Gina

Here is a design I'm going to try for the middle section of the casing.

Open position.

ADDENDUM I have the need to modify more 28BYJ-48 stepper motors as mentioned above but I found that I was unable to get the motor back together - the end of the rotor shaft would not go back into its bearing hole in the plate. As a result I decided to try to cut the PCB track without taking the motor apart. I carefully drilled a hole through the blue plastic connection cover to access the PCB where the strip wanted cutting through. Then I was able to take a very small screwdriver and scrape through the track without disturbing anything else. This is shown in the close-up photo below. As before the coils are orange-pink and yellow-blue. Do not connect the red wire.

This shows the probable position of a drive gear. This can be on a shaft coming out of the side of the main casing.

Here are a couple of photos with the cover attached to the lens and the RPi placed beside the camera.

Seems alright so far but there's the drive from stepper motor to the gear to sort out with particular attention to sealing the motor from damp. The only way I can think of getting the drive from the inside to the outside is by a shaft. And not out of the top or it would need a waterproof gland. I have most of the parts to complete the rest including an RPi HAT, stepper motor and driver module so I should be able to design a casing to suit.

Changed the design of the cog part for more strength and printed it, then glued it to the cover part. The final version will want a bit of cleaning up of course but this is just a test of the design.

Now to the drive mechanism for the cover.

Here is a design for the lens tube with bracket for the cover axle added. Now printing.

A couple of photos.

That went fairly well and I think I shall be able to produce a usable print. I shall print it in black ABS and thicker. That print is just 2mm thick.

I'm seeing if a dome top could be printed on its edge.

The cover and its operating mechanism will need making in several parts which could either be made of ABS and glued together or made of PETG and fastened together with nuts and bolts. Think I favour the former - my Titan printer is equipped with fume extraction so fine with ABS. Fumes and nano-particles are blown into the loft.

Going for my smaller high resolution printer, "GinaRep Pilot", for these parts and I'll leave my bigger "GinaRep Titan" for the bigger casing parts. A bit later :- Hmmm... Pilot printer is not working properly. Oh well, have to put up with fast but coarser printing

As I thought the dome was rubbish. It needs finer printing but that takes a lot longer. The aesthetics are not important - it just needs to work! The flat "roof" could have a slight slope on it. I don't really want to spend too long on this project but I want an ASC working again. I can be too fussy at times

I think there might be problem printing this unless I reduce the support spacing as the filament is drooping inbetween but I'll eave it printing and see if I have enough clearance from the lens tube. Whilst a dome is esthetically nice a flat top is much easier to print.

Designed and now printing the main part of the domed cover.

Designed and now printing a test lens tube (to see if it fits).

Here's another diagram. If I print the lens cover in black filament I can use it closed for taking darks and eliminate hot pixels. I shall probably print the main casing in white ASA filament as that is UV safe and will stay cooler in bright sunshine.

Checking the materials used between camera and lens I find they are all black anodised aluminium but at least there would be less aluminium conducting the heat. The only way round this would be to attach lens to camera with plastic but this has its own problems. Maybe the anodising on the threads of the various adapters will help with thermal insulation. Just have to suck it and see but it probably means the Peltier TEC cooling will be needed. Maybe I could arrange a heat conducting copper strip from the hot side of the TEC to the lens Copper conducts heat much better than aluminium.

The lens support being aluminium will conduct heat from the camera to the lens which might be useful if the camera was allowed to warm up as it would warm the lens and help prevent dew. However, a warm camera produces more noise and this was the reason for adding the Peltier TEC cooling. The cooling pad can be seen between the camera and the lower aluminium heat sink, which dissipates heat to the aluminium pipe that supports the whole unit. If cooling is off the camera can warm up when in use but if the camera were mounted directly to the aluminium block it would be cooled to near ambient. In view of the sensitivity of the camera and good light throughput of the lens, this would probably be adequate cooling. But if the lens were at ambient temperature in the winter there is a strong probability of dew settling on the lens. I really think the lens could do with being heated. The upshot of this is that the lens wants to be thermally insulated from the camera. Then the camera can be cool to reduce noise and the lens can be heated to prevent misting up. In other words the lens support is a nuisance. I think I shall try the ASC without the lens support. I'm not sure about the Peltier TEC cooling but the cooler pad is already there and powering it with control from the RPi is no problem. Similarly heating the lens would be no problem - I just need to decide the best method of heating it. Heating the air in a dome is easy - just a string of resistors. For the lens it might be better to use Nichrome wire insulated with Kapton tape (high temperature thin insulation).

Coming now to the rest of the ASC, here are two photos of the insides. With and without the lens support.

Skirt and lens tube extended and taper increased slightly to improve clearance.

If the pivot is further out the problem is lessened.

Here is a cross-section of the lens tube and cover together with a pivot about which the cover might move. The problem with any cover with a long skirt is the cover catching on the tube as it opens or closes. This is shown in the two diagrams below for a typical case - shown to scale with a 15mm skirt.