RA Graph Showing a large peak every 10 Minutes - Using ZEQ25 GT Mount

[Dilip Sharan]

Hi, 

I am new to guiding and I am getting a large peak of 12 arc-secs about every 10 minutes which also so up in the images being captured at the same time as the peak occurs. I am trying to understand what it causing this. Is it a flaw in the gear? If so will PEC recording/ playback help remove this flaw?

I attach a jpeg with the RA Graph and also the associated logs. 

In the graph large peaks show at 20:06 PM, 20:16 PM, 20:26 PM, 20:36 PM and 20:46 PM. I was imaging M45 (Pleiades) which was in the South-East and doing 3 minute exposures. 

Equipment: 

1) Imaging Camera - QHY 5L-II Color

2) Imaging scope - - Adapted 9 x 50 SkyWatcher Finder scope

3) Mount: iOptron ZEq25

4) Connection - Uses the ST4 port on the mount   

Regards,

Dilip Sharan

[bw_msgboard]

Hi Dilip.  I’m sorry you’ve encountered this problem just as you were getting started with guiding.  Bad luck. L  Because the problem is so periodic, it’s most likely a problem in the mount.  I doubt that periodic error correction will be able to deal with this sort of error because it’s an impulse type of error, not a smooth variation in guide speeds.  If you look at the graph, you can see there are two components to each deflection, one to the west, followed by one to the east.  The first looks like the mechanical problem while the second is probably a consequence of PHD2 trying to correct for the initial event.  This doesn’t look like binding in the drive train because the directions seem reversed – the initial problem sees the mount tracking too quickly.  But I don’t know anything about your mount, including whether it uses gears or belts.

 

Since the initial problem appears to be caused by something in the mount, I’d suggest doing a test to confirm that, something you can use to get help from iOptron.  You can just run the PHD2 Guiding Assistant for about 20-30 minutes, long enough to get 2-3 of the big deflections.  Guiding will be disabled during this time, so there won’t be any confusion about that.  If you wanted to be completely rigorous about it, you could also disconnect the ST-4 guide cable at the mount end once the GA run starts.  All of the tracking data will still accumulate in the PHD2 log file, so you’ll have a clear picture of how the RA drive is behaving (or mis-behaving).

 

Good luck – let us know what you find out.

 

Bruce

 

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[Dilip Sharan]

Hi Bruce,

Thank you for your response. I will run the PHD Guiding Assistant to collect more data. 

I have one question. Can I run using the "Camera V2 Simulator". I'd still hook up to the mount but feed it simulated camera data. The reason I ask is because we have very cloudy conditions where we are in the UK and are not likely to have a clear night for some time. 

Also to mention some additional information. I had a look at the ZEQ25 manual. It uses a a work gear drive and it takes the worm gear 600 seconds [10 minutes] to make one complete revolution. So I'm assuming the error is occurs once every revolution of the worm gear. 

Regards,

Dilip Sharan

[bw_msgboard]

Hi Dilip.  Sorry, the simulator functions in PHD2 aren’t useful for dealing with any real-world gear problems.  So I’m afraid you’ll have to wait for some partial clearing. L  It seems pretty likely that the problem is tied to the worm period of the mount, as you say.  I’ve seen quite a number of logs from iOptron mounts but I’ve never seen anything quite like this.  IMO, 10 arc-sec impulse errors should not be present.  Even if they could be reduced to some extent with a periodic error correction, they really shouldn’t be there in the first place – better to find the underlying cause and eliminate it.

 

Good luck,

[peter wolsley]

Dilip,

I took a look at the guiding log you provided and created the attached graph.  I used the PHD2 pulse guiding commands to create a culmulative RA guiding movement trace which attempts to represent what your mount's RA axis was being told by PHD2 to do in response to the RA spikes.  I believe it roughly represents what your mount's PE curve looks like.  You can clearly see why Bruce says that it looks like an impulse type of waveform. I also don't know anything about your mount.  Training your mount's PEC is definitely worth pursuing.  You should take the time now to read up on how to do this.  Your mount's PE appears to be very large and it will require very good PEC logic and training to compensate for it.

Peter