Re: AP900 DEC sawtooth guiding

Roland Christen

That kind of sawtooth guiding is very indicative of loop gain greater than 100% due to faulty calibration parameters. It says something like "send a 2 arc second correction for a 1 arc second error". It's called overcorrection or Loop Gain > 100%, etc. The software is misinterpreting the actual error and sending a very much larger correction signal to the mount. I'm guessing at least a 200% overcorrection, possibly due to interpreting a wrong binning setting or a wrong calibration parameter.
Not being familiar with PHD, I cannot begin to guess where the error might be. In Maxim, it is easy to see the actual calibration numbers, and you can even modify them to the correct value for 100% stable operation.
It's almost like the software is interpreting the smaller RA parameter number to be applied to the Dec axis. That is the danger of calibrating away from the celestial equator where the two numbers (RA and Dec) would be the same. If they are not the same, then you know right away that your calibration was not accurate.

-----Original Message-----
From: anismo@... [ap-gto]
To: ap-gto
Sent: Thu, Sep 22, 2016 2:59 pm
Subject: Re: [ap-gto] Re: AP900 DEC sawtooth guiding

Additional info: Instead of the PHD log, I have it loaded in PHDLab

Here is a 13.5 minute with normal guiding:
Here is the case showing the "sawtooth":

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