Slit-Scan Disc Camera – Part 2 (3D Printed + Planetary Gear)


In the last video I set myself the task to make an unusual photographic camera using a 3D printer. The camera I began making combines two forms of photography – slit-scan in which photographic film passes along a slit to produce an image which removed the time distortion created by a shutter, and a rotary disc camera which was a 80s gimmick. The first camera I made had a direct drive which meant the turning handle was connected to the rotary disc, and for the second I added a reduction gear to an anulus gear on the rear of the rotary disc. This meant I had to the turn the handle almost 6 time to make one full rotation of the disc which would hold the photographic paper.  But I ran into trouble because I couldn’t rotate the disc slowly enough by hand to expose the paper and produce a recognisable image.

In this video I attempt to add a planetary gear to the camera, to further reduce the rotational speed of the disc.

Ok so if I’m already losing you, maybe watch the first video if you haven’t done so already although if you have done so already, I may have already lost you.

So planetary gears are a type of gear assembly normally used to increase or decrees torque at the expense of speed. The higher the torque the slower the speed. The most common application for us woodworkers, would be in our drills and you can see some examples on screen now. Now I don’t want to reinvent the wheel with this, so I happen to find an example on Thingyverse by Aubenc in May 2012 – it was quite a while ago. I was having trouble importing the files into Fusion 360, so I printed them out produced a little model and aligned that to the camera that I was working on. I took the measurement from the 3D printed planetary gear set, and than produced the appropriate fitting on the camera’s body. I found a few videos of people assembling this particular gear set. I am not sure who or which was the person who designed it – and often the videos are really badly filmed and it wasn’t clear how this thing came together. So I’ll just describe that in this section now.

The outside gear with the teeth facing inwards is the annulus or ring gear, and the one in the centre is the sun gear. The three between those are the planet gears and these put together produce a set. I put the three planet gears onto an arm which holds each in a set position – in this case at 120 degrees between each one. (Get it while it’s hot) These are then centred between the annulus gear. The sun gear has a flange which clips onto the shafts for the arm that holds the three planetary gears. The sun gear is longer than the other gears and bridges the sets, stepping the gearing down along each set stepping the gear down along the sets. The more sets you add the higher the torque and the lower the gearing speed. I was really struggles to imagine how this work – which is why I printed this out. I could physically see the parts come together and understanding how I might go about utilising the design or designing something similar.

So I probably need a few more stages but essentially if I can replace this handle with the gear on the outside – that bit looks like an ok size as well. I should be able to get this disc to turn really slowly with one of these.

I am now going to edit the 3D model of the camera.

I’m going to modify this section of the turning disc – so I can get a positive lock from the planetary gear that I’ve just printed from Thingiverse. What I’ve done already is extended the back plate so that the heads of the screws can fit inside. I will lock those down with a nut and build the planetary system onto the plate, so it’s a little more rigid. So I’m going to create a new sketch on the top section, the mouse is a bit shit at  the moment. What I’m going to do, is make a circle that is 8.2mm – that’s the outside. And then I’m going to measure between between the lowest point  of the tooth that 5.4mm.

I then counted the number of teeth I would need to make space for. In this case nine. I created a sketch for a single tooth spaced between the two circles I drew, and then performed a circular pattern command to repeat that around the central point. What I should be able to do is create a circular pattern. I’ll select these four lines. And the centre will be over there. And if I make nine. I extruded the sketch downwards cutting it from the spur-gear, but I was left with a raised cylinder which was part of an original sketch for a mounting screw. I deleted that and extruded an additional cylindrical recess for the shape of the marrying part.

Put a circle in there, and make it a little bit bigger so I know it’s going to fit. 2.8mm. And that is 3mm down. And that bit should fit this section here.

Ok lets see if this fits.

I used red PLA as I began to run out of black PLA, and I wanted to test the print before committing what I had left.

It’s letting a lot of light through. You can see my fingers in the background.

3,2,1 I just noticed that… the 3D printer is really loud when the directional mic is pointed at it. I also noticed that the disc is press tightly onto the section that is meant to hold the slit. And if it remains like this that means when the photographic paper is put in there, plus the slit and the tape to hold those, it’s going to be very difficult to turn the paper. The camera which needs to be light tight may not also close. So I am going to drop the surface of the disc back by extruding it 1mm.

So this project is as much about learning how to use a 3D printer as it is about making a camera.

One of the 3d printed threaded rods broke, but the principle works so what I will do is replace those with M4 machines screws, and to hold each section with nuts.

Ok I’m printing a new back. And that’s because I’ve worked out the assembly of the planetary gear. Obviously I am printing it in black because it needs to be light tight and this isn’t. You can see the silhouette of the disc. Also as a back up went and bought some Polaroid instax film this is the squa… this says wide. So hopefully it works on the disc. I just printed another disc as well to make it a little bit thinner – I missed calculated that.

Ok so I’m going to open the packet of the Polaroid paper. What I’m going to need to do is take a piece of paper out from the container while making sure I don’t expose it so I’m going to do that in this changing bag. Yeah it looks pretty dark in there. And then I’m going to place it through the rollers of this pasta maker in the darkroom, in the changing bag. I’ll probably have to sandwich the paper on some leather or bits of chard.

Ok I just took some pictures using this mechanism here. And I did these outside to get a bit more like. And I think there’s something there. You can see a gradient of grey on some of these lines, which I guess is a positive thing. It means it’s been exposed. That ring is something in the slit which I haven’t cleared. So it has slowed it down enough. That’s something there. It’s really hard to tell.

I also tried to use the same mechanism with some Polaroid film, and to develop it in the pasta maker.These two I just exposed the paper in the dark room to the red light so I’m guessing that’s kind of the light. So these ones I didn’t develop on the slit scan mainly because these were too small and I can’t actually rotate them. And the way this stuff works is the developing chemical is in a sachet here, which get squeezed out like kethcup along the back of the Polaroid. And erm, it’s sealed and I think what happens is the remaining liquid gets deposited sachet here or this pouch. The pasta maker isn’t great for it because the actually roller in a Polaroid camera has springs which compensate for this last section here just so that you don’t pop that Polaroid. I’m already bored of this so I’m going to have a break and work on something else… Like the bloody CNC machine I’m trying to build. Anyway thanks for sticking with this one even though the final outcome wasn’t a complete success. I was hoping to use the odd pictures are Christmas decorations but I didn’t produce enough of them to merit putting on a tree. This has been a good learning experience and I feel a lot more confident design things for and using the 3D Printer but if I come back to this I’ll need to work on some kind of better mechanism to develop polaroid that isn’t a pasta roller.


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