Friday, 15 February 2013

Steampunk Firepower–Prototype

Building the prototype

So far I have built the basic body of the gun. The body is made from several layers of polystyrene glued together with Poly Vinyl Acetate (PVA).


The polystyrene was harvested from a bunch of old computer and tool packaging. The hardest part was cutting out usable pieces of polystyrene … most of it is holes and voids so that the manufacturer can save cost.

The laminated polystyrene was then cut using a bandsaw, hacksaw and craft knife, and then smoothed using a 120 grit sandpaper.

I needed to fill some of the holes in the polystyrene, so I did some experimenting. First, I tried filling the voids with more PVA. This worked OK, but the glue is not able to be sanded very well.

Next, I used plaster of Paris. This worked fairly well, but it chips and breaks easily and it also takes a while to go off.

Next, I used a two part epoxy resin. This sands better, but it also eats the polystyrene.


To counteract the corrosion, I applied a coat of an acrylic paint. This worked well and showed up the rough spots well. The paint and epoxy solution takes even longer than the plaster solution … so on with the experimentation.

My next option was auto-body filler. I used a Selley’s multipurpose filler. This is styrene based, and so, also corrodes the polystyrene. I did this in a couple of layers. First, a thin layer that would corrode the polystyrene somewhat, and then build it up with subsequent layers and sanding.

Next I will use a water based wood filler. This will allow me to make the consistency of the filler according to my needs as well as being non-corrosive. I’ll start with a fairly thin layer of filler to seal the polystyrene and then build it up with thicker layers until I have about 3mm coverage. This should give me the thickness that I need to carve with the Dremmel.

The body is now made up of several different materials and so it can only be considered “experimental”, that is, it will not work as a usable prototype.

Electronics Prototyping

I’ve started to solder up some of the electronic circuitry for the bling of the gun. At the moment, my plans are to have a pulsing LED light being expressed through a set of resin “port-holes” in the main body and for a set of chasing LED lights circling the “barrel” of the gun. In total, there are only 9 LED lights (8 x 3mm and 1 x 5mm).

The prototype circuit for the pulsing LED light is under way and I will start on the chasing LED lights next. At the moment, this will be prototyped on two separate PCB, but I will reorganise the circuits so that they will fit on one later.

Pulsing Circuit with 556 Dual Timer replacing 555 Timer

The above circuit is the schematic for the pulsing LED light. The schematics that I found on the interweb call for a 555 timer, I’ve adapted the schematic to use a 556 dual timer instead, as that’s what I had to hand. I may expand the prototype later to utilise both timers in the 556 such as:

Dual Pulsing Circuit with 556 Dual TimerThis circuit will give me two pulsing LED lights, rather than just the one. If I change the resistor of the second LED, then the two LED lights will be out of phase too … that would be groovy. Anyway, the single LED will do for now. I am a novice in electronics, so it may be a bridge too far at the moment.

The main challenge for the lighting of the gun will be manufacturing the epoxy domes. The electronics themselves are fairly straight forward and reasonably inexpensive.

I plan to stow the 9V battery in a compartment in the grip of the gun so that I can easily change the battery when it needs it.

What I have learned

I’d like to get some thicker polystyrene, I will pay for some and get it in sheets. The hardware store sells polystyrene sheets, so some more investment is needed.

Using a non-corrosive filler, such as a water based wood filler is much better and causes far fewer toxic fumes in my workshop.

I will always end up with a lumpy surface after filling, so sandpaper and rasps are my friends.

The most important thing for me to remember is that, starting over is not such a bad thing. The prototype will be invested in silicone so that I can make solid reproductions of it, so getting it right at the start is far cheaper (in time and money) than trying to fix it later on in the process.

When planning your model, plan for space for the electronic gubbins if you are going to add any, it will dramatically reduce the amount of anguish later on when you try to fit the electronics.

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