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richardejm

new mesu, strange star-cross

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richardejm    1

Hello! I am installing and configuring my nice new mesu mount (with SiTech controller) but have come across a strange problem that I hope someone here has seen before or can help me with. I was attempting to get PHD to calibrate but it always failed saying that it could not move RA enough to complete the job. I ran PHD's star-cross test on Arcturus and got a cross in which the RA arms of the cross are almost exactly half that of DEC (see attached).

What is odd is that the guide rate in both axis is the same (5 "/s) and the encoder ticks/rev are about the same: SiTech's config file says:

AlMotTicksPerRev=7952383
AlScpTicksPerRev=10000
AzScpTicksPerRev=10000
AzMotTicksPerRev=7961372

(same in the controller config)

Has anyone seen this before ? More importantly, does anyone know how to fix it?

 

 

star-cross-test.jpg

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vlaiv    281

Don't know if this will help, but try the same at 0 declination star. Further north you go relation of pixel movement to guide pulse is less due to change in declination. See if changing DEC compensation in PHD settings will help. Also make sure that you have correct DEC entered if it does not pull it automatically.

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richardejm    1

Thanks for the tip. I did wonder if the RA rate varied with the declination, I believe it varies with the cosine of the dec angle but Arcturus is at dec 19 degrees so the factor would be  0.94 which is not enough to explain the problem.  However, I will try your suggestions if the clouds ever go away! 

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ollypenrice    16,821

I'm sorry I can't help. But as an immense fan of the Mesu, which I think is mechanically the best amateur mount on the market, I do wish that either SiTech would try to understand the term 'user friendly' or Lucas would find a more accessible control system.  I run two Mesus under the 'old, outdated' ArgoNavis/Stellarcat system and they just work - like a dream.  OK, no good for remote, but they are an object lesson in what 'just work' means. When I buy a new car (very occasionally!) I don't have to 'configure' it. 

Olly

PS  :icon_mrgreen: Mind you, my taste in cars is on the rustic side. Duster and MX5. Low on electronics! I suppose if I bought a Merc I'd have to configure the mirrors-seat-pedals positions and then configure how I wanted it to drive itself for me. Traction control? Where's the fun in that???? :evil4:

Edited by ollypenrice
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RichLD    662
3 minutes ago, ollypenrice said:

I'm sorry I can't help. But as an immense fan of the Mesu, which I think is mechanically the best amateur mount on the market, I do wish that either SiTech would try to understand the term 'user friendly' or Lucas would find a more accessible control system.  I run two Mesus under the 'old, outdated' ArgoNavis/Stellarcat system and they just work - like a dream.  OK, no good for remote, but they are an object lesson in what 'just work' means. When I buy a new car (very occasionally!) I don't have to 'configure' it. 

Olly

I understand that the Mesu is amazing mount but have to say that I'm seeing a lot of issues regarding guiding on this forum. Apologies to the OP as I can't offer a solution to the problem but I do have to agree with Olly here - a mount at this price point should not be this difficult to use. 

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tony210    144

Hi - Lucas sets the RA and Dec tics per revolution individually for each mount -these will not normally  need to be changed if at all until you get to fine guiding - I had to fine tune mine to get best results -guide rate as set is fine (5"/s)- I do not think these settings are your problem - it is important to roughly align the mount and do an offset init before attempting guide calibration as the mount wont track well until this is done -if this has been done then it may be a software setting or computer /mount communication issue - you could email Lucas - he always replied promptly and tried to help me when I needed to get advice but I had a very different issue!-also I assume you have setup the Sitech as per quick setup document on the Yahoo Mesu site as per Steve Richards? This was a big help to me-regards Tony

Edited by tony210

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michael8554    390

Hi Richard

I may be missing the point here, but I think you're getting ahead of yourself with the Star Test - I apologize in advance if you have already covered my thoughts below.

Try moving the mount in RA and then Dec with the PHD2 "Manual Guide", and see if the recorded lines are the same length - you might have to up the Guide Pulse Duration in "Manual Guide" into the thousands to get significant movement .

If your mount isn't moving enough in RA to calibrate successfully, then you should increase the RA step in PHD2 until the mount moves 12 to 15 steps.

"Review Calibration" in PHD2 displays some nice result tables that include RA and Dec rates, but I can't remember if "Review Calibration" will display if calibration failed.

With my LX200GPS, PHD2 calibrates successfully but reports that RA and Dec varied too much (like 12 steps versus 17, due to Dec backlash) but guides just fine.

Michael

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steppenwolf    4,035
11 hours ago, RichLD said:

a mount at this price point should not be this difficult to use. 

I feel that I should set a bit of balance here - the Mesu mount with SiTech controller really isn't difficult to use - I have no 'special' powers but never have any of the issues that are reported from time to time and certainly no issue guiding 1800 sec exposures at 1070mm focal length. The vast majority of 'issues' with users of this system are to do with 3rd party software settings, in this case, most likely PHD. Even the widely reported time incompatible 'jump' did not affect me and for some other users, even this turned out to be a bit of a myth and their problems were eventually found to be caused by either balance or differential flexure. My Mesu with SiTech 'just works'!

Unfortunately, I don't use PHD with my Mesu so I can't assist with the settings specifically but in my very limited experience of PHD with other mounts, adjusting the settings to increase movement has always resolved failed calibration issues.

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RichLD    662
6 hours ago, steppenwolf said:

I feel that I should set a bit of balance here - the Mesu mount with SiTech controller really isn't difficult to use - I have no 'special' powers but never have any of the issues that are reported from time to time and certainly no issue guiding 1800 sec exposures at 1070mm focal length. The vast majority of 'issues' with users of this system are to do with 3rd party software settings, in this case, most likely PHD. Even the widely reported time incompatible 'jump' did not affect me and for some other users, even this turned out to be a bit of a myth and their problems were eventually found to be caused by either balance or differential flexure. My Mesu with SiTech 'just works'!

Unfortunately, I don't use PHD with my Mesu so I can't assist with the settings specifically but in my very limited experience of PHD with other mounts, adjusting the settings to increase movement has always resolved failed calibration issues.

Of course Steve, quite right and apologies if I sounded a little blunt. I don't own the mount (perhaps someday?) but have to say that the problems that people on SGL have reported have certainly made me think twice about getting one - I can only imagine the frustration of dropping that kind of cash on a dream mount only to have issues that lose you valuable UK imaging time.

I appreciate that the Mesu offers very good value for money,  considering it's payload and accuracy. As you say, third party software tends to be at the root of most of the problems.

Having said all of that, things are never straightforward in this game are they? Regardless of who the manufacturer is and how much they charge...

All the best

Rich :icon_biggrin:

 

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richardejm    1

Thanks everybody for your help! I will try these suggestions the next clear night (if that ever happens).

 

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steppenwolf    4,035
1 hour ago, RichLD said:

Of course Steve, quite right and apologies if I sounded a little blunt.

Absolutely no apology required - I just wanted to put another side to the argument in light of my own experience with this mount! I mentioned that the software for the SiTech is a little 'quirky' and it most certainly is and this can be off-putting but its quirkiness hides a very powerful driver that adds to the mount's already rich features.

However, as you say, things are never straightforward in this game and the rich feature set adds complexity as a by-product but tapping into that complexity makes this such a powerful system. I control mine completely remotely so it has to be reliable for that idea to even be considered and so far, despite the occasional failed part-session, the mount has never been the culprit, it has always been the 3rd party software (CCD Commander and FocuMax) that makes use of the mount and other observatory components lie the focuser and camera that have been at fault.

It'll probably catch fire tonight now .......... :eek:

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tomato    230

My experience is similar to Steppenwolf, I followed his excellent set up guide and to date the Mesu has just worked. It gets set up and taken down and packed away in a flightcase between sessions, so it will stand up to repeated handling. I followed the RA jumps issue with some concern but my mount has never suffered from this.

I do pulse guiding with PHD2, I always do a Sitech 'offset init' and 2 'calstars' then calibrate PHD followed by a quick drift align in PHD, usually a couple of alignment iterations, then I am ready to go. Total PHD guiding RMS error is typically about 0.75 arc sec.

This is not as good as other Mesu users I know, but this is not a permanent set up.

I'll probably drop it on my foot next session....😳

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Waldemar    251
On 30-6-2017 at 00:09, tomato said:

My experience is similar to Steppenwolf, I followed his excellent set up guide and to date the Mesu has just worked. It gets set up and taken down and packed away in a flightcase between sessions, so it will stand up to repeated handling. I followed the RA jumps issue with some concern but my mount has never suffered from this.

I do pulse guiding with PHD2, I always do a Sitech 'offset init' and 2 'calstars' then calibrate PHD followed by a quick drift align in PHD, usually a couple of alignment iterations, then I am ready to go. Total PHD guiding RMS error is typically about 0.75 arc sec.

This is not as good as other Mesu users I know, but this is not a permanent set up.

I'll probably drop it on my foot next session....😳

From a very well informed source, I heard the 'jump issue' was due to a not very well mounted dovetail...

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tony210    144

Well I think we need to careful commenting about others experience . If a mounted dovetail issue caused the jump problem then at least 4 people I know mismounted their dovetails and the 91zb  firmware to eliminate timing problems was developed by Sitech for no reason? - seem unlikely ... Tony

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Waldemar    251
13 hours ago, tony210 said:

Well I think we need to careful commenting about others experience . If a mounted dovetail issue caused the jump problem then at least 4 people I know mismounted their dovetails and the 91zb  firmware to eliminate timing problems was developed by Sitech for no reason? - seem unlikely ... Tony

Apparently we are talking about different issues then... Indeed very unlikely this would happen to several people with the same mount.
I do not own a MESU, so I did not follow the thread about this. It seems to me the MESU is very reliable, so I understood a little mistake started leading it's own life.

Sorry if I gave the impression to ridicule the problem.

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richardejm    1

I think I know what might be the problem - both SiTech and phd are compensating for declination at the same time. I can turn off compensation in phd but of course, phd doesn't know what sitech is doing so it still thinks that the ra rate is odd. I can still calibrate and get it to guide ok-ish. Dan Grey is going to modify sitech for me so that compensation can be turned off. Phd should then be able to work correctly.

I have noticed another problem (sigh) - all the ra corrections are in the same direction so probably means that the ra tracking rate is slightly off. Fortunately another SGL member (https...../247247-mesu-200-ra-guide-speed-correction/) had the same problem and succesfully adjusted the encoder settings to make it track at the correct rate. When the clouds part, I will try that.

 

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kirkster501    1,437

Try and delete PHD from your computer completely and reinstall.  I had similar issues.  No idea why this fixed my issues bit it did.

And just to balance some of the points raised about/against the MESU.  Every issue I have had can be attributed to user error or dodgy software.  The mount has been, and remains, the bedrock of my system.  It is mickey mouse to use.  You do not need to go into hardly any of the sitech settings as lojg as you follow Steve's (Steppenwolf) guide.  I would buy one again absolutely and recommend the MESU without hesitation.  It is superlative engineering.

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MartinB    1,120

Richard, I strongly suggest you contact Lucas Mesu before you go fiddling with encoder settings and the like - info@mesu-optics.nl  He is extremely helpful and I am sure he will be able to help.  I had a couple of gremlins which he was able to address very simply.  Go to the expert rather than us "a little knowledge" SGL members.

 

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Zakalwe    2,976
On 07/01/2017 at 09:01, tony210 said:

Well I think we need to careful commenting about others experience . If a mounted dovetail issue caused the jump problem then at least 4 people I know mismounted their dovetails and the 91zb  firmware to eliminate timing problems was developed by Sitech for no reason? - seem unlikely ... Tony

^This^

The particular problem that I and others had was neither a myth, a mismounted dovetail or a problem with third party software. It was an issue at the very heart of the mount control software and how that firmware addressed a mismatch with its internal clock and the PC clock.

I'd also disagree about the superb support offered by the maker in fixing this issue. My experience, which is not unique though I will only speak for myself, has left me convinced that I will never buy from a one-man-band maker again. Too much rests on the vagaries and abilities of one individual.

The solution to the problem was found after months of dogged work with assistance from the American maker of the control system. I cannot fault Sitech for their efforts or their willingness to fix. 

I am aware of another user in Spain that has started to experience the "jump in RA" problem in the last couple of months. I found it hard to believe that the list of potential fixes that he was offered did not include a firmware upgrade.

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steppenwolf    4,035
12 hours ago, MartinB said:

Richard, I strongly suggest you contact Lucas Mesu before you go fiddling with encoder settings and the like - info@mesu-optics.nl  He is extremely helpful and I am sure he will be able to help. 

I can only second this advice but if you do decide to have a fiddle with the tick settings yourself, be sure to save a separate named copy of the current settings from ServoConfig so that you can be sure to return to the start point if it all goes wrong.

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tony210    144

Hi - can only endorse above - I think changing tracking rates will not solve this problem-the timing issues were as we have said a very real entity and the new firmware helped my guiding problems a little but in my case after a lot of discussion it was the Sitech controller that was faulty and the mount behaviour was transformed once this was finally replaced-worth bearing in mind-Tony

Edited by tony210

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Zakalwe    2,976

I'd also echo the calls not to start changing the encoder ticks. Making random changes is no way to diagnose a problem. If the tick setting is incorrect then it will evidence itself by the mount either running slow or fast. If you run the PHD Guide Assistant then that will tell you if the tracking is off. A simple calculation will then show you the amount that the tick setting needs to be altered by.

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richardejm    1

The reason I think it is running slow or fast is that :

  • stars show long trails at 1430mm focal length (C9.25+f6.3 reducer)
  • when SGP was  set to continually take 2 second images of vega (while focussing) I noticed that it kept moving from frame to frame.
  • phd does RA corrections all in one direction

I did a measurement of the amount of drift by doing this:

  • got the PA accurate to within 1 arcmin (using sharpcap - very good software)
  • clicked the "freeze declination" option in sitech's config
  • pointed at a star and exposed for 5 mins
  • measured the length of the star trail and converted the length in pixels to arcsecs 
  • worked out the new encoder ticks value, reconfigured it to go faster and took another picture to check......and.....it didn't work :( 
  • reconfigured to go slower and retested....nope!

(I did of course take a copy of the original config file)

So it looks as though I need to take advice from Lucas after all...Ho hum!

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Zakalwe    2,976
9 minutes ago, richardejm said:

The reason I think it is running slow or fast is that :

  • stars show long trails at 1430mm focal length (C9.25+f6.3 reducer)
  • when SGP was  set to continually take 2 second images of vega (while focussing) I noticed that it kept moving from frame to frame.
  • phd does RA corrections all in one direction

 

Mine was running at an incorrect tracking speed (a behaviour that developed over the course of 12 months). It was apparent as PHD was making all of the RA guiding commands in one direction, similar to your findings

try running PHD Guiding Assistant. That will tell you exactly how fast or slow it may be running. From there you can calculate exactly how many ticks to alter the setting by. Lucas was advising me on that problem- the only issue was that he advised to alter the tick setting by a few hundred. When I measured the drift using PHD Guiding it actually needed to be changed by 90,000. By initially changing it by such a small amount I was getting frustrated as I wasn't seeing any difference.

See here for how to calculate the tick setting

 

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tony210    144

Hi - I use the Sitech program and changed the RA rate in "offset tracking rates" in real time while guiding and then watched the PHD guiding graph  behavior - you can quickly make sure all RA adjustments are in both directions and then calculate tic changes from there for subsequent runs- got this advice of the Mesu Yahoo group which is well worth joining.

Does affect subsequent calibrations in PHD but you can get where you want to be fairly quickly with trial and error.

Edited by tony210

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