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Author Topic: Autoguiding issue  (Read 1474 times)

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Offline Anne S

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Autoguiding issue
« on: 11:30:38, 15 February, 2016 »
Can anyone tell me what is causing the issue in the picture below please? I've been trying to solve it for several months. Mount, Mount Hub Pro, EQmod cable and bench power supply have been checked or changed. No difference.
I'm guiding with an Altair miniguider 60mm, DSI pro or INova PLBC2 using pulseguide through EQmod. Mount is a belt drive converted EQ6.

I've a Wave 102mm refractor doing the imaging, so the mount is not particularly heavy and I've balanced very carefully.

The drift in the picture is a sudden move.

Laptop is the only constant apart from guidescope mounting. It's a dual core running XP with 1 meg of ram. Could this be it?

I have also tried tidying the cables but as the MHP is currently being repaired as the laptop won't recognise it as a HID device even the cables have been moved around!
Altair Wave 102, EQ6
Altair Starwave EDT70mm, Ioptron IEQ30pro
SX H694, Superstar guider
Atik 320e colour
Altair Hypercam 178M, Altair Gpcam
Altair Astro Ritchey Chretien 6 inch

Offline Roger B

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Re: Autoguiding issue
« Reply #1 on: 11:59:15, 15 February, 2016 »
and I've balanced very carefully.



Anne  if the scope is too well balanced you could get movement like this as the gears are not perfect a perfectly balanced scope could move in the grearing,  it's always advisable to have nose heavy very slightly so the gears are lifting the kit.    Try off setting the balance very slightly and try again

Roger
Scopes - TS65q, W/O 110 Triplet
Mount - EQ6 PRO via  Eqmod,  Rowan belt modded
Cameras - SX694, QSI583WSG,Lodestar Guidecam, GP-Cam, QHY5II.
TS 9mm OAG
Quantum 7x1.25 EFW, Baader LRGB,Ha,OIII,SII Filters 
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Offline chris.bailey

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Re: Autoguiding issue
« Reply #2 on: 12:04:07, 15 February, 2016 »
Looks like play in the Right Ascension axis of the mount to me. A few possible sources -

Worm and ring gear need slightly tighter meshing. There are two small grubscrews on the EQ6 and getting it right is a pain. First you have to loosed all the main bolts and then loosen one grub screw and tighten the other. We are talking 1/16th to 1/8th of a turn and if you go too far the axis will bind at some point in the slew from one side to the other.

Are you too well balanced? Adjusting the meshing is a bit of a compromise and there will be some small residual play. If very well balanced the axis can rock back and forth so being slightly east and nose heavy can help keep the gears meshed.

Do you know if the end-float bearings were changed as part of the belt mod? On mine one of the original bearings had so much play it was untrue. Changing them to half decent SK bearings was cheap but does involve a dismantle. I did mine with the belt mod.

Check the saddle is fully tight at the top of the mount. There are 3 large grub screws to secure it. They do come loose!

Clutch slip. Its very easy to get some grease onto the mating surfaces of the clutch. If you can move things with the clutches tightened then you can get movement in imaging runs.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
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Offline Einari

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Re: Autoguiding issue
« Reply #3 on: 12:19:38, 15 February, 2016 »
There was just recently a thread with about same symptoms.
Chris gives good advice (and Roger too).
Just like to add (as I did in the other thread) that it could be DEC backlash and the cure could be to use either just North or South guiding - if you are using PHD.
Tapio

Celestron C8, C9.25" & Hyperstar, iOptron CEM60-EC, TS 80 triplet,  Coronado PST, SXV-694,  ASI120MM/ASI174MC Cool

Offline tomhow

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Re: Autoguiding issue
« Reply #4 on: 13:27:13, 15 February, 2016 »
definately RA related... does it keep repeating the jiggle? Or just do it once or twice at random?

What happens if you image without autoguiding?

I'm not familiar with the mount and software - but does it have any form of periodic error correction? does turning this off, or reset/clearing it, make any difference?
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline darkstar3d

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Re: Autoguiding issue
« Reply #5 on: 14:34:58, 15 February, 2016 »
I've seen something very similar with power. When my old dew heater would pulse (send power to the strips) I'd see this type of issue when the stars were double. The pulse took power, guiding put it back on, leaving two hot spots of the star and a line in between. Like little dumbbells.

Offline Anne S

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Re: Autoguiding issue
« Reply #6 on: 15:48:49, 15 February, 2016 »
Thanks for all your suggestions, particularly the dew heater one - I have an extension lead coming in from a mains socket which I run all the power requirements. It's never done it in the past - only started this autumn. My power set up is different at the moment as my mount hub pro would not connect to the laptop so it's off being repaired at present and I'm using an extra string of sockets. I wondered if the MHP was doing something. I've also moved my eqmod usb lead so it goes direct to a laptop port. I can't figure out why it suddenly started when I've used the MHP dew heater for years and I've only one heater running. In the meantime I'm using a spare Kendrick controller and it's still doing it!

As to the mount, that was my first thought but I got Graham Holmes, who did the belt drive mod, to have another look at it and he had it on his rig doing 10 minute subs, so that can't be it. He couldn't see anything wrong with it. I only had it modded in April. Graham also said I should get the balance as good as possible as there's less backlash now. I can certainly try nose heavy tonight and see if it's better.

As to repeating the jiggle, it appears to jump around 6 minutes intervals, haven't timed it exactly, as I got a couple of 150 sec exposures before the next 2 trailed. I haven't got pec enabled as I can't get it to guide long enough without losing the guide star! If I image without guiding, it trails after around 1 minute.

I'll go out now and check everything's tight. Thank you for all your help.
Altair Wave 102, EQ6
Altair Starwave EDT70mm, Ioptron IEQ30pro
SX H694, Superstar guider
Atik 320e colour
Altair Hypercam 178M, Altair Gpcam
Altair Astro Ritchey Chretien 6 inch

Offline tomhow

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Re: Autoguiding issue
« Reply #7 on: 17:22:38, 15 February, 2016 »
any idea which way it jumps? Does it just jump once, or just it jump "back" to where it started?

6 minutes... I think the worm period on an EQ6 is 8 minutes. If it is exactly 8 minutes (give or take a few seconds) then that points to the mount or the electronics / software running it.

It is quite a big jump.. over an arc minute.... that's enough to feel. A daylight test might be to run the mount (as if you are imaging, but with no guiding, obviously) and rest a finger on the belt. Sit there for 10 minutes and see if you feel a bump. And/Or run at a faster speed (i.e. moving the scope to centre a target) and see if you feel any bumps.

This is why I asked what happens if you image without autoguiding. That "jerk" is a different character to normal unguided tracking errors. At as it is over an arc minute long, it should be bigger than the EQ6 PE.

So does it "jerk" when running without autoguiding, or does it only do it when autoguiding?
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

Offline Anne S

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Re: Autoguiding issue
« Reply #8 on: 17:42:44, 15 February, 2016 »
It always jumps in the same direction. Once it's done it phd2 loses the star so I reselect it and start guiding again. I was pointed just to the west of south at M42. In phd's window it was moving north but I've no idea whether that's the tracking direction or not!

I've checked the clutches etc and there was some movement on the ra axis. I've now tightened the knob a little more and there's less. I wonder if Graham had this axis tighter when he was testing it. I'm always worried about over tightening it.

I'll have another go tonight, it looks as if it'll be clear enough to check guiding. If it still jumps I'll turn the dew heater off. I don't want to change too much at once.

I was going to try st4 guiding to see if that improves things too.
Altair Wave 102, EQ6
Altair Starwave EDT70mm, Ioptron IEQ30pro
SX H694, Superstar guider
Atik 320e colour
Altair Hypercam 178M, Altair Gpcam
Altair Astro Ritchey Chretien 6 inch

Offline mechanoid

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Re: Autoguiding issue
« Reply #9 on: 20:55:26, 15 February, 2016 »
I don't own one of these mounts, but does the worm wheel use a grub screw tightening against on a single flat to fix it on the worm shaft ? In my opinion this is a poor way to attach a gear. It's how its done on my Vixen GPDX mount!  I've had numerous occasions when its worked loose and caused just that end result. Worth a check with an Allen key maybe ?

Dave
Skywatcher Quattro 200mm C/F, Vixen GPDX, QHY10
Skywatcher ST80, QHY5II, PHD2
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Offline Anne S

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Re: Autoguiding issue
« Reply #10 on: 21:29:21, 15 February, 2016 »
I've no idea what happens inside my EQ6. I only got it back in December after Graham tested to see if there was a problem with the belt drive mod. There was a slight delay in clear skies! He had it running for 10 minute subs with no problem. It has to be something that I'm doing to it.

I tightened the ra axis clutch earlier and was hoping to test it out but we've got high level clouds coming in and I can't see any stars well enough to test it. That's Wales for you!

28 Feb managed to test my guiding, the problem is solved. Tightening the Ra clutch stopped the jumping.
Altair Wave 102, EQ6
Altair Starwave EDT70mm, Ioptron IEQ30pro
SX H694, Superstar guider
Atik 320e colour
Altair Hypercam 178M, Altair Gpcam
Altair Astro Ritchey Chretien 6 inch

Offline Annie

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Re: Autoguiding issue
« Reply #11 on: 22:07:19, 15 February, 2016 »
Ironically we've got low cloud coming in here in mid-Wales!

Annie
Pulsar Observatory; NEQ6/EQ6 wedge; HEQ5 Pro; TS Star 71 Astrograph; Takahashi FSQ 106ed; Skymax 150 Pro; Nikon D600; Canon 550D modified; Canon 5D Mk11; ZWO ASI120 MM-S; Lacerta MGEN stand alone guider.

 

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