Hovercraft95

RoTech

I'm new too but check this out: http://www.eastcoastrobotics.us/ ...It may give you some ideas.

My stupid opinion is you should have at least three motors but what do I know ...I drive a Rock Crawler (lol).

Hovercraft95

"This site is currently unavailable."

I live in Norway btw.

Paul1981

You can buy ready-made ducted fan units off a lot of RC sites; something like this - http://www.sussex-model-centre.co.uk...d.asp?id=21491

You won't necessarily need the two additional motors if you want to make it really simple though; the hovercraft that I own has a ducted fan with a run-off nozzle built into the chassis that feeds some of the thrust air into the air cushion to inflate it.  Then there are just rudder blades behind the ducted fan to vector the thrust (Google "K&S Scamper hovercraft" if you want to see what I mean).  The only problem is that you need to run the motor constantly to keep the cushion inflated, not like the Tyco Typhoon hovercraft that I got in the late 80's which had a central fan solely for the air cushion.  I suppose there is no reason that you couldn't design something similar and run it off a 3rd channel to keep it independent of your thrust and rudders...

NealF

A great resource from a master model hovercraft builder is here: He's got plans, recommendations on motor sizes and propellers, calculators, etc.... And you'll drool over the photos of his models.

It is common to overestimate the amount of lift-power required for a hovercraft. A 1-kilo, 1/2m x 1/4m model (give or take) only needs a Speed-400 (150-200 watt) (aka a Mabuchi 540 size) motor with a 5-7 inch prop for lift. For thrust, a Speed-280 or -300 sized motor, say 80-100 watts with a 5-inch, 3-bladed prop works quite well. Hovercraft move slower than airplanes, so a multi-blade prop makes a lot of sense. Ducted fans look cool, but at lower speeds they are far less efficient than an open prop. The older Speed-type brushed ("can") motors are easily mounted with straps, whereas the commonly used, outrunner brushless motors for aircraft are firewall or end mounted. The inrunner brushless motors are usually higher kV (RPM) and not suitable for hovercraft.

Another HUGE advantage of an open propeller with a brushed motor for thrust - you can use a car speed control and reverse it. This is actually very useful for maneuvering. Brushless motors are in theory reversable, but good luck finding a speed controller that will do it. Ducted fans are even less efficient in reverse, if not completely useless.

So for thrust, I recommend you skip the ducted fan and instead use a brushed, can-type motor about Speed-280 or -300 size, spinning a 3-blade prop with a diameter of 4-6 inches. If the Speed-400 size is more readily available and perhaps less expensive you can use that too, it will just let you go a bit faster. And use a reversable speed controller. Doesn't have to be fancy, and you don't need a brake feature. If you want to then build a duct around the prop to make it look cool, you can carve an inlet from foam or balsa and use thin plywood to make a duct.

For lift you can go brushless, but pick a motor that wants to spin a 6x4 to 7x5 prop. You can increase the prop pitch (say 6x6, 7x7) or add blades to get more air volume (mass). If your skirt is good even this will be overkill. You can also use a smaller diameter prop at higher RPM, say a 5x5. Again, 3- or 4-blade is an option too, but you can experiment with the props. If your motor gets hot you need to decrease the pitch or diameter, or find a lower RPM motor.

Your duct design and skirt will affect the prop selection and overall efficiency. It is important that the lift fan/prop have a duct around it to prevent air from escaping, and you want to keep the air path "clean".

Another consideration is how do you want to inflate the skirt. Some designs pump air into the skirt and then spill that into the space under the craft. Others fill the cushion directly and bleed air into the skirt. Other split the air flow at the fan, some to the skirt some to the cushion. It is usually better to fill the skirt directly from the fan so you can maintain higher pressure in the skirt. That's what Mark does, that's what I did.

My suggestion is to build a first test model with foam sheet so you can test out some propellers and skirt construction. Foam is easy to work with and inexpensive. I carved my prototype hull from 2-inch thick building insulation foam, then used poster-board foam for the tail and rudders and plastic bag and tape for the skirt. Not pretty, but it was easy to swap out motors and propellers and try different ideas.

Hovercraft95

Can someone se through my list and chech if this will work? Thanks

http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

http://www.hobbyking.com/hobbyking/s...propeller.html

http://www.hobbyking.com/hobbyking/s...ner_Motor.html

http://www.hobbyking.com/hobbyking/s...g_0_14sec.html

http://www.hobbyking.com/hobbyking/s...ontroller.html

http://www.hobbyking.com/hobbyking/s...40v_Input.html

http://www.hobbyking.com/hobbyking/s...x_Mode_1_.html