From: albe albo <richter1956@yahoo.com>
Date: April 26, 2010 12:48:31 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Encoder self-correction question....
Hi Milton,
perhaps my english lacks a little because i'm not sure i understood your words.
The TDM device doesn't work on the mount's PEC but it continuously monitorize the AR axis while it is in a working session and it reads (always in real time) all the rotational errors of the mount and it makes continuous corrections. It could be used in addition to pec and in addition to the autoguide or it could be used to read the periodic error without stars but that is a very secondary usage.
.
Basically it seems that a EQ6 could be easily corrected to +2 -2 arc sec then, but, if you want a higher precision, you may add the autoguide that will be more effective since it will have to correct a very sweet error of 4 arcsec peak to peak instead of a +-20 arcsec.
That device is stand alone: no computer, no pec needed: it does all the job by itself.
That was my idea: putting a precise encoder clamped directly on the RA axis and read the errors relative to an ideal sidereal motion. At this point astroIIDC should use the encoder information to guide realtime the precision of the mount. If the target is +- 2 arcsec i guess that it worth.
Anyway it could be a nice field for an experiment.
I'm frightened by the price of the encoders: i saw one with 0.28 arcsec resolution
http://www.gurley.com/Encoders/Info/8x60.pdf
but i have no idea if it will cost 10-100-1,000-10,000 usd.
Since the complete device sold by Meade is 1350 euros, i guess that industrial encoders would cost less than half or less again. Perhaps 200 - 300 usd could be enough.
After that, the pulse from the encoder must be transformed into a signal that could be handled by AstroIIDC in substitution of the guiding star (only for AR so it is simpler).
well well... who knows?
I hope to have solicited some curiosity or a... WHY NOT to TRY?
Please Milton, returning on the batch multipoint alignment: can i choose all the point in the movies before, memorize them and then launch the multipoint alignment process night time?
TTYL
Da: Milton Aupperle <milton@outcastsoft.com>
A: Astro_IIDC@yahoogroups.com
Inviato: Lun 26 aprile 2010, 19:39:46
Oggetto: Re: [Astro_IIDC] Encoder self-correction question....
Hi Alberto;
That's basically what PEC is. The only difference is that PEC relies on you tracking / correcting a star, and that's subject to turbulence so you need a very steady night to do it or possibly miss corrections too.
A high resolution encoder should remove the need for the star and the turbulence uncertainty factor and human error, but would likely need to be an Arc second or smaller in read out to be worth doing.
Basically what I would envision is that a device is clamped to the RA axis, and then a PEC recording session is made with the amount of drift over several cycles measured. Then this data is processed and a series of PEC offsets are generated and fed back into the PEC for the scope. The next time you use the scope, you can turn PEC on and it corrects all the defects. You could do this task day or night too.
Unfortunately, all the low end mounts I know of do not allow one to read or write the PEC data directly into the mount. So this would have to be done manually by likely putting a fake star on the screen and having you push the hand controller buttons to move the star. Of course there is no feedback from your presses on the hand controller going into Astro IIDC, so you can't tell if you made the right correction or not. So I can't really see it working unless one can upload the PEC Corrections.
And a device already exists that monitors it, so I can't really see a lot of incentive to do this.
TTYL..
Milton Aupperle
On 26-Apr-10, at 9:12 AM, albe albo wrote:
Hello to all.
I just saw the "real" device that I figured out in my mind since long time ago
The principle is very simple and i guess that many people thought to it: a encoder that reads the AR axis rotation detecting any error ( periodic or not) in real time allowing a real time correction.
A kind of autoguide without stars.
Some years ago,when i thought to such device i was answered that such encoder was a dream and that it didn't exist but now i see that someone did such corrector.
The interesting fact is that changing the mechanical adapter will allow to transport the device on different mounts.
Someone have feedback about it?
http://www.mda- telescoop. com/index. php?option= com_content&task=view&id=52&Itemid=82
Now i was thinking to a Mac - Astro IIDC software based version of such device simply buying an encoder (i found one with 3,6 arcsec resolution) and attaching it directly to the AR axis.
I was thinking that even a resolution > of 1 arcsec could be used because the software could read the "trend" and correct it.
http://www.microesy s.com/drcEncoder s/pdfDRC/ Model%20M35% 20Data%20Sheet. pdf
The question for Milton: is such kind of correction so different from an autoguiding?
Which kind of conversion is needed between the phisical encoder and the USB port in order to simulate the data that AstroIIDC get from the guide star?
That device send its control pulse trough the ST4 port like a normal autoguide.
It could be interesting to do some experiments (even with rougher encoders) in order to understand the feasibility.
Thank you for the attention
Alberto