Mesu PA no view of Celestial Pole #mesu


ZS1RA
 

I changed my mount from a SkyWatcher EQ6R Pro to a Mesu e200 which I purchased a year ago and have not touched it since. I was trying to get it to work with Linux and then I had a problem unrelated to astronomy and am now able to get back to imaging.

One of the first things I noticed is that the PA is not as straightforward as I was used to. The SkyWatcher has a fantastic Polar Alignment routine built into the handset and I could PA anywhere even from my "observatory" meaning my balcony where I have no view of the Celestial Pole due to buildings so my "horizon" is at 40 deg and I live at -26 deg (I live in South Africa). Unfortunately this amazing PA routine is not available on the Mesu so I am planning to purchase a Polemaster to assist with PA.
 
My question is, can the Polemaster do PA without a view of the South Celestial Pole?
 
TIA.
 
Shaun
 


Don W
 

Hi Shaun,

No, the polemaster uses an image of the polar region to set the alignment.
But there is a way to accurately polar align without a view of the pole, using the stars at the zenith.  The process was developed  by Roland Christen at AstroPhyisics and presented on the AP forum a couple years ago.  I copied it and attached it here.

Don W


ZS1RA
 

Wow, thanks Don. This is really useful.


paul K
 

PHD2 also has a really easy to use Polar Alignment function which I use with my MESU. It has some nice real time visuals which show PA progress as you adjust.
Paul


David Ibarra Gómez
 

Hi,

when I placed my mesu inside the observatory I had the same problem, polaris was no longer visible. So I could no longer use polemaster with mesu adapter.

The first thing I tried was to build an adaptor like the one in the attached photo (just to jump over the observatory wall/roof). Later I realised there is an adaptor from geoptik (https://www.valkanik.com/buscadores/adaptador-geoptik-para-polemaster-a-pletinas-3-losmandy).

If the problem has to do with an avoidable "obstacle" in the line of sigth of polaris, maybe you can do the same thing.

Then you can do a coarse orientation  using polemaster and afterwards use phd2 to improve the alignment...

Regards




De: Sitechservo@groups.io <Sitechservo@groups.io> en nombre de paul K <paulskirk53@...>
Enviado: jueves, 1 de julio de 2021 10:17
Para: Sitechservo@groups.io <Sitechservo@groups.io>
Asunto: Re: [Sitechservo] Mesu PA no view of Celestial Pole #mesu
 
PHD2 also has a really easy to use Polar Alignment function which I use with my MESU. It has some nice real time visuals which show PA progress as you adjust.
Paul


paul K
 

PHD2 doesn't need sight of the celestial pole. It works very accurately by taking  measurements in other areas of the sky. This explains it well:

https://openphdguiding.org/man-dev/Tutorials.htm

Paul


Yann-Eric Boyeau
 

Hi,

Using phd2 drift align routine with my mesu was really effective and precise. No need to see celestial pole.

YE

Le 1 juil. 2021 à 20:02, David Ibarra Gómez <dibarra21@...> a écrit :


Hi,

when I placed my mesu inside the observatory I had the same problem, polaris was no longer visible. So I could no longer use polemaster with mesu adapter.

The first thing I tried was to build an adaptor like the one in the attached photo (just to jump over the observatory wall/roof). Later I realised there is an adaptor from geoptik (https://www.valkanik.com/buscadores/adaptador-geoptik-para-polemaster-a-pletinas-3-losmandy).

If the problem has to do with an avoidable "obstacle" in the line of sigth of polaris, maybe you can do the same thing.

Then you can do a coarse orientation  using polemaster and afterwards use phd2 to improve the alignment...

Regards




De: Sitechservo@groups.io <Sitechservo@groups.io> en nombre de paul K <paulskirk53@...>
Enviado: jueves, 1 de julio de 2021 10:17
Para: Sitechservo@groups.io <Sitechservo@groups.io>
Asunto: Re: [Sitechservo] Mesu PA no view of Celestial Pole #mesu
 
PHD2 also has a really easy to use Polar Alignment function which I use with my MESU. It has some nice real time visuals which show PA progress as you adjust.
Paul
<1617040917451-1.jpg>


Erik Stein
 

I have no view anywhere near the polar region at my location (tiny backyard on south side of my two story home in a light polluted suburb of greater Los Angeles) and initially experienced difficulties achieving polar alignment with my Mesu 200.  There is too much junk in my backyard and my setup is so close to my home's exterior wall that a magnetic compass has proven to be unreliable.  While I found PHD2 superb for fine-tuning my polar alignment, it was all but useless for getting a rough PA.  In order to use PHD2's PA routine, you need to calibrate your mount/equipment.  In order to calibrate your mount, you need a rough polar alignment (chicken or the egg?).  I wasted countless hours getting PA calibration failures in PHD2 before I figured out that my very poor PA was causing too much drift for PHD2 to calibrate.  I eventually had to resort to old school manual drift aligning to get my initial PA.  

I later discovered that the PA assist function in SiTech is extremely useful.  I start blind tracking, offset-init, then let SiTech take control to automatically build a 10+ CalStar model on my poorly aligned system, which tells me how far off my PA is, and gives clues as to which way I need to adjust.  


Sedat Bilgebay
 

For the rough alignment, I used Sitech PA assist when I first installed my Mesu 200 on a fixed pier. After that, I use PHD2 drift alignment for fine tuning when needed. Last time I needed a fine tuning was some 2 years ago following an earthquake. 


Sedat Bilgebay
 

Meanwhile, Rolando's method may not work for our Mesu mounts because of the inherent slip in the system... especially with the original acceleration parameters the slip can be a couple thousand pixels.


ZS1RA
 

My mount is mounted on a skate as I need to move it out of the way when I’m done imaging. I like Erik’s idea as well as Don’s proposal. Will try as soon as I have clear skies. Thanks 


Don W
 

If you are getting slippage with a MESU mount then you should definitely lower the acceleration factor, maybe by a lot. The acel and decel hardly affect your overall time to slew, but slippage is really bad and will affect everything you do.
Don W


Sedat Bilgebay
 

Precisely! Mine is at the minimum currently.


paul K
 

As Don mentioned a few posts back, it will depend upon the moment of inertia of the system. I've run my Mesu 200 Mk1 with a C14 (30 ish Kg) short physical length scope and there's no slippage.
Having just repaired my Dec drive motor shaft and re torqued it with Lucas Mesu, I think (as mentioned in previous posts) that I'll lower the acceleration to reduce stress as I don't need it to be high in my use case.
The Dec motor shaft broke on my mount when I was moving it by hand with the power off. I had a different mental picture of the drive which was two discs in contact with each other, but that's not the case. The drive shaft is about 2mm diameter and ~30mm long with a ball race at each end. I'll be much more careful moving the scope by hand in future, but I'm not an engineer and don't know whether moving it slowly by hand is good or not, just seems good to me having seen the drive. I'll probably move to the lowest acceleration and see what that does.
Paul


Don W
 

Hi Paul,

I have never seen a Mesu mount, but knowing that it is a friction drive means the drive is highly loaded to prevent slippage.  You have an early Mesu, I understand later versions have a clutch to allow hand movement.  You would be best to not move your mount by hand, but always use the servos to move.  It is simply the safest way.

Lowering the acceleration factor will reduce the loads on the drives.  You probably can see the reduced amperage if you check the SiTech Controller Stuff when you make it move.  But I doubt you will notice much difference in slew time - the time to accelerate is really very short.  Even when guiding, the lower acceleration will not be apparent - it should guide just fine.

Don W


paul K
 

Thanks for the advice Don, I'll use the hand controller as you've suggested rather than move by hand. It makes sense.
Paul