Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

msacco

Synscan - can't manage to star align successfully

Recommended Posts

55 minutes ago, happy-kat said:

Is it not at side real rate but set to Moon speed tracking on the handset

That's an interesting point, if the tracking type was set wrongly could that affect the initial set-up?

Share this post


Link to post
Share on other sites

With 1/2/3 star alignment....

let’s assume your PA is as good as you can achieve.

the start position is “Home” position - scope pointing towards the pole, counterweights down.

if the slew to the first star is “off” then as per discussions above you have two options:

1. Unlock the axes and manually recentre the target star.

2. Use the handcontroller to re-Centre the target star.

what’s the difference??

#1 the mount motors have been driven (energized) for a series of pulses the number of pulses in each axis based on the gear ratio and the calculated difference (RA and Dec) between the home position and the target star. Obviously if the home position is 100% correct and the gear ratio is 100% and the calculation model is 100% the target star will be exactly in the Centre of the FOV. It’s typically assumed any error is due to an error in the Home position setting. Moving the mount manually doesn’t add/ subtract any pulses. This then infers that the pulse count used to move the scope was correct; the next move to the second alignment star with then continue to use the original internal model (ie the gear ratio/ pulses per degree). If the second star is found central to the FOV, then it would probably confirm the packing position was indeed incorrect. If there’s still an issue with the second star, manual correction should not be used.....

#2 making the first star correction using the handcontroller will add/ subtract motor pulses. This correction will then be used by the internal model to change the pulse per degree rate. The model will assume the initial Park position was 100% correct. If the second star is off Centre, using the handcontroller to correct will once again add/ subtract pulses and “ up date” the internal pulse/ degree rate......

It’s anticipated that these rate (pulses/ degree) changes will result in an improvement in subsequent GOTO accuracy.

In a real world, a combination of both methods may be used.

So much for theory.......

I have a permanent well PA aligned mount in the observatory and use EQMod to Park and Unpark the mount (so there should be no error in Park position) and I still find the first alignment star is still repeatability “off” by a degree or so, always in the same direction. Using the manual/ handcontroller correction improves the immediate GOTO, but at start-up the next session still shows the same initial error.

I honestly don’t know why........

Share this post


Link to post
Share on other sites
7 hours ago, Geoff_L said:

1.5x suggests to me (at least for the DEC drive) that you might have the wrong cog meshed with the cog on the DEC driveshaft. The smaller of the two cogs on the motor shaft should mesh with the cog on the DEC driveshaft. I've not had cause to strip the RA motor drive and so can't say whether the same applies to the RA drive. HTH, Geoff

I'm sorry, but can you elaborate more on that? I couldn't really understand what should I do :)

6 hours ago, happy-kat said:

Is it not at side real rate but set to Moon speed tracking on the handset.

Nope.

2 hours ago, Merlin66 said:

With 1/2/3 star alignment....

let’s assume your PA is as good as you can achieve.

the start position is “Home” position - scope pointing towards the pole, counterweights down.

if the slew to the first star is “off” then as per discussions above you have two options:

1. Unlock the axes and manually recentre the target star.

2. Use the handcontroller to re-Centre the target star.

what’s the difference??

#1 the mount motors have been driven (energized) for a series of pulses the number of pulses in each axis based on the gear ratio and the calculated difference (RA and Dec) between the home position and the target star. Obviously if the home position is 100% correct and the gear ratio is 100% and the calculation model is 100% the target star will be exactly in the Centre of the FOV. It’s typically assumed any error is due to an error in the Home position setting. Moving the mount manually doesn’t add/ subtract any pulses. This then infers that the pulse count used to move the scope was correct; the next move to the second alignment star with then continue to use the original internal model (ie the gear ratio/ pulses per degree). If the second star is found central to the FOV, then it would probably confirm the packing position was indeed incorrect. If there’s still an issue with the second star, manual correction should not be used.....

#2 making the first star correction using the handcontroller will add/ subtract motor pulses. This correction will then be used by the internal model to change the pulse per degree rate. The model will assume the initial Park position was 100% correct. If the second star is off Centre, using the handcontroller to correct will once again add/ subtract pulses and “ up date” the internal pulse/ degree rate......

It’s anticipated that these rate (pulses/ degree) changes will result in an improvement in subsequent GOTO accuracy.

In a real world, a combination of both methods may be used.

So much for theory.......

I have a permanent well PA aligned mount in the observatory and use EQMod to Park and Unpark the mount (so there should be no error in Park position) and I still find the first alignment star is still repeatability “off” by a degree or so, always in the same direction. Using the manual/ handcontroller correction improves the immediate GOTO, but at start-up the next session still shows the same initial error.

I honestly don’t know why........

Not being rude of anything, but it doesn't sound related to the issue I'm having right? :)

I mean, my issue is not really about being a little bit off position, is being completely off position looking at the ground ^_^

Share this post


Link to post
Share on other sites

Sorry, based on the discussions I assumed this may have been of assistance.

 

  • Like 1

Share this post


Link to post
Share on other sites
14 minutes ago, Merlin66 said:

Sorry, based on the discussions I assumed this may have been of assistance.

 

No need to sorry, more information is always great, really appreciate that :)

Share this post


Link to post
Share on other sites
14 hours ago, msacco said:

I'm sorry, but can you elaborate more on that? I couldn't really understand what should I do :)

 

The following photos are of the DEC motor and DEC input shaft on my EQ5 Pro. As the first photo shows, the motor is fitted with two cogs, a large one and a small one. The larger of the cogs meshes with the pinion on the motor shaft and the smaller cog should mesh with the cog on the DEC input shaft (i.e. the cog shown in the second photo). It is possible to position the motor on its mounts so that the large cog on the motor meshes with the DEC input. As the large cog has approximately 1.5x the number of teeth of the smaller cog, meshing the wrong cog of the motor with the DEC input would make the DEC drive slew approx 1.5x the correct amount. HTH, Geoff

DecMotor.thumb.jpg.1432a5169ef28d8e34bbc4097d633911.jpgDecInput.thumb.jpg.00ad9ed8946c312a2dd9cdfa1ed05bb0.jpg

  • Like 1

Share this post


Link to post
Share on other sites

I have an EQ5 and Synscan, and have no issue doing a 2 star align, so at the risk of duplicating some other advice on here, here’s my 2p

1. Spend a bit of time getting your Home/Park position correct. You can do this indoors - you just need a small spirit level. I followed these instructions and got the 2axis marked up so I can always start off at the right point 

https://worcspaul.wordpress.com/2011/06/14/accurately-setting-the-“home”-or-“park”-position-on-a-skywatcher-eq5-pro-mount/

2. Download the Polar Scope Align app (it’s free) This will give you an accurate Lat/Long for your position, plus it will show you where Polaris should be, as you look through the polar scope.

3. Don’t forget the date format on the Synscan is mm/dd/yyyy

4. Make sure your mount is level before starting a polar align. Use a compass to make sure the leg marked N is pointing reasonably accurately north.

5. Make sure it’s actually Polaris you are aligning to - yes I know! Do your align at twilight when Polaris is not surrounded by neighbours, then come back later.

6. Use an app like StarMap 3D to identify your alignment stars, if your not absolutely sure. Use a medium powered eyepiece. No Barlow.

7. Choose 2 Star align and it will usually pick a really obvious first star - Arcturus at the moment. It should get close to it, but centre it using the handset, so it knows how far off it was.

8. Let it choose the second star and use StarMap to confirm it’s actually visible from your position. It will get pretty close, but will need another tweak with the hand set to centre.

9. Doing this, I’ve never had anything other than Alignment Successful come up.

Sorry if this all sounds a bit basic, but it’s normally the really obvious things that we forget to do 🙂

Hope this helps, and you get yourself sorted

 

 

 

 

Edited by Davehux

Share this post


Link to post
Share on other sites

If you now suspect the gearing is wrong, the 360 degree indoor test I suggested you do ages ago will test that theory........ 

If the mount returns to the same RA reading or thereabouts, then 360 degrees of movement in the motor's and gears has translated to the correct number of encoder ticks, so the gearing is correct. 

Michael 

Share this post


Link to post
Share on other sites
12 hours ago, Geoff_L said:

The following photos are of the DEC motor and DEC input shaft on my EQ5 Pro. As the first photo shows, the motor is fitted with two cogs, a large one and a small one. The larger of the cogs meshes with the pinion on the motor shaft and the smaller cog should mesh with the cog on the DEC input shaft (i.e. the cog shown in the second photo). It is possible to position the motor on its mounts so that the large cog on the motor meshes with the DEC input. As the large cog has approximately 1.5x the number of teeth of the smaller cog, meshing the wrong cog of the motor with the DEC input would make the DEC drive slew approx 1.5x the correct amount. HTH, Geoff

DecMotor.thumb.jpg.1432a5169ef28d8e34bbc4097d633911.jpgDecInput.thumb.jpg.00ad9ed8946c312a2dd9cdfa1ed05bb0.jpg

I really really really hope that's the case!!!!!!!!!!!!

It actually looks like the DEC motor is set up as should if I understood you correctly:

image.thumb.png.c8d3e3678f0f3441dbf4f13ddae67d8b.png

But the RA motors are set up like this:

image.thumb.png.f9415a9bb3f578832a3b50ecae8f2f89.png

Which seems like it's the error which you might have described?

Either way, one of the motors are not set up the same as the other, which would make sense to me that it's not supposed to be that way.

Can you please verify that so I can try switching that and maybe hopefully finally manage to get star alignment????????? :(

If that's actually the issue, man that would be so great to finally be able to experience the actual abilites of my goto.

 

4 hours ago, Davehux said:

I have an EQ5 and Synscan, and hav

e no issue doing a 2 star align, so at the risk of duplicating some other advice on here, here’s my 2p

1. Spend a bit of time getting your Home/Park position correct. You can do this indoors - you just need a small spirit level. I followed these instructions and got the 2axis marked up so I can always start off at the right point 

https://worcspaul.wordpress.com/2011/06/14/accurately-setting-the-“home”-or-“park”-position-on-a-skywatcher-eq5-pro-mount/

2. Download the Polar Scope Align app (it’s free) This will give you an accurate Lat/Long for your position, plus it will show you where Polaris should be, as you look through the polar scope.

3. Don’t forget the date format on the Synscan is mm/dd/yyyy

4. Make sure your mount is level before starting a polar align. Use a compass to make sure the leg marked N is pointing reasonably accurately north.

5. Make sure it’s actually Polaris you are aligning to - yes I know! Do your align at twilight when Polaris is not surrounded by neighbours, then come back later.

6. Use an app like StarMap 3D to identify your alignment stars, if your not absolutely sure. Use a medium powered eyepiece. No Barlow.

7. Choose 2 Star align and it will usually pick a really obvious first star - Arcturus at the moment. It should get close to it, but centre it using the handset, so it knows how far off it was.

8. Let it choose the second star and use StarMap to confirm it’s actually visible from your position. It will get pretty close, but will need another tweak with the hand set to centre.

9. Doing this, I’ve never had anything other than Alignment Successful come up.

Sorry if this all sounds a bit basic, but it’s normally the really obvious things that we forget to do 🙂

Hope this helps, and you get yourself sorted

 

 

 

 

Thanks, but I don't think a human error is the case here. Well, at least not an 'average' human error, as setting up the motors incorrectly is also a human error, at least not mine...

52 minutes ago, michael8554 said:

If you now suspect the gearing is wrong, the 360 degree indoor test I suggested you do ages ago will test that theory........ 

If the mount returns to the same RA reading or thereabouts, then 360 degrees of movement in the motor's and gears has translated to the correct number of encoder ticks, so the gearing is correct. 

Michael 

So it would make sense on the upper comments, when rotating the RA 360 degrees it doesn't seem to get to the same numbers, it would make sense according to the above discussion.

Really hope that this is actually the issue, thanks!

Share this post


Link to post
Share on other sites
8 minutes ago, michael8554 said:

Okay, so who put that gear on back to front.? 

Looks like Geoff_L gets the cigar! 

Michael 

Well, possibly the one I bought the telescope from, even though he told me that he once had an issue and went to the telescope shop to fix it...No idea if that actually worked for him, but it would make sense that this is the issue? (I'm currently working on fixing that).

Share this post


Link to post
Share on other sites
16 minutes ago, msacco said:

went to the telescope shop to fix it..

That's often like asking a car salesman to diagnose a fault on your car....... 

Only someone with intimate knowledge like Geoff would have spotted the wrong assembly, I wouldn't have. 

Michael 

Share this post


Link to post
Share on other sites
Just now, michael8554 said:

That's often like asking a car salesman to diagnose a fault on your car....... 

Only someone with intimate knowledge like Geoff would have spotted the wrong assembly, I wouldn't have. 

Michael 

Well I was actually about to go to the telescope shop on sunday, the guy there really has so much knowledge about telescopes, that I'm pretty sure that he would've been able to help me, but man if I'll actually manage to get it working on my own, I'd be so happy. (Even though a part of me wanted to go there for a small visit to see about possibly new far future telescope ^_^)

Share this post


Link to post
Share on other sites

Ok so I changed whatever was needed in the RA motors, aligned the mount roughly to north in my room, started 3 star alignment only roughly using stellarium, I'm pretty sure it was spot on! Of course, it's only roughly in my room, but it looked so correct according to stellarium.

I really think that was the issue! I'm so going to try it out tomorrow night.

So hopeful that it will work properly, I have my equipment for a year now, and I really almost gave up on trying to get it working...the first few months I just thought I must be doing something wrong, but then I watched so many videos, that I was so positive I'm doing everything correct, and it still didn't work and it was so frustrating.

I don't want to hail for nothing, as until it doesn't work, I can't really know that, but I'm really much more positive now and I really believe that was the issue.

Thank you so so much, and also thanks for everyone who tried to help me! It's really not obvious.

Edited by msacco
  • Like 1

Share this post


Link to post
Share on other sites

Really glad you seem to have it sussed, well done Geoff_L.  Many of us have had our own battles with our Goto's.  Most of us solve them when SGL point out common errors made with software use or in my case I know it was a weight issue.  Having a motor incorrectly put together isn't something I think most of us would suspect as it shouldn't really happen with good QC during construction.  It's excellent that you have actually been able to re-assemble everything correctly as even that looks a tricky thing to do from the photos - I don't think I would have wanted to dismantle something to that degree.  Well done both Geoff_L and yourself for persisting.

Share this post


Link to post
Share on other sites
12 hours ago, michael8554 said:

Okay, so who put that gear on back to front.? 

Looks like Geoff_L gets the cigar! 

Michael 

I suspect that it's not on back to front as there's enough room on the input shaft to slide the gear up to mesh with the smaller cog. However, the RA might be meant to be like the OP's is. I can't say as I've never removed the cover of the RA drive on my EQ5 Pro and can't check right now as I won't have access to my mount for a day or two. That said, it should be fairly easy to slacken the grub screws on the input shaft cog and slide it up to mesh with the smaller gear, adjust the motor position so that they mesh correctly and then try another 'dry alignment' to see whether that's done the trick. If not, it should only take a few minutes to restore the mount to its current configuration.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.