1100D debayered with added cooling, filter wheel and OAG in one unit

[Gina]

This thread effectively follows on from the 450D version and the DSLR debayering discussion.  I have a couple of changes from the 450D thread - I have decided to go for a 4 position filter wheel and the camera will now be an 1100D

[Gina]

Parts list :-

1. Non-working 1100D body from ebay auctions - but with working image sensor, shutter, main board and power board
2. Peltier TEC model MCPE-127-10-25 from Farnell  http://uk.farnell.com/jsp/search/productdetail.jsp?sku=1639752
3. Digital thermometer DS13B20 1-wire by Maxim
4. Digital thermometer and humidity sensor DHT22
5. Power MOSFET IRFZ44N
6. Arduino Nano
7. Stepper Motor 28BYJ-48

[Gina]

As with the 450D version, the whole unit will consist of a box containing all the camera parts with an optical window so that the inside of this box may be dried with silica gel desiccant, plus an attached filter wheel, OAG and control box.  The control box will be integrated with the FW and OAG.

Within the dry region there will be a cold region, thermally insulated from the rest of the dry region and containing the camera image sensor, image processing board, cold finger and cold side of the Peltier TEC.  A DS18B20 digital thermometer will be attached to the cold finger and thermally connected with thermal paste to read the cold finger temperature while temperature and humidity of the dry region/chamber will be measured with a DHT22 digital module.   The arrangement of parts will be virtually the same as the 450D version but I'll produce modified diagrams for the 1100D shortly.

Here is the Cooling System circuit diagram - blue box is the cold region and red box the dry region.  As shown, the present idea is to have the Arduino outside the dry region.  I'm thinking of putting the other cooling system components inside the dry box though.  Having the power MOSFET close to the TEC will help reduce RFI.

[Gina]

Here's an update the the cooling system circuit diagram.  I think it's clearer too.

[Gina]

Here is a diagram of a new design for the 1100D  assembly.  I have abandoned the copper box used in the 450D design, as it's impractical to assemble the camera into it.  It has been replaced with a printed plastic box in two parts to aid assembly.  The plastic print also provides thermal insulation as a large proportion of the volume is 25% homeycomb with lots of air cavities.

[Gina]

Here is a rough diagram of the top/bottom view cross-section.  Not to scale.

[Gina]

More thinking on the design but not using SketchUp much as it's doing my head in

I have worked out a way to incorporate a 4 position FW with direct drive from the stepper motor.  As with the earlier carousel, the 36mm unmounted filters will just clip in without needing screws to hold them.  It is just 100mm diameter with printed shaped hole to directly fit on the stepper motor shaft as a tight fit.  The carousel weighs practically nothing being 3D printed from PLA with honeycomb internal structure.  The main weight will be in the filters themselves but I'm hoping the inertia will be low enough not to strip the motor gearbox.  I could reduce this problem by limiting the acceleration and deceleration in the Arduino sketch.

I have arranged the carousel and stepper motor as they will fit with the camera and taken a photo.  Take no notice of the very rough plastic print - I have yet to fix the printer.

[Gina]

New design sectional diagram.  This includes the stepper motor in direct drive position and extension to the camera box to include the control circuit with Arduino etc.  I shall probably include a USB hub too.  This part will be separated from the dry chamber by a partition wall (not shown in diagram).

[Gina]

Here is a screenshot from the SketchUp model of the plate that sepatates the camera section from the filter wheel.  ie. it forms the top of the camera and the bottom of the filter wheel.

[Gina]

The IR blocking nose filter I was going to use has turned out to be too big and makes the design impractical so I'm going for the IR filter from the original camera.

[Gina]

Latest design for the separator plate.  This is just a basic design to test size and fit.  Final design will have rounded corners and holes and bosses for screws.  Stepper motor is now fitted from FW side.

Screenshot of camera side.

[Gina]

New design sectional diagram.

[saac]

Gina, I never fail to be in awe of your ingenuity and industrious approach.  The 3D printer will earn it's keep on this project I suspect.  Good luck with it.

[Gina]

Gina, I never fail to be in awe of your ingenuity and industrious approach.  The 3D printer will earn it's keep on this project I suspect.  Good luck with it.

Thank you very much

[Gina]

The separator plate has now become half the dry box surrounding the camera parts.  This is to allow sealing the dry box behind the stepper motor.  Here's a screenshot of SketchUp.  I'll post a photo when it's finished printing (if the print is alright).

[Gina]

Here is the SketchUp model of the design of the FW casing.  I may use an aluminium plate as well to take the scope fitting - I've yet to work that out.  The OAG consists of a surface silvered mirror mounted on the two angle brackets.  This reflects light from a radius of 20mm from optical axis into the guide camera through a hole in the FW casing.  The guide camera will be mounted on the outside of the FW casing.  I've yet to design the mounting but I expect to use 3D printing for that as well.

This screenshot shows the camera side of the FW.

[NickK]

Some thoughts and queries:

* Have you checked the light cone vs sensor & the FW, optical window etc?

* if you're going the whole hog - put a bit of heater wire on the window so that the outside of the window doesn't get condensation?

* is the shutter the camera one or a new one? If it's made and heavy then you'll need to think about how fast it works vs the shadow/gradient it will cause on the CCD

* how are you ensuring that the optical alignment is true? Ie that there's no slight tilt etc of the sensor etc?

[Gina]

Some thoughts and queries:

* Have you checked the light cone vs sensor & the FW, optical window etc?

* if you're going the whole hog - put a bit of heater wire on the window so that the outside of the window doesn't get condensation?

* is the shutter the camera one or a new one? If it's made and heavy then you'll need to think about how fast it works vs the shadow/gradient it will cause on the CCD

* how are you ensuring that the optical alignment is true? Ie that there's no slight tilt etc of the sensor etc?

I have allowed for use on a telescope with an almost parallel light path.  If I were using camera lenses I could get away with smaller filters.  Most of the lenses I own have an exit window that would be fine with 1.25" filters.  The 36mm filters I'm using cover more than the frame size even for parallel light.

I'm prepared to heat the outside of the optical window if necessary.

The shutter is original and these work fine for AP.

I'm going to use a rubber gasket around the edge of the camera housing and I should be able to finely adjust the sensor alignment this way whilst retaining a seal to keep the chamber dry.

[Gina]

I now have the 3D printer working pretty well with the clear PLA (well, a lot of the time) and have produced test prints for most of the casings for the camera assembly.  I have taken a series of photos showing how the various parts fit together.  Next job will be to add the holes and bosses that will allow them to be screwed together but I wanted to check the fit of the camera, stepper motor, etc. before complicating the prints too much.

Here are the photos (not the best I'm afraid but serve to make the point I think - been better done in daylight).  I shall refer to the end that attaches to the scope as the top and the back that takes the cooler as the bottom.

Firstly, the part that connects camera space to filter wheel - referred to as "separator plate" above.  Houses half the camera and forms the bottom of the FW casing.  Shown with the stepper motor in position.  The rectangular hole with recess takes the optical window - the IR filter from the original 1100D.  This seals the dry chamber whilst allowing light to reach the camera sensor.

Next is the other half of the camera housing (dry chamber) with a "tongue" to cover the stepper motor and form a seal with the curved motor housing of the separator plate.  These case parts will be glued together.  It was not practical to print these parts as one unit due to the way 3D printing works.

The next two photos show how these two parts fit together to provide a sealed camera casing (dry chamber).

Finally, the bottom dry chamber plate, shown with the other parts.  This forms the bottom of the dry chamber (alias camera casing), holds the Peltier TEC (square cut-out) and screws onto the cooler heatsink.  In addition to forming part of the dry chamber casing, it provides thermal insulation between hot and cold sides of the TEC.  The raised portion near the bottom of plate in the photo fits the profile of the cooler.  Two slots and holes under the raised portion take the wires of the TEC.

There will be a further casing to contain the electronics.

[Tinker1947]

All coming together now, it been a bit of a trek....

[Gina]

Working out the way to hold things together has provoked some design changes.  I have moved most of the sides of the dry box into the "separator plate" model and reduced the "tongue" part to just tongue and some side wall above it that can be fastened onto the front of the main box.  These two screenshots from the SketchUp models show the approach.

The tongue part printed well but the slicer refused to recognise the base of the separator plate and I can only seem to print the box part.  I've already spent too long trying to get this model to slice properly so I'm printing the box and I'll print the base part separately.  SketchUp with the STL export and Slic3r so often seem to refuse to cooperate   Quite often I've produced a seemingly perfect model that won't slice properly

[Gina]

Still having some problems with the 3D printer with raised lumps of filament on the first layer preventing the second layer from printing in register with the first   Also, sometimes when this is alright I get blobbing later on and the X or Y axis jumping out of alignment.  In view of this I'm reluctant to print a large structure in one go. eg. the dry box shown above would take 4 or 5 hours of printing with a high probability of failure sometime during the print.  So I'm thinking of dividing the structure up into smaller parts to improve the chances of successful printing.

[Gina]

The stepper motor in its housing as part of the dry chamber wall is proving a very tight squeeze indeed and I've pretty much come to the conclusion that I'm wasting my time when I could use a timing belt drive and make things easier to design and construct.  I know most people think I go out of my way to do things the most difficult way but that really isn't true!  It's just that my brain has been suffering from overload recently and now it's just addled   I like challenges and to do things few people would tackle but I like to find the simplest and easiest way of doing them

[Gina]

Been looking into this part of the design again and I see why I wanted to use the motor - the output shaft is offset and close to one side of the housing.

[Dave_D]

I know most people think I go out of my way to do things the most difficult way but that really isn't true!

I think it's called the design process... i did that a lot with code, and then have a flash of inspiration, usually in the strangest places like sat on the toilet