Struggling with my guiding on CEM60

[Douglas Rollain]

I have been struggling with PHD guiding on my one mount iOptron CEM60 with an AT130 on it for months now

I have tried balancing, and rebalancing,  and balancing east heavy. I have tried guiding assistant, calibration numerous times.

It seems like I can not get consistent guiding.  some 5 min subs look good,  others the stars are eggy, trailing stars, or stars with tails. It can go 3, 2 or 10 images without issues, or I can get 10 images in a row that I have to toss out.  

I thought that I had it resolved on July 3rd, after I did another polar alignment, tightened the DEC  belt a little, balanced slightly east heavy,  and created a new PHD profile.  I pulled a 20 min, 10 min, and 5 min test sub all with round stars.  I figured that I was good,  as I usually do 5 min subs on this system. 

The next day, and days to follow, I struggled to get consistent images that I could keep.  

 

I have tried Hysteresis, Predictive PEC, Resist Switch,  etc.  I have tried mirroring my other 2 CEM60 PHD configurations with no luck.  Belts and gears are in great condition,  and there are no odd sounds when the mount slews.  

I am at my wits end with this rig.

tonight I can whack the profile again and start from scratch and provide a log if that would help.

Here are some logs from a couple different days.  Any recommendations are greatly appreciated.

https://openphdguiding.org/logs/dl/PHD2_logs_5neW.zip

Regards,

Doug

[Bruce Waddington]

The problem I see is that you're getting rapid, large tracking errors in RA when pointing 3-4 hours west of the meridian.  These aren't caused by guiding, they are simply happening.  Many of the logs you sent are of no use because you were running with a zero value for focal length.  But there are several logs - 6/28, 6/29, and 7/7 where the necessary information is present.  All three show the same approximate behavior but I will illustrate with data from the 7/07 log.  This shows a sequence of guiding sessions on the same target at Dec = 60, so we're really looking at the mount as it tracks to the west.  RA is shown in red.

Tracking approximately 4.7 hours west of the meridian:

Approximately 3.7 hours west of the meridian:

Approximately 3.2 hours west of the meridian:

Approximately 2.0 hours west of the meridian:

You can that by the time you are pointing only 2 hours west of the meridian, RA tracking is very good and the sharp spikes are gone - be sure to look at the y-axis scale to see this.  

All of your calibrations show the "clumping" of data points that can be a sign of static resistance on the axis (e.g. over-tightening or over-meshing):

You can see the data points are "paired" on both axes, meaning the mount didn't move far enough with the first guide pulse, then over-shot with the second one.  The same behavior is seen during the guiding sessions whereby multiple guide corrections are required to get a response from the mount and then it is prone to over-shooting.

I can't really tell you what to do with the mount to fix this, perhaps you can get advice from iOptron or other iOptron mount experts.

Good luck,

Bruce

[Brian Valente]

Hi Doug

Boy, that is a lot of variables and a lot of data.  It'll take some time to look at the logs and see what to make of it

In the meantime, i suggest you 

1. download install and use the latest dev release
https://openphdguiding.org/development-snapshots/ 

2. follow the attached steps to do a baseline guidelog. Let the unguided run for at least 30 minutes so we can see what the mount is doing. I would also recommend doing a second guiding assistant run on opposite side of pier near the celestial equator (the easiest way to do this is rerun the guiding assistant but choose pier side east insead of west, and then move on to the guiding assistant run). send just the logs from this session.

3. send a few pictures of your setup from a couple different angles. It should show the complete setup from mount to the top of the scope, and make sure to include details of your guiding setup

I can see from your calibration runs they are consistent and show uneven spacing of the guide pulses in both RA and Dec. I'm not sure why that's the case yet. 

Brian

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Brian Valente

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[Brian Valente]

>>> Many of the logs you sent are of no use because you were running with a zero value for focal length.  

Bruce thanks for mentioning the incorrect focal length setting. I was going to point that out

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[Douglas Rollain]

Bruce,

This is great information, and will check my meshing one last time before I take this information to iOptron for their take on it. 

Regards,

Doug