Gina's Mini Dome Observatory for Widefield Imaging Rig

[Gina]

I haven't managed to model a spur gear ring into the model of the dome and can't see any way of doing it ATM but I shall continue to investigate the possibility.  So as things stand I would model a flange around the bottom of the dome and then solvent weld this to a gear ring.

[Gina]

Thought I'd found the answer but it doesn't work for a gear anyway with the way the filament is pushed and spread by the flat ended nozzle I think parts just touching will bone in the printing.  I'm currently running a test print with flanges. 

I've been looking into the shutter arrangement.  At the northern end there will be a fixed part which will be either level with the dome or just below it (I favour the latter I think).  Next would be the moving top part which will be highest ie. furthest from the centre of the sphere so that the rain runs off.  Then the second moving part which will just clear the other parts and which will overlap a short fixed part to the south.  Thus the very bottom of the dome will be a continuous circle.  I'll produce SketchUp models shortly.

Edited June 3, 2017 by Gina

[Gina]

This diagram/model shows the shutter divided into 3 sections of 70° covering the 210° total.  Of course there will be overlaps and the sections will need moving in or out.  I would like to keep the double curvature but I'm not sure it would be worth the trouble - cylindrical pieces would be much easier to design.

Edited June 3, 2017 by Gina

[Gina]

Here's a diagram of the main parts of the shutter (without side flanges).  I have taken advantage of not needing to go far backwards from vertical to allow a greater overlap of the sections.  The fixed north section will directly join up with the dome halves with the other sections being above and running on the flanges of the dome halves.  Flanges on the shutter sections will overlap the flanges on the dome halves to stop sideways wind blowing rain in.

Edited June 3, 2017 by Gina

[Gina]

3D view of shutter parts without side flanges.

[Gina]

Been looking at full-size dome designs or more specifically, shutter designs.  On this small scale I think sideways opening shutters would be difficult to seal at the join of the two halves, which is why I went for a sliding up/down (or rather round) system.  But the way I was thinking of designing the shutter parts would be too difficult to implement so I'm going to simply the designs.

[Gina]

Here is the design for the bottom opening part of the shutter.

[Gina]

This diagram shows a cross-section through the middle of the shutter.  The fixed part is shown in green.

[Gina]

Here is a model of half the middle part.  This and its mirror image would be printed and then glued together.

Edited June 8, 2017 by Gina

[Gina]

Making generally good progress on this project - details are in my large 3D printer thread.

11 hours ago, Gina said:

Photos as promised.

The T shaped bits at the bottom are purely support to hold the shape of the ABS prints and will be removed.

[Gina]

Printed the second and final dome half today and glued in the top part.  Then tidied everything up including repairing poorly printed bits.  Here are a couple of photos of this section outside and inside views.  Now gluing it onto the other parts.  Currently drying before more gluing.

[Gina]

Assembling the dome.

[Gina]

Been trying the shutter parts on the dome.  Needs more work but getting there.

[wimvb]

Nice to see the dome take shape. What is the diameter? It looks rather small.

[Gina]

Thanks   350mm ID.  I worked out that my widefield imaging rig on fork mount would need 300mm so this should be big enough with room for tolerances.

[wimvb]

How are the moving sections kept in place? From your images it looks like they just sit on top of each other and can be lifted off. I assume there will be some mechanism to keep them in place. I think this dome will be impressive when finished and operating.

[Stu]

Looks amazing Gina, I have no idea how you do these things , all credit to you!

[Gina]

12 hours ago, wimvb said:

How are the moving sections kept in place? From your images it looks like they just sit on top of each other and can be lifted off. I assume there will be some mechanism to keep them in place. I think this dome will be impressive when finished and operating.

This is something I'm working on ATM.  I had thought of ledges to hold the loose parts on like this :-

But it would be pretty difficult to implement.  Currently the shutter sections look like this :-

I think the simplest way would be to add hooks on the outside.

Edited June 18, 2017 by Gina

[wimvb]

Gina, is the dome you showed here the real thing or a working model? If it is the real dome, I think that your locking mechanism with hooks /collar may not work with plastic, unless they are going to have a very loose fit. From your posted images (see below), it looks like the left movable section of your dome has a different curvature than the dome and outer section. Locking the sections as per your design image, can cause the sections to get stuck. I don't know how plastic is going to behave when outdoors in the heat and cold, wet and dry. But you may of course already have anticipated this.

This is the image I'm referring to:

[Gina]

I'm hoping this will be the real thing but there is always the possibility that something will crop up that I can't find an answer to.  I know about the wrong curvature problem and have cured it using a craft type hot air gun and brute force, on the print.  The parts will have a very loose fit but I might add extra weatherproofing in the form of draught excluder.

[wimvb]

24 minutes ago, Gina said:

I'm hoping this will be the real thing but there is always the possibility that something will crop up that I can't find an answer to.  I know about the wrong curvature problem and have cured it using a craft type hot air gun and brute force, on the print.  The parts will have a very loose fit but I might add extra weatherproofing in the form of draught excluder.

 

That's the fun of engineering. Sometimes Usually it takes a larger garbage bag than anticipated. And a larger hammer. 

You fixed the curvature really well. Should run a lot smoother now.

I can imagine the completed rig coming to life at night and starting photographing the sky, all by itself. What a sight that will be.

[Gina]

It will be remote controlled - automatic may take a little longer

[Gina]

I think I have an idea of how to drive the shutter and also retain the sliding parts.  I'd like to model it all in SketchUp but it's hard work   I propose a curved rail 2 or 3mm thick all round the outside of the shutter and attached to the dome with 3D printed pillars shaped to fit the dome and glued on.  The shutter control may be with projections on the inner sliding part and cord.  The pillars will act as guides for the cord which will ride over the dome surface.  It is only necessary to control the inner moving part as the outer part will be driven from the inner via lips at the ends.

[Gina]

Here's a model showing the ring to hold the shutter parts.  I'll add pillars shortly - I need to model these in order to get the complex shapes.  Not sure how many pillars will be wanted but a minimum of four I guess, may need seven.

[wimvb]

Your neighbours won't see the difference. To them it will look like a robotic observatory.

I was already wondering how you would engineer the shutter opening. (I just can't help trying to see solutions to possible problems. Sometimes it drives the people around me nuts.) 

So, here goes:

Gina, would an interlocking system like this not be simpler? The image just shows the tapered interlocking parts of the shutter (upper part) and the dome (lower part). It closely resembles your initial solution, but may be easier to assemble and get to work. The hole could be used for a string that can open the shutter (would not be needed in the dome section)