Gina's Mini Dome Observatory for Widefield Imaging Rig

[Gina]

We start with this, then add pivots and flanges for one piece to drive another and form a weather seal :-

[Gina]

Two moving and one fixed of these will give plenty of opening.  However, I won't print each in one go as that would require support filament which can cause problems as well as take a lot of extra filament and in this size doesn't come cheap.  Therefore I shall split each part into two and solvent weld them together.

This half has the outward lip and the other half will have the inward lip.  I have yet to work out what happens at the pivot/axle.

[Gina]

Here is a diagram showing a cross-section through the centre of the clamshell.  The two quadrants coloured blue move and the black one is fixed.  The right-hand one as shown is driven.  The middle one is free to rotate but held by the lip of the driven one.

Edited May 27, 2018 by Gina

[Gina]

This shows the profile of a quadrant placed within the printing area of my Giant printer.  The section is 460mm diameter and it fits in with room to spare.  The minimum diameter required for the imaging I estimate as 380mm.  My thoughts are that I should make as big a dome as reasonably possible without pushing the boundaries to allow for future imaging rig upgrades.

[Gina]

Latest section of clamshell.

[Gina]

Unfortunately either the conversion to STL or the slicing in Slic3r is going wrong   

[Gina]

This is better .

[Gina]

Been trying to print in ABS but getting blobbing of the filament after a few layers.  Also tried ASA which is better but still did it further up (layer 16).  ASA has the benefit in being UV resistant otherwise it's much like ABS.  Similar printing parameters and can be acetone solvent welded and smoothed.

[Gina]

Now I have my Giant 3D printer working again and new design software (well not new - it's a 10 year old version - but seems better than SketchUp) I shall be looking at this again.

[Dr_Ju_ju]

Old ones are always the best....

[Gina]

I'm thinking of resurrecting this project in the foreseeable future though not immediately other than to play with ideas.  This will be in conjunction with my DIY miniature fork mount.

Edited August 18, 2019 by Gina

[Gina]

If I were to go for the standard dome design it would have to be removable to gain access to the imaging rig.  This would add complication over and above the mechanics of the shutter and rotation.  OTOH a clamshell immediately gives access when open and there is only one mechanism to open and close it.  I can't see the extra power needed to operate the dome being any problem - I have several 12v DC gearbox motors in addition to stepper motors.

Conclusion :- I shall go for the clamshell design.

[Gina]

Been playing with clamshell parts in my CAD software and now printing a scale model of one part.

These screenshots show progress of the design.

[whizzbang]

I like the look of this, is it waterproof? its threads like this that makes me want a 3D printer, keep it up, you're inspiring the sloth side of me 

[Gina]

It should be waterproof when it's finished - at least capable of standing torrential rain with a gale.  It's quite a way from that stage though!!

[Gina]

I need to model the whole dome and the DIY fork mount with imaging rig as an assembly to check that everything will fit together.  The plan is to print the dome and mount casing parts on my Giant 3D printer when it's finished and working.  This will limit the size if individual parts to a little under 500mm x 500mm x 800mm but that doesn't limit the overall size as parts can be bolted together.

[Dr_Ju_ju]

For quick modelling I tend to use TinkerCad (https://www.tinkercad.com/), the basic system is free & will do at least 90% of what I want.

If you want something more complicated, there's Onshape (https://www.onshape.com/) which is very good, but is a tad daunting at first....

[Gina]

I use an ancient edition of Autocad Inventor.

[Gina]

That clamshell part was 60° and printed alright in PLA.  If I go for PETG I can probably go to 80° with the greater overhang capability of PETG compared with PLA.  I don't want to use too much PETG for experimenting as I'm down to my last 2.2Kg reel of white.  OTOH I do have some other colours.  White is needed for outdoors but not for testing.

[Gina]

This quote from earlier shows a clamshell design using segments of somewhat over 90°.  90° or over segments can't be printed in one piece without support (which would use a vast amount of filament) so I shall either have to have more segments or make them in 2 parts joined together.  Of course, the more joins or overlaps, the more chance of wet getting in.

On 28/05/2018 at 00:49, Gina said:

Here is a diagram showing a cross-section through the centre of the clamshell.  The two quadrants coloured blue move and the black one is fixed.  The right-hand one as shown is driven.  The middle one is free to rotate but held by the lip of the driven one.

 

[Gina]

Here's a new diagram showing a cross-section through the dome.  The imaging view required is a little above horizontal to the south and about 45° above horizontal to the north (enough to get Polaris in view but not looking into the living room window).  The top arc represents the part that opens and the arc to the north would be fixed.  The opening part can be in two segments.

Edited August 20, 2019 by Gina
Added Polaris.

[Gina]

Two more screenshots showing cross-section of the dome - first closed and second open.  Using printed parts fastened together there would only need be one moving segment.

[Gina]

This screenshot gives an idea of what the dome would look like, less overlapping joins.

[Gina]

Mount shaft added.

[Stub Mandrel]

I use Alibre Atom now, it's very easy to use and fast. It costs about £100.

I can send anyone dropping me a PM a link to a free 6 month licence to try it out.