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Gina

Gina's Mini Dome Observatory for Widefield Imaging Rig

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Following on from my other mini-observatory threads, I'm now thinking of a small dome observatory for my widefield imaging rig.  Several previous ideas for a mini observatory have bitten the dust!

I have a number of thin aluminium sheets the I bought for my earlier cylindrical roof mini obsy that can be bent into the sections of a multi-sided dome.  Why a dome?  Well, it is more compact, requires less power to drive - this observatory and contents will be fully automated - and a dome provides more protection from wind etc.  No space is required inside for a person in this case - just a Raspberry Pi 3 for controlling everything with INDI drivers.  Not even a laptop.

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Yes, me too but I need to sort out my workshop first - I think it would be a bit much for the living room table :D  I'm working on it... Workshop that is :D

That doesn't stop me from planning and thinking about it though :)

Edited by Gina

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I think I may have to make a model of the dome so that I can work out the shape of the sections.  "Messing up" the dome shape is the viewing slot.  For my widefield imaging rig this will need to be a minimum of 4"-5" to allow for the offset as the unit rotates to set the framing angle.  I guess I could make this 6" (or 150mm).  The door could move lengthways or sideways and be single or double.  I don't think a double door is needed for such a small dome.  I was thinking of a sliding arrangement.

There is the problem of sealing the door against horizontal rain.  I think this might be difficult with a sideways sliding door but sliding the other way would need two sections to cover the angle form horizontal to vertical though I don't think this would be impossible.  I think lengthwise sliding could be weatherproofed by having a turned-over lip up the sides.  Unlike the dome itself, the sliding door and frame could be 3D printed.

Another idea I've seen is a flip-opening door but that would catch the wind when open.

Edited by Gina

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Gina,
A thought ... not totally compliant with your ideas so far and not fully-fledged, but might spark something ...
If you had a double sideways door, could you fit something (a rubber wedge?) to the underside of the door (side closest to dome) that would butt-up against the dome when shut, to keep the rain out, but would not obstruct opening? Don't see how this could be adapted to single door (as either only one side would be rain-proof, or the "wrong" side would have to be flexible enough to allow for opening, which could lead to it (i) not doing the job and (ii) snagging when you close the door). Does all this make sense? Not being an engineer, my desciptions may lack a little something ...
As I say, not perfect for what you have described, but may spark an idea of your own ...
Thanks.

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1 hour ago, Gina said:

Another idea I've seen is a flip-opening door but that would catch the wind when open.

I've always found the SkyShed POD design rather simple and appealing...

POD3000-3.jpg

 

Edited by AKB
typo
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28 minutes ago, Demonperformer said:

Gina,
A thought ... not totally compliant with your ideas so far and not fully-fledged, but might spark something ...
If you had a double sideways door, could you fit something (a rubber wedge?) to the underside of the door (side closest to dome) that would butt-up against the dome when shut, to keep the rain out, but would not obstruct opening? Don't see how this could be adapted to single door (as either only one side would be rain-proof, or the "wrong" side would have to be flexible enough to allow for opening, which could lead to it (i) not doing the job and (ii) snagging when you close the door). Does all this make sense? Not being an engineer, my desciptions may lack a little something ...
As I say, not perfect for what you have described, but may spark an idea of your own ...
Thanks.

I see what you mean but I think this would be difficult to engineer.  Thanks anyway :)

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7 minutes ago, AKB said:

I've always found the SkyShep POD design rather simple and appealing...

POD3000-3.jpg

 

That is a possibility and yes, I had thought of it.  Two problems as I see it - less shelter than a standard dome and the problem of sealing the two halves when closed.  Thanks for the suggestion though :)  All suggestions gratefully received :)

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1 minute ago, Gina said:

the problem of sealing the two halves when closed.

Less difficult than other designs, perhaps?

  • the edge to seal is simply the arc of a circle.
  • the inner, fixed, half dome can have a ridge along this edge which acts as a gutter and a surface for the outer, moving half to seal against.

Easy to say, of course!  I leave it to you to engineer a good solution!

 

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5 minutes ago, Gina said:

That is a possibility and yes, I had thought of it.  Two problems as I see it - less shelter than a standard dome and the problem of sealing the two halves when closed.  Thanks for the suggestion though :)  All suggestions gratefully received :)

Would there not be a good size overlap incorporated into it when shut? There should also be a small gap between the two parts and I would consider a bead of silicone sealer and or adding a folded return on the edge of the inner panel to stop the wet and allowing it to run down and out.

@akb beat me to it....

Edited by spillage
too slow
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It's certainly an interesting thought.  I was thinking it didn't give a view directly upwards but if the dome is slightly larger than the minimum size the mount could be positioned slightly to one side.  I shall give this some thought :)

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Remote control for a SkyShed Pod type system would be a bit different from a standard dome and the dome INDI driver would not be suitable but I dare say I could devise a suitable driver.  When I looked at INDI dome drivers the SkyShed Pod way not among them.  OTOH under most conditions the dome halves could be completely open and give nearly 180 degrees AZ view.  The situation where anywhere near 180 degrees is needed in an imaging run is a rare event at this latitude.  So in most cases the dome could be open - I could make the actual AZ angle manually controlled through Ekos and INDI.

Have to say this is far less complicated than a standard dome and only needs two stepper motors to control the dome.  And no motors on moving parts (other than on the mount).

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Apart from the actual shape of the sections, the overlap and sealing of the two halves needs looking into and the dome will need two rotating rings rather than one but I don't see any problem there.

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Eventually found a video showing how the SkyShed Pod actually opens and it isn't what I thought which was that both halves of the dome rotated on a vertical axis on rollers.  But it doesn't - one half is attached to the other with a horizontal axis and has to be lifted to open the observatory.  This method would not be practical for remote operation as I see it.  (Unless it was carefully balanced by a counterweight.)  It is unsatisfactory for exactly the same reason as my cylindrical roof.

OK so I can't copy the Pod - I'll have to design my own sealing/weatherproofing system.

Edited by Gina

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9 minutes ago, Gina said:

it isn't what I thought which was that both halves of the dome rotated on a vertical axis on rollers.

...but it could be.  What's wrong with your idea of two concentric half shells which rotate like that?  I'm sure that sealing is always a challenge, but you're definitely up for that. 

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Yes, I expect you're right - thanks :)

My main ROR observatory uses brush type draught excluder to keep the weather out and it works :)   Maybe not completely watertight but what does get through just runs down inside and out through holes in the floor.  In other cases a large overlap does the job.  With the dome, I could arrange gutters.

Edited by Gina

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mine is all flat panels and should be easy for you to fabricate and scale down.image.thumb.jpeg.645d0ddb820eec5c0e90e7c3035c2b60.jpegimage.thumb.jpeg.babc87bf361cfcee0be12ffa46d453e7.jpegimage.thumb.jpeg.3b31996882f5cd92e5cd18135a9da6c6.jpegimage.thumb.jpeg.a82f0bd5d488705f179fa69b81e5ab25.jpegimage.thumb.jpeg.da5420cab519c915ebcf2a8940a6b069.jpeg

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Thanks Michael :)

I'm planning an octagonal dome with curvature in one direction only.  In fact the curvature will provide strength.  Probably just an overlap with pop rivets to hold the pieces together and some sort of foam sealer between.  I just need to make patterns to use to cut the aluminium sheets.  They're easy to cut with tinsnips. 

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no problem. mine is a combination of squares and equilateral triangles that are very strong when joined together. 

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Now the real problem - the shape of the sections.  This is a wire-frame model.

5903a93bcaa01_FrameModel.png.913b95ed002a0eeabc81da1f57cda541.png

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I've worked out how to get the measurements for the shape of each pane/section of the dome.  The wire-frame model above has an octangular base and circular sides.  Filling in the geometric section from the curve to the centre and then dividing the 90 degrees from base to apex into 9 parts and then joining the points on two adjacent parts gives horizontal lines representing the width of ali sheet at regular intervals.  Hope the diagrams below make this more comprehensible :D

5903b1796ec9f_FrameModel04.png.3e3114c19192f55fc73d5e1599310db4.png

5903af54d498e_FrameModel02.png.a01215b2a2de5b84576276cd58651f53.png5903af53f416f_FrameModel03.png.03aeb692a0d100053be9681e9332fe6a.png

Edited by Gina

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it runs on a ring beam and ball bearings.

here is the original thread if it helps

 

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2 minutes ago, Gina said:

I've worked out how to get the measurements for the shape of each pane/section of the dome.  The wire-frame model above has an octangular base and circular sides.  Filling in the geometric section from the curve to the centre and then dividing the 90 degrees from base to apex into 9 parts and then joining the points on two adjacent parts gives horizontal lines representing the width of ali sheet at regular intervals.  Hope the diagrams below make this more comprehensible :D

5903af54d498e_FrameModel02.png.a01215b2a2de5b84576276cd58651f53.png5903af53f416f_FrameModel03.png.03aeb692a0d100053be9681e9332fe6a.png

to complicated for me. I bow to your skills.

 

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I've edited my post to include another diagram which might help - I agree that it's pretty complicated.  3D geometry take a bit of getting the ole brain round :D

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