Electronics 10 beantillon: Engineering an Extinguisher

Now...THIS...has probably been my favorite part of the project, tied only with Rick Rolling the class earlier in the course with my Annoy-a-tron Toy.

Sometimes, my best ideas owe their inspiration to a dream. Such was the case this time.

In order to achieve the maximum time bonus (based on flame extinguishing methods) in the firefighting robot competition, the rules state that a robot must use a non-contact, non-wind method to put out the candle flame.

Ideas were thrown around, many of which involved a high-pressure canister, water deflection, a water squirt gun...but none of these were sufficient, and a few of them exceeded our budget restriction of $20 (retail).

--A high-pressure canister (CO2 cartridge) would require a robust control valve, which was expensive and too complex to interface to the VEX brain reliably.

--A cheap plastic squirt gun creates a narrow stream of water, which translates to a very small margin of error in a platform and environment with a high level of unpredictability, and it was also difficult to construct a mechanical method of triggering the squirt gun quickly so that it built up enough pressure to project water at the flame.

Thus, it begins...

My search criteria was simple: a small container, capable of withstanding relatively high internal pressures while being easily triggered (mechanically). I began cleaning out my closet the weekend before when I noticed I had a can of silly string from about 5 or 6 years ago.

I punctured the sidewall of the can, purged its contents, cut it in two with the assistance of an air-powered circular die grinder and inspected its operational equipment. Inside was a straw leading up to a high-pressure valve, easily operated by exerting a finger's effort of pressure on the spray nozzle at the top exterior of the device. It was just what I had been looking for; it even had the Dollar Tree price tag still adhered to the plastic cap.

I requisitioned a Schrader valve from a discarded bicycle tire, set it into the sidewall of the can through a small circular hole from the die grinder and sealed the whole construction with JB Weld.

The result was a small device, capable of withstanding relatively high pressures while being easily triggered by pressing on the spray nozzle. Critical to its continued success is that it is also reusable: by removing the pintle assembly inside the Schrader valve, the can is capable of being preloaded with plain water before the valve is replaced and the canister is pressurized with air compressed by a bicycle tire pump (through the same valve!).

The device worked exactly as designed, but a greater cross-section was needed to remove the off-chance that the robot did not properly align itself with the flame. The original nozzle was a non-atomized design to spray silly string, and so the opening was relatively large to accommodate the flow of the suspension. By searching through the cleaning products and other aerosol devices around my house, I was able to locate a nozzle which 1) created the desired wide cross-section and atomization of the contents and 2) fit over the neck of the can's control valve--a suitable nozzle was lifted from a can of stainless steel cleaner.

I have since stress-tested the modified device and found that it is capable of pressures in excess of 70psi, which is far more than is needed for the desired operation. I almost lost my sight and hearing in the process when the can had a catastrophic failure and exploded at the seam of the Schrader valve and the JB Weld--Super Glue is suspected to have weakened the area from the runoff of a previously attempted repair.

I have also since purchased two more cans of silly string and an air horn (for its nozzle) from Dollar Tree, and these have undergone the same treatment as the first, providing me with a total of three working extinguishers of different sizes and capacities (the original can had a piece of dried silly string lodged in its valve and could not be repaired).