CEM70 not performing in RA - suspect mechnical issue please help
Sebastiano Romano
- Mount well balanced (3d axis)
- No cables drag since I use CEM 70 cable management
- Calibration and guide assistance done
- New profile created when I have setup the built-in guide scope in the CEM70, which I am using for guiding
- Gear is mounted quite solid in a fixed pier (no tripod) and PA doesn't change when mount rotates...tested with iPolar)
- Guided with RA hysteresis mode since seems getting better results then using PPEC mode
- DEC backlash quite high by PHD2 seems managing it (my concern right now is on the RA)
Bruce Waddington
Sebastiano Romano
bw_m...@earthlink.net
Ok, I hope you can get it sorted out. Over the past year, I’ve seen a growing number of situations where people have gotten knowledgeable and specific help from iOptron, so I think it would be worth asking about. They are by now accustomed to seeing these kinds of analyses.
Bruce
From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> On Behalf Of Sebastiano Romano
Sent: Tuesday, March 7, 2023 8:57 AM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Re: CEM70 not performing in RA - suspect mechnical issue please help
Thank you Bruce for the detailed analysis and explanation. I will run a few more testing at DEC 0 on both sides of the pier as you have suggested. I will also check the gear mesh on RA and DEC (I have iOptron instruction on how to adjust). Perhaps that will solve part of the problems. I will do some visual inspection of the belt tensions (both RA nd DEC) and if any loose screw in the worm gear assemblies (but for this a further disassembly may be required which I may need to think twice).
I will provide outcome once I have (weather permitting) the opportunity to run another night session.
All the best,
Seba
On Sunday, March 5, 2023 at 4:40:16 AM UTC+1 bw_m...@earthlink.net wrote:
It's a bit hard to see what's going on because you've done so many short guiding sessions and you didn't run them anywhere near Dec = 0. By guiding at Dec=47, the results are understating the RA tracking errors by over 30%. It also looks like you were working in fairly poor seeing conditions, especially in the beginning. I'm basing the following comments only on the longer guiding sessions you had in the March 1 logs. It does look like you have some unusual higher-frequency tracking errors in RA:
These large peaks occur at intervals of approximately 116 seconds, 171 seconds, and 344 seconds. Those are likely to come from three different components of the RA drive system - iOptron will probably know what they are. There's also some stiction in the Dec axis as seen here:
The stiction is characterized by the delayed response to the initial guide commands after a change in direction, followed by the immediate large over-shoot.
None of these things are being caused by guiding. Stiction can be caused by an overly tight gear mesh in Dec and the RA tracking errors may come from a similar mis-adjustment in the RA mesh.
If you want to get a more accurate measure of the mount's performance, you should run extended guiding sessions on both sides of the pier close to Dec = 0, the same sky area where you do calibrations. After doing a fresh calibration without getting a calibration alert, I would let the guide sessions run for at least 30 minutes each. You should temporarily disable PHD2 Dec backlash compensation for the tests. Then run an extended Guiding Assistant session of 15 minutes to get a clear view of the native RA tracking. With this data, it will probably be easier to communicate with iOptron and get some help.
On another topic, I will be surprised if the built-in guider on the mount will serve you very well. It results in a very coarse guider image scale (6.45 arc-sec/px) and is subject to differential flexure. You haven't said what you're using for the main telescope/imager, but unless it's a short focal length setup, you will probably want to move to a better guiding solution. But none of that is causing the problems mentioned above.
Good luck,
Bruce
On Friday, March 3, 2023 at 10:00:31 PM UTC-8 sebastian...@gmail.com wrote:
Hi Team,
I have purchased a CEM70 (used) reported to be excellent performant. But it is quite disappointing (my EQ6R was doing way better and I am already regretting to have it sold).
Issue: the RA seems not tracking well and most of the time with an RMS higher than DEC.
I have put the link of my debug files (2 nights). Both have data of GA and the second one includes also calibration (done in position where celestial equator and meridian meet)
What I have done:
- Mount well balanced (3d axis)
- No cables drag since I use CEM 70 cable management
- Calibration and guide assistance done
- New profile created when I have setup the built-in guide scope in the CEM70, which I am using for guiding
- Gear is mounted quite solid in a fixed pier (no tripod) and PA doesn't change when mount rotates...tested with iPolar)
- Guided with RA hysteresis mode since seems getting better results then using PPEC mode
- DEC backlash quite high by PHD2 seems managing it (my concern right now is on the RA)
By reading some post on CEM70 i suspect some mechanical issue (RA bearing , worm gear??) but hopefully nothing like that if you can diagnostic for me the debug files and point to the right direction where to look it will be very much appreciated.
Thank you in advance!
Seba
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