PHD2 RA

[TheoM]

Greetings everyone I hope y'all doing well,

For the past few days my guiding is not going well. First let me kick off by saying that my polar alignment is almost perfect (done it with Sharpcap and 00°00'03" PAE) and I did balance very well toward the East to compensate those spikes. I've done the maintenance of the mount (HEQ5 Pro) very recently because there was some play in the RA when the mount was lock tight. I this a series of test and tonight I've done it towards Capella. Things were better from the past few nights ago but i can't get near 1" of RMS. I know that Skywatcher said that the RMS should be around that number but I manage to get 0.70" RMS month ago. I'm using ASCOM and pulse guiding combine with APT. The gears looks great and I've got the mount last year. Notes that i've been using PHD2 for 5 month now and I'm new to it. I try to read and get as much information as I can but I can't manage to get a proper guiding. I hope that some of you will light me up.

PS : My mount has not been Belt-modded but I really considered to buy the Rowan Belt mod.

Thanks a lot,

Theo

Attached Files

PHD2_GuideLog_2021-03-07_201745.txt

[PeterCPC]

Have you tried the latest PHD with multi star guiding?

[TheoM]

Yes ! This log was with the multistar. Someone suggested me to increase the SNR..

[michael8554]

Hi Theo

Here's what your RA in Guide Assistant looks like:

 

  

When GA is selected, RA guiding is paused, and you see the RA performance of the mount.

RA Error climbs from zero at the left of frame to a peak of 10arcsecs, then starts to fall.

That's Periodic Error, quite normal.

What isn't normal is the regular 2.5arcsec oscillation superimposed on the Periodic Error.

This has a period of 13.6 seconds, see second graph.

That's too fast for PHD2 to correct, hence it shows in you RA guiding.

I'm not familiar with the mount, but this is not unusual from what I remember of other posts.

Someone will chip in with the cause, gearbox maybe ?

Michael

Edited March 8, 2021 by michael8554

[kens]

11 hours ago, michael8554 said:

Hi Theo

Here's what your RA in Guide Assistant looks like:

 

  

When GA is selected, RA guiding is paused, and you see the RA performance of the mount.

RA Error climbs from zero at the left of frame to a peak of 10arcsecs, then starts to fall.

That's Periodic Error, quite normal.

What isn't normal is the regular 2.5arcsec oscillation superimposed on the Periodic Error.

This has a period of 13.6 seconds, see second graph.

That's too fast for PHD2 to correct, hence it shows in you RA guiding.

I'm not familiar with the mount, but this is not unusual from what I remember of other posts.

Someone will chip in with the cause, gearbox maybe ?

Michael

13.6 seconds is the gear tooth mesh period on the HEQ5. Every spur gear tooth engages and disengages its counterpart at that period. A spike at this period indicates that the gear mesh should be adjusted at one or more points in the drive train. Often the motor housing positioning is the culprit. A belt mode can help as long as the belt is properly tensioned.

[TheoM]

43 minutes ago, kens said:

13.6 seconds is the gear tooth mesh period on the HEQ5. Every spur gear tooth engages and disengages its counterpart at that period. A spike at this period indicates that the gear mesh should be adjusted at one or more points in the drive train. Often the motor housing positioning is the culprit. A belt mode can help as long as the belt is properly tensioned.

Ok so I need to adjust the gear mesh ? I've already followed this tutorial (https://www.youtube.com/watch?v=-k3zFA4-zWA) to get rid of the grinding noise and the backlash for DEC and RA but might as well take it apart again and take a closer look.

[TheoM]

Greetings everyone,

Did some PPEC with PHD2 last night. Things were definitely better but I feel like the mount can do better (i don't know too much about PPEC, still learning). I manage to get less than 1" RMS with wind and some clouds rolling out.

PHD2_GuideLog_2021-03-10_200044.txt

[kens]

The 13.6 response is still quite high. PPEC wont help as it is too short to be easily guided out. it is making up the bulk of your RA RMS value.

[TheoM]

2 minutes ago, kens said:

The 13.6 response is still quite high. PPEC wont help as it is too short to be easily guided out. it is making up the bulk of your RA RMS value.

It is actually.. Any idea on how to make it longer/better ?

[kens]

You cannot make is longer as it is a function of the mechanics of the mount. The video you followed gives the right approach to sorting out the gear mesh so you may need to redo the RA axis. Unfortunately you can only try it and star test till you get it right. It may not be fixable by adjustment. A belt mod could help if you wanted to go down that path.

[TheoM]

I can't do better with the gear mesh. This is by far the best result i could get on PHD2. For sure there still some heavy RA RMS, i'll try to balance East heavy next time, but purchasing the belt mod will be less of a headache to sort all that stuff out. Thanks again kens.

[Merlin66]

Theo,

Unfortunately I’m not convinced the belt solution is the ultimate solution.

I’ll be interested to see how it pans out.

 

[redfox1971]

The belt mod on my neq6 did not make any difference except for removing the grinding noise only thing that made guiding better was how seeing was on that night.

 

[michael8554]

Kens,

Pretty sure I've seen advice from the PHD2 gurus to try PPEC with a fixed 13.6 second Period in this situation ?

 

Theo,

I may be wrong, but to minimise this unwanted oscillation involves removing the culprit gear, and reinstalling it moved one tooth with respect to the gear it meshes with.

Then testing.

And moving it another tooth and retesting.

Until you find the best combination.

I don't think you've had time to do that ?

Michael

 

[kens]

I doubt PPEC would work on such a short period. Targetted PPEC is often recommended for PE in the 100 to 200 second range. In this case it could be used to attenuate the 122 s period although it is not too bad at 0.2" RMS compared to the 0.6" RMS of the 13.6s period.

The problem is that it is not caused by just one tooth - its every tooth mesh and it is across three gears. And given that they are not in whole number ratios then you would expect every combination of tooth to tooth to come about during normal rotation.

This article shows how the belt mod can help: https://www.amateurastrophotography.com/heq5-pro-belt-improvement-1

You replace two points of tooth contact with a belt that engages multiple teeth on each gear.

Here is a graphic illustrating the tooth mesh: http://www-mdp.eng.cam.ac.uk/web/library/enginfo/textbooks_dvd_only/DAN/gears/meshing/gearAnimation.gif

If one tooth disengages before the next one engages you get this kind of periodic error

[TheoM]

On 12/03/2021 at 10:51, michael8554 said:

Kens,

Pretty sure I've seen advice from the PHD2 gurus to try PPEC with a fixed 13.6 second Period in this situation ?

 

Theo,

I may be wrong, but to minimise this unwanted oscillation involves removing the culprit gear, and reinstalling it moved one tooth with respect to the gear it meshes with.

Then testing.

And moving it another tooth and retesting.

Until you find the best combination.

I don't think you've had time to do that ?

Michael

 

Michael, i don't think that moving tooth by tooth, then testing is worth the test, I already did this for a couple of nights and things remains the same. Like I said I manage to get a "decent" RMS for the first time, and I think that I cannot do better on playing with the gearing. I might considered buying the belt mod, it not only removing the noise but I saw multiple thread about how "crucial" it is to do this mod. Like kens said it will likely improve the mount performance. I'll be imaging tonight if there's no wind. I will post and image and log to see what you guys think.

Once again thanks everyone,

Theo