How It Works: Creationism
Mechanically, hovercrafts are simple creatures. An air intake above the top plate takes in air. This air is expelled below the plate through a clever series of holes and hoses. A skirt skirting the edge of the plate holds the air under the plate until there is sufficient air pressure to lift the plate enough that the skirt no longer touches the ground and the air is able to escape. At equilibruim, this system looks like this:
Of course, this setup can only hover, not move.
More thought was necessary.
It was realized that attaching a powerful floor fan to the base would push the whole assembly forward, and that adjusting the direction the fan blew in would turn it.
A system was thus devised by which a signal sent to a Lego motor would turn a series of gears and worm gears to which blades were mounted. These blades sat in front of the floor fan's output side. Redirecting the airflow also redirected the hovercraft's motion.
Another Lego motor was attached to the switch of the fan, and a third was detailed to turn the ShopVac on and off. All three are connected to potentiometers, whose function is described in the circuit section.
Manufacturing the Hovercraft
Both the ShopVac and the fan came whole and were modified
to suit the requirements of the hovercraft. The ShopVac's canister, filter, and ventilation plate were all removed, a plastic tube was taped to its output, and it was screwed upside down to the plate. The Vornado fan's switch mechanism was opened and the wires were extended for easier access, and the pipe holding it to the stand was removed. It was set on two contoured plywood slats to hold it perpendicular to the plate, and the gears for the fan were taped to the fan on the bottom and suspended from the top with twine. A Lego man was attached to one of the gears for balance. A housing was built for each of the remaining motors and a device to turn the switch it was connected to.
The 23.5" diameter base was water-jet cut from a 24x28x1/8" sheet of aluminum. Holes were drilled in it for the ShopVac's ventilation plate, for the zip ties holding the motor housings and plywood fan supports, and for the hose attached to the ShopVac's output. The plastic tarp skirt was pleated and attached around the bottom of the plate. It was then duct taped along the top rim for security. A string was strung through the bottom, allowing us to gather the skirt.
The hovercraft was now securely fastened together and fully capable of upward and forward motion (however slow). This seemed acceptable to us, so we stopped.
How It Works: Evolution
Hovercrafts are simple creatures. Left to their own devices, they would spend their days grazing on the kelp berries in the North Pacific Ocean. They rarely reach diameters of more than 5 inches in the wild. Their natural predators include the sea otter, the pelican, and the human. The first two often mistake them for mobile floating oysters, while the latter harvests them for their chewy underbelly. In the common form, an air intake above the top plate takes in air. This air is expelled below the plate through a clever series of holes and hoses. A pseudopodic skirt skirting the edge of the plate holds the air under the plate until there is sufficient air pressure to lift the plate enough that the skirt no longer touches the ground and the air is able to escape. The hovercraft is one of the most recently domesticated animals - the first ranches were founded by English entrepeneurs in the 1850's. They hoped to breed them for diameter and lift, but were unable to find more than a niche market for their new transports.
Millenia of evolution provided an optimal escape method: a powerful fan located at the rear of the to the base push the whole assembly forward, and adjusting the direction the fan blew in would turn it. A system was thus devised by which a signal sent from a variable resistance nerve attached to one of the blades of the fan relayed signals indicating the degree the fan blades had turned to the central nervous system, keeping the fan blades from overextending themselves.
Hovercrafts form their plate through aluminum secretions in the air intake/output. This is the first to form, with a rudimentary hose extending fromthe output. Pores on the hose and pseudopod secrete the aluminum, which is gradually spread wider and wider. The pseudopod stretches to fit across the growing plate, puckering slightly at the bottom. The propelling fan usually begins to develop after 3-6 months. It begins as a mere propellor, gradually maturing until it is up to 8" across and has a complicated vortex-inducing grate of some kind.
The hovercraft, with its unique propulsion, is truly a marvelous example of the miracle of evolution. It is able to easily traverse both land and sea, and has elaborate methods to escape predation.
Of course, this setup can only hover, not move.
A system was thus devised by which a signal sent to a Lego motor would turn a series of gears and worm gears to which blades were mounted. These blades sat in front of the floor fan's output side. Redirecting the airflow also redirected the hovercraft's motion. Another Lego motor was attached to the switch of the fan, and a third was detailed to turn the ShopVac on and off. All three are connected to potentiometers, whose function is described in the circuit section.
Both the ShopVac and the fan came whole and were modified
to suit the requirements of the hovercraft. The ShopVac's canister, filter, and ventilation plate were all removed, a plastic tube was taped to its output, and it was screwed upside down to the plate. The Vornado fan's switch mechanism was opened and the wires were extended for easier access, and the pipe holding it to the stand was removed. It was set on two contoured plywood slats to hold it perpendicular to the plate, and the gears for the fan were taped to the fan on the bottom and suspended from the top with twine. A Lego man was attached to one of the gears for balance. A housing was built for each of the remaining motors and a device to turn the switch it was connected to. The 23.5" diameter base was water-jet cut from a 24x28x1/8" sheet of aluminum. Holes were drilled in it for the ShopVac's ventilation plate, for the zip ties holding the motor housings and plywood fan supports, and for the hose attached to the ShopVac's output. The plastic tarp skirt was pleated and attached around the bottom of the plate. It was then duct taped along the top rim for security. A string was strung through the bottom, allowing us to gather the skirt.