Mesu 200 RA speed correction

[tomato]

Although my 8 year old Mesu mount guides at 0.4 arcsec total RMS, with some 70 + kg of kit on board,  I still get frequent corrections in RA all in the same direction. I know folks have adjusted the RA speed successfully but I just want to be convinced that it this and not some other factor before I proceed. I think two other possible causes of frequent RA corrections are an out of balance assembly and poor polar alignment. For the former I would suppose the direction of corrections would reverse after a meridian flip but mine stay on the same side before and after. For poor PA, my DEC corrections are small and in both directions so I’m assuming this is OK, but I will do a drift align in PHD. 
 

I have let the mount track unguided and it is moving quite a lot in RA but not DEC as the guiding confirms, so if the PA is good it has to be the RA tracking rate that needs adjusting?

[ollypenrice]

Your logic seems sound to me.

There's a quick way to test your PA. Take the first and last images from the same continuous run and place one on top of the other. Align them such that a central star from the top image is perfectly placed over its equivalent on the first. This will show the total rotation over the run. (To be more precise, the rotation will be around the guide star so, if you happen to know where that is on the image - if it's on the image - you could align the two at that point.)

Olly

Edited April 2, 2022 by ollypenrice
typo

[AKB]

I’m in exactly the same position, and have been wondering whether to do anything about it, since it has zero impact on image quality.

I saw a post from Lucas once on how to calculate and set the necessary parameters, but don’t recall where that was …. 🙁

Tony

[Seelive]

Try here:

https://stargazerslounge.com/topic/247247-mesu-200-ra-guide-speed-correction/

 

[tomato]

40 minutes ago, AKB said:

I’m in exactly the same position, and have been wondering whether to do anything about it, since it has zero impact on image quality.

I saw a post from Lucas once on how to calculate and set the necessary parameters, but don’t recall where that was …. 🙁

Tony

I know what you mean, I don't think it will improve the guiding by very much but it bugs me seeing all of the constant RA  corrections and the PHD guide points offset from the centre. I will do a bit a more investigation but then I am going to alter the speed, I'll be certain to make a note so I can revert back if it all goes pear shaped.

[Laurin Dave]

Steve..  just save the old and make a new servo config .car file with the new rate.. that way you’ll have it to go back to 

Dave

[tooth_dr]

11 hours ago, tomato said:

have let the mount track unguided and it is moving quite a lot in RA

How much is a lot?  I recently noticed when running Guide Assistant that my RA graph drifts upwards when guiding is disabled. After 2 minutes it’s at 4” and continues to rise. Are you seeing similar or worse? 

[AKB]

1 hour ago, tomato said:

but it bugs me seeing all of the constant RA  corrections

Yes, I’m OCD too!

[tomato]

2 hours ago, tooth_dr said:

How much is a lot?  I recently noticed when running Guide Assistant that my RA graph drifts upwards when guiding is disabled. After 2 minutes it’s at 4” and continues to rise. Are you seeing similar or worse? 

When I measured the RA drift at the end of October last year it was 4.27 arcsecs per minute, so roughly twice as bad the drift you are seeing. @Singlin, who started a thread on this back in 2015 had 10.2 arcsecs per minute, and made a successful adjustment to the encoder tick count to fix it. I guess if you are seeing constant RA corrections and the trend is off set from the zero line, it's worth making an adjustment.

[tomato]

I have made the tick adjustment, will that be enough tinkering to ensure a cloudy night tonight?😉

[tooth_dr]

2 hours ago, tomato said:

I have made the tick adjustment, will that be enough tinkering to ensure a cloudy night tonight?😉

Thanks for the reply.  Hope you get an opportunity to test it out!  I've always been fairly fortunate with clear skies after adjustments.

[tomato]

Well so far the cloud curse has come to pass but I got a brief 20 minutes of guiding which look promising, RA trend is now both above and below the line with corrections in both directions....

[dan_adi]

On 03/04/2022 at 00:10, tomato said:

Well so far the cloud curse has come to pass but I got a brief 20 minutes of guiding which look promising, RA trend is now both above and below the line with corrections in both directions....

I plan to move to Voyager and phd2. Last night I guided with phd2. The RMS was good at 0.33 arc sec. I also noticed that RA corrections are all in the same direction. I checked my RA drift, it's around 1.2 arc sec per min.

Did adjusting the ticks in RA worked for you? My guess is I should substract the calculated ticks from the current value, since adding them would slow the tracking further. Did you add or subtract?

Thanks

[tomato]

Before embarking on the tick adjustment option, do make sure your mount balance is as good as you can get it, particularly if, like me, you have a high load capacity on the mount. An out of balance in RA can produce the same effect, see what happens after a meridian flip.

I’d be happy with 0.33 arc sec total RMS BTW.

[dan_adi]

36 minutes ago, tomato said:

Before embarking on the tick adjustment option, do make sure your mount balance is as good as you can get it, particularly if, like me, you have a high load capacity on the mount. An out of balance in RA can produce the same effect, see what happens after a meridian flip.

I’d be happy with 0.33 arc sec total RMS BTW.

I balance using an amp meter after I do it by feel. Yes 0.3 RMS is quite good. I will test and see what happens. I don't have to make a big adjustment just a few thousands ticks.

Could it be also the guide speed in servo config? I have the default 0.33x. Did you try 0.5x sidereal?

[tomato]

No, I have kept the guide speed at 0.34. To answer your original question, my RA speed was too slow so I added the tick correction value to the original. I get around 0.3 arc sec total RMS on a good night, but usually it is closer to 0.45. I have got 70+ kg riding on the mount.

[whipdry]

Within SiTech Features tab there is Offset Track Rates where you can adjust both Dec & RA drift in Arc Seconds Per Second over a period of your choose in Minutes... fairly easy to use, lets say in 10 min. you 4 arc sec. drift just add these into boxes provided & hit Calculate, result is -0.0067 hit Save Rates & your done, use Rate to Zero to cancel... these setting aren't saved revert to zero when you restart Sitech.

FYI minus arc sec. can be used.

Peter

[dan_adi]

19 hours ago, tomato said:

No, I have kept the guide speed at 0.34. To answer your original question, my RA speed was too slow so I added the tick correction value to the original. I get around 0.3 arc sec total RMS on a good night, but usually it is closer to 0.45. I have got 70+ kg riding on the mount.

Last night was clear for a couple of hours. I substracted the calculated ticks and it was a little bit worse. I didn't spent all night tinkering since I wanted to do some imaging too.

Next clear night I will add the ticks since substraction made things a little worse.

Thanks 

[dan_adi]

12 hours ago, whipdry said:

Within SiTech Features tab there is Offset Track Rates where you can adjust both Dec & RA drift in Arc Seconds Per Second over a period of your choose in Minutes... fairly easy to use, lets say in 10 min. you 4 arc sec. drift just add these into boxes provided & hit Calculate, result is -0.0067 hit Save Rates & your done, use Rate to Zero to cancel... these setting aren't saved revert to zero when you restart Sitech.

FYI minus arc sec. can be used.

Peter

Thanks, I will try it.

[dan_adi]

I had a few clear nights. I ended up adding around 8000 ticks to RA ticks. 

It seems I don't have RA corrections in one direction anymore. I wonder why these numbers aren't set accordingly from the beginning. I'm in my 5th year and still optimising. Those 10 micron mounts seem more and more appealing.

Anywho, below is a guiding run after optimisation. Spikes are dithering. Current RMS 0.27".

 

Edited May 13, 2023 by dan_adi