Firefighting Hovercraft

I have always been fascinated by hovercraft. These ground effect vehicles are incredibly versatile and can often navigate terrain other vehicles cannot. This project will focus on the design of a small firefighting hovercraft (~350mm long). Everyone loves driving RC vehicles and getting wet while having fun. This water-going hovercraft is a perfect Summer Fun project for aspiring makers.

Fusion 360: This was used for all of the part and assembly design

GrabCad: Various commercial parts (pump, motors, etc) can be sourced from grabcad users

FDM 3D Printer: If we were to construct this hovercraft, most parts can be made on a traditional 3D printer

Whenever we design something, we should start by asking a few questions. What will it do? How will we make it? In the case of this hovercraft we want it to be able to move, steer, hover, and create a fire extinguishing water stream.

-Move: We will use two powerful brushless motors with standard 5045 propellers. These parts are commonly used on quadcopters.

-Steer: We can achieve yaw (left and right steering) will differential thrust on our drive motors. This means that if we want to turn, we will turn one motor higher, and the other weaker which will help us to turn.

-Hover: Two brushless blower fans are used to generate the force to hover. The key parameter here is the static pressure they can provide. We can use this pressure to make sure the fans are powerful enough to lift our craft. We will also need a skirt to keep air in and allow for us to travel over bumps.

-Firefighting! we will use a small fountain pump to suck water up from beneath the vehicle, it will then be sprayed out through a nozzle. The water stream can be aimed using a micro geared motor to rotate the platform the pump and nozzle are on.

The image for this step contains all of the parts of the hovercraft. From left to right they are: propellers, drive motors, drive motor mount, blower (lift) fans), watertight electronics box, aiming motor, pump and nozzle. The black fabric around the perimeter is the skirt.

When creating your own design, you often must design around commonly available parts. I start my design with the base of the hovercraft. In this image you can see how I use the part dimensions to lay out the hovercraft. At the front we have space for the rotating pump and nozzle, behind it we allocate space for the electronics box. Beneath that are the lift fans - with rectangular holes cut out to insert them. Finally we leave space at the very back for our propellers and motors.

Here we see a cross-section of the craft. On the right you can see the profile of the base, ball bearing, and rotating platform. The bearing will help for smooth and easy rotation of the platform. We leave the center open to allow for the pump to pump water up through a tube. Because we do not want water to ruin out bearing, the rotating platform has a sleeve that goes below the bearing - preventing water from entering.

The "black box" (in this case red) is the electronics box. How will we go about controlling this hovercraft? We will use an RC receiver and controller, paired with various motor controllers. Starting with the drive motors, two single direction Brushless DC ESC (electronic speed controller) will control these. Remember, that we need to be able to vary their speeds to turn and change speed. Next - the lift fans. In this case we do not need to vary speed. We always want these to be fully on. We can wire these to power (12V) with a switch connected to the Rx enable. The aiming motor and pump are both Brushed DC motors, we can used a Brushed ESC for each. In the case of the aiming motor the ESC has to be bi-directional.

Hopefully this tutorial has been a good introduction to hovercraft design. We reviewed design parameters, parts of a hovercraft, and control electronics. I know that I had lots of fun designing this, and I'm sure that it will be great to use when I make the physical copy. I hope everyone had a great Summer