3D printing a reloadable Super 8 cartridge??

[Will2]

Could be steam powered:
http://www.thingiverse.com/thing:25624

Awesome.

I'm ready to donate to a steam powered Super 8 camera Kickstarter project. Right now. Today.

[aj]

The cost of an entry level 3D printer in Australia, I found, is currently AUS 995 which is a pretty good price. The resolution is 0.2mm. The build volume is a 12cm cube.
C

Is this 0.2mm resolution anything near the 0.03 tolerance you dug up earlier.
And how flat is a surface when it is in one pane?

Luckily it is only a thought excercise

[Nicholas Kovats]

Carl,

Your ability to whip up a visualization based on a discussion is formidable. Very impressive and forum members are salivating. However I have a few engineering suggestions with a declaration that my perspective is based on examination and usage of 16mm Aaton XTR Prod/Arri SRII and Photosonic 1P coaxial magazines.

I would be willing to send to you some non-functional Photosonic 1P 200FT or 400Ft coaxial magazines for your examination and/or measurement. The Photosonic mags are not optimal regarding final design intent of a prototype S8 coaxial mag as they also contain the transport system. However you may ultimately be inspired from a design and material perspective. I could also contact LIFT regarding spare Aaton or Arri mags.

Criteria:
1. Design a CNC Aluminum prototype.
2. Strip the above professional mags to a minimal functionality relative to S8 50ft film lengths/loads.
3. A hinged or removable door such that a user can reload Super 8 film.

The experienced gained from this particular Super 8 project would lend itself to future camera projects.

[carllooper]

The cost of an entry level 3D printer in Australia, I found, is currently AUS 995 which is a pretty good price. The resolution is 0.2mm. The build volume is a 12cm cube.
C

Is this 0.2mm resolution anything near the 0.03 tolerance you dug up earlier.
And how flat is a surface when it is in one pane?

Luckily it is only a thought excercise

Yes, I spoke about 3D printing ages ago. Was the printer I mentioned previously 0.03mm? With a 0.2mm resolution that's obviously not as good as 0.03mm. In 3D printing you get the volumetric equivalent of pixels, called voxels, ie. looking closely you'll see the voxels. For 0.2mm rez there'd be 127 voxels per inch (25.4 / 0.2).

Obviously mechanical parts would need to be designed to whatever the rez the printer will be. So atomic sized mechanics are ruled out.

[carllooper]

The experienced gained from this particular Super 8 project would lend itself to future camera projects.

thanks Nicholas, but that's okay. I've got the idea of how the cart works now.

I've got a couple of junk Bolexes here I've been examining. Have been working through claw mechanism designs - whether for a camera, or projector. The Bolex has a gear with a pivot offset from the gear centre to which is attached two claws. As the gear spins the claws are constrained by a pole on each so that they exhibit a clawing motion. The shape of the claw with respect to the pole constraint determines it's motion. Due to the circular drive one claw is insufficient to complete a full pull. So therefore two claws. As one claw exhausts it's engagement the other takes over. It also exploits centrigufal forces to ensure the claw doesn't touch the film during the flyback phase. That had me stumped for a while. Very elegant design - using what looks like the simplest possible mechanism (minimum number of parts) - the required action embodied in the intelligent shape of the claw, as it moves against it's constraint. I'm going to have a go at computing the shape of the claws based on their required action.

I've always wondered why a pressure plate needs some give. My current guess is that one can't be sure if a film is correctly lined up for claw engagement so the claw has to glide across the surface of the film until it finds a hole. Without a pressure plate the claw would dig into the film. The pressure plate allows the claw to push the film/plate away from the claw until the claw finds it's hole, at which point it engages and holes will be lined up next time around.

C

[carllooper]

So this is a rough idea of how one of the Bolex claws works. The other one uses the same strategy, but a different shape, and there is some overlap in their engagement . One taking over from the other to complete the push. The all important backbone curve of the claw needs to be computed in such a way that optimises the sprocket engagement. The backbone curve here was done by hand using splines and a lot of trial and error. A computer program would do a much better job as it could compute the ideal curve.

[PyrodsTechnology]

Carl i am not sure which Bolex is in your hand but in my EBM the upper claw works only for reverse motion, and lower claw only for forward motion.
Rob

[carllooper]

Carl i am not sure which Bolex is in your hand but in my EBM the upper claw works only for reverse motion, and lower claw only for forward motion.
Rob

Thanks Rob. It's a bit hard to tell on my junk Bolex as it's in pieces. When analysing it I noticed both claws moved in the same direction, one after the other, roughly a quarter phase each. But on further investigation, with my working Bolex it seems only one claw engages during forward motion - I could be wrong as I can't watch it in slow motion (and don't want to take it apart). On that point I can't see how to put either of the Bolexes (Bollei?) in reverse. It's probably something really obvious but it's completely escaping me.

I've found the back plate for the junk Bolex which helps more to see what's going on (so the claws are constrained and don't wave their arms all over the place). So the way it seems (latest theory) is that both claws do participate in forward motion. The first one seems only to briefly engage the film and might be an initialising 'hole finding' engagement, ie. lining the film up for the second claw to do the push/positioning proper. During normal operation this first claw would be next to invisible to see as it is so fleeting. The second (more visible) claw would put the film into the correct place for exposure.

Re. claw shape. On closer examination of the Bolex claw shapes I notice the first one has a straight spine as distinct from my curved spine - which would account for it's brief engagement with the film. It is the second claw which has the custom spine that would allow it to engage the film for the required interval and bring it into precise position for exposure.

Re. 3D printing a claw. Since the claw is so crucial for precise positioning of the film a 3D printed plastic claw, with 0.2mm rez may not be a very good idea. The bumpiness need not be an issue. If it positions the film the same way on each cycle it's self correcting. Although I suspect the required rotation-to-translation transform requires a fairly tolerant zero point solution, ie. any bump away from this point could introduce some unwanted fragility during disengagement. A pointy ended curve/motion path could do the trick here. The other issue would be simple wear and tear, ie. the shape of the claw gets "sanded" away over repeated use (don't know), and/or (more importantly) could have a certain amount of give that induces unwanted oscillations. May just mean coming up with some alternative claw design that works with bumpy plastic rather than precision machined metal.

cheers
C

[carllooper]

This is an example of the solution space one would be exploring in any search for the right point relative to a straight spined claw. The three green curves represent the motion paths for three different points relative to the same spined claw. Recollections of Spirograph from my childhood suddenly come to mind here. In a computer generated solution one could also auto vary the radius/positions of the drive pivot and pole constraint in search of a solution to a desired target motion. The more difficult computational problem will be computing the curved back claw. That's my next task.

[Nicholas Kovats]

PyrodsTechnology and Carl;

Pryods is describing is a second variation in Bolex's transport design as per the EBM and EL cameras. I quote Jean-Louis Seguin from an earlier email he sent me today regarding a related topic, i.e.

"In the EBM and EL they changed the design of the gear train from simple spur gears to helical gears."

"

[carllooper]

"In the EBM and EL they changed the design of the gear train from simple spur gears to helical gears."

Thanks Nicholas. Yes, I'm looking at the older "spur gears".

cheers
C

[carllooper]

Here's a start on the computer model of the claw action based on Bolex

Animated wireframe:

http://members.iinet.net.au/~carllooper ... index.html

As the arms move to the right they move the film. As they move to the left the arms need to be disengaged.

C

[cameratech]

Good grief, this is like some Monty Python skit where scientists from the distant future are examining a fork and confidently explaining the reasons for its complex curvature and specific harmonics of the prong spacing..

First off, the spur/helical gear thing has nothing to do with how the Bolex pulldown mechanism works. It's to do with transmission efficiency and noise reduction and is further down the gear chain. The EBM pulldown mechanism is the same as the other H16 models until you get back to really early Bolexes.

The H series Bolexes have a forward run claw and a smaller reverse run claw that pivot from the same spindle and are compressed on to that spindle by spring washers that allow the claws to pivot with a small amount of drag. The forward claw points down, the reverse claw up. When the camera is run the spindle rotates eccentrically in a direction that (due to the drag) forces the forward claw towards the gate and the reverse claw away from the gate against a pin. The eccentric pivot drives the forward claw back and forth in a groove in the gate that is protected by a nylon pad. When it moves down the claw catches a perf and advances the film to the exposure position. When it moves back up it slides across the film, which is kept from moving by the pressure plate.

To operate in reverse, the motor is disengaged and the rewind crank used. The claw spindle turns in the opposite direction and the reverse claw is now pushed against the gate, while the forward claw is pushed out of the way against a pin.

There were many, many different pull-down mechanisms devised over the years. A 16mm mechanism that pulls-down from the back side of the film as used by Bolex (and Scoopics, Pathes etc) isn't much use to you if you're interested in a mechanism for Super 8 cartridges. For a start the claw needs to engage from the emulsion/gate side. Most S8 mechanisms I've seen tend to use a very simple spring-loaded claw.

[carllooper]

Good grief, this is like some Monty Python skit where scientists from the distant future are examining a fork and confidently explaining the reasons for its complex curvature and specific harmonics of the prong spacing..

The main idea is to get some sort of inspiration for a claw design that can be printed on a 3D printer. So I'm starting off with a junk Bolex H16 and looking at how it's designed. What particular problems did the original designers face? What sort of ideas did they embed in their design. The purpose of the computer model isn't to "explain" the mechanism as such. It's to compute a shape based on the mechanism, ie. that can be 3D printed. It involves testing the mechanics, be it by pen and paper (drafting), and/or computer modelling. From which it can then be printed.

First off, the spur/helical gear thing has nothing to do with how the Bolex pulldown mechanism works. It's to do with transmission efficiency and noise reduction and is further down the gear chain. The EBM pulldown mechanism is the same as the other H16 models until you get back to really early Bolexes.

Ah okay. I wouldn't know about any of that. Just looking at the pull down mechanism.

The H series Bolexes have a forward run claw and a smaller reverse run claw that pivot from the same spindle and are compressed on to that spindle by spring washers that allow the claws to pivot with a small amount of drag.

Yeah, that's what I'm visualising in the wireframe. Again it's not necessarily to "explain" anything. It's to find what sort of shapes, following the same idea as an H16 claw mechanism, could work.

The forward claw points down, the reverse claw up. When the camera is run the spindle rotates eccentrically in a direction that (due to the drag) forces the forward claw towards the gate and the reverse claw away from the gate against a pin. The eccentric pivot drives the forward claw back and forth in a groove in the gate that is protected by a nylon pad. When it moves down the claw catches a perf and advances the film to the exposure position. When it moves back up it slides across the film, which is kept from moving by the pressure plate.

Yep - that's what I've got happening in the wireframe. At the moment it's just a skeleton onto which I can then compute some optimum curves.

To operate in reverse, the motor is disengaged and the rewind crank used. The claw spindle turns in the opposite direction and the reverse claw is now pushed against the gate, while the forward claw is pushed out of the way against a pin.

Ah okay. You use the rewind crank to rewind.

There were many, many different pull-down mechanisms devised over the years. A 16mm mechanism that pulls-down from the back side of the film as used by Bolex (and Scoopics, Pathes etc) isn't much use to you if you're interested in a mechanism for Super 8 cartridges. For a start the claw needs to engage from the emulsion/gate side. Most S8 mechanisms I've seen tend to use a very simple spring-loaded claw.

Latest version of computer model is here. Here I'm computing the maximum bounding surface for an armature constrained by the right pin, to moving just left and right.

http://members.iinet.net.au/~carllooper ... index.html

C

[cameratech]

Carl,
I appreciate your curiosity, I really do, but you're not listening.

The H series pulldown design won't work for a Super 8 cartridge, because it acts from the wrong side of the gate.

The pin has no relation to the forward claw movement when it runs forward, it only acts as a stop when the movement is run in reverse. What keeps the claw engaged with the gate is the friction of the turning spindle, which needs to be strong enough to keep the claw pressing against the gate, but not so strong that it pulls on the film as the claw pulls back (in conjunction with the pressure plate tension).

Even the cheapest movie cameras used metal claws - perhaps plastics technology wasn't as advanced as today, but I don't think a coarsely manufactured plastic movie camera claw is worth investigating.

You're missing the point that the main design factor with small gauge film movements is not the claw shape or movement curve, which tends to be quite basic, but the various tensions involved - claw spring, pressure plate and take-up.

With professional 16 and 35mm movie cameras the pulldown curve becomes much more important, but there are also so many other factors involved.