If it's a snag it will show up during an unguided exposure as a shift rather than a spike in the guider graph. Whenever you are troubleshooting a problem, guided data is not useful because guiding tends to hide or compensate for an anomaly. That's why I always want to see unguided data if possible.

Same is true of star images that have defects. Defocus the image of the star and this can instantly tell where the problem lies, whether it's in the main optics or somewhere further down the imaging train.

Rolando

-----Original Message-----
From: Brian Valente <bvalente@...>
To: main@ap-gto.groups.io
Sent: Mon, Jan 31, 2022 1:34 pm
Subject: Re: [ap-gto] Mach1 RA guiding spike

Hi Yanzhe

I had a chance to go through your guidelog and have a few observations. I think you still need to track down the source, but we can probably rule out a few things

I don't think it's in the guiding: they happen independent of dithers and they are instantaneous, so guide pulses are causing these

I don't think it's mechanical, or at least part of the gearing: there is no clear periodicity to them, and they happen in very limited circumstances (in 6 1/2 hours of guiding i counted 6 total, all relatively close in time together)

this is the time between the spikes (in secs):

261

139

155

575

90

I did notice it only appeared to happen when the mount was pier side west, so it could be something related to shifting equipment, snags, etc.

you might try replicating that pointing position and see if it repeats in the same place @ Hour angle = -1.20 hr, Pier side = West,  Alt = 50.0 deg, Az = 151.1 deg

if it does, try disabling guiding and see if it shows up in unguided output

Also the guidelog did not include a calibration run or a guiding assistant (unguided output) so those would be helpful to include if you post a guidelog again

On Mon, Jan 31, 2022 at 11:14 AM yanzhe liu <liuyanzhe@...> wrote:

There is no backlash.
I am using OAG and it has never had any issue.

--

Brian 

Brian Valente

portfolio brianvalentephotography.com 

--
Roland Christen
Astro-Physics

There is no backlash.
I am using OAG and it has never had any issue.

Brian,

This issue was solved by Roland.  He provided some updated Mach2 settings to accommodate my heavy OTA.  I was really shocked by the improved performance.  But, I think I was using 3s settle times when I was experiencing the anomalies.  I went through several rounds of changing the APPM variables when I was troubleshooting.  Nothing helped.  After initializing the new settings from Roland I did several test maps with very aggressive settings (2x2 3s exposures, 1200x slew rate, 2s settle time) in order to stress test it.  No bad solves.  Then I did that 600+ point model that I mentioned in another thread.  I had 6 bad solves, 2 were due to clouds and the others were likely wind gusts.  For that map I toned it down to 2x2 3s exposures, 1000x slews, 3s settle time.

Eric

Bill,

I’ve had this Mach2 since Dec 20 but have only now tried a full sky model since I’m not in an observatory. Ive had the TOA130NFB a bit longer. It used to sit on a Chinese mount until I found A-P. The affected points are all relatively low on the southern horizon where I never image. I’ve used a number of Dec arc models successfully over the past couple months without a single plate solve failure, but they’ve all been higher. I also use my gear for visuals and haven’t seen anything but stellar tracking performance with no guiding. No anomalies. It wasn’t until last night during a 522 point all sky APPM run that I saw this behavior. 22 points failed to solve, all 22 showed trails/oscillation. 2 others failed due to clouds near zenith. The remaining 498 show round stars. 20 of the 22 were on the west side of the pier with CW down (below the CW up plane but near horizontal). The OTA was pointing relatively low towards the southern horizon for all 22. I had a couple fail at Dec +5 on the west side, but most failed below Dec 0, also on the west side. 

I suppose I could improve my moment arm a little by keeping the dew shield retracted but it helps with the house lights I’m surrounded by. Why people feel that the need to illuminate their houses and yards all night is beyond me. I’ve got a flipflat on the OTA, but it weighs practically nothing. My setup isn’t anything really out of the ordinary. Like other TOAs, it’s a little forward heavy, but I’m anal with balancing and tend to use a hex wrench to get the clutches slightly tighter than hand tight when I’m imaging. 

I’m curious to see how your TOA150 with imaging train fares as well. Run a 500+ point model when you can and share the results please. 

Eric