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Possible Mod to Meade LX200 GPS Fork Mount

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#1 sunrag

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Posted 09 July 2020 - 09:28 AM

Since the OTA+Fork-mount combination of LX200 GPS is quite heavy to carry (even for a 8"), I was wondering if there is a way to modify the fork-mount so that the OTA can be easily mounted/dismounted. Sort of like the Celestron 8SE but with two fork arms with saddles that you can slide in the OTA.

 

I have seen a 10" telescope which uses the same Fork-mount as the 8" telescope, but to accommodate the 10" OTA, it uses a 1" spacers at the base of the fork arms (in between the fork-arm and the base). So the 10" fork-mount already has enough space to accommodate dove-tail saddles on either side to hold a 8" OTA I think.

The wires in the fork arms probably have enough slack to allow me to put 1" spacers.

 

Are there any mechanical restrictions to prevent from doing this to my 8" LX200 fork-mount ?

 

The accuracy of go-to movements will suffer a little bit.

 

Thanks for reading!



#2 carolinaskies

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Posted 09 July 2020 - 04:35 PM

Since the OTA+Fork-mount combination of LX200 GPS is quite heavy to carry (even for a 8"), I was wondering if there is a way to modify the fork-mount so that the OTA can be easily mounted/dismounted. Sort of like the Celestron 8SE but with two fork arms with saddles that you can slide in the OTA.

 

I have seen a 10" telescope which uses the same Fork-mount as the 8" telescope, but to accommodate the 10" OTA, it uses a 1" spacers at the base of the fork arms (in between the fork-arm and the base). So the 10" fork-mount already has enough space to accommodate dove-tail saddles on either side to hold a 8" OTA I think.

The wires in the fork arms probably have enough slack to allow me to put 1" spacers.

 

Are there any mechanical restrictions to prevent from doing this to my 8" LX200 fork-mount ?

 

The accuracy of go-to movements will suffer a little bit.

 

Thanks for reading!

First, the only difference between an 8-10-12-14" are the fork arms. The larger the OTA the more the fork arms are made to support the weight, girth, and length of the OTA.  

The difficulty in doing this two fold.  The alignment of the forks themselves and then the alignment of the OTA within the forks. 

First, both fork arm spacers would need to be exactly identical so the outward spacing is correct. Second, you would need to ensure both fork arms are mirror image in exact position in offset of the attachment point.  If you look at the fork you'll note the holes in the fork arms allow a lot of adjustment so making sure both arms are aligned will be a devil of a time. That's both in up-down, forward-backward, and tilt.  

Once you get the fork arms trimmed right then you'll have to figure out how to allow adjusting the OTA within whatever method you use to mount it in place.  The OTA carriage-arms are shaped to the curvature of a specific diameter OTA. You'll have to allow adjustment once again in relation to the DEC axis and RA axis. If either of these is not perfectly square/parallel/perpendicular you'll induce more error. 

The error that you create in the system is what is called 'cone error' which is the difference in alignment between where a fully aligned system knows it is pointed and where the OTA is actually pointed.  Cone error is mainly seen in GEM/CEM mounts where the saddleplate or the OTA is not align to the DEC.  In your system it would also include the same issue with RA.  

Visually small cone error is acceptable.  For AP it induces guiding issues.  

Not to say it can't be done, but creating a 'repeatable' alignment of the OTA would be critical.  

Better is the methodology of the 16" LX200 and the LX600 series where the forks are split 



#3 Peterson Engineering

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Posted 10 July 2020 - 10:32 AM

About 16 years back I worked with Ted Agos on a saddle approach for separating the LX200GPS fork from the optical tube.  Ted modeled this on a 10".  Rather than dove tails on both forks this approach used a plate that connected to both forks and the scope would drop onto it for simple mounting.  The plate was a cradle shape so that the centerline of the scope wasn't displaced.

 

Seem to recall that the reason that Peterson Engineering gave this a pass was the cost of the cradle assembly and problem was that the upgrade was too complex for many customers.

 

Good thinking though SUNRAG


Edited by Peterson Engineering, 10 July 2020 - 10:33 AM.

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#4 junomike

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Posted 10 July 2020 - 04:12 PM

I'd seen a few Mods before but most were tricky/complex.

This is most likely the reason Celestron released the SE/Evolution series and Meade the Lightswitch series



#5 OzAndrewJ

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Posted 10 July 2020 - 05:33 PM

Gday Pete

 

Rather than dove tails on both forks this approach used a plate that connected to both forks and the scope would drop onto it for simple mounting.  The plate was a cradle shape so that the centerline of the scope wasn't displaced.

I also looked at this years ago, and note some of the new ETX units have a cradle approach.

I was also going to go the dual dovetail route, but realised to get the strength at the axle joints

i needed to pack the lower fork arm joints as well, so gave it up as too much work.

 

Andrew Johansen Melbourne Australia



#6 sunrag

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Posted 11 July 2020 - 04:59 PM

Thanks for the advice, guys. One of the reasons for doing this is because I like the Alt-Az mount very much, and would try to use it for my other telescopes or possible a bino. Hence the thought of modifying it, but this is something to do if I ran out other things to fix/do!



#7 Daveatvt01

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Posted 13 July 2020 - 07:11 PM

I had a kinda similar idea with a set of spare 10” LX200 Classic forks. It works for RA tracking on a wedge with shorter length scopes. I have never tried to see if the goto is accurate.

IMG 0511

 

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