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Radio Controlled Hovercraft

Ryan Trinh, Kelsey Krushel, and Sam Waterman, Dept of Mechanical Engineering, University of Ottawa

 

Objective

The objective of this project is to design and build a radio-controlled hovercraft. Hovercrafts have the advantage of being deployable over several types of terrain, ranging from flat ground, to ice, to calm water. Further, a hovercraft has the potential for very high top speed because it is limited almost exclusively by air friction when travelling across terrain.

Figure  SEQ Figure \* ARABIC 1: Hovercraft flight concept

 

Basic Operation of the Hovercraft

The two basic requirements for a hovercraft are the lift and thrust. The lift is created by fans that draw air in from above and inflate a flexible skirt below. The air then is forced out from underneath the skirt leaving a thin layer of air between a line of contact on the skirt and the ground. This results in very low friction between the ground and the hovercraft.

Because of the low friction, only a small amount of thrust is required to move the hovercraft. This is typically done with one thrust motor that has its propeller in a duct which rotates, or has a rudder system to direct the air.

Materials and Components Used

Since the goal of the project was to have a radio controlled hovercraft, we took apart an RC car and used its RC circuit. The remote has four sensors: Up and down, which control the direction the thrust motor turns, and left and right which control the direction the rudders turn.  REF _Ref282273142 \h Figure 5 shows the gear reduction of rudder motor and how the circular motion is turned into linear motion. It is not shown well but the pinion attached to the shaft of the rudder motor has a slip fit which allows the motor to continue to rotate even once the traverse of the arm is expended.

The lift motor used is an 18V PM DC motor. The propellers used are 6 in diameter with a pitch of 2. One major issue of a hovercraft is weight; therefore we used the lightest materials to make the craft. The hull is made from polystyrene insulation foam while the rest is mostly Styrofoam, plastic or wood. At first, rain jacket material was used in Prototypes 1 and 2, but then garbage bags were used in prototypes 3 and 4. Garbage bags were used as they are much easier to work with when designing a skirt.

       

Figure  SEQ Figure \* ARABIC 2: Original materials and components used

 

Figure  SEQ Figure \* ARABIC 3: RF circuit

 

 

Figure  SEQ Figure \* ARABIC 5: Gear reduction of rudder motor

 Table  SEQ Table \* ARABIC 1: Parts List for final design.

ITEM NO.

PART NAME

DESCRIPTION

QTY.

1

Lift Motor

18V PM DC

1

2

Hull

Extruded Polystyrene Insulation sheet

1

3

Skirt

Black garbage bag

1

4

Batteries

9V Battery

3

5

Trust Duct

Ice cream tub (polyethylene)

1

6

Propeller

6 x 2 (width x pitch)

2

7

Receiver Circuit

PCB Circuit

1

8

Rudder Gearbox

N/A

1

9

Thrust motor

N/A

1

10

Switch

N/A

1

11

Rudder pivots

Tooth picks

4

12

Rudder

White Styrofoam

2

13

9V battery clip

N/A

3

14

Wires

50cm approx

N/A

15

Controller

4 sensors (up, down, left ,right)

1

Prototyping & Problems Faced

Prototype 1

This prototype used two lift motors with two 45-degree pitch fans. This one also featured a contact surface with the ground that was cut from a rectangle of foam. This design proved too heavy to hover on its own power, especially when using batteries, as the batteries could not provide enough current.

Figure  SEQ Figure \* ARABIC 6: Prototype 1

 

Prototype 2

The second prototype used a single lift motor. At first the 45 pitch propellers were used then they were switched out with propellers with a much smaller pitch (2). Since the pitch on these propellers is much smaller than the previous ones, the new propellers cut the air much easier which puts less torque on the motor allowing it to spin faster, creating more lift.  Like prototype 1, this design featured the foam contact surface with the ground. This design marks the first successful test run using batteries for lift. However, this prototype did not travel very well, which we determined was due to the foam contact surface.

Figure  SEQ Figure \* ARABIC 7: Prototype 2

 

Figure  SEQ Figure \* ARABIC 8: Prototype 2 (underneath with original propeller)

 

Prototype 3

The main change to prototype 3 is the skirt. In Prototype 1 and 2 a flat foam contact surface is used between the air and the ground. This causes a large amount of friction. A good way to improve this is to make a skirt out of plastic. This causes the contact surface between the air and the ground to be a single line contact along the perimeter of the bottom of the inflated bag.

Figure  SEQ Figure \* ARABIC 9: Building of an inflatable skirt

Figure  SEQ Figure \* ARABIC 10: Prototype 2 vs. Prototype 3

Prototype 4 (Final Design)

For the final design, a more robust bag was chosen for the skirt. A duct was added for the thrust fan, as well as two rudders placed nearer to the thrust fan blade tips. It was found that the airspeed nearer to the blade tips is greatest for most fans, and so we took advantage of this fact to improve the manoeuvrability of the craft. 

Figure  SEQ Figure \* ARABIC 11: Prototype 4 (Final Design)

What we Learned

During the design process, we learned about the basic operating principles of production hovercrafts, such as the need for a flexible bag as the contact surface, the reason for using two rudders rather than a single rudder, the need for a duct for the thrust fan, as well as the requirement for very lightweight materials. Further, we learned, through analysis of the PCB used, how commercial radio control units use simple transistor amplifiers to amplify radio signals, and their use of zener diodes for voltage spike protection. We also discovered the limits of batteries in terms of runtime, as they are incapable of supplying large currents for long periods without losing power.

Conclusion

Our final design functions as desired. Given the weight of the three batteries, and the two motors, the hovercraft travels at a high speed, manoeuvres well, and has a run time exceeding several minutes. This was made possible by the use of a commercial PCB, rather than breadboards, to save on weight, as well as our choice of lightweight materials for all other components. Future improvements that could be made to the hovercraft could include the use of rechargeable batteries with a higher power density, the use of lightweight motors, the use of an Arduino Mini and servomotor instead of the PCB and steering mechanism, and a rigid plastic shell rather than insulation foam for the hull. In the end, our project met all the performance criteria we set out at the beginning, and a lot was learned about commercial PCBs and electronics.