hover on tut

8/13/2019 Hover on Tut

http://slidepdf.com/reader/full/hover-on-tut 1/17

A Tutorial

RC Hovercraft



Contents

Introduction

Forces

Manoeuvring

Requisite material Electronics

Transmission

Placement of components Drifting and Rotation

Frequently faced problems



Introduction

Hovercrafts operate by creatinga cushion of high-pressure air

between the hull of the vessel

and the surface below.

Typically this cushion is

contained within a flexible

"skirt”.

A propeller is used to drive thefloating hovercraft forward.



Major components



Forces on a hovercraft

LIFT: The lift motor provides the force which balances

the weight of the hovercraft.

THRUST: The drive motor provides the force which

drives the hovercraft forward.Lift and thrust can be integrated and produced through a

single motor.

These forces can be provided by

-Standard RC Brushless Motors

-Duct-fans



Manoeuvring

Using one propeller/ductfan to provide thrust and

(a) a rudder to givedirection.

(b) thrust vectoring togive direction.

both (a) and(b) willrequire a servo motor each.

Using two propellers/duct

fans to provide thrust andusing differential speeds ofthe two motors to providedirection.



Requisite material

Balsa wood/Coroplast/Styrofoam –

main structure, rudders, duct

Styrofoam – skirt boundaries, duct

Wood – motor mount, rudderstructure, strengthening

Adhesives – Standard epoxies,

Bond Tite, Bond Quick, Tape

A thin inflatable polythenematerial – Hovercraft skirt



Electronics: Battery

Lithium Polymer (LiPo) Batteries are by far the most longlasting batteries used for RC applications. Deliver twice

the capacity in nearly half the weight of conventional cells.

Cost and Weight: More the current and voltage rating and

capacity, more is the cost and weight.

Example:

Minimum Capacity: 1000mAh

Configuration: 3S1P / 11.1v / 3Cell Constant Discharge: 20C

Peak Discharge (10sec): 30C

Pack Weight: 87g



Electronics: Servo

Voltage : 3v ~ 6v

Weight: 9gSpeed : 0.12

sec/60(4.8V)

Torque : 1.6 kg-cm



Electronics: Brushless motors

• Out runners

• High RPM

•

Will require an ESC (Electronic Speed Controller)• Control is via PWM (Pulse Width Modulation), following

certain specifications

• Time Period = 20ms

•

On time = 1 ms –

2 ms



Electronics: Duct Fan

Control by PWM

Simple DC Motor

High Power Requirements

Requires Large Current rating IC to control it. Relays can also

be used.



Electronics: Motor drivers/speed

controllers

The current required to drive any motor is very high

Hence an appropriate motor driver is required

For example

L293D : max rating 1 amp L298 : max rating 2 amp

Relays for high current duct fan.

The current by them may not be sufficient

hence in such a case high Power Transistorscan also be used.

ESCs are generally used to drive brushless motors.



Transmission

For wireless transmission, RF communication can be used.

- Buying an RF module

- Hacking open an RF toy car.

The following links may prove useful:(a) http://extremeelectronics.co.in/rf/rf-communication-between-

microcontrollers-part-i/

(b) http://extremeelectronics.co.in/avr-tutorials/rf-

communication-between-microcontrollers-part-ii/ (c) http://extremeelectronics.co.in/avr-tutorials/rf-

communication-between-microcontrollers-%e2%80%93-part-iii/

http://extremeelectronics.co.in/rf/rf-communication-between-microcontrollers-part-i/


http://extremeelectronics.co.in/avr-tutorials/rf-communication-between-microcontrollers-part-ii/


http://extremeelectronics.co.in/avr-tutorials/rf-communication-between-microcontrollers-%e2%80%93-part-iii/















































Placement of components

Placement of the componentsdecides the CG of the vehicle

The CG should be perfectlyaligned with the Thrust line

Since the system is afloat it willexperience some rogue torquecaused by this misalignment ofcomponents

Too many actuators may alsoprovide torque and add to theinstability



Drifting and Rotation

The hovercraft system suffers fromthe inherent problem of drifting.

This requires a flawless mechanicaldesign.

A good electronic system may notbe able to counter all theseglitches.

Rotation can however be regulated

by an effective control system Rotation is caused due to the

principle of conservation ofangular momentum



Frequently faced problems

Please keep the following aspects in

mind :-

Hovercraft tends to drift outward

at curves.

Natural tendency of the hovercraft

is to drift and rotate.

Sufficient momentum might be

required to climb up a slope which

is an obstacle in the finale.

At the U-turn towards the end ofthe arena, the hovercraft may tend

to turn in one direction

preferentially because of the

angular momentum of the lift fan.

hover on tut

Documents