| Thanks Ivor - both of these were my inclination.
I have been playing with a copy of the PEMPro (?) program. Unfortunately I
do not agree with its premise (at least for the cheaper-smaller toothed Meade
worm gears) that you can use FFT transforms to model the behavior of the
gear error terms. There seem to be too many high frequency components
of a non-sinusoidal nature in the RA centroid motions when I just study the
drive system (PEC turned OFF and no guiding).
I get fairly reproduced types of errors when I collect data over 3 different
HA zones (I use a 'locked down' permanent mount where I never change
the section of the RA gear actually used). The data set I now have was
taken with seeing about 3" arc and a well balanced scope and expose-
read cycles of 2-3 seconds. I'm not exactly 'synched' to the phase of the
worm detector - but it's sort of (weird) fun to try to phase match the
data [like an odd variable star with a known period but small dwarf-nova
outbursts].
There are some well-known issues with PEC "update" actually being a
form of 'new data set averaged with ALL the old' . I'm going to trust
what the guider centroids tell me - but take care of the loading of the PEC
table through the
COM interface rather than the GUIDER input pulses.
I like to see the raw data (PEMPro good) but massage it myself (PEMPro
restrictive).
Summary- I'll massage and study the data I have - and retake it after I
get an "East-weight" (I'll use a pulley and cable). Simple CCDOps and
Excell work can do just fine for this data (as others have found).
Steven Nelson
PS
PEC local background. The first PEC system was conceived and birthed
at Lick on the 3m Shane reflector by Bob Kibrick, a programmer and several
mechanical engineers. It was needed (late 70's) after electronic auto-guiding
determined the extent of wear-and tear on the 20 year old giant worm drive.
An Apple II type processor (6502) ran the whole thing - after programming
information was collected by the auto-guider.
PPS
"Fighting" autoguider and PEC - it seems the phase of the correction is critical
when there are high frequency error components. This is why I'd rather study
the system driving with no guider feedback working (i.e. unstable servo system)
-----Original Message-----
From: Ivor Barker <ibarker@...>
To: norcal_ai@yahoogroups.com
Sent: Wed, 24 Dec 2008 9:05 am
Subject: RE: [norcal_ai] LX-200 PEC training expert? 0A
There’s conflicting advice out there, one is to turn PEC off
and let the autoguider make the corrections, otherwise you can get autoguiding
and PEC corrections “fighting”.
The other is to use the autoguider to make the PEC adjustments.
When I had an LX200, I used the autoguider to make PEC corrections,
then used the autoguider normally when imaging.
I always added a counterweight on the East fork arm to make sure
that the RA drive was always under pressure.
Cheers
--Ivor
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