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GP-DX understanding Problem (RA Axis)

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#1 yashi

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Posted 21 October 2012 - 06:12 AM

Hi,

ive got an understanding issue with my new GP-DX. I dont get how the RA circle works

Posted Image

from left to right. theres an Arrow pointing to the black circle and a noniusscale on the green metal casing.
it would make sense if these + the black scale are used to find objects. BUT the small thumbscrew fixes the blackscale to the casing, which means it wont move if you rotate the scope around the RA axis.
The next ring with a scale(the shiny/silver/white one) is fixed to the axis, but i take it that this one is for the polarscope if i attach the protective cover im not even able to see that scale.
Posted Image
this is what i would see when im done setting the scope up. the black scale is fixable and isnt fixed to the axis. How am i suppost to use that if bose scales are fixed to eachother o_0

:tonofbricks:

#2 rmollise

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Posted 21 October 2012 - 08:48 AM

It is a little confusing. If I recall--I have never used the tiny setting circles on GEMS much--you Leave the screw loose during object location. When you are on an object, you tighten it down so the RA reading will remain the same as the mount tracks. The black scale is a vernier to increase your accuracy somewhat.

#3 yashi

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Posted 21 October 2012 - 09:49 AM

thanks for your reply.

en you are on an object, you tighten it down so the RA reading will remain the same as the mount tracks.


This would mean the ra axis and the ra circle dont have a hard connection, otherwise it would block the ra axis too if i tighten the thumbscrew.

Right now my ra circle is just "floating" on the ra axis. sometimes it moves sometimes it doesnt. i already opened the whole thing. but i dont see how this should work :/. circle and axis obviously can be connected with a screw -> would render the blocking screw useless

here are a few more pictures of the inside
http://arnholm.org/a.../gpdx/index.htm

#4 rmollise

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Posted 21 October 2012 - 10:13 AM

I'm not at all sure what you mean by "hard connection." You tighten the little screw above the circle to _keep it from changing as the scope tracks_. If you do NOT do that, your RA circle's reading will become progressively farther off. If it sometimes moves and sometimes does not move, you don't have the thumb screw either loose or tight enough.

#5 yashi

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Posted 21 October 2012 - 10:59 AM

with hard connection i mean screwed to the axis for example. this would mean i couldnt lock the ring because it would lock the axis too.

right now i can lock the ring. but if i do not lock it it will just float randomly around the axis. its not bound at all to the axis.

#6 rmollise

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Posted 21 October 2012 - 12:33 PM

The little setscrew doesn't have anything to do with locking the mount's axis. Don't believe me? Try it. ;)

When it's not locked down, that exactly what SHOULD happen.

#7 yashi

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Posted 21 October 2012 - 01:25 PM

The little setscrew doesn't have anything to do with locking the mount's axis. Don't believe me? Try it.


i know. if i screw it down i lock the circle

if i dont screw it down the circle rotates freely. with free i mean moving the axis has no effect on the circle because its not connected in any way to it

#8 Starhawk

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Posted 21 October 2012 - 05:21 PM

It's free to move so you can align it with local time. The polar scope has to be aligned with the pole, so it is separate.

I know this sounds odd, but at the end of the day, they aren't really all that useful. It is vastly easier to point at an object (like Vega or Sirius, for example), and use it to set the setting circles if you want to use them.

-Rich

#9 rmollise

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Posted 21 October 2012 - 07:04 PM


i know. if i screw it down i lock the circle

if i dont screw it down the circle rotates freely. with free i mean moving the axis has no effect on the circle because its not connected in any way to it


One last time:

Loosen the setscrew to find objects.
Tighten to track.

But it is your mount, and I think you should use it any cotton-picking way you want to... :lol:

#10 yashi

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Posted 22 October 2012 - 01:34 AM

losening the setscrew has virtually no effect. it still wont turn with the ra axis (its not connected to it in anyway, it just touches it)

if i losen the setscrew and put the protective cover on, the ra circle will be fixed, because the drag of the protective cover on the circle overcomes the drag between the circle and the axis. the cover is just an example it doesnt even need that much drag to stop the ra circle from moving. even without any resistance at all the ra circle wont follow properly

#11 rmollise

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Posted 22 October 2012 - 06:42 AM

Should definitely turn with the RA axis when the setscrew is fully loosened...

#12 yashi

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Posted 22 October 2012 - 07:50 AM

exactly.
and i want to know why my isnt doing it/ how the ra circle should be connected to the axis, because i can not find anything about it :/ i even took it apart but there is nothing to connect the axis with the circle.

#13 rmollise

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Posted 22 October 2012 - 11:22 AM

I believe that typically there was no connection, friction caused the circle to move with the RA axis. Sounds like your circle is loose.

#14 yashi

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Posted 23 October 2012 - 04:55 AM

thanks for your help.

but the parts do not look worn down :/

it would be awesome if someone with the same or similar mount would take a look at it. i Really want to know how it is suppost to work.

#15 Wouter D'hoye

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Posted 23 October 2012 - 05:14 AM

Hi,

I own a GP-DX and I have to agree with Rod. Now it's possible that the ring is loose and that you need to somehow tighten it on the shaft so it has better grip and rotates with the shaft. Mabe just applying some tape on the shaft so it fits more snugly could do the trick.

I have one too, i'll try to take a look at it when I get home this evening.

Kind regards.

#16 yashi

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Posted 23 October 2012 - 07:32 AM

thanks this would be awesome!

if it all fails i will do it with tape. but seriously i thought the gp-dx is decently made...how worse could it be, if i have to fix a mechanical instrument with duct-tape O_O

#17 yashi

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Posted 24 October 2012 - 08:47 AM

so far i couldnt find a solution

#18 planet9

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Posted 26 June 2013 - 05:23 AM

hi Sorry for digging out old thread, but this is very relevant to what I am up to these days. Have you got answers to this questions? cheers.

#19 orlyandico

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Posted 26 June 2013 - 05:33 AM

Search on Google for the Takahashi EM10 manual.

It has a very good description of how to use these setting circles.

They are actually very cool. Poor man's GoTo that works all the time...

#20 John Carruthers

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Posted 27 June 2013 - 03:05 AM

You can find the gp-dx manual here;
http://arnholm.org/astro/gpmanual/

The verniers are good but take some getting used to. If you ever used vernier calipers it comes easier.

As mentioned, off set from a known target is a quick way to get aligned.

#21 photonhunter

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Posted 28 June 2013 - 11:47 PM

You tighten the set screw when using the polar alignment scope to use the RA ring as an hour graduation ring. Normally when observing it should be loosened.

The RA ring (with the set screw loosened) should have enough friction to follow the RA axis as it turns.

#22 planet9

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Posted 01 July 2013 - 07:30 AM

hi

Do I need some kind of auto tracking or GOTO interface for the auto tracking with GP-DX mount? I have just the GP-DX fitted with RA and DEC motor and DD-1 two axis controller. I can move the scope with the controller to both axis, but I do not know how to activate auto tracking.

When stationery, I can hear the GPDX motors ticking away, so I was under impression that they are auto tracking, but when I check the EP, they are not.

Thanks.

#23 rmollise

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Posted 01 July 2013 - 09:11 AM

The mount will track when turned on. Remember, it will be very slow movement. For go-to you will need new motors and a new controller.

#24 planet9

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Posted 01 July 2013 - 01:15 PM

Is a lot slower than it should be?

#25 John Carruthers

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Posted 02 July 2013 - 02:43 AM

how slow? it should track at 1 rev / day.

I suspect you have MT1 motors and a basic guiding handset.
If you can find an old Vixen Skysensor 2000 it might help. I fitted a Skywatcher Synscan goto drive set to my Vixen SP but the Ioptron drive set will also fit.






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