Sunday, May 13, 2018

Chaotic Shortbus functional completion

Does anyone remember the Chaotic Shortbus? Probably not, but it's a build that's been on my mind recently. It's been several years since work started with, thus far, too little to show for it. As of the last update, this project consisted of a nifty concept, a sorta-ugly shell, and a pile of half-completed internals with vague plans for how everything would eventually fit together. There was still nothing that actually shoots, despite the fact that this build started in 2015. Since then, we've seen the end of the great motor drought, seen the rise and beginning of the stagnation of the Rival line, seen the rise of 3D printing as a widespread tool in the hobby, seen the rise of brushless motors, and seen the development of the Caliburn - but, at least as far as the Chaotic Shortbus is concerned, nothing worth writing home about.

There were reasons for this, mostly having to do with the fact that I wasn't confident in how to proceed in certain key areas, but . . . these were not really good reasons to shelve the build, in as much as waiting hasn't helped to make answers to those questions appear, resulting in a half-completed project rattling around and taking up space nigh-indefinitely - a situation which, I realized, was doomed to persist until those still-present obstacles are simply ignored and completion attempted regardless.

So, it's time to finish this darned thing.

Let's start with a firing demonstration, largely because it's satisfying to finally be able to do one. This blaster could, in its current state, be carried into a game. Improvements are due, but it does at least fire:

Wiring this blaster was non-trivial in several ways. First, a decision was made early in the build to use a pair of 12V relays (in parallel, so as to share load) to control the current to the flywheels; this was deemed necessary as any microswitch small enough to fit into the grip might not be able to reliably handle the simultaneous inrush current of three sets of flywheel motors. 12V was the lowest activation voltage that I could find locally at the time, and I glued the relays in while making the shell, thus committing to their use. Experimentation has shown that these relays do not in fact need 12V in order to trip; 5 fully charged NiMH cells suffice but 4 do not. This, in turn, suggests that while as few as five NiMH cells could be used to power the relays this would make the blaster unreliable as it would suddenly stop working once they were partially discharged.

That black box is a pair of relays glued end to end
Several options were considered for controlling these relays. I'm going to list all of them as a way to illustrate the decision-making process that was involved here:
  • NiMH secondary batteries could have been placed throughout the blaster, with a total voltage sufficient to trigger the relays. This would allow the blaster to function with primary batteries of any voltage. As only a small current would be required, loose AA or smaller cells would suffice. However, even such cells would be cumbersome to include due to the number that would be needed and the limited space available. Some could be placed in the remaining Stryfe battery tray - but not enough. More could be placed in various gaps throughout the blaster - at the cost of requiring additional wiring in a blaster whose wires are already troublesome enough. Sufficient cells could be placed in the main battery box alongside the main batteries, thus grouping all of them together and simplifying wiring - but this would further limit the space available for those main batteries. In any case, having to maintain the charge of this secondary power system would be an inconvenience (of some degree depending on where the batteries are placed) and would introduce an additional failure condition. 
  • I have a few Trustfires - they came with a blaster that I bought - that could easily provide enough voltage from the stock Stryfe battery tray and no other use for them. Given the low current required, they should be relatively safe in this application . . . but being Chinesium, still not entirely safe. Besides, some games ban Trustfires in blasters regardless of how they are used. 
  • A more stable battery system could have been acquired for this purpose, such as a LiPo or 9V PP3 NiMH. However, I've standardized on larger NiMH packs and getting into a separate battery ecosystem just to power some relays would be a major faff. 
  • I could use a 9V PP3 alkaline, which would also fit in . . . no, just no. The problem with non-rechargeables is that it is always tempting to try to squeeze more use out of them, which in this case would create a risk of sudden failure.
  • Some number of NiMH cells could have been used as a booster and powered the relay in series with the main battery. This would ensure that the relay receives sufficient voltage even if a low-voltage main battery is used, but raises the possibility of feeding the relays too much voltage. 
  • The main batteries could simply be used to power the relays. This is the simplest solution, in terms of wiring, further decision-making, and maintenance. However, this would limit this blaster to the use of main batteries that can reliably produce voltages sufficient to trigger the relay. 
Quick'n'simple circuit diagram
In the interest of expediency, I went with the last option listed. In retrospect, it should have been more obviously a good solution - it works with the batteries that I currently have, and a booster secondary battery would be easy to add later. That's what overthinking does to ya. Avoid it. Something that's functional now is better than something that's perfect never.

Speaking of which - 'the battery packs that I currently have' - this blaster runs off of a pair of 5-cell sub-C NiMH packs in series, which gives it a nominal operating voltage of squarely 12V. That's equivalent to 3S, which is a reasonable voltage for a variety of different motors.

The motors in the blaster right now are Rhinos - there's room for 180s, but I don't have enough unearmarked 3S 180 flywheel motors on hand and want to keep the cost of this build down. Swapping the flywheel cages for ones with better motors should be straightforwards if I decide to do so. Rhinos certainly aren't the punchiest motors out there, but they rev high enough to fire near-as-makes-no-perceivable-difference instantaneously, and rev high enough to fire hard in less than a second. They're certainly usable.

The story regarding wire routing is just as long and the ending is the same: fruitless pursuit of the 'best' solution was abandoned, and the simplest solution that could be made to work turned out to be a pretty good one. There were, in case this is non-obvious, several different ways that the blaster could have been wired. The power for the motors could split off at different points, the relays could have been either prior to or followed the motors in the motor-relay circuit, and likewise for the rev trigger and relays control . . .  and all of this affects how wires snake through cramped spaces. The circuit diagram shown above was sketched quickly, then I set about finding a way to make it work.

See those APPS? That's how the flywheel cages disconnect
Here's the short version: Swapable flywheel cages were made by gluing Anderson Powerpoles into stock Stryfe cages, using a Stryfe shell as a guide while the glue set. Only minor modification to the cages themselves was needed in order to get the APPs to fit. The built-in side-to-side dart guides had to go, but they won't be missed. In stock blasters, those dart guides are theorized to help to guide darts that are badly mangled or that would otherwise slip sideways against flywheels with no foam buildup that don't adequately grip the darts at the moment of first contact. In this blaster, they are a source of friction and nothing more. Given that this blaster can fire up to three darts at a time with a mechanical trigger, anything that makes that trigger pull smoother is good.

I quite like how these swapable cages turned out.  There's no need for anything special to be done to hold the wires and connector down, as there is in some other interchangeable cages, as the connector is held in place by the flywheel cage and the wire is held at both ends between the connector and the gap in the shell through which it runs, with no need for slack. It's a simple solid system with a minimal number of moveable parts.

Here's a prime example of how overthinking can cause one to overlook obvious solutions: have moving parts? Have wires? Want to keep them separate? Trying to figure out how to route the wires through parts of the blaster where those moving parts won't be affected?

Why don't ya just use PVC to keep the wires away from your moving parts, and then put your wires wherever you want?

Complex problem, simple solution

Those white wires are all 16 AWG, by the way.  The flywheel cages are wires with 18 AWG (with each terminal having its own wire; you can fit multiple wires into an APP crimp hole), and the orange wires are 14 AWG. In other words, all of the wires that carry the full current for all of the motors are 14 AWG, all of the wires that carry the current for only one of the three cages are 16 AWG, the wires that carry only current for one motor are 18 AWG, and the wires that carry current only for the relays are also 18 AWG. I could have fit thicker wire into some parts of this blaster, but this setup is plenty good enough.

There are some oversized joins here, where a multiple wires converge onto the same terminal. Fortunately, these relays have nice and big power terminals, and I have a soldering gun large enough to heat multiple 16 and 14 AWG wires at once. This build would have been a real pain otherwise, as I would have had to use many separate splices. 

Structurally, this blaster has six major pieces. As seen from the perspective of someone holding the blaster:
  1. The left half of the left Stryfe. This can be screwed firmly onto the second piece, as all of that Stryfe's remaining screw ports are exposed. 
  2. The right half of the left Stryfe, merged with the left half of the Demolisher's outer shell. This piece is intended to be removed easily (the first piece comes away with it), as this is what allows access to the batteries. That requires leaving out a number of screws, for a reason that I'll explain later.
  3. The left inner Demolisher shell. This part largely serves as a cover for the internals that lie in the right half. 
  4. The right half of the Demolisher inner shell. This part holds most of the moving parts and most of the electronics. The relays, microswitch, and most of the wires are all stuck to this part, with only a total of four wires leaving to deliver current to the leftmost and rightmost flywheel cages. 
  5. The right outer Demolisher shell, merged with the left half of the rightmost Stryfe. 
  6. The right half of the rightmost Stryfe. 
There are three main structural challenges resulting from this.

First, a way was needed to carry current to each of the three flywheel cages that would allow the blaster to be disassembled. Simply wiring everything together would not suffice, as the wires would hold the pieces together. This was relatively straightforwards. You've probably noticed a pair of sideways-pointing APPs glued to piece #4 that has appeared in two pictures thus far. Those connect to a pair that is glued to piece #2, which in turn contains the flywheel cage for the leftmost Stryfe. There's also a pair of wires that goes through a hole in piece #5, into the rightmost Stryfe. Those wires terminate in a pair of APPs that connects directly to that Stryfe's removable flywheel cage. They are held in place only be the fact that they travel through a narrow gap between the Stryfe's stock battery box and the top of its shell; it's a tight fit. There is enough slack in the wires to allow the pieces to separate and, once the cage is removed, they can pull through the hole (which is barely big enough to allow APPs to pass through) and allow the pieces to completely separate.

Second, a way was needed to allow pieces #1 and 2 to separate easily from the rest of the blaster, to allow convenient access to the batteries, while not being at risk of falling apart. My original plan for this was "Magnets, probably. Otherwise I'll think of something." Some of the screws that would normally hold down piece #2 had to be omitted - these are the screws that hold the inner and outer shell pieces together, which are only accessible from inside the blaster. Leaving those screws in would mean that the middle of the blaster can only be disassembled by separating pieces #3 and 4, which are held together by many screws. The rest of the screws holding down #2, I wanted to omit, simply because it would be nice to be able to access the batteries without fiddling with a screwdriver. Several magnets are in place throughout the blaster and the sideways APPs mentioned previously are nice and clicky and provide a small amount of structural integrity. However, whenever I hold the blaster without any screws holding parts 1 and 2 to the rest, a visible crack forms along the spine of the blaster and I have a horrible feeling that it's going to fall apart in my hands. So, I've left two screws in - one immediately above and behind the Demolisher's jam door, and one in the Rapidstrike stock. That's less than ideal, especially considering that these screws go into plastic and I'm not completely confident in the long-term durability of a plastic screw hole given frequent insertion and removal.

Adding a charging port would partially alleviate this problem; this could easily be hidden under the remaining Stryfe battery tray door. I'd still want to be able to swap the batteries in and out to use them in other blasters, but this would reduce the frequency with which the shell needs to be opened. In any case, the current solution is at least workable.

Third, pieces #5 and 6 don't stick together very well. Most of the screw ports on that Stryfe were covered up when it was merged with the Demolisher. There are enough screw ports remaining that these pieces aren't at risk of coming apart, but the crack between them is ugly. This could have been avoided with a little foresight, if I had made these screw ports accessible from the inside of the Demolisher instead of closing them off entirely. Maybe I'll drill through to them. This isn't something that needs to be done; it's just a potential fix for a minor aesthetic issue.

Speaking of aesthetics: when I started work on this blaster, my goal was to produce something that would look like a stock blaster to someone not sufficiently familiar with nerf to recognize its components. On a certain level, I think that I've succeeded - it looks stock at a distance. If you saw a crowd of human HvZ players wander past, this blaster would blend in as well as any huge yellow handheld object possibly can. On closer inspection, though . . . it looks like a well-used and somewhat dinged-up yet well-maintained power tool. Which, I suppose, it sorta is. I like that.

What I don't like, aesthetically, is the combination of a square front and flat top. Let's pull up that firing video again:
So, you probably noticed the Recon Mk2 barrel extension. It's short, but the combined length of a Demolisher barrel plus this is just a little too long for a straight-fluted Recon barrel replacement, and there's no way to hollow it out without removing the orange front end. It's not going to stick around. The reason why it's there in the first place, though, is simple: I like the way it looks. It breaks up this blaster's square front end. I'm currently thinking of making something similar using the front end of a Barricade - the pseudobarrel will be wide enough to never even touch the dart, and the overbuilt look will compliment this blaster well.

Other than that, there's a long list of little things that I'd like to touch up and improve, but they are just that - touch-ups and improvements. This blaster is finally almost finished.

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