All Sky Camera Revisited

[Icosahedron]

Hi Gina,

Please forgive me if I appear to be rude but I'm trying to help and save you from future disappointment. I think you must accept the fact that by nature this 3D-printed material will never ever be waterproof on a molecular level. Effectively you are mounting a dome on a sponge with waterproof material between the two. Over time the housing will absorb water which then evaporates both to the outside and inside where it condenses when the temperature drops. I would suggest you mount the parts in a waterproof outside junction box designed for the purpose. By all means, 3D print the parts you require inside and outside of this enclosure like the cover for the dome.

I worked for a company that developed a product that despite all their efforts failed to remain waterproof right to the bitter end. My suggestion that they approach NASA with their product to be used as an endless water supply on Mars was not appreciated.

 

[Gina]

Thank you for your post, I'm always grateful for suggestions and opinions.

I have tried so-called waterproof enclosures for the ASC casing but found them worse than 3D printed casings.  I have produced 3D prints which hold water fine but I do appreciate that there's a difference between holding water and being totally vapour-proof.  I don't think any plastic is entirely vapour-proof.

I have come to the conclusion that a totally vapour-proof casing is so near impossible that another approach is needed.  This is to apply a slight positive air pressure inside with dried air.  I would hope that any permeability or leakage would be small and that the airflow through some silica gel desiccant sachets would be minimal so that I won't need to change them very often.  I'm thinking of a small radial fan for providing the air pressure.

[Gina]

With the dome cover being very tricky to design and taking a long time I'm thinking of leaving that for now and producing an ASC without it so that I can get an ASC working to allow me to see the sky conditions for imaging.  Coming up to new moon I could do with it.

[Gina]

I've been looking again at plastic boxes for the ASC casing but not found anything really suitable.  This one is the nearest I've found.  It has a big enough flat area on the top for attaching the dome with sealing O ring but the bottom makes for less easy attachment of the ASC to the mast pipe while keeping things sealed.  It's also a little on the shallow side and the waterblock connections would protrude below the bottom.  I'm thinking about it - it could shorten the time to get the ASC up and running again if I can get round the limitations.

[DaveL59]

kinda why I went with a non-working metal cased PTZ dome camera and mod'd it to be used inverted. Mind it's bolted to the side of the shed rather than on a pole so also easier but then I'm not trying to add cooling blocks and other electronics but it is fairly spacious inside once the PTZ bits are removed.

[Gina]

Been looking at how I could use the box and reckon I can solve all the problems - probably.   It should be better in a couple of ways.  I have ordered one.  I can't be sure everything will work until I get it.  Should arrive tomorrow.

Edited September 14, 2020 by Gina

[Gina]

Been designing parts for the ASC using that PVC box.  With this case I can have a longer focus lever giving finer control.  As with the other design I can still use the little 28BYJ-48 gearbox stepper motor with cam.  This can be mounted inside the box from the lid top.  Here are some screenshots of the assembly.  The Peltier TEC fits in the cavity against the red casing of the camera and the waterblock onto that being secured by screws into the 4 holes around the camera casing.  The model of the box is approximate since I don't have complete details.

 

Edited September 14, 2020 by Gina

[Gina]

Waterblock modelled and added to assembly.

[Gina]

Here is is with both parts of the box - shown in Blue (clear).  This shows the pipe connections on the waterblock poking through the bottom.  However, I believe I have an answer to this.  Add an extension to the case with a sealing O ring in the same way as the dome is sealed to the top.  Then, the water hoses can go through holes slightly smaller to provide a seal.

[davefi]

I went with similar, but slightly bigger (enclosure):

https://www.amazon.co.uk/gp/product/B0151KNM

If it is the same as mine, be careful with the seal - I assumed it was rubber and pulled it out to keep it safe while I was drilling holes in case I caught or nicked it, and the bloody thing just ripped in two, as its some cruddy foam seal.

Edited September 14, 2020 by davefi

[Gina]

That link isn't working for me.

[Gina]

I have another idea.  I have another waterblock which is 40mm x 40mm x 10mm with side connections/pipes.  This is easily enclosed within the box and the water pipes could come out in a different part of the box.

[davefi]

33 minutes ago, Gina said:

That link isn't working for me.

Oops, sorry copy & paste error!

https://www.amazon.co.uk/gp/product/B0151KNMB2/

 

[Gina]

Ah yes, that's the other one I was looking at.  It's a lot bigger than needed (and wanted).

[Gina]

Possible mounting methods.

Edited September 15, 2020 by Gina

[Gina]

I think my preference is for the waterblock with downward pointing pipes.  This is a model of an extension I could clamp to the bottom of the box with an O ring for sealing.  The pipe connection in the middle is for the air pipe (to apply slight positive pressure) and the water pipes are a tight fit in the two holes.

With round cone attachment to mast.

[Gina]

The box has arrived and I'm not very impressed!!  The top is alright but the bottom will make it difficult to seal the extension to it.  It isn't waterproof as the lid fixing screws are inside the rubber seal.  I hadn't noticed that.

Edited September 15, 2020 by Gina

[DaveL59]

a small neoprene washer under the screw may help with sealing, but isn't a good design to have not thought of where the seal went. Seems a lottery these days sourcing a good IP56/66 case 😞 

[Gina]

I'm now printing some of the parts to see how they fit in the box, starting with the biggest.  This is the camera housing both holding it and providing thermal insulation.  It is attached to the box lid by the legs using 4 of the dome fixing bolts.

[Gina]

Sorted out how to produce an extension to the bottom of the box to contain the waterblock connections.  This will be sealed to the flat part of the bottom with an O ring and fastened with either bolts and nuts or self-tapping screws.  A smear of silicone grease should seal any tiny surface irregularities.

[Gina]

I've been trying the parts in the box and there's not as much room as expected.  I was planning to put the dome towards one end of the box giving maximum length of focus lever but now it looks like the RPi and HAT will need to go at the opposite end from the focus stepper motor as there isn't room for both motor and RPi in one end.  The focus lever may still be longer than with the 3D printed casing though.  I still think I can get everything in but there won't be much empty space!

[Gina]

Thought I'd look at a double linkage for a dome cover (thought if it isn't inverted it won't catch the rain) but it won't work.  I've tried various lengths of linkages and various positions for the pivots/axles but the parts always interfere before the cover clears the FoV.  Guess there are other variation (an infinite number) with different linkage lengths.  This could take a lifetime without previous knowledge of all sorts of linkages, which I haven't got!!

[DaveL59]

would you not also have the cover potentially scraping up one side of the dome you're trying to protect? Unless you over-size it enough to allow clearance.

How about on the right hand lever making that L shaped and pivoted around the end of the L:
 

 

[Gina]

That was just one of a number of problems!! Although the cover is a lot bigger than the dome, it has to lift higher to clear.  I'll continue experimenting...

I'll look at right-angle or curved linkages - good idea.

Edited September 16, 2020 by Gina

[Gina]

I think I have it.  I've only modelled the linkages on one side - they will be on both sides in the final construction.