Toward the Development of an Interactive Modeling, Simulation, Animation, and Real-Time Control (MoSART) Hardware/Software

Testbed for a Tilt-Wing Rotorcraft

John S. KoenigArizona State University, Tempe AZ

IEEE Student Member #40351269

IEEE Region 6, Southwest Area,

Student Paper Contest

San Diego, CA

Saturday March 27th, 1999

Introduction

• Motivation

• Contributions of Work

• Test Stand Pitch Dynamics

• Controller Design

• MoSART Environment

• Utility of Environment

• Summary and Future Work

Motivation

• High Speed Autonomous Rotorcraft Vehicle (HARVee) Project at ASU – Tilt-wing aircraft which combines the benefits of a

helicopter and an airplane– NEED: Automatic control for safe hover flight

Motivation

• Hardware Test Stand– Lab-scale test bed for control system development– NEED: Mathematical modeling, simulation, and

real-time control

• Nonlinear and linear model development

– 1 DOF Test Stand Pitch Dynamics

• Linear controller design

• Tilt-Wing Software Environment

– Open-loop and closed-loop simulation

• Modeling, Simulation, Animation, and Real-Time Control

(MoSART)

– Interactive tool for control system design

– Can be connected to hardware to form integrated

hardware/software testbed

Contributions of Work

Test Stand Description

• Four degrees-of-freedom

• Replicates all hover mode control inputs

(except has only two main engines)

• Fully constrained and contained

Modeling

• Second order, non-linear model

– 1 DOF pitch dynamics

– Three Point-Mass Representation

Three Point-Mass Model

Non-linear model:

32321 x1x2

yx3x2x1

y321

y

z dTdTI

1cosdmdmdm

I

gsinmmm

I

gd

Where,

17

1i

2z

2xiy ddmI

i

Incorporate known parameters:

1T4.1425

25s

4.14)s(P

2

Linearize (sin, for small angles):

Determine transfer function:

1T4.14sin25

Model Development

Open-Loop Stability

• Plant Transfer function:

• Root Locus Plot:

Open-Loop Poles

at s=±5

)5)(5(

4.14

25

4.14)(

2

ssssP

-5 +5

imaginary

real

unstable

Controller Design - Part One

• Controller design proceeds in two parts– Part One - Series Compensation

PStep

K1

Chose K1 such that:2s2s2

CL

K1 is given the following form:

s

)5s)(as(k)s(K1

Controller Design - Part One

0

2

0 2 4 6

Time

Pit

ch

An

gle

2s2s)as(k4.14)5s(s 2CL

486.0k

25k4.14

286.0a

2a)486.0(4.14

2ka4.14

2s2ska4.14s)5k4.14(s 22CL

Controller Design

s largefor , kss

)5s)(as(k

Closed-loop transfer function has the form:

kas)1k(s

)as(kTF

2CL

Derivative action [(s+a) term] produces large magnitude response to a high-frequency input.

Controller output when s is very large:

Eliminate overshoot by employing a feed-forward loop.

Step 25s

4.142

s

)5s)(as(k

ks

ks)s(K2

0

2

0 2 4 6

Time

Pit

ch A

ng

le

Controller Design - Part Two

K1(s) and K2(s) are improper and the following modificationsare made to make them strictly proper:

2

1 50s

50

s

)5s)(as(k)s(K

2

2 50s

50ks)s(K

Closed-loop transfer function now takes the form:

kas)1k(s

kaTF

2CL

Controller Design

MoSART Environment

• System specific, interactive software

environment for Modeling, Simulation,

Animation, and Real-Time Control (MoSART)

• Runs on Pentium PC platform under

Windows 95/NT

• Written in C++, using Microsoft Foundation

Classes (MFC) and Direct-3D

• Utilizes MATLAB for analysis purposes

MoSART Environment

• Environment structured around four modules:

– Program Interface Module (PIM)– Simulation Module (SIM)– Graphical Animation Module (GAM)– Help-Instruct Module (HIM)

Program Interface Module

• Interactive System Diagram

– Block diagram

representation of

system

– Point-and-click

access

• Standard Windows 95/NT Interface

– User Friendly

– Menus

– Multiple windows

– Control toolbars

Simulation Module

• Numerical Simulation– Fast compiled C++– Faster than real-time simulation is possible

• On-the-fly Parameter Editing– Change model– Edit controller parameters– Adjust reference commands (step, sinusoid, etc.)– Different integration methods (Euler, 4th order

Runge-Kutta)

• Dynamic linking to MATLAB engine

Graphical Animation Module

• 3-D Animation (Direct-3D)– Texture-mapped, light-shaded polygons

• Visualization Tools– Real-time 3-D and graphing windows

Help-Instruct Module

• On-line Help– Instructions on using the environment

• HTML/PDF Documents– Model documentation/references– On-line tutorials

Utility of Environment

• Open-loop simulation– 3-D visualization of unstable system– Change between linear and non-linear models

– Utilize MATLAB for data analysis and comparison

Utility of Environment

• Controller Design - Series and Feed-Forward– Animation

• Visualize positive and negative aspects of a design– Series controller = large overshoot (negative)

– Series+feed-forward = small overshoot (positive)

– Graphing Windows• Real-time plotting of user-specified parameters

– Pitch angle vs. time

• Utilize MATLAB engine for analysis– Such as comparing the linear and nonlinear responses

Utility of Environment

• Controller Design - High vs. Low Gain

– MATLAB processing of data gives precise measure of linear error

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 1 2 3 4 5 6 7

Time (sec)

Err

or

(deg

rees

)

– (k) and (a) values adjusted with with point-and-click interface

– Effects of controller changes can be seen in seconds

Future Work

• Link hardware test stand with MoSART environment– Hardware/software testbed will be an effective

control system design tool– Provides real-time control of actual hardware

• Mathematical model development– 4 DOF test stand dynamics– 6 DOF tilt-wing rotorcraft dynamics

Summary

• Linear and nonlinear models developed

– 1 DOF pitching dynamics

• Linear controller developed

– Tested using linear and nonlinear models

• MoSART software environment

– Simulation, Animation, Analysis, Control

– Interactive tool for controller design