LX200GPS - External encoders & de-clutched manual slewing?

Omaroo (Chris Malikoff) · #1 25-09-2007, 05:13 AM

Hi all

I'm just wondering if anyone has heard of, or has seen reference to additional encoders for the LX200GPS?

One of my main problems with this telescope is the slewing noise. My back yard is surrounded by Colorbond fencing which tends to amplify the noise in the dead of night to the point where've actually had neighbours stick their heads our of their windows at 2:00am and ask what the hell's going on. Not that my LX is any louder than the next - it's just part and parcel of the breed. Those motors are not, uhmm.. quiet.

The main problem is that when you set up and achieve alignment, all movements from that point must be under motorised control in order to maintain the alignment.

What I'd love to be able to do is de-clutch and manually slew, silently, to my next object whereupon I'd re-engage the clutch to track the object I've found and want to stay with. The only problem with this is that the LX200GPS loses all sense of position if this is done, and uses the last-motored-to point as its last reference.

IS there an external Argonavis-type external encoding system that would allow me to move the scope manually in push-to mode? I notice that Wildcard Innovations (Argo Navis manufacturer in Australia) lists installation kits for most SCTs but excludes, in particular, the LX200.

I guess that if there was you'd then use either the Autostar OR the push-to system but not both. It would be nice to have the external system feed back the current pointing parameters to the Autostar so that even de-clutched and moved it would still know where it was.

At least if de-clutched and manually moved, the scope forks would still sit there and track in RA for photography. You wouldn't need GOTO just to achieve that unless you planned to move to another object under Autostar control - which I have star maps to guide myself with anyways.

Does anyone have any experience in this at all?

Cheers
Chris

nightsky · #2 25-09-2007, 07:09 AM

G'Day Chris,
If you don't get any help here,maybe you should try this group
http://tech.groups.yahoo.com/group/LX200GPS/
and here is another one worth trying.
http://tech.groups.yahoo.com/group/MelbMeadeScopes/
Good luck
Cheers
Arthur

AndrewJ · #3 25-09-2007, 01:03 PM

Gday Chris

There are two things you can do to keep the noise down
1) You can set a maximum slew rate in the Hbx
This limits the slew rate to whatever you enter in degrees per second.
Thus your slewing to target may take a bit longer, but the motor noise dies dramatically at the lower rates, and the autostar alignment stays good.

2) If you are polar, you "may" be able to declutch without losing alignment, but "only" if you are polar.
I havent tried ( accuracy wise ) with large sky traverses, but the HBx has a synch function, which effectively reorientates the scopes idea of where it is pointing
If you were on one target, you could select yr new target via the Hbx but dont hit goto. This preloads the scopes target data to the new object.
Declutch and manually slew to new target. Use HBx to do a fine centre, then do a synch. This tells the system to set its idea of where the encoders are to match the new target.
That "should" work, but it relies on "you" getting the target ID correct, as you cant use the HBx readout to tell you where you are whilst doing this.
( You can use the manual setting circles in the normal manner to assist in doing the manual slew, that will get you very close )

Andrew

Omaroo (Chris Malikoff) · #4 25-09-2007, 01:12 PM

You've probably just answered my questions Andrew. Thank you. Move the scope after de-clutching and "Sync" to a known new target. OK - time to try it out

The scope is in polar mode, and that's not a problem. It will still be aligned with the SCP wherever it is. It's the wedge surface that retains the alignment- not the forks.

PS: Even on the minimum acceptable mechanical slew rate, the motors are still too noisy. My backyard is pin-drop quiet at night, and I don't really want to advertise an expensive telescope to some of the neighbours we have - hence all of this.

Cheers and thanks!
Chris

LX200 · #5 25-09-2007, 01:39 PM

Chris i think you can manually go to where you want
1st select where you want 2 go
the computer then calculates and shows on the screen
move manually
then centre and sync

Mind you i haven't tried this yet

Omaroo (Chris Malikoff) · #6 25-09-2007, 01:44 PM

Andrew - you've saved me. It works a treat! I feel like a complete twit not knowing about the sync feature. How fabulous is that! I've managed a wedge-based polar alignment such that I get a target into FOV on slew, but never knew about sync - after owning the scope for nearly a year!!!

Thanks!
Chris

Omaroo (Chris Malikoff) · #7 25-09-2007, 01:47 PM

Quote:

Originally Posted by LX200

Chris i think you can manually go to where you want
1st select where you want 2 go
the computer then calculates and shows on the screen
move manually
then centre and sync

Mind you i haven't tried this yet

Yep - works well Robert

I really can't fathom why i never knew about this. I was always under the impression that you just had to slew everywhere under motor control!

Yay! I feel like a new man

One does have to love this site for the right reasons.....

AndrewJ · #8 25-09-2007, 07:32 PM

Gday Chris

Re

Quote:

I've managed a wedge-based polar alignment such that I get a target into FOV on slew,

When i mentioned this process "may" affect yr alignment, it was specifically to do with slewing.
The LX200GPS creates a basic error map if you do a polar twostar align.
( Ie how far off the pole you are aligned ), and factors this into its object calculations. However, this only assists in goto accuracy. Doing synchs like you are doing may/will mess this up a bit, but it wont affect you if you are doing manual slews.
Once tracking again, this polar error isnt factored in, so its moot.
And anyway, if you find yr std gotos show bad accuracy later
a quick realign will fix it.

Andrew

Omaroo (Chris Malikoff) · #9 25-09-2007, 09:54 PM

Quote:

Originally Posted by AndrewJ

Gday Chris

Re

When i mentioned this process "may" affect yr alignment, it was specifically to do with slewing.
The LX200GPS creates a basic error map if you do a polar twostar align.
( Ie how far off the pole you are aligned ), and factors this into its object calculations. However, this only assists in goto accuracy. Doing synchs like you are doing may/will mess this up a bit, but it wont affect you if you are doing manual slews.
Once tracking again, this polar error isnt factored in, so its moot.
And anyway, if you find yr std gotos show bad accuracy later
a quick realign will fix it.

Andrew

Andrew - thanks for replying again. When I previously used the word "aligned", I meant that situation when the scope's software and real sky were in alignment - i.e. the scope knew where it was in three dimensions (four if you include time) after a two-star alignment such that GOTO's work to within a standard 25mm EP's FOV. Being in polar mode, it should be taken that the fork axis was already pointing directly at the SCP - which is where I really should use the word "alignment" in its proper context I guess. Given this, a manual slew to an object, followed by a clutch re-lock should allow object tracking in RA irrespective of whether or not the scope was re-synced or not on that new object - no? Of course, it's easy enough to do that now!

Thanks for the help on the sync capability again. What a ripper!

Cheers
Chris

AndrewJ · #10 26-09-2007, 07:21 AM

Gday Chris

Quote:

When I previously used the word "aligned", I meant that situation when the scope's software and real sky were in alignment - i.e. the scope knew where it was in three dimensions (four if you include time) after a two-star alignment such that GOTO's work to within a standard 25mm EP's FOV.

After doing this manual procedure, the scope should stay fully aligned as per above,
ie normal gotos should still work, just the accuracy may drop off a little.
Ref caveat at bottom though.

Quote:

Being in polar mode, it should be taken that the fork axis was already pointing directly at the SCP -

Ahh but its not normally, its nearly always off by a bit.
With the Meades, when you do a twostar in polar, it factors this true error into its later calcs, but that doesnt affect tracking once on a target,
Only goto accuracy.

Quote:

Given this, a manual slew to an object, followed by a clutch re-lock should allow object tracking in RA irrespective of whether or not the scope was re-synced or not on that new object - no?

Correct. Tracking is just the RA motor running at sidereal.
( Plus tracking rate and PEC if selected )
Ie No different to a basic RA clock drive
However, just starting your scope unaligned in polar starts the drive,
so if you want a really quick and quiet ) full manual operation, just turn on the scope and use the clutches, dont even bother to align or do synchs.
It wont know (or care) where it is, but it will track.

One caveat for anyone else thinking of doing this.
The Meade uses an encoder count from home to ensure it doesnt crash into the hardstops. Doing this procedure for all sky slewing will almost certainly make it lose the plot ( even if you do synchs ).
Thus, if you do use this method, DONT use normal goto slews again without properly realigning first, as you "may" end up crashing into a hardstop at full speed.

Andrew