Thanks again Alfred for your advice, although I don't understand the shipping costs. I understand that you have ordered the bearings from McMasters because they are cheaper??. I would like to know how much the total cost is since I was thinking of ordering a pair for my AR shaft.
I am also waiting for you to inform us of the improvements in tracking and guiding when you change the bearings and of course advise us to make that change.

Juanjo: I understand that you have ordered the bearings from McMasters because they are cheaper??

It's the other way round, I ordered from Boca Bearings since shipping costs are much lower and the bearings are a bit cheaper, too.

Juanjo: I would like to know how much the total cost is since I was thinking of ordering a pair for my AR shaft.

Total cost was 4x SR4-ZZC #7 PS2 $11.47 + $15.95 shipping = $61.83.

I don't expect too much improvement, seeing still has a much bigger effect on total RMS than the bearings. But I fully expect to get rid of my DEC spikes. I'll report back how it goes!

Hi!

The improvement one can gain from new bearings depend on how bad the existing ones are. I suggest you peruse the messages at least a few years back in the Losmandy user group - there has been extensive and repeated discussions on bearings. For my own part, changing bearings a few years back was a major improvment, removing bumps in the guiding.

Be very careful when removing and inserting the bearings - it is very easy to damage them (for instance by using a hammer of some sort to make them fit in the holes....).

Magnus

I had a very interesting night tonight. I can now confirm there is an issue with DEC calibration/guiding. The night started out with good calibration and OK guiding. It was a hot day for September (29°C) and my rig was placed on top of a 7 storey building where the house was dissipating heat and everybody had their windows open to to get hot air out. So atmospheric seeing was good but local seeing was awful.

First calibration run:


Guiding:


Considering local seeing guiding was good.
Later that night the moon came up which regularly leads to deteriorating guiding. I changed objects and had a second calibration:



Guiding was still OK.


After hours of flawless guiding suddenly DEC drifted away. According to the guide graph, ever increasing correction pulses were sent to the mount but obviously it did not receive them as DEC continued to drift away further. I stopped guiding and did a another calibration run:



WHOA! My first thought was: "This looks familiar!" Remarkably the error did NOT occur after guiding was abortet, after a new object had been targeted, etc. It happened right in the middle of an active guiding run! I then did all kind of things to remedy this. I quit KStars and the Indi-server, restarted and had another calibration run, this time with PULSE guiding active (all other calibration runs were via ST-4 cable):



Back to ST-4 guiding calibration:


That was the time when I activated logging. I did another calibration run with loggin active. Logfile attached. (I reached the max number of attachments so this is to be continued...)

Hi!

Unfortunately, I can not see any log file... was it attached?

The first guiding session resulted in a total RMS of 0.51"? That is really great! But the calibration looks odd. So, at what declination did you calibrate? And why did you re-calibrate for the second object?

Something happening in the middle of the run might indicate that something happened to your mount. Cable snagging? My first suspicion when I read it was if the Oldham coupler slides on one of the axes - I've had that. It can happen if temperature falls, and you tightened it in warmer temperature. And if there is grease on the axis. Now, those couplers are held in place by very small screws, and it is very easy to make them round, so one needs to be careful there. But that is one place I'd check.

If you can attach the log file, I'll have a look at that too.

Magnus

I got out to my rig, tested DEC movement by pressing the N and S buttons on the hand piece with GUIDE speed active. That did work as usual. I then tested with Ekos - mount - mount control N and S buttons with GUIDE speed. That did work as well! I then had yet another calibration run and it worked like nothing ever happened and continued to do so for the rest of the night! The 2nd logfile was created during this successful calibration run.

I also attach the full guiding logs for both sessions, before and after the re-start of Ekos.

I found a few other things that IMO need to be discussed which I will create a separate topic for.

Magnus: "Unfortunately, I can not see any log file... was it attached?"


It's attached to part 2 of the message.

The first guiding session resulted in a total RMS of 0.51"? That is really great! But the calibration looks odd. So, at what declination did you calibrate? And why did you re-calibrate for the second object?


Well, it was around .5" provided no "DEC freak" was incorporated into the calculation. So once a freak happened, RMS was thrown out to like 1.2" and then slowly returned to around 0.5". Until the next freak happened. Also dithering distorts the RMS calculation. I've see several dithers that quite obviously impacted RMS:







Even worse when focusing was added to the mix:







Magnus: Something happening in the middle of the run might indicate that something happened to your mount. Cable snagging? My first suspicion when I read it was if the Oldham coupler slides on one of the axes - I've had that. It can happen if temperature falls, and you tightened it in warmer temperature. And if there is grease on the axis. Now, those couplers are held in place by very small screws, and it is very easy to make them round, so one needs to be careful there. But that is one place I'd check.

That was my first thought, too. I went out and checked. But cabling and everything else was perfect. Clutches were locked, everything was snug and tight. I have all cables in a "cable canal" attached to my mount. This put cabling issues to rest for a number of years. And it was back to normal just a couple minutes later, without any change to the rig whatsoever. The coupler is something I should also have a look at but heck, why should all our DEC couplers suddenly fail and then perform wonderfully again... We have received several reports of failed calibration runs, on a number of different mounts (I think Gonzothegreat just recently had the same issue with a CEM25). I just couldn't reproduce it - until tonight!

HTH!

With regard to at what declination did I calibrate at: I know I should calibrate somewhere close to the equator and the meridian. However, this never impacted my guiding results, it simply doesn't make much difference. Sometimes I calibrate at the proper place (I think one of the runs yesterday actually was close to the equator/meridian) but I never get away with the feeling that guiding improved from it.

I usually do re-calibrate once I sense another calibration run could improve guiding results. Most of the time I do re-calibrate right at the object that I am targeting. That's why most of my calibration runs show differing lengths in RA and DEC. Yesterday I was observing objects in Cepheus/Cassiopeia which I am aware is sub-optimal for calibration but at the end of the day 0.50 RMS on top of a heat block isn't too bad.

Hi!

Thanks for the logs. Nothing strikes me from looking at them immediately. You have some 76-sec error and some contribution from the gear-box (31.9 sec period), but noting that is out of the ordinary. It would be very helpful if you can produce a 30 min unguided run, similar to what PHD2 does with the Guiding Assistant. Simply let the scope guide for 30 mins but without sending any pulses to the mount. That is very informative.

However, the DEC bursts and dither issues are something else. That is definitely some mechanical issue. I note that the S and N versions of the dither curves are very different, as if it took much more time to recover from dithers to the south. Is that consistent? That would in my mind indicate that it is off balance. I know a G11 is difficult to balance precisely - I always achieve best balance by actually removing the worm drive, but then I have the hassle of adjusting it again....

Secondly, I've had that kind of jerks when things have been too tight. So that the motor increases power (based on feedback that it does not move enough) and suddenly it comes loose, and there is a jerk.

And it could be related to your grease. Have you regreased it yourself, and in that case, with what grease?

The relative sudden onset of the jerks could point to balance being an issue - if the mount moves to a position where the momentum (I'm not sure about the english term right now) becomes bigger, then that might cause jerks, particularly if you a) have it very tight, and b) use a grease that is not well suited for this kind of pressure (lateral).

Just a few ideas.

I'd carefully check the pressure of worm on gear ring, making it not too tight, and the screws on the coupling, then run a 30 mins test run with no pulses to the mount.

Magnus

Hi again!

And, on calibration: I never re-calibrate once I have a calibration I'm satisfied with. I calibrate near the equator, and then just keep it. That is also the standard advice when using PHD2. I don't see a reason for redoing it and spending time on it, unless something has changed on the mount or the optical train.

I wonder what happens if you do a series of calibrations, near the equator. Do they all look the same? It is very common for a G11 to have some backlash (I'm still not convinced that you don't) and that should be identified and compensated in the calibration. I'm not sure what the internal guider does, I use PHD2.

But such a test would be interesting.

Magnus

Many thanks for your suggestions, Magnus! Looks like you're pretty knowledgeable in the matter! I added a "dither settle" of 3s for tonight, had it set to 0s before, which could play a role, not sure. I'll definetely do the 30min unguided run tonight.

With regard to some other considerations: Since the new bearings are on their way to me, I'd wait for them to be installed and do the tests again. I'm curious to find out which issues remain and which will be gone.

Grease... yes I did re-grease my mount twice. If I recall correctly I tried Synco Lube multi-purpose synthetic grease with Syncolon and Liqui Moly SM47 or some other black, MoS2 based product. I didn't notice any difference in performance. Most important IMO is how the worm is positioned relative to the gear ring. Currently RA is rather tight but I did not receive any feedback that it does not move enough nor did I see any RA freaks that I would associate with stiction but of course I could be wrong. Currently I am quite happy with my RA guiding so I would rather not touch it unless I have to.

Usually I don't re-calibrate either. But since we were discussing Bill's calibration issues I tested calibration over and over again. That's how I ended up with that many calibration plots.

I'll also do multiple calibrations near the equator/meridian tonight.