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Using my Meade lx200 *" GPS SMT like a 70s Model

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#1 p3aul

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Posted 28 March 2020 - 06:00 PM

I posted a similar question on FB in Lx200 group there and got some good info but didn't get any satisfactory answers to my problem. Many of you may not remember the 70's or have scopes back then but perhaps a few may be able to help me. 

 

I had a Celestron C8 back in the 70's before electronics. It had a motor. I put it on a wedge , looked up RA and DEC an found the object and turned the motor on. The tracking was like a clock so no sidereal rate, but it kept the object in view long enough for others to view also. I'm not into AP so visual is enough for me.

 

In getting back into Astronomy, I purchased a Used lx200 8" GPS and as far as I can determine it is in excellent condition both physically and electronically. My biggest problem is LP and being unable to find a dark site close enough to me. This is why I want to use the scope the old way  as I can't see alignment stars. The scope was expensive even used and I want to at least see and track something while I relearn the constellations and DSO objects I have forgotten after the kids came along and I had to sell my C8 bawling.gif

 

Can I do this the old fashion way on my Lx200 GOTO?

 

Thanks,

Paul

 

 



#2 OzAndrewJ

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Posted 28 March 2020 - 06:14 PM

Gday Paul

Yes you can, but what i suggest is you set up on the wedge and do a proper polar one star align.

You should be able to see the "bright" stars easily in the finder.

As you are visual, if you cant see the align stars, you wont see anything else, so it wont hurt.

Also, what you can do with an LX200GPS is you can slew to a new area, find a known bright star

and do a synch. Then you can use the basic goto functions to place local objects into the EP.

Andrew Johansen Melbourne Australia


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#3 nitegeezer

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Posted 28 March 2020 - 06:24 PM

Like Andrew says, and he is the true Meade expert, you must use a wedge for this to work. Without the wedge, the scope is in Alt/Az mode and without alignment it has no idea where it is. In Alt/Az mode, both motors are needed to track where with the wedge only one motor is needed.

#4 OzAndrewJ

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Posted 28 March 2020 - 07:02 PM

Gday Chuck

Actually, even in AltAz, you can do a dummy align if required

and the mount will track quite well. Just level the base best you can before starting

Again find a nearby bright star and goto it then centre/synch and it will track happily

and also do reasonable gotos in the local area.

 

Andrew Johansen Melbourne Australia



#5 nitegeezer

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Posted 28 March 2020 - 07:09 PM

Like I said, Andrew is the EXPERT!!! Thank you for that update. I did not think that would work in Alt/Az mode!! That could be useful at outreach events where I want to get up and running fast!!

#6 OzAndrewJ

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Posted 28 March 2020 - 07:34 PM

Gday Chuck

 

Its very useful.

Most people dont realise that when you place the mount in "Level North"

thats not really what you are doing. You are pointing to Alt=Az=0

( Thats why users in the Sth Hemi still need to point the OTA North.

As soon as you start the one or 2 star align, the mount starts tracking

and sets its encoders to Alt=Az=0, and slews to the first star using

the fact it "thinks" it is at Alt=Az=0. The first synch refines the encoders.

 

However, on booting in AltAz, it also sets the encoders to zero

As such, the cheatiest ( if that is a word ) way to get going quickly is

Set the base level as you can

Set to home position best you can

Boot the mount and enter date/time

( you must boot with the mount already in home position )

Manually set it to Astronomical mode and the motors wil starts

You are now aligned and tracking

Just do a goto and synch as reqd.

 

Andrew Johansen Melbourne Australia



#7 p3aul

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Posted 28 March 2020 - 08:01 PM

In the auto-align mode,(the first method in the manual) I can do  all the alignment except the two stars. So the Scope knows my location, knows magnetic north and has figured out "True" North. I set it very accurately to magnetic north with a good quality map compass. One thing I'm going to check though. I can set it up in my living room and make sure the time and date is set correctly. I saw that on another post. It may be the reason It couldn't locate Venus correctly. The Scope is about 15 years old and I understand that somehow the T&D didn't work correctly? Other than the star alignment(I just pressed Enter for each star) It went through the set up with no problem. Thanks for the info about skewing to the Venus and letting it track from there. It does seem like once it knows where North is it could just track Venus if I use my wedge.

 

How do you do a synch?


Edited by p3aul, 28 March 2020 - 09:47 PM.


#8 nitegeezer

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Posted 28 March 2020 - 08:05 PM

Hi Andrew,

Thanks a bunch.

As long as we are talking about encoders, is there a known index mark for absolute position or are they just relative?

The bolts on the GPS arm holding the bracket came loose a few years ago. I am going to try again to get then properly positioned. It would be a lot easier if I could put DEC in a known 90* position.

Paul, that is something you will want to check on your scope. There are three screws on each side of the OTA where it mounts to the arms. They are 2 different Allen wrench sizes, the middle one is smaller than the two outer ones. I had to cut down Allen wrenchs to get them to fit. Getting perfect alignment is not much fun, so making sure yours are tight could save you a headache. If they are loose, it is good to know as that does give slightly interesting behavior, and I think it would be catastrophic if they came all the way out.

#9 nitegeezer

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Posted 28 March 2020 - 08:13 PM

Paul,

You will want to update the firmware, the GPS had a roll over issue that was not handled correctly. Andrew is the best one for help with that.

To synch on a star, first tell the mount to go to it, and it needs to be one you can recognize when the scope does not point at it. Center the star with the hand controller and then hold down enter for 2 or 5 seconds, I can't remember which. It will say Enter to Synch and just push Enter again. The scope is then good for gotos in that area of the sky.

#10 OzAndrewJ

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Posted 28 March 2020 - 08:25 PM

Gday Paul

 

knows magnetic north and has figured out "True" North. I set it very accurately to magnetic north with a good quality map compass.

The mount only very crudely knows magnetic north and hence is less accurate for true North.

You are much better not doing an auto align.

Manually set the mount to "True" North and Level, then do a manual 2 star.

 

It may be the reason It couldn't locate Venus correctly.

There is a known bug in the firmware in that when it calcs planets, it is using J2000 coords so can be a fair way off on some planets at some times.

There is a patch out to cover that, but first things first, after your mount gets a fix

use the alternate handbox menus to check that the date/time and LST are correct for your location.

If you have been hit by the GPS bug as well, you will also need to patch the firmware,

 

Andrew Johansen Melbourne Australia



#11 p3aul

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Posted 28 March 2020 - 10:50 PM

This is a heck of a lot of information I couldn't have got out of the manual! Thanks, you Guys! I have made a PDF out of this topic so I can keep it for reference when I'm outside. If I have any questions I hope I can come back here?



#12 nitegeezer

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Posted 28 March 2020 - 10:53 PM

If I have any questions I hope I can come back here?


Just out of curiosity, where else would you go??!!!

#13 p3aul

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Posted 29 March 2020 - 01:37 PM

THIS IS THE PLACE! 

 

I have one more question! Well, It's just as I feared! The time and date are wrong. If I set the T & D manually, it reverts back when I switch off the scope. So I have the firmware issue. Now the fix is difficult involving an RS-232 cable and all, so I'm not ready yet for that. My question is: Can I enter the T & D manually for each session and do  the alignment manually like Andrew suggested? Would that work? 



#14 nitegeezer

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Posted 29 March 2020 - 01:44 PM

That works fine, I had to do that for an outreach event. Make sure you have the GPS turned off so it does not override the time you have entered. Don't have my scope or manual near me, but it is found in the telescope settings.

#15 nitegeezer

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Posted 29 March 2020 - 01:57 PM

If you change locations, you may also want to update that. It will impact how much error it has in pointing to the first alignment star.


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