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Gina's Mini Dome Observatory for Widefield Imaging Rig


Gina

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Here's the above diagram with an end panel superimposed.  I haven't shown the triangular bits of ply.  It occurs to me that the fixed aluminium panel could be extended vertically downwards as far as necessary to keep rain/sleet/snow off the mount.  Likewise, the south side would benefit from an aluminium sheet over the plywood and extended down below the mount.

591837b77c03e_CylindricalRoofandMount08.png.865fde878f0b4f93c4f7e65bbe3c9337.png

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Here's a new diagram showing the triangular plywood pieces  and extended aluminium panels.  One thing is apparent, if the mount were made slightly smaller the large plywood panels would shield it from the weather (as was the original idea).  I have yet to build the mount so the design of that is not yet "carved in stone" also the imaging rig has not yet been modified for fork mount so that could possibly be changed to reduce its length.

591839f9d53c0_CylindricalRoofandMount09.png.3f54e4760f99aeaf0d7dbeadaaf7d90b.png

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This diagram adds the large bicycle sprocket and shows that this might obscure the view to the west at low altitudes.  I've thought of another possible problem too - there might not be room for a dew shield on the lens.  I could increase the length and park the rig horizontally before closing the roof.  But I would much prefer a roof that can be closed without the need for parking. 

I don't think I'll be doing any cutting of panels or building until I've sorted this out.  I might even dump this design (again) and go back to a dome.  Anyway, I have more urgent matters to attend to :(  This project just continues in my rest periods from the domestic problems.

5918421f7ded1_CylindricalRoofandMount10.png.b40e325c61cb0257733896c37e1a0b2d.png

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Thinking mode...  Coffee break :)

  1. The idea for the roof above could be applied to the shutter in a standard dome design (I think) - well the way the moving sections overlap and one pulls the other anyway, couldn't use the quadrants :D
  2. I shall be looking into reducing the length of the imaging rig but I think any wide open roof will need the lens to have a dew shield - don't know about a dome with just a slot.  Unless I can shorten the imaging rig I this this current design is doomed.
  3. The idea of a dome with two halves rotating horizontally is simply not practical. 
  4. A standard sort of dome with shutter and made up of segments of aluminium sheet does seem possible. 
  5. A 3D printed dome would need a lot of separate parts.
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Here is a model/diagram of a standard style dome of 800mm diameter with a 160mm slot.  I have extended the hemisphere 100mm below centre to permit a view down to the horizon with the imaging rig fork axis at the centre of the sphere.  But instead of using a vertical cylinder I have extended the sphere.  This is where I propose to put the rotation gear.  I could extend the sphere a bit further to add extra weather protection.

59186063c9bd7_StandardDome01.png.0798dba45018678326df14c4dfe4e5d4.png

Standard Dome 02.png

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I think I want more than 8 sections to make a decent dome so I've drawn a diagram showing a 12 section dome.

5918685909d87_StandardDome03.png.59846f7e1818eb665820134b787638f7.png59186b5f68ebe_StandardDome04.png.e86d50e78dc6375c3c76710e016f47eb.png

Edited by Gina
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I've had a good look at the widefield imaging rig and reckon it could be made shorter.  It was designed to use a dovetail bar and go on a GEM so it needs a fair bit of redesigning to use a fork mount anyway.

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Here is a photo of the present imaging rig with the access panel removed to show the insides.  As can be seen, there is quite a lot behind the camera that could be rearranged and save on the length.  It would also help with the mini observatory to have the rotation axis the same as the optical axis.

Pretty much a complete redesign is indicated to suit the fork mount as expected though some of the parts can be the same as well as the electronics.

591883958be31_GEMversion01.thumb.JPG.7c875a11a5c36f5e70464e3ff2c16f50.JPG

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From measuring the widefield imaging rig with 135mm f2.5 lens (the largest I intend to use with the fork mount) and allowing for the plugs on the back of the camera I get 280mm as compared with 390mm for the GEM version of the rig without dew shield.  Now that is a big reduction even allowing for the mounting which shouldn't be more than 20 or 30mm.  We can probably say 300mm for the length of the rig, a saving of 90mm.

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I've thought of one possible problem with an aluminium dome roof - I wouldn't be able to use WiFi for control and capture.

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7 hours ago, Gina said:

I've thought of one possible problem with an aluminium dome roof - I wouldn't be able to use WiFi for control and capture.

Would fibreglass be a better option? Should be ok for wifi, and would probably be lighter too. Might also be easier to get the shape you want too

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I've been looking at the various lenses that I plan to use in the widefield rig (and have used before).  Shortest is the 28mm f3.5 and if I keep the camera position the shorter rig this produces plus the wider field would seem to indicate sticking with a 150mm wide slot in a dome.  I don't think having a 150mm wide slot would be any more difficult than a 100mm wide one anyway.

The longest focal length lens with dew shield gives a rig length of 300mm.  Assuming I can mount the rig onto the fork at the halfway point, I should only need a 300mm diameter dome rather than 600mm though some allowance for tolerances will be wanted.  A dome of 350-400mm diameter should be quite within the scope of 3D printing :)

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Here's a model of the dome but without slot so far.  I think I should be able to model the dome with slot by intersecting this with a rectangular block.  The other parts such as guides and rotator could be modelled separately, 3D printed separately and solvent welded together.

591b5e6034ff8_StandardDome05.png.920c4c52741efb596e904a259b1202e3.png

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Managed to get it to work - eventually :D  A couple of views of the dome sections and one of the cut out piece from which the shutter parts can be developed.  I think two moving parts with overlapping lips should do it, sliding over a fixed part - rather like the cylindrical/clamshell version.

591b692a4a65d_DomePart02.png.a42312375cc7c89b82c7753b316d2537.png591b692bce538_DomePart01.png.f4e18397f0501753ddcd00c553469019.png591b69289d7ee_ShutterPart01.png.1c4722686388967c4da8ea106e64e613.png

Edited by Gina
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I've now bisected the half dome, again using a rectangular block to form two quarters which are small enough to print using my large 3D printer. 

The method (in SketchUp Make 2016) for both creating the slot and bisecting the half, is to create a dome, select it and from the RH menu Make Component.  Then make a block away from the dome, select the block and Make Group, move the block to bisect the dome, Select All and from RH menu Intersect Faces > With Model.  Next Explode (RH menu) and delete the block.  Finally, select the two surfaces of the dome part and delete, then delete the remaining curved lines and draw line across thickness at a corner to reinstate an edge surface.

591c2777d9e89_DomeQuarterA01.png.e402fd1ae22aaee45fd27151c757b132.png591c2778d0503_DomeQuarterB01.png.3ce9597aceb31362abcaa599b7aa0c4b.png

Edited by Gina
typos
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As a test I reduced these two pieces to half size and printed them on my "Pilot" printer - came out fine :)

The two parts solvent welded together.

591e11f043d73_DomeQuarterA02.thumb.png.477e1a8b9c4e74e16a5b85a49904f723.png

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  • 2 weeks later...

I'm now working on my large (Titan) printer and using the dome parts as a test.  It's looking promising and I'm hoping to produce some dome parts.  I have separated a quarter of the spherical part into two parts taking a quarter off the top.  I'm currently printing the bottom part - ETA 2½ hours.

592fdf1eb9d13_DomeSection06.png.89a39c1c6a3aa0a76801a12a1422863e.png

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Print wasn't very good so I reduced the printing speed and that resulted in the print taking 3h 15m but this time it printed fine.  Very strong and more so than needed so the thickness can be reduced from the current 5mm, which will shorten the printing time.  I plan to redesign the dome anyway as these spherical parts will need flanges for the shutter.

Outside.
593016fc15327_DomeSection10.thumb.png.b1a875faefeb649666de3a6904453c03.png

Inside.
593016e7cdc46_DomeSection11.thumb.png.c19a830e5800afba260db388cc851775.png

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That was for a 400mm diameter dome with 5mm wall thickness which is bigger than needed.  Minimum size needed is 300mm internally so I've redesigned the dome with 350mm ID and 3mm wall thickness.  Half the dome part would fit in the Titan printer build volume and take just under 7 hours.  I haven't looked at the shutter yet.  Nor have I added the flanges on the sides of the dome parts.

5931315c42e43_DomeHalf01.png.2a5659a14feeae352a786283b31e06e8.png

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Now designed a new dome with 2mm thickness to see if it's strong enough - printing time reduced to 5½ hours.  Using brim for better bed adhesion and support for the top.

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I think the answer is yes, 2mm will be strong enough.  As it is, it's flexible but very strong.  The flexibility can be taken care of with the parts it will be joined to such as the fixed parts of the shutter slot.  I've managed to model flanges to the half dome and I'm going to see if I can include a large spur gear for the dome drive.

Here are a couple of photos of a printed half dome (no flanges yet), not perfect but adequate for the purpose.  It will look alright at a distance and besides which it doesn't have to look perfect, just do the job of keeping the weather off the imaging rig when closed.  The final version will be printed in green ABS.

Outside
5931ba5dcf961_DomeSection19.thumb.png.3b41fc0c1bdbf0a9faa582d5d8fa31d1.png

Inside
5931b64f347b4_DomeSection18.thumb.png.341bd5325365bcc5ab18431fa2f21721.png

Edited by Gina
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