Guiding is underwhelming for my AM5, how can I improve it?

[sean.m....@gmail.com]

Hi all,

I just made the big step after years of using an AVX and picked up a ZWO AM5.  I feel that the guiding could be way better for this mount.  I'm seeing numbers around 0.67 and then over the course of the night I'm seeing these numbers increase despite being under bortle 4 desert skies with crystal clear seeing.  Polar alignment is spot on.  I primarily use the Polemaster for polar aligning, and have also used the ASI AIR polar alignment tool.  I strictly use PHD2 for the guiding software.

I created a profile, ran a calibration to the south above the celestialequator as described in the best practices. After calibration, I also ran the guide assistant for about 5 minutes and applied the suggested numbers and then started imaging using predictive pec, and resist switch.  As stated the numbers are slightly underwhelming and steadily increase over the night.

Looking for suggestions from people as I can't seem to find what this thing likes for settings.

My gear is a Stellarvue SVT70-IS, ASI174MM Mini guide cam, ASI294MC Pro, ZWO EAF.


Attached is lastnights guide log.  The one that starts at 00:15 for 3hrs 1m was my main imaging run.  After that run you  can see where i'm playing around with settings, but the numbers keep increasing.

[Bobby]

I've had an AM5 for over a year now.  I almost got rid of it early on as I was getting poor results and ZWO was not keeping up with driver upgrades.  Since then, I've gotten a handle on it and routinely get .25 to .35 with a 240mm, 2.4 micron, Bin 1 guide scope.

First step: Go over EVERYTHING that the PHD best practices guide talks about.  I poo pooed it until I found out that my guide scope was not aligned to my imaging scope.  Check cables, tighten everything, eliminate possible future fails like nylon tips on guide rings, screw your guide camera onto the guide scope, etc.  Do your best on trying to achieve a decent balance.  I know that this seems stupid, but it can't hurt.

Second step: I have found that the AM5 has a 'drinking problem'.  Not alcohol, but electricity.  I was getting weird spikes (a little bit like on your graph but larger) that went away when I changed out the transformer.  In addition, the AM5 is the ONLY device on that transformer.  No piggy backing other 12v devices.  I use a large 8 amp brick, now.  If you are running off of batteries, get a 'bucker' and make sure that the AM5 is getting at least 12.5 volts.  Anything less and it's starts complaining.  Doing this got my guiding a lot more under control although many at the ZWO forum think I'm nuts.  If you are using the carbon fiber tripod that ZWO makes, hang at least 25 pounds from a chain or rope from the center below the mount.  It's not a bad set of sticks, considering how much they weigh, but a bit of heft will settle it down a bit more.
I use predictive PEC, but only started to recently.  I would run the default algo's until you start seeing better results.  I think that might make it easier for you and others on the list to figure things out.  Also, a lot of AM5 users run 1 sec exposures (or less).  I found that my Polemaster was less than accurate when I checked it against PHD's guide assistant run for 5 or 10 minutes.  Can't speak for ASI AIR.  I use Sharp Cap's polar set up.

Don't give up hope.  The AM5 does have a big learning curve and ZWO still doesn't have a decent driver for it.  (After a year of complaining, I still can't park my scope using the APT button.)  Practice, practice, practice.  Bon chance.

Bobby

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Bobby Sapovits
www.equusbicycle.com

[sean.m....@gmail.com]

My power supply is a Jackery 300 20ah power supply, but its powering the mount from the 12v 10amp out, and from the mount side dc out port its also powering my asi294mc pro, asi air mini, and EAF.  There should be plenty of power from the power supply, but tonight i'll try running the mount from a power brick on one of the AC outs and power the cam and everything else on a separate power supply.  Everyone seems to be powering it the way I am without issues though, but i'll try anything at this point in addition to also running the guide assistant longer than 5 mins

[Bobby]

Any chance of running some AC to your scope?  Or a second battery?  I still think that running everything off the Jackery might not help you out.  Take a voltmeter out as well.  While you may think that you are well under the AMP limit, the only way to be sure is to measure everything.  From your list, I see at least 15 amps and you don't mention dew prevention.  You might try not turning on the 294 cooler to keep the amps down.  As I mentioned, the AM5 does not like running less than 12 volts and even at 12 volts you may have problems.  I can't run my AM5 directly off my 100 AH AGM battery.  It does not supply enough volts for it to be happy.  Only after installing the bucker that converts any voltage from 6 -12 volts to 13.8 volts could I consistently use the AM5 all night.

Bobby

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/9cb3353a-97ae-4470-8b5e-f71e54351a8en%40googlegroups.com.

[sean.m....@gmail.com]

Sorry what i was saying that tonight i'll run the mount off the Jackery only via the ZWO powerbrick AC adapter and run everything else off a separate power supply.  Not using the camera cooler isnt going to be an option, its currently 105 where I am and 75 at night and i'm doing 3 minute subs.

[Bruce Waddington]

Hi Sean.  I'm going to take a somewhat different approach on this and suggest that you may need to adjust your expectations.  Total RMS of 0.67 arc-sec with nearly equal results in both RA and Dec is not a bad result at all.  Getting down below that level on a consistent basis is going to depend a lot on the seeing conditions and your comment about "under bortle 4 desert skies with crystal clear seeing" has me wondering if you've figured out astronomical seeing.  Your description there relates to the sky transparency, not the seeing.  Astronomical seeing is a measure of stability, a very different thing.  If you're operating from a low-desert location with daytime temperatures above 100, it may be difficult for you to ever get truly good seeing conditions.  Depending on your site, you can expect thermal convection to be a major factor for many hours after sunset.  One way to judge whether you are seeing limited is to examine the guide star excursions in Dec and see how they compare to those in RA.  The Dec motor is idle most of the time, so the question of tracking accuracy in the mount can be set aside.  Here's an example near the end of the long guiding session, a time period you were unhappy with (Dec in green):

Look at the largest guide star excursions for both RA and Dec - both axes show spontaneous deflections of 2-3 arc-sec.  None of the largest excursions in Dec were the result of guide commands - they just happened.  These look like seeing-induced movements to me unless there is some other weird source like vibrations or wind or something.  Bottom line, I don't think these have much to do with the mount and they aren't going to be eliminated by fiddling around with guiding parameters.  You can read more about astronomical seeing on page 15 of this document:

https://openphdguiding.org/tutorial-analyzing-phd2-guiding-results/

The concern about using short exposures in that paragraph has been mitigated to some extent with the introduction of multi-star guiding in PHD2 - something that happened after the document was written.  One other concerning part of your setup is the coarse guider image scale - 5.75 arc-sec/px.  I consider this to be too coarse if you are trying to do any sort of high-resolution imaging.  And if you aren't, it's unlikely that improving the guiding below 0.67 arc-sec is going to make any difference to your imaging. In other words, there's no point in obsessing about guiding results if they aren't having any real effect on your final images. If you make a conservative estimate that the star positions on the guide chip are being measured with an accuracy of, say, 0.1px, then with your setup, you probably have a performance floor as high as 0.6 arc-sec.  Is that good enough?  If not, you should probably do something to reduce the guider image scale, an OAG being the most direct approach.

Regards,

Bruce