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Old 18-08-2010, 04:10 PM
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BlackWidow (Mardy)
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Help Please PEC using PemPro

I am wanting to ask a few questions. I am about to get my first Wedge for my LX200 scope, so at this stage I have not ever Polar Aligned.. I am wanting to make sure the scope is up to scratch and has been updated with Peterson Gears. I have read that the PEC training that comes with the scope (meade) is not very good. I am looking at purchasing PemPro software. The question I have with doing the PEC training is if it is done once the scope is Polar Aligned, or does it get done in ALT AZ Mode.

The other question I have is once a scope is Polar Aligned and the setting is changed in the hand box to Polar Mode, I then assume that the GOTO function of the scope no longer works? or does it allow for the Polar Alignment.

I have just been using my scope in ALT AZ Mode untill my Wedge arrives (been 4 months so far)...


Any assistance would be a great help


Mardy
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Old 18-08-2010, 04:29 PM
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Octane (Humayun)
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Martin,

You would have the scope in polar mode to begin with.

The goto will work in polar mode once you've synchronised with a couple of objects.

H
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Old 18-08-2010, 05:21 PM
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Gday Mardy

PEC in the LX200GPS scopes can be done in Polar or AltAz.
When Polar, the Meade PEC "model" is normally quite acceptable,
but as you are in the Southern Hemisphere,
the data has to be inverted after training before it will work correctly.
In AltAz, i wouldnt bother as the PEC code Meade uses is severely broken.

That said, when polar, PEMPro will get you a true "Periodic Error" model, and hence will be better than the std Meade Model, which includes all the non periodic errors as well.
How much better will depend on how bad your original PE is ( the Meades can vary quite a bit ).

Goto functions perfectly well when polar, but its accuracy really depends on having a good polar alignment. Meade have a polar 2 star routine, but this doesnt always work properly, and should be avoided for permanent setups,
Do a good drift align, then just do a fake manual one star align and you are away.

Andrew
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Old 18-08-2010, 05:21 PM
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A word of warning. PEC training is only as good as the quality of the RA mechanics. LX200 scopes aren't that good. My LX200GPS has +45/-67 arcsecond PE (using PemPro) After a great deal of training I got that down to +/- 7 arcseconds. However, when I slewed the scope 90 degrees, the Pe was up to +/- 15 arcseconds. So even though you might be able to train the PE at a certain point on the RA drive, the lack of drive quality means you will not see consistant results.

In simple terms, if you need low PE on an LX200 scope then you need luck (to get a scope that just happens to have a quality drive).

Also note that Meade do not warrant PE and they stated to me that any amount of PE was acceptable - ie no fix for the poor quality of the drive will come from Meade just because you hace high and/or inconsistant PE.

I've been living with it for 10 years now and am thankful for auto guiding but it does become a major problem when no guidestar is available...
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Old 18-08-2010, 05:34 PM
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BlackWidow (Mardy)
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Thanks Guys. I think I am getting my head around all this. I Guess when using PemPro I will first need to Polar Align the scope first (Never Done this). Before I can do any Pec Correction? and do I keep the PEC turned off in the Scope once it has had PEC Correction uploaded from PemPro?

If I choose to use my Modded Toucam as a Guide Scope is it still worth while to use PEC correction?

Regards
Mardy
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Old 18-08-2010, 06:33 PM
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Martin,

I think you'll find a lot of your questions are actually adressed in the PEMPro help file. I had a quick squiz through it this afternoon. Will take about 10 minutes of reading through the LX200 section.

H
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Old 18-08-2010, 06:57 PM
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I think you will find the quality of the gears etc in the LX200 is quite good (as long as your's has the brass transfer gears and not the plastic ones). The main problem lies with the crappy motor/transfer gear/ worm mounting bracket they use. A small error when drilling the holes to mount the motor through the drill drifting will cause the mesh of the transfer gears to be less then satisfactory by any stretch of the imagination (mine had about 30% engagement at best). Of course this is not adjustable. The Peterson kit is definately a step in the right direction as it allows you to do something about it. Once you have the drive nice and tight and have retrained it in "polar mode" on the wedge, you will find the next problem. These scopes are not designed well enough to be mounted on a wedge. The fork arms just aren't rigid enough to carry the weight and the slightest hint of a breeze will ruin any exposure you try. They are very stable in alt/az mode but not polar. You can use pec to remove any error after you have fixed the drive train but I have never found a way to fix the forks (bar pulling the scope off the mount and putting it on an EQ mount). I have a solid permenent pier (200mm steel) sitting on a 3 tonne steel reinforced concrete block and it still wobbles.

Mark
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Old 18-08-2010, 07:22 PM
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Thanks Mark for your help. I am getting my head around it slowly. Thanks also for your advice Octane. But before I posted on this site I read all of the instructions including the section on the LX200 setup. As I am new allot of the terms and references are new to me. I could not find any information about needing to align before doing PEC. I have also had problems understanding if you need to KEEP PEC tuned off in the LX200, or if you turn it back on once the New PEC cure is uploaded...


Regards
Mardy
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Old 18-08-2010, 07:46 PM
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multiweb (Marc)
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Quote:
Originally Posted by BlackWidow View Post
Thanks Guys. I think I am getting my head around all this. I Guess when using PemPro I will first need to Polar Align the scope first (Never Done this). Before I can do any Pec Correction?
PemPRO will compensate for drift so don't stress too much about polar alignment.
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Old 18-08-2010, 07:51 PM
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Martin, if you want reliable PEC data you need to get everything else right first and including polar alignment would be helpful in getting an accurate indication of where corrections need to be made. Once you are sure its all setup properly do a run with at least 4 or 5 turns of the worm to make sure it is consistent. Smooth the curves a bit and upload it to the controller then turn on the PEC function. Do a few more runs with the PEC on to make sure your corrections have been effective e.g. you have less PE.

Mark
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Old 19-08-2010, 08:20 AM
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Gday Mark

Just a few comments

Quote:
I think you will find the quality of the gears etc in the LX200 is quite good (as long as your's has the brass transfer gears and not the plastic ones).
Just for info, many people still use the original plastic gears quite happily
and they are quite fit for purpose when correctly installed.
When you look at the toothcounts and gear reduction involved, it takes around a 1% "relative" error in the transfer gears teeth to give 1arcsec error at the OTA. The rest of the geartrain swamps this.
The biggest problem generally identified with the Meades are they use straight cut wormwheels, vs fully enveloped worms, and this can result in more point contact and hence tooth to tooth variability on how the worms interact.

Quote:
The main problem lies with the crappy motor/transfer gear/ worm mounting bracket they use. A small error when drilling the holes to mount the motor through the drill drifting will cause the mesh of the transfer gears to be less then satisfactory by any stretch of the imagination (mine had about 30% engagement at best). Of course this is not adjustable.
The transfer gear mesh IS adjustable within a set range, and most peoples drives do fall within this range.
You may have been unlucky, but most do fit reasonably well.
The original factory fitting sometimes leaves a lot to be desired,
but most of it is easily tweaked.

That said, the gears in the Meades are not good enough in most cases to allow long duration unguided tracking with long focal lengths.

Andrew
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  #12  
Old 19-08-2010, 06:48 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Mark

Just a few comments



Just for info, many people still use the original plastic gears quite happily
and they are quite fit for purpose when correctly installed.
When you look at the toothcounts and gear reduction involved, it takes around a 1% "relative" error in the transfer gears teeth to give 1arcsec error at the OTA. The rest of the geartrain swamps this.
The biggest problem generally identified with the Meades are they use straight cut wormwheels, vs fully enveloped worms, and this can result in more point contact and hence tooth to tooth variability on how the worms interact.



The transfer gear mesh IS adjustable within a set range, and most peoples drives do fall within this range.
You may have been unlucky, but most do fit reasonably well.
The original factory fitting sometimes leaves a lot to be desired,
but most of it is easily tweaked.

That said, the gears in the Meades are not good enough in most cases to allow long duration unguided tracking with long focal lengths.

Andrew
G,day Andrew

When you mentioned ajustment, are you referring to method 1 in the Peterson kit i.e. loosen one mount bolt whilst tightning the other to engage the gears at a slight angle? If there was another means provided I certainly could not find it and pitching the cogs on an angle is not a viable method as far as I am concerned. I may yet machine up a fully adjustable tray for mine as I am not totally happy with the peterson solution either. The plastic gears may be OK but accurately machined brass or bronze will always be better and when we consider the effect backlash has on autoguiding even if it is only a 1% will improve things (remember I only had about 30% engagement in my RA transfer wheels at best). When setup properly my meade tracks well (certainly good enough to correct with an auto guide camera) but the wobble in the forks kills it. A light breeze puts an end to imaging for the night. I don't know of many mounts that can be used unguided for long focal length AP, and certainly not at the prices meade charges for their mounts in any case.

Mark

Last edited by marki; 19-08-2010 at 07:05 PM.
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  #13  
Old 19-08-2010, 08:25 PM
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Gday Mark

Quote:
When you mentioned ajustment, are you referring to method 1 in the Peterson kit i.e. loosen one mount bolt whilst tightning the other to engage the gears at a slight angle?
Its loosen 2 and tighten 2 but yes.
In the doz or so units i have worked on, the mesh has been quite close,
so this didnt result in any appreciable "tilt" in the gearmesh.
I agree when a large change is reqd, this method cannot be used,
but an offset bushing could be used quite cheaply.
( Not sure if Pete provides them in his kits )

Quote:
I may yet machine up a fully adjustable tray for mine as I am not totally happy with the peterson solution either
For the RA, what i looked at doing was just putting the coupler plate on my mill, and slotting 2 of the three motor mounting holes.
This allows perfect fitting, but i found i didnt need it.
The DEC is more of a problem due to the slomo mechanism.

Quote:
The plastic gears may be OK but accurately machined brass or bronze will always be better
Dunno there. To me, its like gaffa taping a micrometer to the end of a wooden ruler. The major PE in the Meades comes from the GBx and worm. Properly aligning the geartrain gives much more benefit than changing transfer gears.

Quote:
and when we consider the effect backlash has on autoguiding even if it is only a 1% will improve things
Ahh but again, you are bashing yr head against a brick wall
When guiding in Polar, the RA never reverses, hence lash is no problem.
In DEC, the Meade code to apply backlash correctly is broken, and good gears wont fix this. ( I am currently trying to patch this ).
Also, for many people, retrograde motion is more of a problem than lash. Ie again it comes down to the massive variability in the Meade mounts.

Quote:
A light breeze puts an end to imaging for the night
Clouds normally kill me

Andrew
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Old 19-08-2010, 08:53 PM
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BlackWidow (Mardy)
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Someone take a U-Turn please... your heading in the wrong direction.. I wanted this thread to help me understand the PEC process using PemPro. I think its now about I think I know more than you debate on gears and mounts... Interesting stuff but did you use an ND Filter on that? and those gears are Brass? but what was the copper content of them? they may be they are too soft!



Cheers Mardy
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Old 19-08-2010, 08:59 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Mark


Dunno there. To me, its like gaffa taping a micrometer to the end of a wooden ruler. The major PE in the Meades comes from the GBx and worm. Properly aligning the geartrain gives much more benefit than changing transfer gears.



Ahh but again, you are bashing yr head against a brick wall
When guiding in Polar, the RA never reverses, hence lash is no problem.
In DEC, the Meade code to apply backlash correctly is broken, and good gears wont fix this. ( I am currently trying to patch this ).
Also, for many people, retrograde motion is more of a problem than lash. Ie again it comes down to the massive variability in the Meade mounts.

Andrew
Hi Andrew

Once I took up the slack in my transfer gears there was almost zero movement in the gears. My backlash settings went from about 70% to 10% and it was easily possible to use an autoguider to get 10 min + subs (I could not do this before I made the adjustments). I also took the time to fiddle with the worm mesh etc as I had the whole thing apart in any case and no doubt this also helped. If they were serious about accurate drive systems they would use the ball type setups found in CNC machines. I also thought of slotting the holes on my mounting plate with my mill but have come up with a much better idea I think and will try it when I get a chance if I don't rip it off the fork first. Interesting info about the behaviour under guide commands. Are you saying the mount will not respond to a guider command to reverse the work to get things back on track?

Mark
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Old 19-08-2010, 09:03 PM
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Quote:
Originally Posted by BlackWidow View Post
Someone take a U-Turn please... your heading in the wrong direction.. I wanted this thread to help me understand the PEC process using PemPro. I think its now about I think I know more than you debate on gears and mounts... Interesting stuff but did you use an ND Filter on that? and those gears are Brass? but what was the copper content of them? they may be they are too soft!



Cheers Mardy
Hi Mardy

Sorry for hijacking your thread and i will desist. You might do well by reading the stuff we are talking about though as it will directly affect what you are trying to do. Unless you get your mount to perform consistently PEC will be of no value to you at all. Couple this to the cost of a wedge......... expensive mistake???? By the way Andrew does know more then me about these mounts, I believe he works on them for a living. That said I think the best advice anyone can give if you are really serious about long exposure AP is save the money you intend to spend on a wedge and put it toward an EQ mount.

Mark

Last edited by marki; 19-08-2010 at 09:21 PM.
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  #17  
Old 20-08-2010, 07:46 AM
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Gday Mardy

Quote:
I wanted this thread to help me understand the PEC process using PemPro
But as Mark noted, you must also understand the way the gears work, so that you understand that even with PEMPro, you may not achieve a good result.
PEC can only correct "periodic" errors, and the Meade gears have many non periodic errors in them, and a wide machining tolerance.
Just bear that in mind when you see your results.

Quote:
By the way Andrew does know more then me about these mounts, I believe he works on them for a living
I dont work on them for a living, but i do minor fixes for red wine
My main knowlege is how the firmwares work.

Andrew
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Old 20-08-2010, 08:02 AM
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Gday Mark
( Mardy, the following is still useful to you as PEMPro
has a lash setting screen as well )

Quote:
My backlash settings went from about 70% to 10%
The critical part is what were the drive train results, not the %.
( Read lower bit as to why )

> Interesting info about the behaviour under guide commands.
> Are you saying the mount will not respond to a guider command
> to reverse the work to get things back on track?

Not quite. When guiding in RA there are no problems.
In DEC, the motor must reverse at times.
Most guiders now use the "pulsegide commands" where a PC sends
a command to slew "at guide speed" for ddd ms
What "should" happen when reversing is the scope should first reverse by the drive train value, THEN by the requested guide time
ie it should take out all gearslop on reversing first,
before doing the requested guide.

When you do a drive train, the scope measures total gear slop.
The "Percentage" merely tells the scope how much of this to do at high speed on reversing ( and it does it in one hit, its not ramped )

If the percentage is set to 100, then the whole lash is applied, but you also normally get a visible "kick" in the EP, due to inertial braking.
Thats why when setting the lash, you try to set the percentage as high as possible without seeing the kicking.
Ie, this process leave "some" unapplied lash
which is ( 100-%) * Drive train arcsecs worth of slop to go.

Currently, the LX200 firmware only accounts for the high speed portion, and leaves the residual unapplied. Thats what im trying to patch now

This unapplied slop has to be accounted for by the external guide commands, and can cause confusion in some calibration routines.
The better your geartrain mesh ( ie the lower the drive train values)
the less of a problem it becomes.

Andrew
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Old 20-08-2010, 06:39 PM
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Thanks for the info Andrew, very interesting but in a sense I have moved on. I have managed to overcome enough of the drive hurdles to get it guiding right but will never be able to overcome its biggest weakness, the forks when polar mounted, no amount of tweeking will fix that. Now I use EQ mounts and refractors (I know I am a woose) for AP and will eventually de-fork the meade tube and use that on a larger EQ mount with decent tracking. I may have some sadistic tendencies but I do know when to call it quits. Mardy I would think very carefully before you take the road you have proposed. It is expensive and will always lead to tears. Take the time to ask a few of the old hands around here, I am sure they will tell you the same thing.

Cheers

Mark

Quote:
Originally Posted by AndrewJ View Post
Gday Mark
( Mardy, the following is still useful to you as PEMPro
has a lash setting screen as well )



The critical part is what were the drive train results, not the %.
( Read lower bit as to why )

> Interesting info about the behaviour under guide commands.
> Are you saying the mount will not respond to a guider command
> to reverse the work to get things back on track?

Not quite. When guiding in RA there are no problems.
In DEC, the motor must reverse at times.
Most guiders now use the "pulsegide commands" where a PC sends
a command to slew "at guide speed" for ddd ms
What "should" happen when reversing is the scope should first reverse by the drive train value, THEN by the requested guide time
ie it should take out all gearslop on reversing first,
before doing the requested guide.

When you do a drive train, the scope measures total gear slop.
The "Percentage" merely tells the scope how much of this to do at high speed on reversing ( and it does it in one hit, its not ramped )

If the percentage is set to 100, then the whole lash is applied, but you also normally get a visible "kick" in the EP, due to inertial braking.
Thats why when setting the lash, you try to set the percentage as high as possible without seeing the kicking.
Ie, this process leave "some" unapplied lash
which is ( 100-%) * Drive train arcsecs worth of slop to go.

Currently, the LX200 firmware only accounts for the high speed portion, and leaves the residual unapplied. Thats what im trying to patch now

This unapplied slop has to be accounted for by the external guide commands, and can cause confusion in some calibration routines.
The better your geartrain mesh ( ie the lower the drive train values)
the less of a problem it becomes.

Andrew
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