Gina's Mini Widefield Imaging Observatory

[Gonzo]

As mentioned in another thread, I have another idea for the roof.  The Avalon Merlino observatory inspired me   I'm considering a cylindrical roof or an approximation to it.

You probably know this post http://stargazerslounge.com/topic/68379-rotating-roof-obsy-pics/

[Gina]

Yes that's the one I was thinking of - or at least one of them.  There was another with two roof sections.

[Gonzo]

  There was another with two roof sections.

I think I know the one you're talking about, seen two on the Cloudy night forum.

[Gina]

I sahll need to do some measuring up but it looks like the length wants to be about 600mm and the diameter also about 600mm.  Using cylindrical pieces, I think the roof would need 3 moving pieces to clear the imaging rig and NEQ6 when in use.

[Gina]

Been trying things in SketchUp and I think I may be able to get away with three roof sections overall with just two moving.  Here are a couple of screenshots with the roof closed and open.  South is to the right in these sketches.

[Gina]

I think I might make a scale model to see how it will work when I've sorted out a full design including the end sections.  I shall also need to check measurements of the mount and imaging rig in various positions.

Of course, if I had my Giant 3D Printer done I might be able to print the full size thing - HA HA

[Gina]

Just a couple of rough calculations based on my estimated measurements...  If the cylinder is 600mm diameter and roof sections just over 90 degrees, the length of the roof pieces would be 1/4 x Pi x 600mm = 471mm.  Adding 29mm for overlap would give 500mm.  Estimated roof sections would be 600mm x 500mm then.

[Gina]

Going from 2D to 3D and including end sections.  These will overlap much like the cylindrical parts, with flanges to weatherproof the joins where required.  These could be reinforced with brush type draught excluder like I used on my main observatory.

[Gina]

Here's the roof open.  I've only modelled the end quadrants for one end so far and have yet to model the bearings and motor drive.  I have worked out the opening and closing sequence though.  The inner moving part will be driven and in closing will connect with the outer part by the flanges when at around 90 degrees.  Then the next 90 degrees will lift the outer part until the roof is closed.  The reverse will happen when the roof opens.  Both part will move together for the first half of the time then the outer part will sit against the body while the inner part opens fully.

[Tinker1947]

Going to be interesting what to make it out off, taking into account condensation, and it keeping the right shape with out being to heavy.......

[Gina]

I was thinking of sheet aluminium, maybe 1.2mm thick, for the curved parts and plywood for the ends but I'm open to suggestions for alternatives.

[Gina]

I've now got the NEQ6 on its tripod in the living room with the triple widefield rig mounted on it.  Have to say, the NEQ6 dwarfs the imaging rig and really looks quite ridiculous.  I was a bit out on the length of roof required, it's more like 700mm than 600mm but will depend on the counterbalance weights.  ATM the cameras are on the medium triple imaging rig in the main observatory and I don't want to disturb them ATM.  Might be clear sky tomorrow night though the forecast changes almost hour by hour   The three 460EX cameras are quite heavy.

I'm considering resurrecting my home made mount project and maybe sell the NEQ6 with tripod though I guess it might just about be usable if I manage to get to star parties.  Or is it?  Not at all sure - I can only just lift the NEQ6 mount itself and it's a very awkward shape.

[Stu]

Hi Gina,

I hesitate to dampen your enthusiasm for another project... [emoji6], but would using the NEQ6 as it is not allow you to get your mini observatory up and running much quicker? Plenty to do just getting that cover sorted as it is?

Cheers,

Stu

[Gina]

Well... yes it would   I could even go back to my earlier design of a wooden apex roll-off roof, I guess.  But I do rather like the cylindrical roof.

[Tinker1947]

Materials for the roof, ply, plastic, hardboard nothing else come to mind atm i'm sure other will make the list longer, what to cover it with fibre glass, rubber, paint , my own roof is ply with a 4" X 1" treated timber frame round the edge, covered in rubber, size for the front piece 7' X 4' can be pick-up with one hand, doesn't get any condensation on it, so maybe curved ali angle for the for outer edges, and flat curved support inner and outer held together with stainless bolt, so coating with Fibre Glass either ply or hardboard that could work but i don't know about condensation, fibre glass domes seem to attract condensation and could be costly with electric to keep dry. well this is something to kick about or chuck it out, i'm still thinking while i munch my way through 3 more mince pies.....

[Gina]

For the curved parts - aluminium sheet with plastic foam glued to the inside to stop condensation.  For the flat end pieces I can only think of plywood ATM for its light weight and stiffness.  It would be nice to use UV resistant plastic for its zero maintenance aspect but large pieces are expensive.

[Tinker1947]

I seem to remember seeing greenhouses with bubble wrap on the inside of windows,,,??

[Gina]

These would be good for making the ends from - except for the price

And that the shape wanted would actually be this :-

[Tinker1947]

The ring at the bottom could be bits stuck on a  round circle and a fantail to give a larger glue area, make a  inner and outer piece with a middle circular ring glued to the pieces either side..., make for a sturdy 30mm thick bearing retainer.

[Gina]

I wonder if 0.9mm thickness of aluminium would be enough for the curved panels.  The curvature would add stiffness and the thinner the lighter.  I guess I could get one sheet and see what it's like.

Then there's the question of the ends.  I've got some 6mm exterior plywood left over from the main observatory build but maybe not enough.  Not sure how I'd attach the aluminium sheet to plywood that thin either.  I do have a couple of sheets of twin wall polycarbonate 10mm thick, 610mm x 2m...  I wonder...

[Gina]

The ring at the bottom could be bits stuck on a  round circle and a fantail to give a larger glue area, make a  inner and outer piece with a middle circular ring glued to the pieces either side..., make for a sturdy 30mm thick bearing retainer.

That's a good point   Only trouble is that two of those discs would be £120.  I guess not that much compared with everything else I've spent on astronomy   And I guess it would make for a good sturdy construction and also I could use tapped holes and screws to attach the aluminium sheet.  They also do 5mm thick perspex but I'm not sure that would be thick enough.

There is one other problem - the roof sections need to be spaced apart a bit and hence the end quadrants need to be slightly different sizes.  I suppose the aluminium could be spaced away with some sort of flexible strip material.

[Tinker1947]

You could ask if they do a slightly smaller disc say 580mm save you having to cut 1  down ....

[Gina]

You could ask if they do a slightly smaller disc say 580mm save you having to cut 1  down ....

That's a thought   Though actually I think I might have to go a bit larger.

[Tinker1947]

Well there's always 10mm marine ply......

[Gina]

Well there's always 10mm marine ply......

Yes, I guess that would be a better idea   As would a router to cut the curved edges   I've often thought of getting one.

From what I've seen there's 9mm then 12mm - I guess the 12mm would be easier to attach the aluminium to and the price difference isn't that much.  Any thoughts?

This supplier claims to do very good quality marine ply