Wednesday, 11 March 2015
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I finally finished my fully 3D printed proton pack the other week. I've spent the final days implementing the lighting system using a simple Microchip PIC and a charlieplexed array of LEDs.
The traditional circuit for lighting a pack consists of a 555 oscillator to produce a clock, which is then fed into a couple of shift registers, the output of which drive NPN transistors to drive the LEDs. This produces a column of lights that rises then resets.
A decade counter (with transistors) is used to illuminate the LEDs in the 'cyclotron', the 4 large circles at the bottom of the pack.
This seemed a bit over the top to me, as not only being complicated, with around 13 LEDs in the column, the wiring of some implementations is a bit challenging with a cable per LED.
So I designed some circuits to implement the same effects, but with far fewer wires. Not only does this simplify the wiring, fewer wires should also increase reliability.
I created a very simple circuit which brought out the I/O of a PIC (16F684) to a few connectors:
And a second circuit which gave me a charliepxed matrix:
I did this as two separate circuits as the pack has two LED columns, one on the pack and one on the thrower. A smaller PCB is used in the thrower with a second PIC board which means each LED column has a LED board and a PIC one. I chose a board pair solution as there is limited room in the thrower housing where the LEDs are mounted.
Charlieplexing works by utilising the tri-state ability of microprocessor I/O pins, in that only two pins are ever outputs at any one time. To implement this I used two look up tables: One to hold the port I/O register states (e.g. which pins were outputs, and which were not). One to hold the pin values (e.g. which pin high and which pin low).
I also included 16 levels of dimming per LED by implementing PWM in software. With the PIC running flat out at 2mips I can control each LED individually with dimming without flickering:
Here is the finished pack:
And here I am ready for Zuul with youngest as My. Stay Puft:
The proton pack parts can be downloaded from Thingiverse. And a few others worldwide have joined me in making this:
Iron Man of Maine.
Monday, 2 February 2015
Sunday, 1 February 2015
tommyb345 suggested that I check out a pre-made mount to attach my proton pack thrower to the proton pack.
Trouble is these seem to start at $75 for decent ones, and the guy selling them on ebay doesn't export. So I decided to make my own.
The proton pack thrower mounts to a sloped fitting on the proton pack, this I made out of several layers of 3mm aluminium sheet:
A special fitting is required to mount the thrower to this. I designed one and bent it on the sheet metal bending machine we have at work:
This needs to be fitted to the proton pack thrower. The problem I had was that a screw solution would result in a raised profile on the inside of the mount. This would clash with the proton pack fitting, so I decided to weld the mount to a steel plate fitted to the base of the thrower.
I dragged out my trusty Clarke MIG welder with matching BOC Argoshield gas.
And my solar powered welding mask. This is great, you can see through the protective glass, but when the welding arc starts, the glass instantly darkens. Which means can can get set up for a weld without looking through very, very dark sunglasses.
I'm not a trained welder, but I managed to fasten the two pieces of metal together:
And after going over with the angle grinder, it wasn't too bad:
Saturday, 17 January 2015
The 3D printed Ghostbuster's proton pack that I'm making needs some lights. Today I concentrated on the 'cyclotron' lights. These plans have been created by dedicated fans who have stop framed the original film to produce accurate drawings.
These need to be red when illuminated, but as dark as possible when off. To achieve this, I 3D printed a LED diffuser using clear PLA.
Using superglue, I stuck this to some car window tint that I had left over from creating the skeleton effect for halloween:
This makes the diffuser look 'black' when the LED is powered off:
But reveals a nice red when the led is illuminated.
I'm using TLCR5800 hight brightness LEDs that normaly fit into my Lasertag muzzle flashes.
Sunday, 4 January 2015
My Ghostbusters proton pack replica uses several pneumatic fittings that were available to the prop builders in the 80', but are no longer manufactured.
A result of limited availability and demand has led to some crazy prices for these parts.
The parts that can cause problems are: The Legris Banjo:
I've seen originals of these going for $100 each on ebay, and a resin cast replica which needs some finishing will cost over 20GBP with postage from the US.
Another part is the Legris straight fitting:
These again will cost me around 30GBP to import from the US as a pair.
So I decided to make my own.....
I asked the Iron Man of Maine to measure the ones he has, and I coincidentally had some brass hex bar of exactly the right dimentions.
I had to make two of these, so first I parted the bar:
Then I turned it down to give the pipe exit 'nipple':
I then drilled the hole to 5mm. I did this after the turning down as the nipple walls are quite thin and I didn't want to risk damaging them whilst turning down.
I then turned the part around, and reduced the bar diameter to allow me to thread it, using the oldest tap and die set in my collection. I used this as the threads of the metric dies I have seemed too coarse compared with the reference picture:
I used the end stop chuck to hold the die against the workpiece to get it started:
To create the circular depression in the top of the part, I used an old lathe tool that was made by my wife's late grandfather. This has a really small tip and is right angled to allow me to apply it to the end face of the work piece:
It came out looking really well, but too shiny. So I applied some dilute ferric chloride solution to the machined surfaces for a couple of seconds to dull them, before washing off with water:
For the Legris Banjo, I decided to try 3D printing. They came out quite well, and I smoothed them out with acetone vapour. For a brass like effect, I bought some some antique gold metallic paint. But it was too 'gold' So I added a trace of black.
It came out looking OK, but I tested it on a brass bar I had lying around:
After painting the banjo, I think this is not too bad. I've put the parts on Thingiverse.