All Sky Camera Revisited

[Chriske]

I'm not 100% shure here, but could it be that the ring is to thin and by screwing the O-ring to tight you accidentally introduced leaks because of bending the ring a tiny bit..?

[Gina]

I presume you mean the 3D printed flangesd may be too thin.  You could be right.  Though the worst leak is at a bolt.

Edited May 9, 2019 by Gina

[Gina]

Printing a new base with thicker flange, for what it's worth.  I guess I might as well try to forget about getting this thing imaging until I solve the sealing problem.

[Gina]

I could do with some good ideas and I seem to be fresh out of them!!!  Maybe I should shelve this project and do something else...

[Davey-T]

3 hours ago, Gina said:

I agree but to produce a smooth groove is not easy.  3D printing is not necessarily perfect.

A small router with appropriate bit and jig would work and maybe more bolts to spread the load.

2 hours ago, Gina said:

Still leaks.  Not as badly but evident in two places around the flange.  So that's another idea gone.

I'm thinking the only solution will be to make the flange joint permanent and if I need to repair anything inside I'll just have to either break it apart or saw it open.

Don't let it beat you now after all your effort 

Dave

[Gina]

I wondered about more bolts.  16?  24?  Currently using 8 but with 120mm ID they're still a couple of inches apart (ooh I love mixed metaphors measurements!).

[Davey-T]

If you're giving it a rest for a bit and print another ring  I can send it off with the O ring to my son in law to CNC a nice groove for it as long as you're not in a hurry as he works away a lot so doesn't get a lot of time to do stuff.

Dave

[Davey-T]

Another idea how about an aluminium ring each side of the joint to bolt through to sandwich the plastic ?

Dave

Edited May 9, 2019 by Davey-T

[Gina]

Both good ideas - thank you - but I think I'll have one more go with the O ring and 3D printed parts.  I can make the flanges a lot thicker and double up on the number of bolts.  I have observed that most pipe flanges have a very large number of bolts to hold them together.  The current leaks might be due to the remaining silicone sealant on the body top part.

[Gina]

Strange thing is that the dome is leak free and only has 4 bolts into threaded holes in the PETG and sealed with silicone sealant.  There is a 3D printed ring on top of the dome flange.

[Gina]

I have a tube of this RTV Silicone Gasket Maker - looks like it might be better than the clear or white stuff.

[Oddsocks]

From your description of the problem it seems that the contact area and limited compression range of a standard Viton or Nitrile rubber ‘O’ ring is just too small to accommodate the flex range of your casing when it is bolted together.

How about a wide flat gasket cut from closed cell expanded neoprene rubber, with a large compression range and  increased contact area it should cope easily with distortion of the casing when bolted together.

As long as it is not over exposed to UV it should have a good few years of life.

Fairly easy to cut from a flat sheet with a sharp craft knife or scalpel using a printed paper template as a guide.

Might be a solution?

I have a few offcuts of low density 6mm thick, self adhesive, expanded neoprene sheet here, left over from when I insulated my observatory’s glass fibre dome roof last year, I can put a couple of bits approx’ 300mmx300mm in a postal tube and mail them off to you .f.o.c. Just send me a pm with a suitable delivery address if wanted.

Otherwise, here is a link to a set of closed cell neoprene foam sheet gasket material on eBay:

https://www.ebay.co.uk/itm/Neoprene-Rubber-Sponge-Rubber-Nitrile-Cork-Sheet-GASKET-Material-Foam/191593795500?hash=item2c9be14fac:g:U1IAAMXQvTlRgzTV

William.

[Gina]

Thanks very much for your offer, I'll let you know.  Meanwhile, I think I'll print a couple of test parts to try the RTV Silicone Gasket Maker.  Going by the instructions, I think this stands a chance of working.

I think you're right about the O ring being too hard to compress and seal properly.  Closed cell sponge should be much better.

Edited May 10, 2019 by Gina

[Starlight 1]

If you made the two parts to look like a L it will have a wall on the inside and outside water can not get in.

[Gina]

Agreed an L shape would be better but not practical.  At least not as I've found so far.

[Gina]

Test parts printed so I'll be applying the goo shortly and testing...

[Gina]

That didn't work on two fronts.  The print itself leaked at the top and there was a smaller leak at one point round the flange.  I suspect the flange leak was due to insufficient goo.  Sealing round the rest of the flange was fine.  So there is some good news.  I think this will work with oodles of messy goo!

[Gina]

I'm going to change the design of the ASC housing to provide a wider and better sealing area between top part and base.  At the same time I can attach the focus motor to the camera casing and have it further up so that the motor pinion and lens focus ring gear can be at the same level as the focus ring.  This is now possible due to using the 4" dome.

[Gina]

Working on the detailed design of the ASC casing, I find the above is not practical due to the relative positions of camera lens and dome so the focus gear will need a skirt with the motor lower down.  The present focussing system works well enough so I see no need to change it.  I will still change the design to make for better sealing, incorporating an L shape but this being at the top rather than a flange at base level.  The casing will have a greater diameter than the present one.

Edited May 12, 2019 by Gina

[Gina]

Here's a cross-section of the main casing.  There will be a ring on the top with a lip over the edge of the casing and taking the dome.  The bottom has a groove to take the funnel shaped part that connects the ASC to the hollow mast (aluminium pipe).

[Gina]

This is the top part that takes the dome and overlaps the side of the main body.

[Gina]

Another view of the main body.

[DaveL59]

Hi Gina

now wanting to hijack your thread, but this inspired me to get around to picking up the idea I had a long while back but had never got around to it. Since I have a couple spare mini-IP cctv cameras with Sony IMX291 starvis sensors, I bought a dummy dome cctv for a couple £ to test the idea. Fitted up the camera into it and sealed with clear RTV since the clear dome just pushes into the body and fixed it to the pergola by the shed.

Not an ideal setup as its only a 2.8mm M12 starlight lens, needs to be 1.7 I think for this to be workable and focus isn't quite right plus the dome isn't optically great hence the abberations in the image, but... it seems to work so far. One concern I've always had is - do you get the sensor burning out with the sun tracking across it? I do have an IRcut filter behind the lens so hopefully that'll help?

I know I'll have a problem with the security IR lighting so masked the facing edge of the dome to hopefully reduce that a bit, can't move the IR illuminators unfortunately, so will see how hazy the image turns out tonight I guess. If this all works out then I'll look to order in a wider M12 lens and a proper CCTV dome housing (or camera and strip it to retrofit this camera module). 

Nothing as professional as your setup but might be a neat cheapo solution for me 🙂

[Gina]

I went through those stages way back when I was experimenting.  I found CCTV cameras nowhere near sensitive enough for nighttime and I coundn't find a lens with short enough focal length to cover the whole sky.  A sensitive enough camera takes you into the astro camera category.  What's more it needs to be cooled to get a low enough noise level to show lots of stars such as in the Milky Way.  A fish-eye lens to cover the whole sky needs to be around 1.5mm focal length with a 1/2 inch sensor camera (CCTV cameras as generally 1/4").  I've found the ZWO astro cameras are not damaged by full sunlight when used with very short exposures.

Maybe I should add that I am aiming for the best night views I can achieve and my location provides views down to the horizon over a lot of the total field.  For some, a narrower view would be sufficient.

Edited May 15, 2019 by Gina

[DaveL59]

thanks Gina, I'm currently playing with the spare kit I have, being between jobs means limiting the spend somewhat so an astro camera is a bit out of reach for now 😉

Here my back yard is not that big and with a large oak tree to SW of where I might put the camera plus houses at around 20-30 degrees above the level a 150 wide would likely do for me at the mo. Will see how it plays, I've ordered a 2.1 and 1.7mm lens so will have a play and see how they go. Might try a 5MP starvis module later on as they can be had for under £20 now, assuming that the current play rig turns out to be viable...