**??Autoguider to train drive PEC??**

[dugnsuz]

Hello...
Happy to say managed to get all the bits and bobs of my autoguiding setup to talk to each other and work!!:eyepop:

Then a thought arose, (lookout, dangerous cogs turning!)...

Could I use the webcam and software etc to train the drive on the mount in PEC mode?:shrug:

...I thought, probably not as on the SynScan V3.10 handset it looks like a manual affair by pushing buttons but I wondered if it might be possible on my low-end setup. I'm sure I've read it being possible on dedicated autoguiders.
Anyone tried?
Cheers
Doug:thumbsup:

[EzyStyles]

heya doug. Autoguiding will compensate for any PEC errors, inaccurate polar alignment etc :) , mine is "shocking" :P

[Alchemy]

ii agree with ezy, i cant see why you could not use it to train your pec , however if you auto guided over the top of your corrected setup i imagine the pec would turn off or retrain, thereby defeating the purpose.

[dugnsuz]

Hi Eric,
I hope to optimize all the variables - best polar alignment, least PE etc in order to give the autoguider an easy ride!!:lol:
Doug:thumbsup:

[avandonk]

PEC is really only a measure of the quality of mechanical drives of your mount. With autoguiding it is irrelevant.

Backlash and any microjumps in gears (if present) are far more of a problem.

Bert

[turbo_pascale]

Well, not quite "irrelevant".

If your PEC has been trained (in any way - including an autoguiding setup), the autoguider will have smaller corrections to make (because they will have already been compensated for). Hence, systems such as the ones in the Meade LX200 allow you to "Train PEC", and then "Update PEC" to further refine it.

[dugnsuz]

That's what prompted my question I think Bert.
When watching the star being guided by PHD there seemed a regular glitch in its motion. The scope was out of balance - DSLR had been replaced by the Toucam and I hadn't rebalanced in my rush to test out the autoguiding:doh:
I hope that's the cause.
As to backlash - there is the possibility of setting backlash, but I have no idea what figures to enter or know if the figures I enter relate to the backlash I have!!! QUE!!!!!!:lol::lol::lol: Sounds Rumsfeldian!!!

:sadeyes: I don't know what I know I don't know anymore:sadeyes:

Doug!!!:thumbsup:

[alan meehan]

hi doug just set your backlash to zero

[g__day]

Absolutely you can, provided you can find some autoguide software that is happy to run the LPI from.

I initially trained PEC on my mount using the autoguider OTA -> Meade DSI -> ASCOM -> PHD -> Shoestring adapter -> Mount hand controller

Next step for me is to better polar align my mount and then and only then train PEC from the primary OTA not the autoguider OTA.

The next step beyond this is to do multiple training runs - throw the data into software like PEMPro to statistically average it and take the resultant master curve and upload this to your mount. Doing this would even out corrections triggered by seeing rather than mechanical properties of your mount.

[JohnG]

Providing your PE is even and is not subject to sharp spikes, your autoguider should be able to handle it without being trained.

Probably the best way I have found to handle PE is to weight your OTA slightly to the East, ie if the tube is on the western side pointing east, slide your counterweight down very slightly, if your OTA is on the eastern side, slide your counterweight up slightly, this keeps an even weight on your worm and it is in constant contact. If you balance too finely, your worm can occilate slightly causing your stars to elongate slightly if there is a lot of play in the gears.

As already said, set you backlash to zero, PHD will do a check on your backlash and compensate accordingly.

Cheers

[dugnsuz]

Thanks all
Doug

[g__day]

For simplicity what John just said is great advice. For best results I would advocate eliminate or minimise as many sources of error as can be achieved.

Your treatable sources of error include

1) polar alignment error - the better you have it - the fewer corrections are required, the fewer corrections are required - the fewer mistakes may be made

2) mechanical faults - backlash, poor mating of gears, imperfection of the gears. This is pretty common. If you can see you gear run through a complete worm cycle you can look for disruption to smooth flow. If the gears are too close together, have crud on several of the teeth or are not perfectly circular then they may stall or briefly lock then jump in places when enough torque has built up to force through the blockage. This is highly undesirable. You may be able to change the separation distance of the power gears (vs the worm and main gears) to avoid locks and stalls. However doing this increases the play and backlash so it's a balancing act that is ultimately determined by how clean, smooth and circular are your gears and how well machined are their teeth.

3) balance issues - close to perfect balance is preferred. A slight imbalance is of little concern - provided it is slight (e.g. maybe 500 grams of weight imbalance)?

4) Once the gears are as closely positioned and clean as suits, and polar alignment is excellent - then PEC training could and should help address bad PE curves so again PemPro or PrecisionPEC should help. Do an average of say 10 runs every 3 months to account for wear and tear on the gears.

5) Seeing errors - well I guess the light reach, seeing conditions, focal length of autoguider versus prime OTA, pixel size of your guide CCD will determine how well you can distinguish mechanical or alignment corrections from seeing aberrations. The main things I can suggest is the closer your guide OTA is in focal length to your prime imaging OTA and the finer your seeing and the finer your guide CCD micron size - the better you can determine and correct true tracking versus seeing errors.

Start simple and get more adventurous as you build up experience.

[dugnsuz]

Thanks g_day for an excellent breakdown of the points
Cheers, helps a lot
Doug

[jase]

All very sound advice by others, JohnG and Matt (g_day) in particular.
Simply training PEC while autoguiding is better than no PEC at all. If you’ve got a mount capable of PEC, you’d be foolish not to use it to extract maximum performance. Anything you can do to reduce the quantity of guiding corrections made by the auto-guider is a benefit. Each guiding correction is a chance for error such as over correction, troubled seeing etc.

As Matt highlights, the best possible way to record PEC is to perform multiple runs. A single run is one revolution of your worm/gear. If your mount supports it, you can record multiple runs and average them. This is something can be performed with the Gemini system. Most mounts only allow one PEC run.

By performing multiple runs, it is possible to eliminate seeing conditions influencing the result thus what you get is the raw PE of your mount. Software such as PEMPro will do multiple runs and analyse your data to produce a PEC curve which is then uploaded to your mount.. I’ve been using it for approx two years and swear by it. Version 2 now supports a polar alignment assistance tool which is quite handy.

As luck would have it, a few nights ago I used PEMPro to re-record PEC, so I’ve attached a few sample screen shots. The first image, shows the PE over 5 worm/gear revolutions - note the inconsistencies between each run (though there are some similarity between runs at ~1:20mins & ~4:40mins - total worm period is a bit over 5 mins for the Titan). The second is the PEC curve PEMPro recommends after the analysis. You can tweak this curve further if desired, but usually it’s sufficient as is. I’ve gone from a PE of +2.9/-2.3 down to +1.7/-1.5. I feel sure I could correct it better – considering I’m using a short focal length instrument (FSQ-530mm) to record this. For a wide field instrument, demands are considerably less. A longer focal length would obviously emphasise PE more. Ultimately, you should record the PEC curve at the focal length you’re imaging at or what ever is the longest instrument you have.

Happy to answer any questions you may have regarding PEMPro.

Note, PEMPro V2 now supports webcams for PE analysis.

[g__day]

Jase,

I'm still waiting for Ray Gralak's next release - but do you know whether PEMPro V2 supports a Meade DSI directly?

I got the feel you need KCCDTools or MaximDL to run some/all supported CCD chips and this feeds the image for review into PEMPro for analysis - is that how it all works?

Matt

[jase]

Yes, that is correct Matt. Camera control is performed by either CCDSoft or MaximDL. The only exception to this is when using a webcam as this uses Microsoft DirectShow.

So, if you operate a camera that is supported by either software package it will work. MaximDL is certainly the premium package when it comes to camera support. For example it supports the following cameras: Andor Technology, Apogee, Audine, Canon EOS, Cookbook CB245, DTA Scientific Instruments, Ethernaude, FLI, HiSIS 22/44, Lumenera, Meade DSI/LPI/Pictor, Nikon DSLR, Olympus DSLR, Optronics, Orion Starshoot, SAC, SBIG, Starfish, Starlight Xpress and Yankee Robotics. It can also support other cameras under the proviso that they're ASCOM compliant. This is achieved through camera plug-ins.

So, to cut a long story short - Yes. You can use PEMPro with a Meade DSI through MaximDL. There is no benefits for PEMPro to have direct support for a specific camera such as the DSI. Its easier for the software to remain autonomous and leave camera control API calls to software such as MaximDL or CCDSoft. Thus, you maybe waiting a long time for "direct" support.

The camera control package is used to take calibration images that you must interact with. i.e. one test is an exposure with no guiding enabled. You then select the star trails (from start to finish). PEMPro analyses this to work out camera rotation and arcsec/pixel combination. There are a few other tests which determine mount movement methods, not to mention the tracking of a star through the multiple worm cycles. The process is rather fool proof.

I should note that if you have a Takahashi mount, they don't support PEC. I don't know why. I know they track extremely smoothly and have a low PE... but when considering this, so does the ParamountME but it still has PEC support. ?weird?

Hope this helps.

[avandonk]

I still am of the opinion that a stochastic variation superimposed on a slowly varying 'PE' will not benefit from any pec training as far as autoguiding is concerned. It is even more apparent when no two cycles are the same. If the mount has very high pe variation then it will inevitably have backlash and poor 'jumpy' gears.

I have two mounts with belt drives and they have no discernible backlash and are very smooth. There are no gears. In fact if I set the aggressiveness to high I can get lovely 2 or 5 second of arc oscillations with constant period as the system starts off by chasing the seeing and then keeps self overcorrecting.
If I set any backlash value the same thing happens.

It basically is a matter of balance to get all the variables correct. I think it is foolish to correct for something that is itself unpredictable unless you have a lookup table for a 360 deg cycle. Then you have to know where you started!

Or am I missing something?
Bert

[g__day]

A periodic error one would expect to be predominantly non stochastic (random). If ever circuit of the gears has varying motion you have much bigger concerns to settle. Yes if that were the case motion could be smooth or jerky - I don't know what you are assuming.

But if an error is significantly consistent it can be distilled (averaged) inverted and modeled out - think of how active sound dampening systems can kill 80% of regular noise (like a jack hammer) when switched on.

Seeing error can be modeled out with multiple runs and few simple f or z tests given you'd expect a Poisson distribution curve (a.k.a. a normal distribution curve). If tracking errors changed with temperature over the course of a night you'd have a greater challenge modeling this out unless you modeled PE against temperature and had a more sophisticated PE system that had a temperature look-up against multiple PE tables.

Large smooth error is simple to guide out. Consistent error can significantly trained out. Large, jerky, inconsistent tracking errors are a total pain - shifting weight balance alone may or may not help depending on why the gears and bearings are causing said behaviour. Put simpler I can see mechanical machining issue where weight imbalance would help and other situations where it could hurt - or of course the situation where both types are encountered in a revolution of the gears.

PE training is an averaged, non temperature adjusted 360 lookup table of your entire gear though one complete revolution of the worm (versus the main gear). It should help remove consistent errors and most users who share there findings online say it does.

My mount for instance knows exactly where it is when you start PEC training - be it on gear tooth 1 or 360 or anywhere in between. Average enough runs and you signal to noise in track error should be so high consistent error is mapped out - and that is all PE correction training should ever be.

Backlash plays multiple roles and it certainly comes into consideration when issuing corrective commands. If backlash settings are poorly modeled then executing any correction - from PE or auto-guiding - can make things worse.

[avandonk]

Thanks g__day for your explanation from your obvious experience. I have an EQ6 with heavy duty steppers and belt drives instead of the usual gears. It is all run by a Mel Bartels system. It has got a facility for PEC but I dont bother to use it as I have to set the correct point on the RA worm pulley to correspond with the software correction point. I will check it out to see if it is worth it for autoguiding.

Autoguiding is working very well without it. Is there a stand alone program to measure PE from a guidescope image?

Bert

[g__day]

There are several free or commercial variants or free fro propreitary mounts - I'm still experimenting myself.

AudeLA is free http://www.audela.org/english_audela.php

PrecisionPEC is expensive and only for Paramount's https://www.bisque.com/PPDL/default.asp

PECTool is free but only for Celestron mounts http://www.celestron.com/c2/images/files/downloads/1143676297_pectoolinstall1.zip

PEC Utility Tool is free but only for Meade LX200GPS or RCX400 mounts http://www.meade.com/support/auto/pectoolinst.zip

PEMPro is commerical, but requires a camera control program like MaximDL or AstroArt or CCDSoft5 http://www.ccdware.com/Files/PEMProV2-2.00.31.exe

[AndrewJ]

Gday

Re

Just a caveat
I cant say for sure with the RCX, but if you have an LX200GPS/R
and have late version firmware ( ie with 3turn 24min RA PEC ),
the Meade PEC tool will corrupt your data if you write back to the scope.
Also, it can only show ( badly ) what is recorded in the scope, it cant "analyse" a webcam image etc.

PEMPro currently will work with std webcams, you no longer need dedicated astro software packages to make it work.

Andrew