So, my cousin, my brother and I built a soda bottle boat a while back(made a post about it here), worked okay, had a good time. We're looking to move up now. We want to make a hovercraft. Here's the conditions we've applied to the project to make it a bit more interesting:

Must be self-contained and electric powered, which means rechargeable batteries.
Must be constructed entirely of recycled materials(excluding, perhaps, the batteries and the motor).
Must either be capable of supporting all three of us, or, we have to make three individual boards(not sure which will be harder, but we're aiming for one big one that can support all three of us).

And we would like it if we could take it out on water, but that's not that necessary.

Here's the hitch though; I'm not really sure what kind of motor to look for. Obviously, we're going to want a motor/propeller setup that's capable of putting out PSI at least equal to the weight of us and the craft itself, but hopefully comfortable exceeding that. Anyone have any ideas?

A quick search turned up these:

http://amasci.com/amateur/hovercft.html

http://www.twofoos.com/hacks/hovercraft.html

Must be constructed entirely of recycled materials(excluding, perhaps, the batteries and the motor).

and where supposed to draw you up some plans without even knowing what you can get your hands on?

http://www.xinventions.com/

No, no, I'm not looking for plans or anything, we've got plans out the ass. I was just looking for possible motor recommendations.

Motors? You'll need a very high power to weight ratio. Large brushless RC airplane motors are perfect for this really - some of them output 2hp and are no bigger than a tin of beans. Some people have used them on electric bike conversions and been able to break chains with the power...

However, they're also not cheap...think $600-1000 for a used motor and then $200 for a controller.

As for batteries, they're also going to cost a fair bit. Lead acid batteries (as used in cars) have a very low energy to weight ratio so you'll need to use a big NiCd bank. They're well suited to this sort of use as they're happy to output high current and be deep cycled.

A bank of el-cheapo no name A cell size NiCds suitable for running a high power brushless motor for a reasonable amount of time should run you about $400 minimum.

I think a battery powered hovercraft able to hold three people is a bit ambitious. You'll need to put a good $1500 minimum into motors and batteries alone.

As for the impeller itself, I'm a bit unsure of what's best. A centrifugal blower will give the most pressure, but an axial fan gives greater velocity. What's more important for a lift fan?


However, it's a lot cheaper and easier to use a fuel powered leaf blower or an engine for the lift fan power source.

Try using PVC pipe to distribute the air from 3 or 4 leaf blowers.

Not completely recycled but powerful and modular enough to allow for the addition/subtraction of blowers.

Im not sure how well this will work but I think if one can support one man then 4 can support 3 men and a thruster. Add a fifth to account for an extra battery pack or gas tank for extended range.

Battery-powered lawnmower with modded propeller/blade?

Gas-powered mower would be even more powerful.

For batteries, get marine batteries or traction batteries. They look just like a car battery but can put out sustained amperage. They are used in golf carts and have a slightly better power/weight ratio then standard car batteries

For propulsion, get one of those industrial fans used to cool warehouses:
http://www.actionpartyrentalsinc.com/Rental%20Items/images/Tents/INDUSTRIAL-FAN-36%27%27.jpg

ditch the idea of using batteries to power this thing. An electric motor powerful enough to lift a hovercraft and 3 people will be 1) heavy 2) expensive and 3) require a large supply of batteries to run for any period of time.

A much better idea is what keepontruckin suggested and use a gas powered lawnmower engine with a modified blade for a lift fan (and put a cage around the blade so you don't kill yourself with it). People throw out lawnmowers all the time, so just pick one up for free, and get it running. For thrust, a small two-stroke engine may be ideal, hooked to the blade from a large fan. An engine from a lawn edger could work well, and because they have centrifugal clutches will start easily for you.

Look up the hovercraft episode of "Juknyard Wars", for some inspiration. I drew up some basic plans for one a few years back, but lost them.

Other pointers:
-Plastic tarp for skirt material (cheap, available, waterproof, and durable)
-plywood deck with wood only in places of structural need (make it like a skeleton)
-use styrofoam insulation board to fill in where plywood does not cover
-put shrouds over all fans so you don't get sucked in.

I built a hovercraft a while ago and posted some pictures in another thread a while ago. I'll place links to the pictures when I find them.

It uses a leafblower and has a tarpaulin skirt. It can support a decent amount of weight on a smooth surface, but it will barely travel over grass. The only surfaces that it can support me on are concrete and asphalt.

For a battery I suggest you look at this business: http://www.thunder-sky.com/home_en.asp
They don't look hi tech, but they produce LiFePO4 cathode lithium ion batteries. The best part is they are dirt cheap (about as much as lead acid). I don't understand why electric vehicles aren't common when these batteries are high capacity, relatively high current and cheap.

If you want to travel over water it is wise to add in flotation devices. These don't have to be intrusive - it is easy to place foam within the skirt. If the lift engine fails and the skirt has foam in it, the skirt will have a large enough volume to be buoyant enough to support the rest of the hovercraft.

Use a 1-2hp lawmower motor....

What and where is your intended use of this hovercraft OP? I beleive that with a proper layout of motors and batteries and human weight, the craft + 3 passengers could get off the ground with no problem, maybe even more smoothly than one powered by gas engines... it would just be restricted by short range. Electric motors can run at a wide range of very precise speeds, and put out unholy amounts of torque at any of them. This is acheived by powering the motors with PWM instead of cheap DC dimmer resistor switches. PWMs are more of a pain and cost than just going to the hardware store and getting like 12V 30A dimmers, but they are superior in performance and efficiency.

Dimmers take the full voltage from the power source and simply apply however much resistance is set by the user, thus giving a reduced voltage to the device (your motor). The resisted power dissipates from the dimmer as heat, and depending how much you're resisting in an application like this, you could and probably will lose a ton of electrical power. Your motor also has exponentially less torque the farther you get from its intended operating voltage. This would make adjusting the amount of lift for different conditions (# of passengers, terrain your hovering over, etc) very difficult and unsteady.
PWMs take in the full voltage (Assuming 12V from car batterys in your case) and then deliver the same full voltage to the device in very quick pulses. The pulses have a width which is modulated (Pulse Width Modulator) by a potentiometer in the circuit. The voltage switches on and off (12-0-12-0-12-0-12) so fast that the motor interprets it as a constant flow of electricity instead of what it really is. The higher you crank the potentiometer, the wider and closer together the pulses get, until full power when a truly constant voltage equal to the power supply's is being delivered. Using one of these will let you run your DC motor at very low speeds without any noticeable loss of torque. I built a magnetic stirrer and the motor in it runs off one... I can run the thing at 15% of its top speed before seeing ANY drop in torque (Down to 12% or so it still shears the wayyy over-kill magnetic attraction between the driving magnet and the stirbar before it stalls the motor). A PWM big enough to run motors like this would have some pretty big heatsinks, but they are just to get rid of small amounts of intense heat from certain components.

Doing the PWM would allow you to buy a lesser motor and get the same results. This would be nice because a 5 pound motor from some big model airplane that puts out x power is going to cost you a lot more than a 15 pound motor from some power tool or automotive application that puts out x power. The money you save will come in handy for other components, and a less intense motor is going to be more reliable and easier to keep cool. The better performance from running it on PWM will more than make up for the added weight. You could probably even find such a 15 pound motor putting out 1.5x power for far less than the 5 pound x power one. (none of those weight and power statements were specific... just speaking figuratively)

One thing you might consider is using a single larger motor instead of several smaller ones. You could have it run a system of belts and pulleys to each of your lift fans. Large fans could be found at a junk yard, and a lot of them use pulley systems allready, and they are on bearings mounting them to their frame, so that gives you an easy leg up. If the belt drive pulleys aren't the right size to gear it for the RPM you need, you could probably find compatible replacements at Autozone.
The only problem I can foresee in doing this is that you can't easily adjust the lift on just one side/corner of the craft. You would need to plan weight distribution of people/batteries carefully so that doing so is never needed.



If you want to be able to go for joy rides on this thing, look into gas engines instead. An electric craft would definately be fun and interesting and probably very plesant to zoom around on, but it would be a bear to deal with. It will probably be twice as heavy as a gas powered competitor, so transporting it by truck or something would be tough, and you gotta be diligent about charging your batteries when they are low, or your max capacity (and ride time) will start to drop fast. Thennnn you gotta go and get more new batteries so theres another ~$400.

Look around on ebay for motors. Try search terms like

12V dc motor
dc motor
12v motor
dc automotive motor


stuff like that. there should be some possible matches for your needs.
sorry this post is way to fucking long. hope it was somewhat helpful though.

-Jon

Household dimmers use PWM. Most motor controllers use PWM.

With AC sources the switching is done at the AC frequency (ie 50 or 60Hz) and distorts the sine wave. The hovercraft will be battery powered so this is a DC source. Now there are two broad categories of motors: brushed and brushless.
Brushed motors are generally less efficient, shorter life and cheaper. They use mechanical contacts for commutators. Brushless DC use electronic commutators, so there are no rubbing parts. Essentially they are an AC motor with electronics to make them run off DC.

DC motor controllers switch at a higher frequency ( typically 1 - 20kHz). Brushless DC motors are more complex than brushed since they have to convert to AC.

Over the past few years prices for brushless DC have dropped. There aren't many second hand motors the size that you are looking for that are brushless DC.

Your idea of an Electric hovercraft is not only feasable, but is under developement by an American Engineering firm. Currently, they have 2 designs under construction. The first will be made public in about 7 months. The 2nd is even better. Both cases, the craft is very light and easy to construct. they have an email address-- Caldwell_Engineering@yahoo.com[/email] they are a R&D firm but they are very friendly and will answer any questions you have.