The chassis is constructed mainly from Makerbeam 10mm extruded aluminium, and associated accessories. The Nema 17 stepper motors use the Makerbeam metal bracket, and the servo motors use the lasercut acrylic servo mount. Arms for the pinch rollers are attached using the bearing mounts, and the PCB slots between two 10cm beams. The Raspberry Pi in a Pibow case is attached to the front beam with long steel M3 screws in place of the standard nylon ones. A long camera ribbon cable goes from the Pi to the camera.
Various parts in the telecine were 3d printed. A fair amount of precision is required for the film handling. It's important that the film path is pretty level - from film-spool to motor to gate to motor to take-up spool. Shapeways and 3dPrintUK were used. Shapeways offer a variety of materials and colours, and 3dPrintUK are slightly faster and cheaper for larger items - but only in white nylon.
Parts were designed in Freecad, and STL files were sent to the 3d printing service. Freecad allows designs to be made based on cross-sectional drawings, and results have been very good.
- Film Gate
- Pi camera mount
- Film roller on stepper motor
- Pinch roller
- Film Idler rollers
- Spool tables
- Light box
- Makerbeam end-stop (protects rubber band)
The film rollers and pinch rollers were printed in Shapeways' frosted detail plastic, as this gives a good smooth surface for gripping the film edges. First version in white standard nylon slipped more. The pinch rollers use bearing races so they can rotate freely. The film rollers fit steppers with a 5mm D shaped shaft. A little bit of electrical tape was used on the shaft to make a tight fit.
Pinch rollers are mounted on swinging arms, and use rubber bands made from an old bicycle inner tube to hold the roller in tension with the motor mounted (capstan) roller. The arms can be released in order to remove the film.
The light box serves to mix the colours of the white and turquoise LEDs, and to diffuse the light to create a flat area of illumination behind the gate. The gate and camera mount fit into the slots on the Makerbeam - allowing adustment while keeping alignment straight.
[Original 3d models and STL files are here](../hardware/3d Models/).
3d printed lightbox, gate and camera/lens-mount in situ
The film spool tables are attached directly to the splines of the servos. The servos are standard inexpensive TowerPro MG995s (or copies), but modded for continuous rotation by pulling out a metal pin that stops the gears rotating 360 degrees, and removing the feedback potentiometer. The control PCB was also removed, and two wires soldered directly to the motor - effectively turning the servo into a compact simple geared motor. There are various instructions dotted around the net for this process.
The advantage of using servos is the simplicity of attaching the spool table - it just uses a single m3 screw, and holds extremely securely. However any DC motor would be suitable. Film spools are not fixed on the tables - they are designed to rotate freely so film can be pulled off the reel, and the take-up spool rotates with a little bit of friction, rotating enough to take up the slack. The motors are designed just to rotate in one direction - in order to pull the film onto the spool.
The camera is screwed onto a 3d printed bracket which fits into the slot in a short piece of Makerbeam. It can be fixed securely, but allows for adjustment and focusing the image. To focus closer the Raspberry Pi camera's lens needs to be carefully unscrewed almost as far as it can. This is not enough to get an 8mm frame large enough in the frame, so an additional lens is required.
The first version of the camera mount allowed fixing of a simple (and inexpensive) smartphone close-up/macro lens. These can be got for cheap from Ebay. Results using this lens was just about acceptable - the centre of the frame was pretty sharp, but got softer away from the centre with a fair amount of colour fringing. My first examples on Youtube use this lens. Not bad for a lens that costs less than a fiver.
Much better is its replacement - a coated Steinheil triplet, available for a reasonable price from Surplus Shed in the USA. This lens is much sharper with little chromatic abberation and has less distortion than the smartphone lens. It was suggested for macro use by rkinch in this thread on the Pi forums. The camera mount design was adjusted for this lens.