Am5 issues with ascending targets

w7ay

MrAstro Using Polemaster, I couldn't get better than 1' or 2' as PA error in PHD2 viewer

With cheap mounts, you need to apply the technique of tightening the alt-az locking bolts while you are approaching final adjustment of the polar alignment. So that the final adjustment is made against a mount that has pretty much been locked down. If you don't do that, and only lock the alt-az platform after attaining polar alihnmnet, the mount will move.

The other thing that helps is to only adjust the RA axis against gravity (i.e., each altitude adjustment fights against gravity). If you overshoot, do not go back and forth, reset the RA position on the other side of gravity and start again. I.e., approach RA alignment in only one direction.

The solution is to pick a better mount. Well-machined mounts have less of a problem, but when you buy a Chinese consumer product, you have to be contented with the quality (and quality control) that Chinese consumers are used to.

Chen

Steve-Harpo

Hi Chen, Kevin,

Hi All,

Last night was clear, albeit a little later than usual, but I was able to run a test.

I polar aligned using the ASIair - Dec to 0 Arcseconds and RA to 6 Arc seconds. I ran a quick test of the guiding but it was very slowly drifting South. Switching the guiding to North held Dec very steady at 0.5

RA agression 35%, DEC aggression 45%. RA duration set to 250ms, DEC duration set to 250ms. I left DEC at this setting initially to make sure I saw the original problem first. Once I saw the problem occur I then switched this to 1ms.

When the problem first started I would set up and get about 30 minutes without issue and then the problem would start and remain until the mount flipped. It appeared to be once it got to a certain elevation and so, given I was setting up later, I expected the problem to manifest immediately. However, it ran fine for the first 30 minutes or so before I got the first error, so the '40 Degree' was apparently a bit of a red herring. I don't see why 30 minutes would be relevant but Im wary of coincidence's when troubleshooting a problem.

Once I saw the problem I stopped the guiding, set the DEC duration to 1ms and set to guide to the North. It was holding at 0.5. I watched the guiding for the next few hours and saw the problem, or at least a similar pattern, but obviously reduced magnitude. With the initial testing Dec would hold steady at 0.5 but now it was dropping suddenly to 1.0, 1.1 and then slowly back up to 0.5 and then continually repeating this cycle.

After the meridian everything was fine.

Shed any light on potential cause?

Cheers
Steve

w7ay

Steve-Harpo I polar aligned using the ASIair - Dec to 0 Arcseconds and RA to 6 Arc seconds.

After you finish polar aligning on the ASIAIR, home the mount, and then immediately perform a second polar alignment.

What is the initial reported polar alignment error for this second try? Is it still a few arc seconds off, or is the reported error much larger?

Chen

Kevin_A

From a mechanical standpoint… i do not find the asi120mm mini a very good guide camera when run way past its nominal gain of 28. I have run it at 69 but never at 100 and expect good results especially without darks enabled. I do not know what guide scope you are using either as these mounts like better guiding input data. You also may want to check that all the alt and az bolts are tight as well.

Steve-Harpo

w7ay

Hi Chen,

Thanks for your reply.

I will try on the next clear night and report back.

Cheers
Steve

Steve-Harpo

Hi Kevin,

Thanks for the reply I appreciate any help I can get.

Yes I always check that that Alt and Az are fully tightened. I understand that the 120 is not the best camera, However I have had no issues up until a couple of weeks ago and I don't believe this explains why everything is always fine once the scope has flipped. If the camera is the issue I would expect the problem to occur throughout the whole session. The high gain is unfortunately my fault. I turned it up while trying to chase the cause and neglected to turn it back down again. Normally it runs at around the 70 mark which I found I helped with the 1 second frequency. It has been running at that level since November 2022 without incurring these problems

There is no guide scope, its off axis.

Cheers
Steve

Kevin_A

Steve-Harpo ok, still the 120mm mini is very very bad for an OAG so just fyi.
It could also come down to the skies are contributing as they are much worse at this time of year. I am not saying this is your issue, but rather that this will add weakness to your setup. With any fast guiding you want at least 12 stars. Have you tightened the hidden screws, the ones behind and inside the base? Some people have reported slop due to them not being tight enough.

Kevin_A

Steve-Harpo I too always do 2 back to back polar alignments. I added 2 nylon flat washers on my big knobs too so they are semi tight all the time and that helped keep things from randomly changing.

Steve-Harpo

Hi Kevin,

Yes I agree that the 120mini is not the best choice, it's just kinda worked as the system has evolved from an EQM 35 with a small guide scope into what it is now so hasn't been a priority. I will get around to replacing it at some point. I think your idea of back to back polar alignments is worthwhile based upon the test I did and I've seen people recommend this on an ASIAir before. Once we have a clear sky I will do multiple alignments and report what errors I see each time. when aligning I first loosen and then align. As I get close I tighten them up, but not fully. Once aligned I fully tighten before a final check with minor adjustments if required. So long as I am careful with the final tightening I don't usually have to adjust further, however I don't perform two alignments so it will be good to see the results.

Prior to the OAG I was using the 30mm F4 guide scope from ZWO and my guiding actually significantly improved once I moved to the OAG. I have checked the screws previously as I also saw similar reports. I'm also using the helical focuser which is locked down.

The AM5 is mounted on a Skywatcher Pier tripod rather than the TC 40 it came with.

The skies here (Northern Thailand) can be changeable and does cause problems sometimes.

The thing I find very strange here is that the problem appears to be specific and repeatable (at least the last 12 outings) where the mount starts off fine for a short while (say 30 minutes) - then the problem manifests until the meridian is reached, and then everything is fine after the flip has taken place and the session continues. So far this has been the pattern every time. Following Chen's advice to set the DEC pulse to 1ms at least gave me workable subs on the last outing.

I did create a case with ZWO support on the 17th of January but despite me trying to nudge them a couple of times they have yet to respond.

Apologies for the long winded reply and thanks for the help. I'll update once we get a clear night and Im abole to get out and perform the multiple alignments.

Cheers
Steve

w7ay

Steve-Harpo back to back polar alignments

You need to repeat it until the start of a polar alignment reports a good alignment (and you can simply quit the process once you find that it is already aligned). Otherwise, you mount is not polar aligned, no matter what it said before you locked it down the previous time.

Remember: you need to polar align so that the polar axis of the mount points at the celestial pole after you have locked everything down.

Chen

Kevin_A

Steve-Harpo one thing I do when doing PA is…. Is do AZ always first. Then when doing Alt I make sure I have my mount set always lower than Polaris so I am always moving my mount Alt screw upwards. If I go past I drop it down quite a bit and nudge it up again never dropping, always in one direction nudging it up…. Just having the mass push against my turning of the Alt adjusting screw until I am within 15sec. Done….

w7ay

Kevin_A one thing I do when doing PA is…. Is do AZ always first. Then when doing Alt I make sure I have my mount set always lower than Polaris so I am always moving my mount Alt screw upwards.

This is also why you need to level the base of your mount perfectly (both E-W and N-S directions).

If the mount is not leveled, an adjustment of the altitude axis will affect where the azimuth axis is pointed at (and vice versa); they are not independent (orthogonal axes).

You can do it unleveled (i.e., make the polar axis point at the pole), but you will be going back and forth readjusting the azimuth axis after making an altitude adjustment (and vice versa) Spending a few minutes leveling you mount will have oodles of time and frustration while polar aligning.

Chen

Kevin_A

w7ay I am lucky as my patio is very level and my second PA usually just confirms the first was spot on. I think asiair originally had a glitch but mine seems better now. Tonight will be the first clear night for me in 7 weeks and I get to test out my 50mm septuplet guide scope finally.