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Angle gauge /Accelerometer mounting on truss dobs?

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#1 drneilmb

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Posted 08 March 2018 - 09:56 PM

I'm building my second truss dob and considering object locating systems. I've used unit-magnification finders (split pupil) on my other homemade scopes, but I'm quite interested in a poor man's push-to system. I use SkySafari at the eyepiece for alt-az coordinates.  I can make setting circles for the dob base, but I can't figure out how to reliably mount an angle gauge on my truss dob.

 

For visual reference  here's what the OTA looks like on the way outside last night to lean up against a lawn chair for "zeroth light"

 

20180307_205921_crop_562x1185-281x593.jpg

 

I envy the tube dob owners because they can just put a magnetic Wixey gauge on the top of the tube and I assume that it reads by default the angle between the (normal to the) device's base and the vertical, so as long as it's right on top of the tube they're off and running. (These are assumptions, I've never even seen a digital inclinometer.) 

 

But on a truss dob that doesn't have a surface psrallel to the altitude axis like the very  top of a tube dob, how do you use an angle gauge? How do you mount it so that the reference surface is parallel to the altitude axis? Once you do that, do you carry a spirit level and tip the scope to straight up, then zero (ninety?) the gauge?

 

I bought some accelerometer chips with the intention of making my own little Arduino inclinometer, but I can't figure out how to use it with this telescope design (which I otherwise love).

 

I fear that I am missing something obvious and making this more complicated than it needs to be  but I haven't figured it out yet, so it's time to reveal my ignorance on the Internet and beg for mercy. 

 

Has anyone else run into the issue that I'm describing? Has anyone figured out a solution?

 

Thanks in advance for any help you can offer.

 

-Neil 



#2 aeajr

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Posted 08 March 2018 - 11:22 PM

You want a 360 degree dial on the base and an angle gauge on the scope.

 

Using an angle gauge to help find targets
https://www.cloudyni...y/#entry8120838



#3 drneilmb

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Posted 08 March 2018 - 11:34 PM

You want a 360 degree dial on the base and an angle gauge on the scope.

 

Using an angle gauge to help find targets
https://www.cloudyni...y/#entry8120838

You're exactly right Ed, that is what I want. The 360 degree dial on the base is no problem.

 

But where do I put the angle gauge? Your XT8 has a tube and if you can get the angle gauge to sit right on top of the tube, then the angle that it reads between the vertical vector of gravity and the vector pointing out of the bottom plane of the gauge is the altitude angle of your tube. I'm having a hard time finding any surface on my truss dob that is aligned that way.

 

I know that an inclinometer is what I want, I just don't know where to put it so that the angle it reads is the altitude angle of the telescope. Maybe somewhere down on the altitude bearing?


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#4 beatlejuice

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Posted 09 March 2018 - 12:01 AM

How about attaching something like a 1 x 2 inch piece of metal to fit on one of those cross sections on the side of the cage.

 

Eric


Edited by beatlejuice, 09 March 2018 - 12:02 AM.

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#5 NiteGuy

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Posted 09 March 2018 - 01:26 AM

For what it's worth the Magnetic Wixey units go on sale every few months at Rockler for $19.99. Sign up for their email stuff and qualify for free shipping on all orders over $35.00. I've got one and now just need to finish the scope it's going on.



#6 junomike

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Posted 09 March 2018 - 07:35 AM

I'd find a clip/brace which fits over the circular UTA giving you a small platform

 __

I    I

I    I      Place Wixey here

I    I___________________

 

This will get you a platform for the wixey which you could move if required.

Perfect leveling isn't required as you can "zero" the Inclimometor

So If the co-ordinance of  Polaris (SkySafari) aren't the same as what the Wixey reads, you can fix it so it is.

 

Lets say that Skysafari is showing Polaris as 45° but the Wixey reads 47°. I merely lower the OTA until the Wixey reads -2° and then hit Zero.

Now both will show 45° when viewing Polaris and the Alt is now set.



#7 clearwaterdave

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Posted 09 March 2018 - 01:48 PM

I made a few of my own.,not fancy but get me there most times without a problem.,I used a protractor and a sharpie.,choose whatever material works for you.,

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#8 clearwaterdave

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Posted 09 March 2018 - 02:00 PM

Different view of them.,

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#9 aeajr

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Posted 09 March 2018 - 04:40 PM

 

You want a 360 degree dial on the base and an angle gauge on the scope.

 

Using an angle gauge to help find targets
https://www.cloudyni...y/#entry8120838

You're exactly right Ed, that is what I want. The 360 degree dial on the base is no problem.

 

But where do I put the angle gauge? Your XT8 has a tube and if you can get the angle gauge to sit right on top of the tube, then the angle that it reads between the vertical vector of gravity and the vector pointing out of the bottom plane of the gauge is the altitude angle of your tube. I'm having a hard time finding any surface on my truss dob that is aligned that way.

 

I know that an inclinometer is what I want, I just don't know where to put it so that the angle it reads is the altitude angle of the telescope. Maybe somewhere down on the altitude bearing?

 

Where is yours finder going?  Put it on the finder.

 

OR

 

You built the secondary ring.  Just add a shelf in the framework to hold the angle gauge making it parallel to the focal plane of the scope.   

 

Once you do that you put the angle gauge on it and point it at a known object, say Polaris or Sirius.   Read the angle specs from an on-line app to get it exactly right for that moment. I use Stellarium.  If it is not exactly right, just put a shim where needed to get it right.  

 

 

In practice, if you are hunting for the target using your AZ dial and your angle gauge you will typically see it in a 50 mm finder scope.   Or use an eyepiece with 1 degree FOV or wider  and you should have no trouble hitting the target. Again a little sweep left and right usually catches it.  

 

I do this with my 8" Dob and I don't have an AZ dial.  I use a 9X50 finder, but sometimes the target is too dim so I use a 2 degree FOV eyepiece as my finder.  I just approximate AZ with a compass on my phone, then sweep left and right to find it. 

 

 

Easy Peasy.


Edited by aeajr, 09 March 2018 - 04:50 PM.


#10 drneilmb

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Posted 10 March 2018 - 08:46 AM

In true CN fashion, all of your answers together have led me to completely change my mind. ;D

Junomike's clip suggestion got me thinking about the surface of the bottom ring of the UTA and clearwaterdave made me re-evaluate the need for anything electronic at all. I plan to use a protractor mounted on the underside of the ring with a plumb line as the indicator.

Ed, the scope doesn't have a finder (so far). I've always built my own like this one http://www.jerryolti...upil_finder.htm but I haven't made one for the new scope yet. I'm playing with all sorts of ideas for what I'll do. One possibility is to JUST have the angle and azimuth gauges and no finder "scope" at all.

I have a 9x50 telescope finder, but it's more weight in the wrong place than I want to mount on this scope. Since I observe alone, I've even been considering green lasers for pointing. I have a sketch for a holder that could take a laser pointer or a split pupil finder for when the GLP isn't welcome. I even found that if you shine the GLP into the eyepiece, then the image of the beam shines up where the scope is pointing.

#11 aeajr

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Posted 10 March 2018 - 01:08 PM

If you have the AZ dial and an angle gauge you may not need a finder.   

 

Assuming a 1200 mm FL, a 38 mm 70 degree ( this is what I have) gives you 31.5X and 2.2 degrees.  That should be good enough.

 

This is the digital angle gauge I use.

https://www.harborfr...auge-63615.html

 

Consider the plumb bob in a breeze.  May be tough to take a reading.



#12 clearwaterdave

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Posted 10 March 2018 - 08:08 PM

My plumb line is a piece of copper wire.,no problem in a breeze.,I have seen a picture of a scope where the Alt gauge was mounted on the underside of the scope.,but I have always put mine on top.,

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#13 drneilmb

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Posted 11 March 2018 - 04:11 PM

My plumb line is a piece of copper wire.,no problem in a breeze.,I have seen a picture of a scope where the Alt gauge was mounted on the underside of the scope.,but I have always put mine on top.,


I just ran across a scrap of slightly stiff wire while cleaning up the house today. I think that it might even work to "shim" the angle reading by bending the wire to change its relation to the center of mass of the weight that hangs down.

I'll try to remember to post pictures of what I come up with when I've tried it out on Polaris.


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