Re: Spikes in Dec


Seb i seem to recall you using lowpass2 in PHD which is the correct algorithm for high res encoders

On Thu, May 6, 2021 at 12:54 PM Seb@stro <sebastiendore1@...> wrote:
Hello Roland, Howard,

Thanks for the heads-up. I will hover to the PHD2 forum with this additional info as you suggest.

Strange thing is while I created the guiding profile, I did check the precise encoder mount box (or whatever it’s called). And guide speed was set to 1x. I also followed all recommendations I got from the Guiding Assistant. Maybe this isn’t enough which such highly precise mounts though, as you suggest.

There’s also the fact that I’m using the latest dev5 version (to benefit from the multi-star guiding functionality). I might revert back to the stable version for further testing.

Again, many thanks for your very professional support. Much appreciated.


Le 6 mai 2021 à 15:19, "chris1011@..." <chris1011@...> a écrit :

Hi Sebastien,

Howard has been going thru your log files and discovered some problems with your PHD setup:

"PHD2 is indeed commanding moves of 2 – 3 arc-seconds, all of them south.  It is also sending many moves of single digit mSecs.  There were 60 instances of  :Ms1#  in the one APCC log file.  That’s calling for a move of ~ 0.015 arc-seconds.  The screen below shows 11 move commands in a row, most or all of which were too small, followed by a ~2 arc-second move -  :Ms130#."

Basically you have PHD set up to respond to every tiny error in such a way that no movement occurs for many cycles, which is then followed by a single large movement. This type of Dec algorithm was developed for mounts that had huge backlash where the mount does not respond to move commands in a timely way, and then finally PHD sends a large correction command in order to get the mount axis moving. That's when the spike occurs.

Apparently you have set up your Min and Max moves wrong as well as choosing the wrong algorithm for a precision mount. never should guiding software send 1 millisecond ( 0.015 arc sec) move commands because the mount basically will not move at all, or so slightly that it will never register in your guide star motion. You may even have set your guide speed wrong - it should always be left at 1x sidereal, never anything else.

I would suggest that you go to the PHD group and let someone there analyze your log files and look at your settings. I am not an expert when it comes to PHD, I have only a rudimentary knowledge, so it would be est to ask the users on that group to help you. I know that the Mach2 will guide extremely well with your setup, even if you have some small unbalance. I put a 3000mm focal length 10" Mak-Cass on my observatory Mach2 last night and guiding was smooth and slick as snail snot on a door handle. I even set it purposely out of balance and still it guided the same.

And thanks to Howard here who sifted thru your log files and spotted the discrepancies.

Roland Christen
Astro-Physics Inc.


Brian Valente

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