Thursday, June 11, 2015

It has a name now: progress on the Chaotic shortbus

Remember this? Progress on this build has been slow as I've been doing bits here and there in my spare time, which I don't have much of at the moment. I've also been experimenting with different techniques, and on that front there has been enough progress to merit a post.

The name, in case anyone is curious, comes from here.

 Ensuring proper alignment was a reoccurring issue for this build. This picture shows how the bar connecting the pushers was glued into the Demolisher's pusher; the wood and jam doors are there to ensure that it was at a perfect right angle. I later discovered that the plastic used in the Demo's pusher does not bond to the MMA (methyl methacrylate adhesive) that I use, so this bond was reinforced with superglue. Corresponding rectangular holes were cut in the other pushers carefully using a sharp knife.

 The right side of the Demolisher and the left side of the Stryfe are both reasonably flat, so the first bond was made in these areas. The pushers were present in each blaster (and connected), as was a magazine in each magwell which rested against a vertical block, to ensure proper alignment when the bond was made. Solvent cement was used because the area was large and I wanted something that set quickly; the markings on the Stryfe were there to indicate the areas to be smeared with cement.

 Once the first major bond had set, six-round mags were put in each magwell and glued to a block of wood. This created a template of sorts to ensure even spacing when attaching the second Stryfe to the other side.

As you can see in the picture, a lot of elastic bands had to be used to hold the shells together in the process. You can also see the tip of the connecting rods, which were cut to length such that they barely reach through the holes on the Stryfe pushers, with the ends beveled to allow for easier assembly.

 The original plan called for PVC to be used to fill in the gaps between the shells, but I discovered a better way to patch small gaps: apply tape over the gap, smear epoxy or the like over the inside of the tape, and then remove the tape once the epoxy sets. Smearing epoxy over the tape before applying it also works, and is good for smaller gaps which are not accessible through the inside of the shell.

MMA was used here instead of epoxy because these bonds serve as the primary connection between the Demolisher and the leftmost Stryfe, so they need to be strong. Besides, MMA is less prone to running before setting, cures to a reasonable working strength and rigidity faster, and is generally nicer to work with than epoxy.

This technique is not suitable for producing neat surfaces, for a variety of reasons. It tends to slightly underfill the gap, air bubbles are hard to eliminate and leave pits in the surface, and the resulting surface attracts grime very strongly, presumably due to residual adhesive from the tape. However, it is fast and should make a good base for smearing on epoxy putty.

In this picture, you can see part of the beginning of the battery box. Speaking of which . . .

 Those magnets are there to hold the box together while the glue sets - there are corresponding magnets on the inside. They are on a dividing line between two pieces of PVC which does not show very well in this picture. This division will be necessary to allow the blaster to be disassembled and to allow access to the batteries.

Cutting PVC edges square enough to match without a strongly visible line - or, worse, daylight showing through - between them is not easy. Hand tools just won't cut it, if you'll pardon the somewhat malapropos figure of speech. Cutting the sheet PVC in a mitter box works well enough, except that the maximum length of a neatly made cut is set by the width of the box - and, here, that isn't quite long enough. The battery packs that I intend to use stick out of the back of this box by a few mm.

The panels of this box were aligned using a flat surface, offsets of regular thickness (K'nex) and a large rectangular block (a thick hardcover book). The result was . . . well, not satisfactory. It didn't look too bad at first, but the angles were slightly wrong and the box was asymmetrical in a way which would have looked really bad once a stock was mounted on the back.

So, the box that you see here is now gone. The current plan calls for a box to be fabricated off of the blaster, and then put in place once I am satisfied with it.

 This was an idea that I tried and then ultimately rejected. Deodorant cap motor covers would have drawn the eye away from the nearby distinctive features of the Stryfe, making it slightly less recognizeable. However, they don't quite "fit" aesthetically with the rest of the blaster and, worse, are made from a plastic which neither MMA nor solvent cement can bond, meaning that a firm attachment would require a significant amount of fabrication surrounding the caps.

There are two options that I'm considering for the motor covers. The first is to use an old Rayven jam door, which is conveniently just about the right size. This jam door is also made from a non-bondable plastic (this seems to be another reoccurring issue with this build!) but it is a single, large, piece with square edges that should make fabrication straightforward and allow for a sufficiently strong mechanical bond.

The second is to simply fabricate the whole thing out of PVC. 

Speaking of jam doors: having the jam doors be joined and open as a unit would be convenient for reloading the blaster through the jam doors, and making the sliding jam door on the Demolisher obsolete would allow for a little extra room inside of the shell, which might be useful for wiring. However, doing this would mean that the jam door would then need to be painted, and I'd rather just leave them orange to match the barrel lugs/trigger/lower Demolisher shell. Ultimately, the deciding factor will likely be whether I need the internal space for wiring.

Some magnets have been installed on the inside of the shell, with very good results. Ferrite magnets are very hard and very brittle, which makes it nearly impossible to sand and/or cut grooves in them to ensure that they are securely adhered to the shell. However, the force provided by each pair of magnets is small enough that I'm not greatly concerned about them pulling out when the shell is pulled apart.

To do (initial build):

Fabricate and install battery box
Construct stock
Make motor cover
Place more magnets to hold the thing together
Figure out wiring
Figure out what to do with the jam doors
Epoxy putty and sand remaining gaps and crevices
Make holders for extra missiles

To do (planned upgrades):

Put 180 motors under those motor covers
Make power adjustable (Diodes? Swappable cages with different motors?)
Improve Demmo missile HAMP seal

(Torukmakto4 Edit: Bumping post so it has time at the top.)

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