RADIO CONTROLLED HOVERCRAFT

BUILDING A RADIO CONTROLLED HOVERCRAFT


Here is the way to design a remote controlled hovercraft or ACV(air cushion vehicle) that will be tested for speed, maneuverability and handling on various terrains likes Sand, mud, water, gravel, concrete.




MAIN PARTS OF HOVERCRAFT


HULL
It is the main body of the craft which acts as a base for attaching other parts of the hovercraft.

HULL

LIFT SYSTEM
The lift system consist of a fan or a propeller attached to a motor or a engine which provides air for filling the cavity underneath the craft and also for filling the skirts.

LIFT AND THRUST SYSTEM

THRUST SYSTEM
It is same as the lift system but it propels the craft forward by virtue of the reaction force supplied by the air.
The propeller used for generating the thrust is provided with the duct to increase the velocity and thereby increasing the thrust.


SKIRT
It is the flexible wall that is attached all around the bottom of the craft. The skirt prevents the pressurised air from escaping from the plenum chamber.

SKIRT

SKIRT

CONTROL SYSTEM
This system are fitted with rudders which is used to change the direction of thrust to steer the vehicle left or right.

RUDDERS

DESIGN CONSIDERATIONS

WEIGHT
Light weight materials must be used for construction ,but at the same timethe model must have good strength.

PRESSURE IN PLENUM CHAMBER
Lift force= pressure x area of the craft
Sufficient pressure must be generated so thatlift force > weight of the craft

MOMENTS
As rotating parts are involved .the unbalanced moments particularly dueto the lift fan must be balanced to avoid spinning of the craft

POWER SYSTEM
or an generay moor-propeer sysem avng sac rus >0.4x(weight of the hovercraft) will generate hover , provided skirts areproperly attached.

SKIRT DESIGN
a bag skirt is generally preferred as it is easy to build andgives good performance

DUCT DESIGN
The duct although do not have much effect on thrust due topropellers ,they must be used for safety from propeller blades.
In design a duct should have a decreasing area towards exit, suchthat velocity of air ,leaving the duct increases and hence thrust increases



ELECTRONICS AND CONTROLLERS


BRUSHLESS MOTORS
They are a bit similar to normal DC motors in the way that coils and magnets are used to drive the shaft. Though the brushless motors do not have a brush on the shaft which takes care of switching the power direction in the coils, and this is why they are called brushless. Instead the brushless motors have three coils on the inner (center) of the motor, which is fixed to the mounting.
On the outer side it contains a number of magnets mounted to a cylinder that is attached to the rotating shaft. So the coils are fixed which means wires can go directly to them and therefor there is no need for a brush.

BLDC MOTOR

Generally brushless motors spin in much higher speed and use less power at the same speed than DC motors. Also brushless motors don’t lose power in the brush-transition like the DC motors do, so it’s more energy efficient.

Brushless motors come in many different varieties, where the size and the current consumption differ. When selecting your brushless motor you should take care of the weight, the size, which kind of propeller you are going to use, so everything matches up with the current consumption. When looking for the brushless motors you should notice the specifications, especially the “Kv-rating“.

The Kv-rating indicates how many RPMs (Revolutions per minute) the motor will do if provided with x-number of volts. The RPMs can be calculated in this way: RPM=Kv*U An easy way to calculate rating of motor you need, check out the online calculator eCalc. It’s an amazing tool that helps you decide what components to purchase depending on the payload that you want to carry.




ELECTRONIC SPEED CONTROLLERS

The brushless motors are multi-phased, normally 3 phases, so direct supply of DC power will not turn the motors on. Thats where the Electronic Speed Controllers (ESC) comes into play. The ESC generating three high frequency signals with different but controllable phases continually to keep the motor turning. The ESC is also able to source a lot of current as the motors can draw a lot of power.

ESC

The ESC is an inexpensive motor controller board that has a battery input and a three phase output for the motor. Each ESC is controlled independently by a PPM signal (similar to PWM). The frequency of the signals also vary a lot, but for a Quadcopter it is recommended the controller should support high enough frequency signal, so the motor speeds can be adjusted quick enough for optimal stability (i.e. at least 200 Hz or even better 300 Hz PPM signal). ESC can also be controlled through I2C but these controllers are much more expensive.

When selecting a suitable ESC, the most important factor is the source current. You should always choose an ESC with at least 10 A or more in sourcing current as what your motor will require. Second most important factor is the programming facilities, which means in some ESC you are allowed to use different signals frequency range other than only between 1 ms to 2 ms range, but you could change it to whatever you need. This is especially useful for custom controller board.




BATTERIES

As for the power source of the quadcopter, I would recommend LiPo Battery because firstly it is light, and secondly its current ratings meet our requirement. NiMH is also possible. They are cheaper, but it’s also a lot heavier than LiPo Battery.

LiPo battery can be found in a single cell (3.7V) to in a pack of over 10 cells connected in series (37V). A popular choice of battery for a QuadCopter is the 3SP1 batteries which means three cells connected in series as one parallel, which should give us 11.1V.

LI-PO BATTERY

Another important factor is the discharge rate which is specified by the C-value. The C-value together with the battery capacity indicates how much current can be drawn from the battery.

Maximum current that can be sourced can be calculated as:MaxCurrent = DischargeRate x Capacity


For example if there is a battery that has a discharge rate of 30C and a capacity of 2000 mAh. With this battery you will be able to source a maximum of 30Cx2000mAh = 60A. So in this case you should make sure that the total amount of current drawn by your motors won’t exceed 60A.




RECEIVER TRANSMITTER SYSTEM

HOVERCRAFT can be controlled by RC transmitter in either Rate (acrobatic) or Stable mode. A three channel radio system is suitable for running a hovercraft system.

rc system

SERVOS

.A servo is a kind of electronic actuator that rotates
by only a fixed angle ,like 45 degrees, from the neutral position. It can hold it’s position at an angle and is used in rudder mechanism for the model
A 9gram servo is ideal for rudder mechanism

SERVO MOTOR

BRUSHLESS MOTOR SETUP:

• choosing the right motor
• Lift motor-a high kvmotor is generally used with a 6”-7”propeller.
• Thrust motor-a low kvmotor is generally used with a 9”-11”inch propeller.Suggested motor setupsSuggested motor setupsSuggested motor setupsSuggested motor setups:Lift motor.

EMAX BL2210/25+ 20amp esc+ 8”x4” propeller

Turnigy2730 1500kv + 10 amp esc + 7”x3.5” propellerThrust motor

Turnigy2830 100kv + 20 amp esc +10”x 4.7” propeller

Hobbyking800kv +12 amp esc +10”x6” propeller

Turnigy2217 860kv+20 amp esc +11”x4.7” propellerBatteries

• 11.1v batteries with rating from 1800mAh to 2700mAh and adischarge rate of 25-30C I recommended.

• A 3mm prop saver or prop adapter should be used forattaching the propeller to the motor shaft Prop adapter.

TROUBLE SHOOTING

CENTRE OF PRESSURE AND CENTRE OF GRAVITY

• The centre of pressure is basically the geometric centre of the plenum chamber .But the lift is in general contributed both by thrust due to motor and the pressure force,such that the point where total lift force acts gets shifted towards the lift motor.
• The centre of pressure and the point of action of lift force must coincide for leveled hovering.

INSUFFICIENT TURNING:

• Increase the rudder area or the servo throw.throw.throw.throw.

NO HOVER:

• Check if the skirts are fully inflated
• The skirt should allow a minimum amount of air leak from the plenum chamber. check for any rapid air leaks
• Insufficient power of the lift motor

UNCONTROLLED SPIN:

• Provide a slight rudder trim rudder  in direction opposite to spin

RC HOVERCRAFT

CONCLUSION

Thus an rc hovercraft is build consistently with all available resorces which can be controlled wirelessly :)

.Enjoy building !!