Internship Report

A graphical user interface (in LabVIEW) for

controlling a Vertical Take Off and Landing system

(VTOL)

A project by

Rishabh Prakash

Department of Electronics and Communication Engineering

Haldia Institute of Technology

At Indian Institute of Engineering Science and Technology

Shibpur

________________________________________________

Dr. Subhasis Bhaumik

Professor and Head,

Aerospace Engineering & Applied Mechanics

Coordinator

School of Mechatronics and Robotics

IIEST Shibpur

Index:

Introduction:

Labview

LabVIEW is a highly productive development environment for creating custom applications that interact with real-

world data or signals in fields such as science and engineering.

The programming language used in LabVIEW, also referred to as G, is a dataflow programming

language. Execution is determined by the structure of a graphical block diagram (the LabVIEW-

source code) on which the programmer connects different function-nodes by drawing wires. These

wires propagate variables and any node can execute as soon as all its input data become available.

Since this might be the case for multiple nodes simultaneously, G is inherently capable of parallel

execution. Multi-processing and multi-threading hardware is automatically exploited by the built-in

scheduler, which multiplexes multiple OS threads over the nodes ready for execution.

LabVIEW ties the creation of user interfaces (called front panels) into the development cycle.

LabVIEW programs/subroutines are called virtual instruments (VIs). Each VI has three components: a

block diagram, a front panel and a connector panel. The last is used to represent the VI in the block

diagrams of other, calling VIs. The front panel is built using controls and indicators. Controls are

inputs – they allow a user to supply information to the VI. Indicators are outputs – they indicate, or

display, the results based on the inputs given to the VI. The back panel, which is a block diagram,

contains the graphical source code. All of the objects placed on the front panel will appear on the

back panel as terminals. The back panel also contains structures and functions which perform

operations on controls and supply data to indicators. The structures and functions are found on the

Functions palette and can be placed on the back panel. Collectively controls, indicators, structures

and functions will be referred to as nodes. Nodes are connected to one another using wires – e.g. two

controls and an indicator can be wired to the addition function so that the indicator displays the sum of

the two controls. Thus a virtual instrument can either be run as a program, with the front panel serving

as a user interface, or, when dropped as a node onto the block diagram, the front panel defines the

inputs and outputs for the given node through the connector pane. This implies each VI can be easily

tested before being embedded as a subroutine into a larger program.

The graphical approach also allows non-programmers to build programs by dragging and

dropping virtual representations of lab equipment with which they are already familiar. The LabVIEW

programming environment, with the included examples and documentation, makes it simple to create

small applications. This is a benefit on one side, but there is also a certain danger of underestimating

the expertise needed for high-quality G programming. For complex algorithms or large-scale code, it

is important that the programmer possess an extensive knowledge of the special LabVIEW syntax

and the topology of its memory management. The most advanced LabVIEW development systems

offer the possibility of building stand-alone applications. Furthermore, it is possible to create

distributed applications, which communicate by a client/server scheme, and are therefore easier to

implement due to the inherently parallel nature of G.

Benefits:

1. Interfacing to Devices

2. Code compilation

3. Large Libraries

4. Code re-use

5. Parallel Programming

6. User Community

Hardware (VTOL System):

The QNET vertical take-off and landing (VTOL) system consists of a variable speed fan with a safety guard mounted on an arm. At the other end of the arm, an adjustable counterweight is attached. This allows the position of the weight to be changed, which in turn affects the dynamics of the system. The arm assembly pivots about a rotary encoder shaft. The VTOL pitch position can be acquired from this setup. Some examples of real-world VTOL devices are helicopters, rockets, balloons, and harrier jets. Aerospace devices are typically more difficult to model. Usually this will involve using software system identification tools to determine parameters or actual dynamics. Due to their inherent complexity, flight systems are usually broken down into different subsystems to make it more manageable. These subsystems can be dealt with individually and then integrated to provide an overall solution.

QNET Vertical Take-off and Landing (VTOL) system

System Schematic:

Component Description: Rotor Actuator: There is a EM150 DC Motor and EP2245X6 Rotor.

Pulse-Width Modulated Power Amplifier : A PWM power amplifier is used to drive the VTOL DC

motor. The input to the amplifier is the output of the Digital to Analog converter (i.e. D/A) of channel

#0 on the DAQ. The maximum output voltage of the amplifier is 24 V. Its maximum peak current is 5 A

and the maximum continuous current is 4 A. The amplifier gain is 2.3 V/V.

Analog Current Measurement: Current Sense Resistor: A series load resistor of 0.1 Ohms is connected to the output of the PWM amplifier. The signal is amplified internally to result in a sensitivity of 1.0 V/A. The obtained current measurement signal is available at the Analog-to-Digital (i.e. A/D) of channel #0. The current measurement can be used to monitor the current running in the motor. 6

Analog Voltage Measurement: Voltage Sense The analog signal proportional to the voltage output of the PWM amplifier is available at the Analog-to-Digital (i.e.A/D) channel #4 of the DAQ. The voltage sensor sensitivity is 3.33 V/V. Digital Position Measurement: Optical Encoder Digital position measurement is obtained by using a high-resolution quadrature optical encoder. This optical encoder is mounted near the top of the VTOL support arm. The encoder shaft is used as the pivot of the VTOL body. The encoder count measurement is available at Digital Input (i.e. DI) channel #0 of the DAQ. Fuse The QNET power amplifier has a 250 V, 3 A fuse. 2.1.7 QNET Power Supply The DCMCT module has a 24-Volt DC power jack to power the on-board PWM amplifier. It is called the QNET power supply. The +B LED on the QNET board turns bright green when the amplifier is powered.

Encoder

Specifications:

The Forces Acting:

Free-body diagram of 1-DOF VTOL

Torques acting on the rigid body system can be described by the equation:

The thrust force, Ft, is generated by the propeller and acts perpendicular to the fan assembly. The thrust torque is given by:

Where l1 is the length between the pivot and center of the propeller, as depicted in Figure 3.1. In terms of the current, the thrust torque equals:

where Kt is the thrust current-torque constant. With respect to current, the torque equation becomes

The torque generated the propeller and the gravitational torque acting of the counter-weight act in the same direction and oppose the gravitational torques on the helicopter body and propeller assembly. We define the VTOL as being in equilibrium when the thrust is adjusted until the VTOL is horizontal and parallel to the ground. At equilibrium, the torques acting on the system are described by the equation:

where Ieq is the current required to reach equilibrium.

Equation of Motion: The angular motions of the VTOL trainer with respect to a thrust torque, _t, can be expressed by the

equation:

where θ is the pitch angle, J is the equivalent moment of inertia acting about the pitch axis, B is the viscous damping, and K is the stiffness. With respect to current, this becomes

As opposed to finding the moment of inertia by integrating over a continuous body, when finding the moment of inertia of a composite body with n point masses its easiest to use the formula:

The Front Panel:

Power Button:

This button is used to switch on the whole Panel.

Power Indicator:

Indicates the power in the panel. It glows when power is on.

Device Selector:

This is used to select the hardware device.

Samplinng rate:

It lets us chose the extent of precision. The more the sampling rate, the accurate is the data.

Digital Scopes:

The digital scopes measure the actual value of position of the arm (in degrees), current flowing

through the motor (in Amperes) and Voltage in the motor. The position is acquired from the

quadrature encoder which sends digital values to the computer in form of pulse-width modulated

wave. The Voltage and Current value is measured through encoder in the fan motor.

Meter:

The meters operate on the basis of data acquired by the digital scopes. It displays the same data as

the digital scopes.

Voltage Slide:

This slide is used to vary the voltage to the Motor.

The Block Diagram: