HEQ5 Synscan DEC drifting problem?

[Alnasl]

Hi there!

I'm a bit of a beginner, please forgive me if I'm not explaining things correctly, I can explain further if needed.

I bought a Sky-watcher HEQ5 mount with Synscan (firmware version 04.37.03), with the plan of using it as part of an art/educational exhibition event, so what I'm doing may sound completely nonsensical, but please bear with me knowing this is not for traditional viewing or photography purposes: it's going to be used to illustrate the motion of the earth in relation to the galaxy, so it will run 24-hours a day with a big wooden arrow on it instead of a telescope (it's very lightweight and balanced, of course, and I checked that it won't hit the tripod), running even when the galactic center is below the horizon and the sun it out. It will always be "pointing" to the center. I hope that makes sense. Strange, I know.

I have been doing some tests indoors before I use it in this project but I'm running into some issues. The coordinates I want to follow are RA 17h 45m 40s / DEC −29° 00′ 28″, the center of the Milky Way Galaxy. It doesn't appear to exist in any of the object databases in the Synscan (as far as I can tell, from looking in the Simbad database, unless I am wrong?) I'm at 59.9º N, meaning the location is most often below the horizon, so the mount will not slew to it 90% of the time when using the 'user defined objects.'

For the sake of my tests, what I have tried to do is to manually slew to the coordinates while the sidereal tracking in on, in the hopes that it will simply follow the motion.

However, I am finding a problem: it will start it at the exact coordinates I slew it to (RA 17h 45m 40s / DEC −29° 00′ 28″), but immediately it starts to slowly drift away in the DEC, one arcsecond at a time. For example, now at 12 hours of running, the DEC is at -28º 38' 16" (the RA remains accurate.)

Tonight I am going to get up at 5am to do a 'user defined object' test, when the location is above the horizon, to see what happens. But for the sake of convenience, though, I would sure like to have the manual slew/sidereal tracking option work as well.

When setting it up, I do just a one-star alignment, but since I am still indoors, I can't visually confirm it's correctness. (But shouldn't that technically not matter? In that the point of the sidereal tracking is to follow coordinates exactly?)

Anyone have an idea as to what's going on here?

Thanks for your time, everyone!

 

Edited April 8, 2016 by Alnasl

[Dr_Ju_ju]

Have you considered bypassing the hand controller & driving the mount directly from a computer using (M$ Windows World), Stellarium\CDC Ascom platform etc. this may allow what you want, but at the 'expense' of a PC, control connector etc....

[Freddie]

As it is just tracking using the RA drive the mount will still need to be polar aligned. How are you doing that?

[Alnasl]

4 hours ago, Dr_Ju_ju said:

Have you considered bypassing the hand controller & driving the mount directly from a computer using (M$ Windows World), Stellarium\CDC Ascom platform etc. this may allow what you want, but at the 'expense' of a PC, control connector etc....

I actually hadn't considered this up to now, because for this specific project, it might not be the best solution because there might be times it is unattended (so I guess I am worried about theft...) and it would be nice to keep the whole thing as streamlined as possible. But it's nice to know this can be tried as a possible solution if I can't get my Synscan controller to work. Thanks for the suggestion.

4 hours ago, Freddie said:

As it is just tracking using the RA drive the mount will still need to be polar aligned. How are you doing that?

Correct, but for now, this is just testing to make sure I understand everything and it is all working—so when I am doing the alignment, I am not making any corrections during the one-star alignment, essentially meaning to the mount that the alignment is perfect. I am indoors just for now (we are getting a lot of rain this spring!) From what I can tell this shouldn't be causing the problems I am having though, right?

And just a question because I am just learning about all this (thanks for the help, by the way), couldn't I use something like a Vixen polar meter?

[Freddie]

The star alignment just gives the mount a map of the sky and will have no impact on its ability to track. A lack of polar alignment will cause your DEC drift.

[Alnasl]

19 minutes ago, Freddie said:

The star alignment just gives the mount a map of the sky and will have no impact on its ability to track. A lack of polar alignment will cause your DEC drift.

Hmmm.... Well, I am not looking through a telescope and noticing, for example, a star drifting in the eyepiece, so to speak. Since I am running these tests inside, I am not actually looking at anything in the sky yet. Maybe  I need to explain the problem like this:

 

1. I proceed through 1 or 2 star alignment process (but since this is happening indoors, I am not adjusting anything and just proceeding through, so it is pointing to a hypothetical "north")

2. Turn on sidereal speed tracking

3. Manually slew to RA 17h 45m 40s / DEC −29° 00′ 28″

4. Leave it alone for several hours

5. The hand controller now reads something different, now RA 14h 22m 57s / DEC −28° 33′ 31″

So my question is: why isn't it simply staying on the first coordinate? Why would it read something else?

 

It is also quite possible I am simply not understanding your correct observation

 

 

 

[kens]

I think what is happening is that the star alignment causes the handset to make a sky model. The sky model tells it that your alignment is not perfect so as it tracks in RA it "knows" that your Dec is also changing, as it is uncorrected. You need to clear any trace of the model from the handset.

[Dr_Ju_ju]

So all you really need to do is after you've configured the initial alignment is to keep rotating the mount in RA...  if that is the case, how about driving the ST4 port (switch) in one direction ?

[Freddie]

Ah, with you now, sorry ignore what I said.

The way you have described it, the mount would think that everything was perfect as you slew to a star (or at least where it thinks the star should be) and confirm that the slew is correct by just accepting it without making any adjustments. It would therefore think its map of the sky was perfect. Unless it gets a command to move DEC the DEC co-ords shouldn't change as it just moves in RA. Will need a bit more thought!!

[Alnasl]

18 hours ago, kens said:

I think what is happening is that the star alignment causes the handset to make a sky model. The sky model tells it that your alignment is not perfect so as it tracks in RA it "knows" that your Dec is also changing, as it is uncorrected. You need to clear any trace of the model from the handset.

Hmmm. OK, I think what I have to do no matter what is get my hands on my friend's telescope so that I can get a really good alignment set, and try other solutions in conjunction from there too. Thanks for this!

 

3 hours ago, Freddie said:

Ah, with you now, sorry ignore what I said.

The way you have described it, the mount would think that everything was perfect as you slew to a star (or at least where it thinks the star should be) and confirm that the slew is correct by just accepting it without making any adjustments. It would therefore think its map of the sky was perfect. Unless it gets a command to move DEC the DEC co-ords shouldn't change as it just moves in RA. Will need a bit more thought!!

No worries! Strange right?? Well, at least I'm glad to know I was also understanding it correctly—that something is wrong. Thanks for helping me think it through, though.

 

12 hours ago, Dr_Ju_ju said:

So all you really need to do is after you've configured the initial alignment is to keep rotating the mount in RA...  if that is the case, how about driving the ST4 port (switch) in one direction ?

True! This is actually a pretty interesting solution... but it seems like it's not something that's going to work with this hand controller, since I think there's no way to isolate just the RA, and also 'lock' the on any coordinate, RA or DEC (which is the whole problem I'm having). Do you recommend using some different method for going about this? Like a specific controller? (Sorry, still so very new with all this!)

 

[kens]

2 hours ago, Alnasl said:

21 hours ago, kens said:

I think what is happening is that the star alignment causes the handset to make a sky model. The sky model tells it that your alignment is not perfect so as it tracks in RA it "knows" that your Dec is also changing, as it is uncorrected. You need to clear any trace of the model from the handset.

Hmmm. OK, I think what I have to do no matter what is get my hands on my friend's telescope so that I can get a really good alignment set, and try other solutions in conjunction from there too. Thanks for this!

Actually, you may be better off just skipping over the alignment steps when they come up on the controller. For the long time periods you are using you will never get a good enough alignment to keep the readings correct.

So you just set up with a manual alignment of the mount then switch on the controller. When it asks "Begin Alignment 1) YES 2) NO" press "2". 

The mount will assume it is perfectly aligned so the readings wont change as it rotates.

[Astrofriend]

If it's not the polaralign, could it be that the mount correct for atmosphere refraction, most goto mount do. It's about 1/2 degree at horizon. But no idea what happens when under horizon, maybe just correct with a neg sign.

 

BR
/Lars

Edited April 26, 2016 by Astrofriend

[Dinu Adrian]

I guess that the mount not being aligned with the Earth's rotation axis together with the One star alignment cause your mount  to point at different coordinates that the ones you want. It is a good chance that it wasn't tracking the center of the Milky Way... Once the mount is set on a target it should only move the RA ( this is actualy the Hour Angle) since the DEC is constant. It is not clear to me why the DEC moves in the first place, maybe the mount is smarter than I thought and knows whether or not it has been polar aliged well. I've also got an HEQ5 and I think that a good polar alignment will make these issues vanish.

[Thalestris24]

If an heq5 could stay precisely on track by itself then we wouldn't have to worry about guiding it!

Louise

[Astrofriend]

It's not possiblie to optimize both pointing and tracking, only one of them. That's because of atmosphere diffraction.

 

Read more in this interesting article:

http://www.dfmengineering.com/news_eng_article_4.html

But this was maybe of topic.

/Lars

[certx]

I know this is an old post, but... I want to respond with two different thoughts.... first about the responses, and second about the actual topic...

The responses: Everyone seems to have completely missed the fact that the OP is not at all talking about objects drifting in DEC or RA in the field of view through a telescope. He is talking about the coordinates shown in the "Show Position" option in the hand controller's display. ie, the mount itself is not staying pointed, on it's own physical axes, at the specified coordinates.

The actual topic: I just bought an Orion Atlas, which is a SkyWatcher EQ6, with SynScan V4 hand controller. I have the EXACT SAME ISSUE. Whether I do an 'x' star alignment or not, use goto or slew using the direction keys, or manually enter coordinates into the user objects. I turn it on, accept the locations it things alignment stars are at, and don't change anything. Slew to a target and start tracking. Go to menu Utility Function -> Show Position, DEC changes on the display by 1 arc second every 20 to 30 seconds. After several minutes, it's several arc seconds off the coordinates I specified, and after a couple hours, it is several arc minutes off of the coordinates I specified in the slew.

A couple additional pieces of information: I have the latest SynScan HC firmware and motor control firmware... HC: V4.39.05/Motor: V2.04. When I have it connected to my computer using Starry Night Pro 7, the RA and DEC that it reports back to STP7, via ASCOM do not match the RA and DEC on the hand controller display. DEC is 1 arcminute different and RA is 2.5 arcminutes different, consistently. Those differences never change.

Has anyone come up with a cause/solution to this?

Edited September 22, 2017 by certx
spelling and add information

[Astrofriend]

Hi,

I'm not sure if I understand this correctly. I don't use my hand terminal to my EQ mount anymore, I use the software EQMOD and use the star chart software CdC to control it.

 

When I use that I got something simular problem wen the polar align is not accurate enough. The star carht display the where the optics pointing based on the postion EQ6 sending back to the computer, RA and DEC coordinates: but becuase I use autoguiding the coordinates change when the autoguiding offset the coordinates when try to following the object.

 

There is also a parameter that could be set in EQMOD that is called drift compensating, that parameter correct the speed of RA motor. It has something to do with the hardware controller board in the mount if I understand correctly, but don't think this happens when controlling direct from hand controller.

 

Read here:

https://www.astrobin.com/296008/B/?nc=user

 

Maybe part of the answer you look for, or?

 

/Lars

[newbie alert]

As has been said above,once the mount has been accurately aligned the mount should only track In RA..youre getting dec drift because its not aligned and the longer it goes on the more drift you will get..

I'd of thought it's never going to be a 100% accurate test as there will be inaccuracies in the gears both RA and DEC ..thats what backlash is..to get a mount that will track more or less 100% is going to be of professional standards..a mount made in Asia isn't.. that's why we use guiding software ...

Edited October 4, 2017 by newbie alert
Phone thinks it knows best

[dph1nm]

On 22/09/2017 at 13:51, certx said:

Go to menu Utility Function -> Show Position, DEC changes on the display by 1 arc second every 20 to 30 seconds. After several minutes, it's several arc seconds off the coordinates I specified, and after a couple hours, it is several arc minutes off of the coordinates I specified in the slew.

What happens if you then tell the mount to go back to that object/position? Does is slew several arcminutes in dec and hence no longer align on the object, or does it stay where it is? i.e. is the problem with the displayed coordinates or does the telescope really think it has moved that far.

NigelM

[Astrofriend]

Hi,

It will never be perfect, you have the atmosphere that bend the lights at low position near the horizon. That effect is normally included in a goto mount how it should compensate for this.

 

Here is an image that show how it could look with bad polar align and auto guiding:

After some hours the object M3 have drift away from its mounts coordinates. It still on target because of the auto guidning but with shifted RA and DEC coordinates. If I order it to go to it's center the mount move it to were it thinks M3 should be, but will not point to M3 anymoore.

You can calibrate it to compensate for this but it still will give a rotation of the field and then not possible to do long exposure photos.

To get a high precission polar align you can do the drift align method, very easy with computer aid, read here:

http://astrofriend.eu/astronomy/tutorials/tutorial-drift-align/tutorial-drift-align.html

 

/Lars

[GliCo]

Hi there,

i saw the same effect with my NEQ6 and i did some experiments.

it is definitly the alignment. if you simulate a poor alignment (min 2 stars), then tracking will "correct" the position. if you simulate a good alignment (2 stars!), you will get nearly no correction while tracking position.

it is strange, that sysnscan modifies the RA/DEC of the tracked object for this reason, but it seems to handle this with a "transformed skymap".

GliCo