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Old 21-03-2014, 10:13 PM
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pvelez (Pete)
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PMX - dodgy firmware??

I posted a few days back on the Software Bisque forum about constant drift in RA I had encountered on my PMX. I reseated the worm, adjusted the cam stop, collected data for a PEC and a 300 point TPoint model. All of this with Protrack made a big difference.


But...



After 3 days of rain, I decided to refine my guiding settings. I found that Protrack threw the tracking out. So I did a plate solve and found that my TPoint model had drifted by over 1 degree over the last 3 days. Rehoming the mount made no difference to this (though Protrack seemed to sort itself out after this).

I rebooted my pc and found that TSX had decided to dump my carefully compiled TPoint model! I'm doing another as I type.

So my question is this - is it possible that I have some dodgy firmware in the mount or a corrupt version of TSX? Because the drift in the TPoint model over 3 days by 1 degree equates to (very) roughly 0.6 arc seconds per minute. Which is not that dissimilar to what I am seeing with my RA drift.

Could these be connected?

Is there a way to check this?

I am quite happy now that almost all mechanical issues have been eliminated - the next step is to swap over the Dec and RA worm. But if its software or firmware related, that might be an easier fix.

Anyone seen this before?

Pete
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Old 22-03-2014, 11:11 AM
ericwbenson (Eric)
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Hi Pete,
Bit of a long shot...but could the clock on the PC be drifting (induced perhaps by the TSX)? Also out of curiosity, how are you keeping the clock synchronized, Dimension4 or NTPD or windows time service?
EB
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Old 22-03-2014, 11:46 AM
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EB

clock in PC is ok - had that issue with an older PC but this one looks fine

using windows time service

Pete
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Old 22-03-2014, 11:57 AM
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And have you asked TSX to use the computer clock?
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Old 22-03-2014, 12:45 PM
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And have you asked TSX to use the computer clock?
Yes

I'm satisfied it's not the clock. If it was, the mount would have been out by 15 degrees after 3 days not 1 degree

Pete
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Old 22-03-2014, 02:16 PM
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Yes, i have seen something similiar. I had a model disappear into thin air, then the pointing would continually be eratic. What i did was download the latest daily build. I deleted my previous sync history and redid my sync and then i redid the model after ensuring the time was at 0 to the naval observatory. You could try that. It worked for me.
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Old 22-03-2014, 02:44 PM
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Is it 0.01as/second (0.6as/minute, 36as/hour, 864as/day) all over the entire sky? Can you turn ProTrack OFF, point to a few strategic positions and measure it? Such as North, South, East, West, Zenith, etc?

The drift amount you have measured is very interesting. There are 86,400 seconds in a solar day. This makes it look like maybe an Axis->Track Rate parameter setting problem. I can see why you might think it's a firmware problem too. Perhaps you might set all parameters to their default values and do a save to mount. Then don't forget to reset the ones you need to change, such as Southern Hemisphere, limits, etc.

How about using a cross-hair eyepiece during the day and pointing the scope at something in the distance with the mount turned off. See any small consistent movement over time? (Ground settling, flexure, etc.)

Last edited by frolinmod; 23-03-2014 at 12:28 PM.
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Old 22-03-2014, 02:57 PM
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Thanks for all the tips.

Paul, I plan to take another TPoint model tonight (weather remitting of course) and then see how it goes on successive nights. A new daily build was released last night so I'll try that too.

It was very off. PEC and Protrack were both off - for example, PEC was out of phase making images much worse. I rehomed and that seemed to fix the phase.

The drift in RA is constant irrespective of the direction I am pointing.

I can't do anything visually during the day - its up at Coona. I have however switched over the RA and Dec worm assemblies. If that fixes it, the problem is with the worm. If it doesn't, it may be firmware, corrupt T Point model, dicky TSX install etc etc.

Will let you know how it goes

Pete
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Old 23-03-2014, 05:15 AM
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Pete,

It does not make sense to say the drift is consistent with any pointing direction. You may see drift wherever you point but I would put $ on the fact that it cannot be the same amount of drift. Think of it this way. If you were pointing directly at a star on the pole you would measure no drift no matter what speed you turned in RA. But, as you moved away from the pole you would start to see drift that changes as the cosine of the declination. At DEC=0 you would observe maximum drift. This is precisely why PEC measurements are done at DEC=0. Some software, like PEMpro by default - can be turned off - will compensate for this by increasing the measured movement as you get closer to the pole. I don't know for sure if TSX does this in the guiding software. Anybody know for sure?

Anyway, I hope your exercise in changing the worm shows something but I think it won't (sorry). I also asked on SB site: Did you put in the correct Lat Lon and elevation for Coona. Could you possibly have left Sydney settings?

Peter

Last edited by PRejto; 23-03-2014 at 09:05 AM.
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Old 23-03-2014, 07:48 AM
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I am not sure how you are mounted but if you have a pier that is on concrete set into the ground then rain can cause the soil to change and the pier to move a bit.

So your polar alignment may now be off.

You can save your t-point models. That way you can reload it if it disappears again.

Something to check.

Also if you changed the configuration of your scope/imaging train the flex may be different and t-point will need to either be redone or resynched. I was finding mine was off after putting a different camera on the scope. I would resynch it would be fine for the night then next use back to square one and I had to resync. I saved the synced T-point model and I load that once TSX is booted up and its all good.

Greg.
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Old 23-03-2014, 08:59 AM
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Quote:
Originally Posted by pvelez View Post
EB

clock in PC is ok - had that issue with an older PC but this one looks fine

using windows time service

Pete
It still sounds like a time base problem to me. Windows time service is actually not that good.

GPS time is decidedly more accurate. NMEAtime is an excellent solution.
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Old 23-03-2014, 12:30 PM
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Personally I think the Windows port of NTP is better. Either way, be sure to disable the regular Windows Time service whenever using something better.
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Old 23-03-2014, 01:32 PM
ericwbenson (Eric)
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HI Pete,
Here is an idea to maybe isolate the problem to either software or mount electronics/mecahnicals as the culprit.
Firstly keep everything as simple as possible as you have done previously, turn off PEC and Protack and have no model loaded, nothing just stock out of the box setup, just good polar alignment (you are sure this is the case right!?!)
-With tracking on, center a star on the CCD about an hour or two from the meridian. Take a short unguided picture (10 sec?), with something else than TSX would be good because of part two below. While leaving tracking on, disconnect the TSX from the mount, and close down the app completely.
-At some time later, before going into the flip zone and long enough for you to be sure you could detect drift, take another picture. Note the amount of drift.
-Now repeat the whole thing, but with TSX connected the whole time, start with a new star that is in the same position of the sky as the first one was when you started, so from a mechanical flex point it's the same.
You essentially need two stars at about 7th mag at the same declination about 1-2 hours apart in RA.

There will be drift over the hour from tube flex, mount flex, imaging train flex, mount gear/electronics "badness" etc. But the *difference* in the amount of drift between the two runs must be due to software/PC clock/OS clock interaction. No difference between the two runs means the problem is in the mount.

Good luck,
EB
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Old 23-03-2014, 05:23 PM
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Thanks to everyone who has responded. I won't say I was tearing my hair out - just cursing quietly at the computer.

The rig is up at Coona and I'm doing this remotely - thankfully with some excellent support from the hosts at iTelescope.

Without wanting to jinx things, I am well ahead of where I was. Last night I was able to take a 120 second exposure in the "nasty" area of the sky with minimal elongation or drift. Tracking the main imaging camera with guiding switched off, I managed rms of about 1.5 in RA over 3 minutes. Much better than before.

More importantly, I've refined my guiding so I can take a decent image now.

So what did I do differently?

There were 3 elements to this:

1. I swapped the RA and Dec worm assemblies. There was nothing apparent when looking at the worm. Perhaps it was the way the worm was seated after switching them.

2. I dumped the old TPoint model and took a 179 point model. I had RMS across the sky of about 8 arc seconds with Supermodel turned on

3, I refined the guiding parameters - more on that in a moment.

With 1 and 2 I took a 10 cycle PEC with Pempro. Switching that and Protrack on - I could image comfortably to 60 seconds and even 120 seconds looked ok-ish. I did see some residual drift in RA - but its much better than it was. I tested this in both the West (previously bad) and East (previously better) at Dec 0 where the drift would be most noticeable.

As Peter R has warned me on the SB forum, its harder to pin down whether it was 1, 2 or both that changed things for me. But at the moment I don't mind. The test will be this evening when I will check pointing again - if it is out (as was last time I held a TPoint model over more than 1 evening), I will know that something funny is still going on.

The PEC is better but I will need to fiddle with it some more.

I have a suspicion that I had 2 overlapping issues. There was drift in RA - which reseating the worm addressed. Its not perfect but its better.

The shift in the TPoint model may just have been a corrupt model. No idea how that happens but Paul H had something similar recently.

I've posted the TPoint observations on the SB site - will be interesting to see what Mr Wallace has to say. He might tell me that it is something else entirely.

Guiding - this was interesting. I found that when I tried to guide out the RA drift, I was not able to bring it into a relatively steady state. The RA drift would resume after each guide pulse and if it was say 2 pixels out, the guide pulse would only bring it back by 0.5 - 1 pixel before it resumed its upward trajectory.

The answer was in the aggressiveness and the maximum guide pulses. I use CCDAP for automation. The author John Smith is quite particular about guide settings - he argues for smaller guide pulses to avoid chasing the seeing. There is a tool in CCDAP that recommends the minimum and maximum guide pulse. My maximum pulse was set to 0.22 seconds. When I upped this to 0.52, the guider became much more responsive. I was able to drop the aggressiveness from 10 down to about 5 or 6. This is with 5 second subs. Dropping them back to 2 seconds, I could drop the aggressiveness further to about 3.

Combining all 3, I could happily take a 300 second image with guiding on. Here is a screenshot of the centre of the image - not perfect but pretty good I think.

Now watch the clouds roll in!

Stay tuned - there may (doubtless will) be more grief ahead!

Pete
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Old 23-03-2014, 05:24 PM
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pvelez (Pete)
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Quote:
Originally Posted by PRejto View Post
Pete,

It does not make sense to say the drift is consistent with any pointing direction. You may see drift wherever you point but I would put $ on the fact that it cannot be the same amount of drift. Think of it this way. If you were pointing directly at a star on the pole you would measure no drift no matter what speed you turned in RA. But, as you moved away from the pole you would start to see drift that changes as the cosine of the declination. At DEC=0 you would observe maximum drift. This is precisely why PEC measurements are done at DEC=0. Some software, like PEMpro by default - can be turned off - will compensate for this by increasing the measured movement as you get closer to the pole. I don't know for sure if TSX does this in the guiding software. Anybody know for sure?

Anyway, I hope your exercise in changing the worm shows something but I think it won't (sorry). I also asked on SB site: Did you put in the correct Lat Lon and elevation for Coona. Could you possibly have left Sydney settings?

Peter
Thanks Peter

latitude and longitude are right - same as the ANU guys next door.

You are right about the drift being different. It is an interesting diagnostic suggestion though - if the drift is the same near the pole, its the optics not the mount. Might need to test that if things go haywire again

Pete
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Old 23-03-2014, 05:26 PM
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Quote:
Originally Posted by gregbradley View Post
I am not sure how you are mounted but if you have a pier that is on concrete set into the ground then rain can cause the soil to change and the pier to move a bit.

So your polar alignment may now be off.

You can save your t-point models. That way you can reload it if it disappears again.

Something to check.

Also if you changed the configuration of your scope/imaging train the flex may be different and t-point will need to either be redone or resynched. I was finding mine was off after putting a different camera on the scope. I would resynch it would be fine for the night then next use back to square one and I had to resync. I saved the synced T-point model and I load that once TSX is booted up and its all good.

Greg.
Good suggestions Greg

The mount is in the iTelescope shed. There is some serious concrete under this mount. I don't think there is any flex there.

The new T Point should be the goods - if its not, it will be interesting to see the pointing error.

Pete
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Old 23-03-2014, 05:28 PM
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pvelez (Pete)
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It still sounds like a time base problem to me. Windows time service is actually not that good.

GPS time is decidedly more accurate. NMEAtime is an excellent solution.
Thanks Peter

I am familiar with timing issues. I had an old FitPC2 with a battery that was giving out. On the old FitPCs you can only change the battery by opening the case and soldering a new one in place. Needless to say I have yet to attempt that and replaced the FitPC.

With the old one, the clock would gain about 18 seconds each minute. Even a time service that polled the pc every minute couldn't cope with the drift in RA.

I'll look into your suggestion anyway

Pete
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Old 23-03-2014, 05:29 PM
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Quote:
Originally Posted by ericwbenson View Post
HI Pete,
Here is an idea to maybe isolate the problem to either software or mount electronics/mecahnicals as the culprit.
Firstly keep everything as simple as possible as you have done previously, turn off PEC and Protack and have no model loaded, nothing just stock out of the box setup, just good polar alignment (you are sure this is the case right!?!)
-With tracking on, center a star on the CCD about an hour or two from the meridian. Take a short unguided picture (10 sec?), with something else than TSX would be good because of part two below. While leaving tracking on, disconnect the TSX from the mount, and close down the app completely.
-At some time later, before going into the flip zone and long enough for you to be sure you could detect drift, take another picture. Note the amount of drift.
-Now repeat the whole thing, but with TSX connected the whole time, start with a new star that is in the same position of the sky as the first one was when you started, so from a mechanical flex point it's the same.
You essentially need two stars at about 7th mag at the same declination about 1-2 hours apart in RA.

There will be drift over the hour from tube flex, mount flex, imaging train flex, mount gear/electronics "badness" etc. But the *difference* in the amount of drift between the two runs must be due to software/PC clock/OS clock interaction. No difference between the two runs means the problem is in the mount.

Good luck,
EB
Thanks for the suggestion Eric.

I was thinking last night whether I could take TSX out of the equation which is not that far from your idea.

Its a bit tricky for me as I'm 6 hours drive away. I may give this a go if I continue to have issues.

Pete
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