Still to do :-

1. Pair of gears for focussing.  Simple.
2. Clamping camera to Peltier TEC.  Not so simple.
3. Outer case design with weather seal.  Difficult.
4. Fixing to observatory.  Relatively simple I think.

The camera clamping could be part of the outer casing.  This would mean the outer casing could be attached to the passive cooler with the four threaded holes in the cooler and M3 screws.  Rubber foam could be used as the seal between casing and cooler.

I think the outer casing is going to have to be in two parts bolted together.

Gap between camera casing and and passive cooler is just 4mm.  From cooler to top of camera housing is 44mm.

I'm just wondering if the bottom of the camera casing and the bottom of the outer casing want printing in one piece.  OTOH I doubt this would be possible without support material.

I think combining the two is on.  There would be a 5mm gap between the housing and the cooler which could be filled with rubber foam for sealing.  The disadvantage would be that this seal would by the only thing separating the camera from the atmosphere unless I use sealant around the Peltier TEC and its leads.

Here's a screenshot of the first CAD model.  I think I'll print one and see how it goes.  There are other bits to add such as clamping for the camera casing top and attachments for the top part of the outside casing.

Not right yet but going in the right direction...  Needs more room for the focus motor.

Next try at the model for the bottom casing.

It's just occurred to me that I was going to use some of the heat from the hot side of the Peltier TEC to warm the underside of the dome to help with dew heating and stop dew on the outside, but now I don't see how I can.  It just seems daft to have heat to get rid of and heat wanted under the dome yet "ne'er the twain shall meet".  I may get thinking again and see if there is any way of using the spare heat.

The Peltier TEC eventually came off the passive cooler so I can change the cooling if I want to.  OTOH passive cooling does have its advantages.

Thought I'd  do a Google search for aluminium boxes with the thought that a Peltier TEC in the bottom could warm the dome and found another possibility :-
ALUMINIUM SQUARE BOX SECTION 11 Sizes 10 Lengths  with one option as 4" square and 100mm high.  That's 4" outside and 3mm thickness.  This makes the inside 95.6mm square.  Now the passive cooler is 95.0mm square so the top of it would fit nicely inside the box section.  It would need clamping on and sealing to keep damp out but it's an interesting idea, I think.

Print finished.  Here are a couple of photos with the top camera casing, camera, lens and focus motor added.  Rather a rough print at high speed just as a prototype - not the finished version.

If it weren't for the enclosure getting hot in the daytime in summer I could go back to having the Raspberry Pi and the other electronics inside the ASC casing rather than in a separate box in the observatory.  Two advantages - it would save having to seal lots of wires, with just power connections remaining and also output heat to warm the dome and with the inside being dried it's only the outside of the dome that can suffer from dew. 

Would it be feasible to fit it on the north side of the warm room where it would be shaded from the Sun to help keep the temperature down?

James

Good thought ?   Though not the warm room as that gets covered by the ROR but I am planning to mount it on the north side of the ROR.  The dome has to be above the roof to get a view of the sky to the south.  I could shade a lot of the casing though.  Last time it was mounted on the south side in the full sun.  Maybe it won't get too hot.

Decided.  Going to put RPi with its HAT and the buck converter in the ASC casing.  Just need to increase the size a bit.

New designs for basing bottom and camera casing top, the latter underside view.

This solves the problem of holding the camera casing together but not attaching the top of the outer casing.  The top needs clamping and sealing arrangements for the dome and for attaching to the bottom part.

The basic top part of the casing, connecting dome to bottom part.  The dome can be attached with a ring on top of its lip screwed to the top ring of the casing, with a seal between.

oops - forgot to allow for the RPi.  OK new design needed... No problem.

If I solder the RPi power input wires directly to the board I can save 10mm height allowing for a slope on the top otherwise the top would be flat which I don't like.  I'm changing the arrangement and having the top go right down to the level of the inside of the bottom part.  That will make clamping top to bottom easier and put the seal lower down so that if there was a leak it would be below the camera.  Not that I intend there to be any possibility of a leak!

Model of the top part of the outer casing.

Matching bottom part of the casing.  This is screwed to the passive cooler with M3 screws and to the top part with M5 screws from underneath.

No testing tonight even if it is clear.  All design work which I think is almost done.