To buy or not to buy a 10Micron GM2000

[DaveS]

There is a bit of "stiction" in the bearings, so it's not totally frictionless, but the mount is *very* sensitive to balance. Fortunately though, the balance tool built in to Autoslew can tell you how far out you are, right down to grams.

Although my rig is dismantled ATM, when I put it back together I will balance around the RA, Dec, and OTA axes. The better you have it balanced. the better the mount will track.

[Barry-Wilson]

Just to add some experience and also understanding to the thread.

Imaging unguided does require a disciplined approach to every aspect of the acquisition.  Unguided is achievable of course however please understand that a methodical approach is vital.

Your entire optical train must be rigid, mirror flop, saggy focusers, drooping refractors with heavy objectives will make for a frustrating time.  It is important to note that scopes can and do sag over a 20 minute sub.  Cable management has to be exacting - in my experience the only method that causes nearly nil effect is to tie your cables over the top the mount to dovetail across the top of your scope, then looping down to a tied point on the counterweight shaft and from there looping to another tied point on the pier/tripod.  Other approaches do work but in my experience mean the occasional sub is sacrificed because of drag or tugging effects on the ccd-end of the scope.  Scope rings with too thick a felt lining can cause minute movement.

You do need an additional item of equipment for 10 Micron's - a method of measuring pressure, temperature and time.  These environmental/GPS units are readily available.  They are required to feed in the data to the mount's computer to enable the unguided algorithm to be calculated and to adjust its tracking.

At my home observatory, I image unguided at a variety of image scales: 3.4"/px to 1.24"/px.  Focal length is a part of this, but it isn't the real determinant - that actually is image scale.  I have imaged unguided at home below 1"/px without issue at a FL very similar to the TEC140/QSI690 but the scale was circa 20% larger.  Per used a QSI583 or 683 so would have been imaging >1"/px or thereabouts.

At e-Eye, with Steve's TEC140/QSI690 and my GM2000HPS, we have imaged unguided shortly after installation with 600s subs without difficulty.  We however chose to guide because when imaging remotely you need options, reliability and robustness in all of your equipment and techniques:- (i) the image scale of the rig is 0.75"/px which, whilst within limitations, is approaching the current limits for unguided imaging even with its modest FL of 1015mm with flattener (increases FL slightly); As an idea of 0.75"/px, see Steve's processing of our M101 data here ; (ii) the position of the cabinet containing PC and other hardware has to be positioned outside of the floor aperture through which the pier is sited.  This means that to run cabling over the mount you will not have sufficient length with a 5m USB cable and will require hubs or USB extensions via active USB leads.  Both will be the cause of unnecessary maintenance issues.  We manage cables by tying off on the losmandy and then looping to the pier.  It works well but does not eliminate drag in the same way as routing over the top of the rig; (iii) the summer heat causes significant turbulence in and around the individual observatories early in the evening when cooling; (iv) imaging at low altitudes with atmospheric turbulence is difficult; (v) good to have equipment redundancy and options when you are hundreds of miles away and intervention takes time and has high cost.

For our Tak at e-Eye, we imaged unguided very succesfully for a whole year.  However just before our installation and maintenance visit in October 2018, we started to find some trailling of stars on a hand full of subs (ie one or two or three subs) a night.  Only slight but enough for our high standards to mean we had to discard the subs.  We hypothesised all sort of likely causes.  When we visited we found that the scope had slipped circa 15-20mm in its scope rings (Primeluce Lab rings) with the glue between the felt lining becoming soft (it is possible that it was also knocked).  The rig was parked in the 'normal' home position, counterweights down pointing to the NCP thus gravity had an effect.  No doubt the glue softened in the summer heat.  The scope rings (advertised as suitable for the FSQ106) do not have sufficient thread in the bolts to tighten adequately.  We did not have a spare set of rings so reset the felt linings and wrapped some good old duct tape around the OTA to give it some extra width so the tube rings could tighten down that fraction more.  We also set both scopes to park with the scope horizontal.  This extra duct tape means that we have minute movement of the scope within its rings and whilst we are able to image unguided at its 2.1"/px we nevertheless chose to guide for the factors listed above.  If we decide to replace the FSQ's scope rings I will feel much more confident about every unguided sub being first class.

Imaging unguided is very satisfying if you have that particular mindset and is readily achievable if you approach it with an exacting discipline.  The ultimate aim though is to have good quality data to create an astro image whatever acquisition techniques you employ.

If you have the appetite for unguided imaging I would heartily recommend 10 Micron mounts.  In the main, the mounts at e-Eye are 10 Micron and ASA - there are other brands there too but the former two dominate (but I do not have exact numbers).

There are plenty of other quality mounts - Mesu, A-P, ASA, Gemini (the GF53 looks interesting for example), Paramount, WS etc etc.

HTH and more than happy to answer any specific technical questions.

Just to add, seeing Dave's comment on balancing - the 10 Micron has a software balancing routine, you first gauge by hand and then use its own mount software to balance.  It is very simple and highly accurate.

[DaveS]

I'll add that the way Autoslew balances is to measure the current needed to move the axis either way. On screen you see two yellow bars and a red line. the scale can run from 7.5A FSD down to 2.2 A. So you'd start at 7.5, do a rough balance, then gradually refine it until the mount is balanced down to grams around that axis. Normally I'd do the Dec axis with the 'scope level and West side, then the RA axis similarly. Finally I'll put the 'scope pointing to the zenith and do the Dec again to check that the 'scope is balanced around the optic axis. Yes it's a bit of a faff, but you can see how you're going, and you only have to do it once for any configuration.

Usually, for the Dec axis I'll do the balance roughly before focusing, then again after I've got the focus position nailed down (Allowing for slight focus shift).

@SlimPaling and @Waldemar have DDM mounts, so may be able to add something. @Waldemar has a DDM 85.

[DaveS]

Adding more, Sequence has routines for determining hysteresis in the system, also when doing the MLPT to refine pointing during the imaging run the 'scope will slew to the end of the run and then back before taking the images and plate solving. You can take as many plates for solving as you like, and also do more than one iteration if you require. Sounds a faff but takes less time than PHD takes to calibrate.

[gorann]

I assume you know that iOptron also have a big mount with absolute encoders. Half the price of the 10 Micron GM2000 but it is rather new and unproven (last time I checked a few months ago before I ordered my Mesu).

https://www.firstlightoptics.com/ioptron-mounts/ioptron-cem120-ec2-center-balanced-equatorial-goto-mount-with-ra-and-dec-encoders.html

[Datalord]

2 hours ago, Barry-Wilson said:

Lots of great info.

Thanks Barry, very good points. 

I will say that no matter what I end up with, I'm going to keep the OAG and the guide camera opertional, so I have the option of using it if I need it.

1 hour ago, gorann said:

I assume you know that iOptron also have a big mount with absolute encoders. Half the price of the 10 Micron GM2000 but it is rather new and unproven (last time I checked a few months ago before I ordered my Mesu).

https://www.firstlightoptics.com/ioptron-mounts/ioptron-cem120-ec2-center-balanced-equatorial-goto-mount-with-ra-and-dec-encoders.html

I did not. That looks almost too good to be true. I saw you were asking about this mount in January 2018, I don't suppose you actually bought it? What stopped you?

[Waldemar]

Like DaveS said:  balancing is important for the DDM mounts, but the balancing routine for DEC and RA is easily done with the software tool in AutoSlew.
Balancing needs to be done in three axes: RA, DEC and Radial, in order to get balance in all positions.
Off topic: radial imbalance causes more problems then recognised in a lot of mounts.

If power fails, the mount just stops and stays where it is at that moment (if balance is ok) There is always a slightly residual magnetism, inherent to the Direct Drive construction, that prevents the mount to go on a walk.

On the forum: http://forum.astrosysteme.com/index.php you can find many interesting subjects, pictures and information, as well as a link to the ASA site where you can download manuals and information that answers the questions you may have.

AutoSlew is the mount's software and Sequence the aquisition programm. SGP works too, but misses some dedicated features. In the past (10-12 years ago) bugs in the software caused some problems, but also the different approach of ASA's software compared to others caused some confusion, but in fact it is just a different approach like with Ikea 'mount it yourself' furniture: Don't think you know what to do, for you don't... Read the manual!!

I fully agree with DaveS : I will never willingly go back to a mount that is not direct drive (for my main set-up)

Don't think the encoders of iOptron are the same as ASA's or 10Micron's, for they are not:  ASA uses Renishaw absolute encoders on both axes and 10 Micron have their proprietary encoders. How ever much I like iOptron, they are not in the same league.

Of course more mounts with absolute encoders are available also. Atmospheric conditions are beyond any encoder, though...

 

[gorann]

2 hours ago, Datalord said:

4 hours ago, gorann said:

I assume you know that iOptron also have a big mount with absolute encoders. Half the price of the 10 Micron GM2000 but it is rather new and unproven (last time I checked a few months ago before I ordered my Mesu).

https://www.firstlightoptics.com/ioptron-mounts/ioptron-cem120-ec2-center-balanced-equatorial-goto-mount-with-ra-and-dec-encoders.html

I did not. That looks almost too good to be true. I saw you were asking about this mount in January 2018, I don't suppose you actually bought it? What stopped you?

I decided to play it safe and went for a Mesu, which all users seem to love, and I do not mind guiding. Not that I heard anything negative about the iOptron, just that very few people had given it a try. That could have changed by now so it may be worth a bit of web surfing, maybe here or on Cloudy Nights....

[RolandKol]

I am reading about iOptron ec2 more and more...
It simply looks more up to date mount...

Lots of power and USB sockets (ver2 ver3), cabling in the head with space for personal cables and etc, - Encoders, maybe, not the Best ones, but they do the job... just...

What is the lifespan of it?  

With Mesu, everyone has a rock-solid assurance of long service terms, but the "steampunk style tech" in the XXI century... it simply does not shine so bright to me anymore....

It is like buying old Mercedes, - runs well, but no climate control, no Autopilot and etc...

[DaveS]

I'm probably biased, but after using a DDM mount any mount involving worms or wheels and reduction systems is not just C20, but downright C19.

[Carbon Brush]

I have read the posts an make no pretence to understand the performance and limitations of the various mounts under discussion.

Taking this aside, if I am understanding the descriptions of the encoders correctly, their difference to mount performance may not be well understood.

Encoders come in tow basic 'flavours' incremental and absolute.
The term incremental being replaced by 'relative' in some astro circles.

An incremental encoder contains a disc (glass or plastic) with a large number of lines photographically printed.
On top of this disc are two small groups of matching lines. The two groups are offset by a 1/4 line width.
A light shines through these to small photodiodes. As the disc turns, each group produces bright/dark signals.
This is where the 1/4 line offset comes in. The two light/dark waveforms are 90deg out of phase, which allows (by simple electronics) direction to be determined.
The resolution of these encoders tends to be restricted by the disc diameter. But can be several thousand counts/revolution.

An absolute encoder can be based around the same sort of idea of a disc and photodiodes.
However, the disc has a pattern that reflects binary (or other code) counting. Not a simple set of radial lines.
This means that the number of photodiodes needed to extract information goes up with resolution.
A 1024 step encoder requires 10 photodiodes, 10 amplifiers, etc.
The compromise between number of tracks (photodiodes) and accuracy is often an issue.

An incremental encoder is much lower cost to manufacture, and will be more reliable in the long term.
They are accurate and give consistent results. I have used them in large machine controls to measure position to 0.01mm.

The absolute encoder has the benefit of knowing where it is after a power loss.

An increment encoder has to rely on a datum mechanism after power up.
Usually this is another photodiode that gives one narrow pulse per revolution, that is coincident with a crudely set microswitch, or proximity switch.

In conclusion, mount performance is not determined by the choice of absolute or incremental encoders as such.
It is the way the encoder information is handled - assuming all else (mechanical, etc) is equal.

Hope this is useful. David.

 

 

[DaveS]

ASA quote 0.02" per "tick" for both the incremental encoders on the DDM60 and the absolute encoders on the 85

So.... (3600 X 360) / 0.02 = 64.8 million counts per rev.

[Datalord]

5 minutes ago, DaveS said:

ASA quote 0.02" per "tick" for both the incremental encoders on the DDM60 and the absolute encoders on the 85

So.... (3600 X 360) / 0.02 = 64.8 million counts per rev.

Which coincidentally matches Renishaw specs. ?

I've been in contact with Rupert and apparently ASA won't produce the "low end" ddm85 anymore. Except for the two they have in stock. So I'm probably going to make a fast decision soon,as the ASA has grown on me. 

[Waldemar]

58 minutes ago, Datalord said:

Which coincidentally matches Renishaw specs. ?

I've been in contact with Rupert and apparently ASA won't produce the "low end" ddm85 anymore. Except for the two they have in stock. So I'm probably going to make a fast decision soon,as the ASA has grown on me. 

That is not coincidentally... ASA uses Renishaw encoders. What do you mean by 'low end DDM85'? Is that the basic model with the tilt mechanism for PA?

Or do you think they will stop producing the DDM85 totally? I really doubt that...
I will ask ASA how to interpret this.

 

[Datalord]

27 minutes ago, Waldemar said:

Or do you think they will stop producing the DDM85 totally? I really doubt that...

Apparently they won't produce mounts below 100kg capacity. Only the highest end ddm85 has that capacity. 

 

28 minutes ago, Waldemar said:

That is not coincidentally... ASA uses Renishaw encoders.

Yes, that was cheeky comment. 

[DaveS]

2 hours ago, Datalord said:

Which coincidentally matches Renishaw specs. ?

I've been in contact with Rupert and apparently ASA won't produce the "low end" ddm85 anymore. Except for the two they have in stock. So I'm probably going to make a fast decision soon,as the ASA has grown on me. 

Oh Bother (Or naughty words to that effect) going to have to 'phone Rupert before I really wanted to.

[Jkulin]

23 hours ago, Datalord said:

Thanks Barry, very good points. 

I will say that no matter what I end up with, I'm going to keep the OAG and the guide camera opertional, so I have the option of using it if I need it.

I did not. That looks almost too good to be true. I saw you were asking about this mount in January 2018, I don't suppose you actually bought it? What stopped you?

I had first light last night with my 120EC and after the firmware upgrade which was vital and amongst blustery winds and terrible seeing I managed on average at 2000mm FL around 0.3-0.4, but when the wind dropped and it went clear it was down to around 0.2, mine is the single encoder as I couldn't justify the extra for the 2 encoders.

The 120 is still a new fish in the sea, but what convinced me was based on how good the CEM60EC was and I knew that if the could get it to surpass that then it would be a winner.

For less than half the price of the 10 Micron I don't doubt that the 10 Micron is a superb piece of kit and if I was operating in beautiful skies and had the processing skills of the likes of Barry then I wouldn't hesitate.

[Waldemar]

The answer from ASA on my question if they will change the production of the DDM85: 

Dear Waldemar,  

We change DDM85 in DDM100, that’s all.

Best regards / Beste Grüße 

Dietmar Weinzinger 

Here is the new line of ASA mounts: https://www.astrosysteme.com/products/mounts to me that seems to be a bit more then just a name change...
Very impressive, I would say! So you were right Datalord...

[DaveS]

I had a long chat with Rupert just after my last post, and he said much the same thing, I think he was a bit miffed with ASA for moving things upmarket.

So it looks like I'm going to have to find £12k for a new mount before I wanted to.

Can't bring myself to get involved with worms, wheels, gears or belts after using a DDM.

[RolandKol]

48 minutes ago, DaveS said:

I had a long chat with Rupert just after my last post, and he said much the same thing, I think he was a bit miffed with ASA for moving things upmarket.

So it looks like I'm going to have to find £12k for a new mount before I wanted to.

Can't bring myself to get involved with worms, wheels, gears or belts after using a DDM.

Unfortunately, l cannot afford a wormless mount!

[Datalord]

1 hour ago, DaveS said:

So it looks like I'm going to have to find £12k for a new mount before I wanted to.

Well, I have just asked Rupert for securing me one of the last ones.

[DaveS]

OK, will have to bell him again first thing tomorrow morning, Hope I'm not too late.

[Datalord]

1 hour ago, DaveS said:

OK, will have to bell him again first thing tomorrow morning, Hope I'm not too late.

Sorry Dave, I just wired my deposit. I hope you will get the second mount.

[DaveS]

So do I.

Picked up Rupert's email a bit late, but have replied, now hoping for an invoice.

Don't mind getting the demonstrator if it's still available.

May end up with a Mesu, my second choice.

[Datalord]

13 minutes ago, DaveS said:

Don't mind getting the demonstrator if it's still available.

That's still available. I just preferred the new, since I want to set it all up myself anyway. Good luck!