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sophiecentaur

Synscan and the 'Home" setting

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8 hours ago, sophiecentaur said:

I don't find it hard work to polar align or to set the mount up with clutches released and using a level in the normal way to do the initial setting up. This is really not the issue. Whatever the accuracy of any alignment process, if I turn off the power then the mount cannot be sure what I have been doing with the clutches (they could even be left disengaged). Does it not have to assume it is starting from Home and that the display when I Show Position should show NCP co ordinates? It is a very simple question which I'm sure can be answered in isolation from all the other alignment questions. If, at the Home Position, the show position gives a value that's nothing remotely like the NCP, how can the mount have a chance of pointing any where near the first star in the star alignment process? Any other system for measuring anything at all, starts with the origin being set to a 'zero' position. This is true for a stop watch, a barometer or an oscilloscope so why doesn't this seem to apply on my mount?

Also, why does no one else seem to have experienced (or considered) this sort of issue?

 

Some of the posts above seem to imply that, even with the clutched disengaged, there are additional encoders that measure the position. That is even more confusing.

The handset assumes that the mount starts in the normal home position and then slews to the first star based upon that, the time, date and location. Once the alignment of the first star has been accepted (pressing enter on he handset) the handset can then start mapping the stars onto the built in database. Without the star alignment the handset only has an approximation of where it is pointing the telescope, so the "show position" option is meaningless.

The new AZ EQ6/5, Star Discovery and EQ8 mounts have dual encoders so you can go to an object in the sky then declutch the mount and manually slew it to another object without losing star alignment. The older mounts don't have dual encoders so you can't declutch the mount once the first star has been aligned. You can, however, select the first star, allow the mount to slew to where it believes this star is and then declutch and manually slew the mount onto the star, re-engage the clutches and accept the alignment. The clutches now have to remain locked to keep alignment.

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13 hours ago, sophiecentaur said:

Does it not have to assume it is starting from Home and that the display when I Show Position should show NCP co ordinates?

Yes, I am sure the alignment routine assumes you are polar aligned and in the home position. It then just needs to know the difference between the RA of the alignment star and the current sidereal time, which it can calculate from the clock time etc. But should Show Position work at this stage? - I would have thought that would depend on whoever wrote the software. My suspicion would be that as there is no sky model yet Show Position would not work - I have never found synscan very sophisticated. I have never checked though, nor, to be honest, felt the need to.

NIgelM

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I think I may have found the source of the problem. Going through the exercise this afternoon (Sun helps the brain a lot) I found that things go ok with the mount not loaded. I have a feeling that the problem is not software but hardware based and that it could be the clutches slipping with my very heavy 10" Newtonian. That could easily be introducing random offsets. I will have to investigate and perhaps clean up the clutch mechanisms.

Is there any expertise in that direction around? 

Thanks for the contributions to this thread, everyone. It managed to convince me to look elsewhere for a solution.

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Just now, sophiecentaur said:

I think I may have found the source of the problem. Going through the exercise this afternoon (Sun helps the brain a lot) I found that things go ok with the mount not loaded. I have a feeling that the problem is not software but hardware based and that it could be the clutches slipping with my very heavy 10" Newtonian. That could easily be introducing random offsets. I will have to investigate and perhaps clean up the clutch mechanisms.

Is there any expertise in that direction around? 

Thanks for the contributions to this thread, everyone. It managed to convince me to look elsewhere for a solution.

 

Whilst it could be the clutches, unless the knob isn’t tightening before the handle hits the casing, is say it’s unlikely.  There isn’t much to clean, it’s just a small brass button that is tightened against a brass barrel/cog.

 

Is your 10” particularly heavy?

 

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15 hours ago, tooth_dr said:

 

Whilst it could be the clutches, unless the knob isn’t tightening before the handle hits the casing, is say it’s unlikely.  There isn’t much to clean, it’s just a small brass button that is tightened against a brass barrel/cog.

 

Is your 10” particularly heavy

 

Thanks very much for those pictures. I now know what's inside that barrel without dismantling it all. If I remove the brass button I should be able to see the state of the brass barrel.  One reason I suspect that it could be slippage here is that it was used for a long time by a previous owner with the 10" Newtonian plus a lot of other stuff on it and I already found that the Wedge Alt mechanism was really mangled. I have solved that problem with a mod which behaves very smoothly at 52 degrees of Latitude (That peg and bolt system really is the pits and the design must have been made and approved by someone resident much nearer the Equator). I could imagine that I will find some load related carnage when I take a look at the clutch. The design of that clutch is not impressive, though. Such a small area of contact for what has to be a pretty low mechanical advantage mechanism. I guess you could argue it limits the possible load on the worm but there are many better ways to achieve that. 

I have to admit that the s/s tripod is amazing. It sits on three slate pads and maintains polar alignment over weeks without attention - no need for a pier at my level of operation.

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Posted (edited)
21 minutes ago, sophiecentaur said:

 

Thanks very much for those pictures. I now know what's inside that barrel without dismantling it all. If I remove the brass button I should be able to see the state of the brass barrel.  One reason I suspect that it could be slippage here is that it was used for a long time by a previous owner with the 10" Newtonian plus a lot of other stuff on it and I already found that the Wedge Alt mechanism was really mangled. I have solved that problem with a mod which behaves very smoothly at 52 degrees of Latitude (That peg and bolt system really is the pits and the design must have been made and approved by someone resident much nearer the Equator). I could imagine that I will find some load related carnage when I take a look at the clutch. The design of that clutch is not impressive, though. Such a small area of contact for what has to be a pretty low mechanical advantage mechanism. I guess you could argue it limits the possible load on the worm but there are many better ways to achieve that. 

I have to admit that the s/s tripod is amazing. It sits on three slate pads and maintains polar alignment over weeks without attention - no need for a pier at my level of operation.

It might not be possible to remove the brass button outwards, unless it sticks to the end of the lever.  I would not recommend dismantling the mount, unless you are fairly handy.

Do you clutches tighten ok? 

Edited by tooth_dr

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4 hours ago, tooth_dr said:

Do you clutches tighten ok? 

They tighten or not, depending to the position - which could be worrying. But I will have to go out and look again, now that you have given me some input.  

If necessary, I can do the dismantling and re-assembly as I have done 'most things' on cars and electrical equipment. I avoid it these days unless there's no option. I find that some of the mechanical design quality in my astro equipment is really quite disappointing, compared with the Marine equipment that I coped with on my sailing cruiser. It was always expensive stuff, though - but so is a lot of the astro equipment. Not safety of life though!

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Posted (edited)

What do you mean tighten or not depending on position? Send a picture of them tightened because there is something awry here.  Even when my mount is very unbalanced the clutches would still hold it. 

Edited by tooth_dr

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On 19/05/2018 at 15:22, tooth_dr said:

What do you mean tighten or not depending on position?

I mean that, at some angles (of the mount) the clutch doesn't seem to hold the load but in others it does. (I can get a reasonable balance) I think I will have to remove the barrel and look at the bearing surface to see if it is scored in some places. I don't seem to have any problem when I hang my ED80 Equinox plus other kit on it.

Whilst I was generally cleaning the mount up in an attempt to make balancing a smoother operation, I noticed another really poor bit of Skywatcher Engineering. The dovetail clamp has a fundamental flaw in its design. There is nothing inherently keeping the sliding part in place except  the two adjusting bolts pressing  on one side of the scope dovetail. Even the cheapest form of bench vise has some taper to keep the moving jaw from jumping out of line when the screw is turned.  You tighten it up and the dovetail just jams into place. To release the dovetail to adjust its position, the bolts have tightened up and there's an inevitable clunk as the jam is released. There is no excuse for that. On the mount, there should be a dovetail to keep the clamp properly down on the bed. I guess it was designed by the same guy who decided to go for the peg and bendy bolt design for the azimuth adjustment on the wedge. These things are well over £1k and the mechanical design should reflect the price. I presume the (even) more expensive mounts do it properly but doing this properly involves no extra cost - just a bit of thought.

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6 hours ago, sophiecentaur said:

I mean that, at some angles (of the mount) the clutch doesn't seem to hold the load but in others it does. (I can get a reasonable balance) I think I will have to remove the barrel and look at the bearing surface to see if it is scored in some places. I don't seem to have any problem when I hang my ED80 Equinox plus other kit on it.

Whilst I was generally cleaning the mount up in an attempt to make balancing a smoother operation, I noticed another really poor bit of Skywatcher Engineering. The dovetail clamp has a fundamental flaw in its design. There is nothing inherently keeping the sliding part in place except  the two adjusting bolts pressing  on one side of the scope dovetail. Even the cheapest form of bench vise has some taper to keep the moving jaw from jumping out of line when the screw is turned.  You tighten it up and the dovetail just jams into place. To release the dovetail to adjust its position, the bolts have tightened up and there's an inevitable clunk as the jam is released. There is no excuse for that. On the mount, there should be a dovetail to keep the clamp properly down on the bed. I guess it was designed by the same guy who decided to go for the peg and bendy bolt design for the azimuth adjustment on the wedge. These things are well over £1k and the mechanical design should reflect the price. I presume the (even) more expensive mounts do it properly but doing this properly involves no extra cost - just a bit of thought.

Hi Sophie

It does seem that overall you are disappointed with your purchase.  I fortunately have not experienced the issues you are having and am really very satisfied with my skywatcher kit so I will leave this topic for someone else to come along and advise you accordingly. 

 

 

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Just checking - have you balanced the load correctly, both in Dec and RA?

I have never looked at the "show position" on my mount, I didn't even know it was there.  Been doing this for some 8 - 9 years. 

You need to make sure your start/Home position is as accurate as possible, make sure all the input data is correct, and everything balanced and all should work OK.  I don't always find my alignment star in the FOV either, its annoying.  Some days it can be spot on and other days I have to slew around to find the alignment stars.  No idea why it differs, I do the same procedure every time.  Once the alignment has been completed the mount is pretty good at finding the chosen target.

Carole 

 

 

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6 hours ago, carastro said:

Some days it can be spot on and other days I have to slew around to find the alignment stars.

Haha - so much for fixed stars!  I wouldn't insult you about your time entering skills?? The SW has that crazy US format option fixed which I can only have confidence in when the day is 13th or more.

Last night I went out and set everything up carefully (with the 80mm ED) - except that I couldn't actually see polaris so I assumed alighment hadn't;t changed. iPhone levelled and az/el scales zeroed and weights down in the home position. Starting from Parked option. Show position gave declination of 89.9' (best I have ever seen) and some random RA number. It went directly to the first alignment star (right in the middle of my not too well set up Telrad) and the other stars were pretty easy to centre up on. Then the mist came in (Humidity 99%) and I couldn't even see the Moon. But at least I proved to myself that the system can work. I have no idea what has been going wrong. Perhaps there is some intermittent in the encoders. 

I will have to repeat things with the heavier Newtonian. Fun fun fun.

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Some days it can be spot on and other days I have to slew around to find the alignment stars.

Haha - so much for fixed stars!  I wouldn't insult you about your time entering skills?? 

Lol, I have checked and double checked on those occasions when it goes wrong, and even got friends with me (at astro camps) to double check and it is right.  Goodness knows why some days it just goes on the blink.  I had a dreadful time at camp recently where the mount just would not go anywhere I asked it to.  Polar aligned fine, level, all input data correct, correctly balanced, astro chums checked the data too and after two horrible nights of a wayward mount I decided to put it back to factory settings and it seemed to behave itself after that.

Carole 

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49 minutes ago, carastro said:

Goodness knows why some days it just goes on the blink. 

I'm a bit of a newcomer to astronomy (i.e. actually owning telescopes) but I do see some amazing inconsistency in quality. A lot of attention is paid to the optics and I believe that is pretty good value because people are aware of that aspect of the subject. But I keep seeing instances where the mechanical ( and software ?)  aspects aren't as convincing. People seem prepared to make allowances in that direction and blame themselves rather than the equipment. Only this afternoon, I was playing with the mount and Parked it a half a dozen times in the process. Each time, the Show position in the parked position seemed to get nearer and nearer to NCP. It finally told me it was at 90/360. What could have been going on there, I wonder? What could (should) have been changing? 

I think your idea of going back to Factory Settings is probably the right thing to do. I guess that the digital arithmetic may run out of precision and the errors can just add up. The processors in the Synscan are probably a bit limited and that could account for a lot. A raspberry pie would probably be a good replacement but we'd all end up paying through the nose for something as extreme as that.

 

Edited by sophiecentaur

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While I'm not overly impressed with my NEQ6 Pro mechanically, I think that Synscan is very robust. I'm the world's sloppiest setter uper. Rack of the eye polar alignment and rough and ready star alignments but I've rarely had any issues. It's very forgiving for visual observation. It just needs doing methodically. 

I did successfully complete a project to use a RasPi as a WiFi interface to allow me to use SkySafari on my Android tablet to control my mount. Works a treat but still requires the SynScan handset  to set-up and align. 

 

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12 hours ago, Paul M said:

Works a treat but still requires the SynScan handset  to set-up and align. 

Not if you use  the Synscan App Pro to replace the handset it doesn't. All the alignment is done in the APP just like the handset !!!!!! 

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I use Synscan on Az/Alt mounts. Therefore some of the aspects will be different from those on an EQ mount. The Skymax Mak. on tripod does not permit the manual adjustments, but my Skyliner Dob has the dual encoders and can be moved manually, and tracks that movement.

As I understand it, the encoders are "dumb" and their supporting electronics just counts clockwise or anticlockwise movement. It is only the electronics that has an idea of real position, by keeping a running count of movement pulses. At power-up, the electronics resets its counters to zero. When you finish a session with the "Park" "Home" option, the software moves the mount (Az/Alt) to level and North, based on that session's alignment. If you power up, without moving the mount, the zeroed encoder counters are also now containing true Az/Alt mechanical zero positions. If you move the mount, with it unpowered, it will not "see" the movement, and so will have lost alignment when re-powered.

With an Az/Alt mount, it is possible to start with the tripod/base canted over, and the OTA pointing at any Az & Alt angle. Clearly, if you do this, the software has to work harder to compensate for a portion of the Az component affecting Alt, and vice versa. If you start with the mount level (bubble level on the Skymax tripod, and I added one to the Skyliner Dob base), then the two axes are decoupled, making the sums easier for the Synscan alignment software. A level Az/Alt mount would be equivalent to good polar alignment on an EQ mount. I tend to use "Brightest Star" 2-star alignment. The software makes its suggestion, and if accepted by pressing "enter", the display gives the target's Az & Alt co-ordinates, and requires the user to use the movement buttons to slew to the target. Once aligned, and the second star accepted, the mount does an automatic slew to the vicinity of that star. I have found that, if the mount starts level and North(ish), that second slew gets me much closer to the target - so speeding up alignment.

I used Stellarium to produce a table of the brightest stars (mine has 14 stars) visible from my garden at dusk, and an hour before dawn; and, for the middle of each month of the year, the table shows, for 3, 4, or 5 of these stars, the direction (N, NW, W etc.) and altitude; with the stars chosen to give approximately 90 degrees azimuth and at least 20 degrees altitude separation. This gives good alignment, and helps me avoid accepting a star behind a roof, tree or fence; or close to the zenith (a literal "pain in the neck" for centring in an eyepiece).

Geoff

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