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Episode 27: Exploding Port-a-Potty, Pole-vaulting car

  • Pole-vaulting car: a car can pole-vault off its driveshaft: mythbusted
  • Exploding Port-a-Potty: a cigarette can ignite natural methane in a port-a-potty mythbusted

Pole-vaulting car

Myth: Car going at speed could have its driveshaft fall off and cause the car to pole-vault.

This myth provided another opportunity to build a remote-control car (Dodge Intrepid/airplane engines, Police car/chained axle, [Impala/JATO][]), this time using a 1967 Plymouth Fury. According to them, this is their most "advanced" one yet, and they did cover more of the actual controls that went into the car. They added a shifter, and the steering control was more precise than the wheelchair-based servos of previous builds. This was all so they could steer more precisely so to hit the pothole, as well as control the shifter to use it to break the driveshaft.

The plan for breaking the driveshaft was to drive at high speed, shift into neutral, rev the engine, and then drop back into gear in order to break a weakened U-joint on the driveshaft and drop it into a pothole.

They setup the test on an abandoned runway at Alameda. They spent most of the day messing around with the car. Jamie, with Adam in the back seat, remote-steered the car through a fence (finally stopped when the auto-kill switch triggered the brakes). Jamie later nearly drove the Fury into the Bay. He had forgot to turn on all the controls before the car got going.

They decided that the remote controls were too complicated for one person, so they decided to have Adam do the shifter, while Jamie concentrates on the main controls. The setup was to have the Fury drive down the runway towards the pothole at about 25mph, with Adam and Jamie in a pursuit vehicle driven by Scottie.

The first day didn't go so well: * Run 1: drive shaft failed to drop. Jammed car into reverse at-speed (accidentally), but still didn't break * Run 2: weakened further, jammed into reverse, and still didn't break. * Run 3: weakened the U-joint too much, driveshaft dropped when car started * Sun is setting... * Many runs later... * Failed to drop the driveshaft once by end of day

Adam and Jamie came up with new rig to drop the driveshaft, instead of relying on a cut-up U-joint. They added a threaded coupler to the driveshaft that loosens when driveshaft is run in reverse (essentially a screw and bolt added to the driveshaft).

In the next day of testing, things went slightly better as they managed to drop the driveshaft, but it missed the hole. They then proceeded to miss the pothole again, and again, and again (the driveshaft usually skipped over the hole).

They decided to slow car down to 15mph. This plan was successful -- the driveshaft hit the hole square-on and popped the car up about 1-2 feet, driving the driveshaft up through the trunk. It wasn't particularly dramatic, and not nearly enough to qualify as "pole vaulting." The fact that the driveshaft went so far into the trunk demonstrated that the it would be very difficult to pop the car up any higher.

Mythbusted (implausible that the scenario would actually occur, and unlikely the car strong enough to actually vault on the driveshaft)

Exploding port-a-potty

Similar to last season's exploding house toilet (bug spray/gasoline/lighter fluid in toilet), in that yet again they would try to set a toilet on fire.

This time, though, the myth is that someone lit up a cigarette in a port-a-potty, igniting methane gas that had been building up. Although this did actually happened in West Virginia, the MythBusters were skeptical that this occurred because of methane-gas buildup.

Adam brought the build team some samples to test for methane: "I've got poo in a box and I'm not afraid to use it"

Tested the methane output of poo. Apparently 40% of the population, including Adam, can produce methane off of poo, though their experiment with three test flasks (urine + poo, water + poo, blue toilet cleaner + poo) produced only small traces of methane.

For the actual mythbusting experiment, they pumped methane gas into port-a-potty rigged with Tory's "improved" version of Adam's ignitor from the previous toilet exploding myth. A pre-charrerd Buster was positioned on top.

They also had a meter in the center of the port-a-potty so they could bring the methane concentration to 10-15% -- too much or too little and it won't explode.

In the first run, the port-a-potty vented too well, with the methane concentration dropping immediately after they removed the hose. They weren't able to ignite anything, so they sealed up all the vents on the port-a-potty.

In a subsequent run they set Buster on fire, but not in the way they intended. The ignitor set toilet paper on fire, which then set Buster's crotch on fire (no methane explosion). They decided to vent the toilet, which fueled the flames on Buster, and in the process destroyed Tory's "improved" ignition system.

With no methane explosions, yet, they moved meter to bottom of port-a-potty so that methane concentration would be even higher. This time they failed to even ignite the toilet paper on the ignitor.

Scottie: "Maybe it's a myth that methane is flammable"

Adam: "It's not a myth, we're just idiots"

They came up with a better idea, which was to put a lit flare into toilet, then add gas until methane explodes. The toilet exploded, blowing open the door with bright red flames -- the meter was at 0.9%. Idea to move meter to bottom backfired, as the methane concentration was probably too high in previous tests.

They exploded the port-a-potty one more time using a candle as the pre-lit ignition source, and then called it a day.

Mythbusted. They had to go to great lengths, using pumped methane and sealing all the vents, in order to get an explosion. The actual story from West Virginia was a guy who worked at a methane plant. He was using port-a-potty, but it apparently was sitting ear a leaking methane pipe.


i heard this happens with four wheel drives or something with higher clearance

FWIW, the drive shaft dropped out of the tranny on my 1968 mustang many years ago, while I was doing maybe 40 mph around a curve.

It made a scary racket, I'd thought the engine mounts had finally rusted through and dropped the motor out, but nothing even vaguely resembling a pole vault.

Incidentally, a small tool box serves as a great tire chock, and will hold a mustang still on a hill.