First a little background...
For those of you that are no familiar with the conference, Shmoocon (hosted by the fine folks at the Shmoo group, an independent security "think tank") is a small hacker/sercurity conference on the Washington, DC, typically some time during the month of February. This past February was no exception.
One of the great things about Shmoocon is the ability to provide instant feedback to the presenter, while the presentation is happening. Ever been to a conference or presentation where you just knew there was something "rotten in Denmark", or you wanted to make a point about some minute, but essential overlooked detail? Shmoocon enables and encourages every attendee to tall the speaker to task: They provide a foam stress ball (aka a Shmooball) at registration for each attendee (and offer more for sale, proceeds going to charity). The organizers encourage you to throw them at the presenters when you have a point to make, or when you think that you're being sold a bill of goods.
As a result, the closing ceremony of the conference has typically found the Shmoo group founder, Bruce Potter, amidst a barrage of shmooballs. Why? Because the attendees could.
In 2007, a group of folks unveiled their Shmooball cannon at closing ceremonies and unloaded at Bruce. It was multi-shot, made from PVC and a 2-stroke leaf blower. It was a great concept, but it was smelly and not incredibly efficient.
This is when I had thoughts of doing better. In 2008, I created a version that was much like a shoulder fired grenade launcher. In 2009, I decided I needed to take it up a notch.
This is the story of the building of the 2009 Shmooball cannon.
I had great plans for 2009 after items that I learned form 2008. I wanted something that was light, easily carried, and easily reloaded. I thought I had come up with a fantastic way to accomplish all 3: create a pistol style cannon, fed with easily detached tubing, and house all of the mechanical and pressurized bits in a backpack.
I came up with my original concept right after Shmoocon 4 in 2008. In typical fashion, I didn't begin the actual execution until 4 weeks before con. Add a wife, baby and large quantities of snow into this mix, and there isn't a lot of time left for construction.
As a result of my procrastination, I realized that I needed to source all of my parts locally: Home Depot, Lowes, Radio Shack and the local paintball supply. I affectionaltly refer to this type of construction "Hacking Home Depot": Come up with an idea, and spend 4 hours wandering the aisles of the home improvement store looking for appropriate parts, and how you can modify them with tools on hand to meet the end gaol. Tons of fun.
Here is what I came up with.
Shmooball cannon initial design
As you can see, I've accomplished the pistol portion fairly well. The barrel is made from 2.5 inch schedule 40 PVC electrical conduit, with a female thread adapter at the butt end, glued with PVC cement. The muzzle break happened to be a feature of the conduit, as a way to connect two lengths together without the need for additional couplers.
The grip was constructed out of a 3 inch to 2 inch schedule 80 PVC "Y" adapter. A table saw was used to trim off the to section of pipe that wasn't needed. The barrel is attached with a clamp at the front end, and 5 minute epoxy was used at the butt end of the threaded adapter. The outer portion of the threaded adapter was almost an identical fit for the internal diameter of the 3 inch "Y", os it was used as a glue point. With out some additional material at the front end of the barrel, it would have off by about 3/8 of an inch. A 2.5 inch female coupler was sacrificed to the shop saw, and utilized as a spacer at the front of the barrel.
The grip "Y" adapter
The actual grip was simply constructed out of a short length of 2 inch PVC with a female threaded adapter on the end. Screwed into the adapter was a threaded clean out plug. The hand grip was not glued, so that parts could be added later (safety switch, trigger and batteries), and so that they could be easily replaced.
At the end of the barrel a make threaded 2.5 inch adapter was used for the butt end. Unfortunately, 3 Lowes stores later (the only store that carried 2.5 inch PCV conduit), I was never able to find 2.5 inch endcaps. I did find 2 inch endcaps, and fortunately these were a close enough fit into the end of the male threaded adapter. Because they weren't a tight fit, PVC cement wasn't an option here, so both halves were sanded with the Dremel and glued with 5 minute epoxy.
Barrel end cap
The pistol is then attached to the valve assembly through standard air tool coiled hose, utilizing 1/4 inch NPT quick release adapters. The barrel end cap was drilled in the drill press, and threaded with the brass adapter. Yes, the PVC is soft enough to have the brass cut it's own threads, I like to hold on to the brass fitting with a pair of vice-grips and welder's gloves, and run the brass fitting through the blowtorch for a few minutes. This makes the thread cutting almost like a hot knife through butter.
At the valve end, I needed to increase the size of the 1/4 inch NPT coiled hose to meet the 1 inch threaded inlet of the i inch water sprinkler valve. This is accomplished with several steel step down adapters and plenty of teflon tape.
Valve step down adapters
Next is the hub of the operation, the 1 inch lawn sprinkler valve. In the 2009 cannon construction, the valve was used as it came from the manufacturer, activated with an 24V solenoid. While we could modify this valve to be pneumatically triggered for faster operation, the solenoid application works just fine.
Feeding the valve is a set of male threaded adapter and end cap, but this time fitted with a 5/8 inch paintball regulator. From there, our 20oz compressed CO2 is attached with a shutoff and quick disconnect. the paintball regulator in this case is a necessity, as the paintball CO2 tank is typically charges somewhere from 800 to 1200 PSI. This pressure, if unregulated to much less (80 to 120 PSI), will quickly turn all of our PVC components into shrapnel. Carrying that around a con full of people would not be a good idea...
Tank regulator and adapter
The last point to mention is the firing mechanism. We need to provide 24V to the solenoid to operate it, allowing the air to propel the Shmooball form the cannon. However, 18v, delivered by two standard 9v batteries wired in series works just fine. the negative lead is connected to the solenoid, and the positive os wired to two switches in series; this way both need to be closed in order for the cannon to fire. I elected for a standard momentary pushbutton for the trigger, and a light up, shrouded saftey switch for the safety.
In order to deliver the 18V to the solenoid, I needed a cable that I could quick disconnect from the hand grip where the batteries and the switches were, to the valve located at the other end of the coiled air tool hose. I happened to have a CAT5 cable and wall jack insert in hand, so I elected to use those. In a twist of fate, the wall jack insert fit perfectly inside the end of the threaded clean out end cap.
Cable goes here!
A 1/4 inch hole was drilled in the end of the clean out end cap, the jack placed inside, and held in with 5 minute epoxy.
CAT 5 jack
Once complete, I found the it was nearly impossible to undo the little clip on the CAT5 cable in order to release it form the jack, due to the insert now being recessed behind 1/8 inch of PVC!. So, the clean out end cap had to be ground down to provide a rounded edge to allow access to the CAT5 cable clip.
Tapered end cap
So, it looked pretty good at this point. That was, until I test fired it 24 hours before the whole assembly needed to be dropped off for transport to the conference. Let's just say that the test fire didn't have the expected results.
I had figured that the failure was due to not having enough airflow from the valve to the barrel. I had figured that it might be a problem ealier on, so I had purchased extra parts as a backup plan.
What I didn't realizes was how far my backup plan would have to go, until 2 hours before con opened. The results of the hotel room testing, the the frankenstein creation are what are shown below.
The final result
So, let's start with the upgrade to the coiled tool hose. It was replaced with a new endcap with a 1 inch brass threaded "hose barb" fitting. I found this bad boy in the plumbing section for flexible hose for artesian well water systems. That sucker was 12.99 for a darned fitting!
New barrel endcap
Regardless, it was attached to a 1 inch clear vinyl tube with a hose clamp , which was then paired to a PVC 1 inch threaded hose barb at the valve end.
Valve end upgrades
Now it required an act of congress to breach load (undo CAT5, unscrew pistol (not endcap!), load, re-screw pistol, connect CAT5, arm, fire.), so muzzle loading with a wood ramrod became the next choice.
Unfortunately, during the hotel room tests, Paul and I also discovered another fatal flaw. The 20oz paintball tank could not feed the delivery system with enough air fast enough to propel the shmooball from the barrel more than 6 feet (and with the sound of a dying cat as well). What we really needed was a tank that could hold a large volume of air that could be recharged from the slow paintball tank, but released quickly.
Fortunately, Paul had suggested that we bring along the 2008 shoulder fired cannon. I also had the hindsight to pack too many tools and extra teflon pipe tape.
The 2008 version featured a large tank mated to an identical sprinkler valve. Thank goodness for modular parts; we scavenged the 2008 tank to replace the direct feed from the paintball tank.
The scavenged tank is fed by a 20oz paintball CO2 tank via remote kit with a 5/16 inch threaded quick release. I needed to convert the 5/16 to 1/4 to mate up with the old regulator in the 2008 design, so a capsule of 1 inch end caps was created to make the adapter (drill endcap, heat fitting, thread, PVC cement to 1 inch PVC pipe). This capsule is then attached using 1.4 inch hose barbs and standard air tool hose to a air tool regulator (more Home Depot hacking!), and then to more hose with a barb drileld and threaded into the tank.
Tank feed and regulator
The tank was originally intended for another application, so it features some additional twists and turns. However, the main chamber is 3 inch schedule 80 PVC with an end cap, reduced to 2 inches, fed to 2 inch 90 degree elbows, reduced to 1.5 inches, reduced to 1 inch, ending in a 1 inch male threaded adapter. That's a LOT of PVC fitting, which are of course glued together with PVC cement.
What Paul and I ended up with at the end of our cannibalization was a pistol design that was appropriatley powered, but with a much larger "back end support" than anticpated. Now, the tank, CO2 and valve didn'f fit so well, and ended up looking like a particle accelerator out of Ghostbusters. Backpack was quickly abandoned in favor of using gaffer's tape to directly strap the tank to my back, and the CO2 tank to my thigh. Nothing like intentionally strapping yourself to a bunch of potentially explosive compressed air!
Who you gonna call? Shmoobusters!
After all was said and done, it was a huge ugly looking success. We learned a lot this year, and made a few notes:
- Pack extra tools and parts. The valve actually failed on stage during the presentation on the build of the cannon. Looks like over pressurization one too many times.
- Bring extra CO2 on stage! I ran out during the demo. Paul got me more. :-)
- Plan early, start construction even earlier! This will allow for more testing and sourcing of more appropriate parts. Sure, hacking Home Depot is a great challenge, but sometimes you have to know when you are beat!
- Use lots of teflon pipe tape. Thought you used enough? Use more. Some is good, more is better, but too much is just enough.
- Have fun and be safe. Remember, melting and or pressurizing PVC and sprinkler valves is not recommended by the manufacturer!
See you at Shmoocon 6 in 2010, cannon in hand. In hand? Maybe there is something else in the works...