen to grab a coffee, come out and andromeda was still in the frame! amazing, no pushing and pulling

it all went a bit Pete Tong later but it may have been my video camera being mounted in the diagonal and nearly falling out when slewing.

The chap I bought the Meade 127 APO off has a 300mm orion reflector for sale £750, it is a very nice piece of kit, big as well. I was tempted but just spent £1500 this close to Xmas, so gave it a miss. A carbon 200 would be very nice. I think Orion do a custom model. I would also recommend a big refractor. The meade is superb.

[DrRobin]

Hi,

Thanks for the advice, I have a USB to TTL converter at work, all this takes to make it in to an EQMOD is a cable so will give that go. I am an electronics engineer so it will be straight forward.

I have also found someone in the US who published designs and sells completed units which convert USB to ST4 for guiding. I like the look of this as you can use the Synscan to set up and point the scope and then use the guidescope to take over.

After my wife didn't want me to buy a new scope she has just given me most of the money for Xmas for a 200 CF so I will take that it as she approves or at least doesn't mind too much.

I might consider a good refractor but the dob will have to go first and I am not sure I am ready to part with it just yet. I think I would like to keep it for Saturn next Spring, it will still be less than a year old so a good purchase for someone.

If I was just in to visual or the planets these dobs are hard to beat but like you I want to have a go at more DSOs and I don't want to be pushing the boundaries too much so an EQ is the sensible choice.

Hope you get some clear skies, the stars are really bright here on holiday but I didn't pack a scope, bummer eh.

[mindburner]

hi

yes give EQmod a go. I built my own EQdir box using a max232. I was quite happy when it worked first time. I have the EQdir connected to an Ebay special USB>serial lead into a hub then everything back to a laptop through a 10m USB active lead. I powered the USB hub off 12v too (using a DC-DC convertor) as to eliminate the wall wart PSU. My aim is to get a neat and remote telescope solution.

I think I will also keep the dob, mostly for planets as the new Wo binoviewers I got for Xmas have problems getting focus in the APO with the 2" diag fitted. The skywatcher should be amazing with the binos, although I needed to get a few bits n pieces to achieve focus with the dob. I still think the 12" dob has the edge over the refractor with Jupiter but another session is needed to test this. Enjoy the holiday:)

[DrRobin]

Hi,

Sounds like you are handy with the soldering iron as well. My USB to serial was bought for work as RS232 but when it arrived it was TTL so need for the MAX232. It's not going to get used at work and it isn't worth sending it back.

I looked up the alignment procedure in EQMOD, looks to have some advantages over a Synscan, but I like the idea of freeing up the computer and the readout the handset gives so might try both and choose the best method.

If you are interested the USB to ST4 link is shown below. I can't decide whether to make one or just buy it complete. I am currently building a USB focuser now just need to box it up, but it's been on the to for 2 months due to lack of time.

Autoguider adapter: USB to ST4 output guider

If you are interested the focuser I am building is shown below. Dave can supply the PIC preprogrammed if you don't have the kit, he sells them for cost, about £7. I note that astrogene is also making one.

SharpSky

I am guessing this is an essential piece of kit for your automated set up?

By the way I noticed one of your other posts about your new refractor, very nice scope, no way could I hide one of those.

[mindburner]

hi many thanks for the info on the focuser. I actually bough a unit from Dion over at Astronomy shed. It was for the skywatcher but I have modded it for use with the Meade 127. It is going a bit strange though with the USB hub I am using, hopefully will be able to sort that out.

Autoguiding id my next challenge. I think I will get the QHY5 and ST80 combo that most use and run PHD. I want this part to be as simple as possible. EQmod should be able to hande the QHY5 without using the ST4 port, although I must get a look at that project.

There is so much more to tinker about with on an EQ. Much more of a technicans mount. My latest mod is a polar scope illuminator. Which turned out to be ahrder than I though to implement. I would definately recommend the EQ5/6. The celestrons are better I think but no EQmod support. I must say I love EQmod. It just gets better the more one uses it.

The seller of the scope also threw in some adapters. One connects into the parallel port of the computer (if it has one lol) and gives a ST4 out.

I am handy enough with the soldering iron, just not a very good circuit designer. I tend to just expand on the vero board then bodge things on with jumpers etc.

Here's a early version of the EQmod. Notice the caps bluetacked on (now changed)

I just couldn't resist the 127 APO. Got it for just over £900, that in combination with an interest free credit card was just too much temptation to resist, although skint for a while, it's a good buy.