University Of Colorado, Colorado Springs

University Of Colorado, Colorado Springs
Unmanned Aerial Vehicle Design, Development, and Implementation
Faculty Advisor
Dr. David Schmidt
Team Members
Patrick Herklotz, Shane Kirkbride, Mike Kopps, Mark Kraska, John Ordeman,
Erica Rygg, Matt Spears, Sam Szarka, and Benjamin Young
Special Thanks to:
Our sponsors:
And especially:
IEEE Pikes Peak Section Executive Committee, Dr. Terrance E. Boult, Ben Udhall,
Brandon Garrison, Daniel Ruiz, Delphine Humphries, Jim Fournier, Ryan Thomas,
Ski Munch, and Katie Collins
Abstract:
The Near Space Unmanned Aerial Vehicle Team (NSUAV) at University of Colorado at
Colorado Springs (UCCS) designed and constructed an Unmanned Aerial Vehicle (UAV).
This project was inspired by the Near Space Initiative which is an agreement between the
UCCS and the Air Force Research and Army Research Labs. As a first step toward
understanding the complexities of a near space environment the NSUAV team chose to
build a basic UAV. The mission and goals of the AUVSI Seafarer’s Student Unmanned
Aerial Vehicle competition are consistent with the NSUAV team goals. The NSUAV team
chose to enter the initial project into the competition to gain an objective mark on their
progress. The process of designing a low cost unmanned aerial vehicle with commercially
available parts is summarized in this paper. The implementation of a navigation system
with capability to follow and fly through dynamic waypoints carrying a two to three
pound payload while taking in video imagery is also discussed.
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Table of Contents
I.
Introduction………………………………………………………………………4
II.
Design Process and Overview...…………………………………………………4
III.
Autonomous Navigation…………………………………………………………6
IV.
Platform Design…………………………………………………………………..9
V.
Power System..…………………………………………………………………..10
VI.
Target Recognition System…………………………………………………….14
VII.
General Safety and Procedures………………………………………………..15
VIII.
Conclusion……………………………………………………………………….16
UCCS 3
Introduction
The NSUAV Team's entry into the AUVSI competition was initiated with the
purpose of submitting a UAV entry that meets the AUVSI competition specifications and
the following goals as stated on the competition rules “…an unmanned, radio controllable
aircraft to be launched and transition or continue to autonomous flight, navigate a
specified course, use onboard payload sensors to locate and assess a series of man made
objects prior to returning to the launch point for landing…”. In addition to this goal, the
NSUAV had further goals of constructing a UAV with off the shelf parts, keeping the cost
under 10,000 dollars, and to design a robust UAV with the simplest possible architecture
to keep complexity low and system malfunctions to a minimum.
Design Process and Overview
The engineering process begins with the identification of specific goals. In this
step the goals of the product to be designed are discussed and settled upon. Next, a system
level breakdown of the individual systems
occurs. Here the different tasks or systems of
the product are determined and defined. An
initial system break down is shown in Figure 1.
After the design is made and the
systems specifications are determined and
defined. Action is taken to implement the
design.
Lastly, the designed product is tested to
determine whether the product meets the goals
and specifications. The individual systems may
be tested independently at first in order to
isolate system specific faults. Later, the entire
product design/prototype is tested to isolate any
Figure 1: Systems Breakdown for a UAV
remaining errors or design faults.
Design Overview
Figure 1 shows the four subsystems which make up the NSUAV design. The
autonomous navigation subsystem is responsible for the actual flight of the UAV. This
system must be robust, contain failsafe capabilities, lightweight, low power, and low cost
The target recognition system was developed in accordance with the AUVSI competition
standards and had low power, low weight and size requirements in addition to minimum
video resolution requirements. The power system powers the electronics both on the
vehicle and on the ground and the batteries within it were required to be as small and
lightweight as possible. The platform system is defined as the mechanical and structural
parts of the design. Each of these systems will be discussed with emphasis on their
construction, components and the specifications which determined the selection of the
components used.
UCCS 4
Autonomous Navigation
Autonomous navigation can be achieved with a complex flight control system
more commonly referred to as an autopilot. A basic autopilot will be able to take
latitudinal and longitudinal coordinate readings of the current position and altitude of the
aircraft. It should take these readings and use them to control the flight of the aircraft in
such a manner as to steer the aircraft
toward the desired target destination.
At the same time the autopilot will
accept the current thrust
measurement and three dimensional
velocity vector (yaw, pitch, roll)
readings and make adjustments to the
aircraft control surfaces in such a
manner as to keep the aircraft in a
stable and level flight pattern. Some
autopilots also have the ability to
take action in the event GPS data is
lost or a communication link breaks
Figure 2: Entire UAV system with starter kit
down.
Procerus Kestrel Autopilot
After considering the complex control system engineering involved in the design
of an autonomous navigation unit, it was decided the purchase of a commercially
available autopilot was to be the
practical time and cost efficient
solution.
The Kestrel Autopilot from
Procerus Technologies, shown in
Figure 3, was selected from
among a number of different
commercially available products
due to its ease of configuration,
small size, weighing 16.7 grams
and 1.29in2 in volume, low voltage
and power requirements (5VDC),
and cost. In addition, the Kestrel
Figure 3: Kestrel 2.2 autopilot with Aerocomm AC4490
makes communications simple
modem attached
with its piggyback modem, and
“plug-and-play” GPS receiver.
UCCS 5
Among the Kestrel's
features is an Inertial Measure
Unit (IMU) which is
composed of 3-axis rate gyros
and accelerometers. Absolute
and differential pressure
sensors provide barometric
pressure and aircraft air
speed. Three temperature
sensors combined with a 20
point temperature
Figure 4: Kestrel 2.x block diagram
compensation algorithm
reduce sensor drift improving aircraft state measurement and estimation. Figure 4 shows
how all of these components work together on the Kestrel.
The Kestrel was originally
designed for a foam delta wing
aircraft powered with a
lightweight electric motor.
However, the NSUAV team
platform is a gas powered
trainer plane. The nitro 2stroke engine vibrations created
a problem which manifested
itself as an intermittent ground
control to Kestrel
communications link. This
problem was resolved by
designing and constructing a
vibration dampening mount for
Figure 5: the autopilot vibration dampening mount for the
the craft and the Kestrel. This is
Kestrel
shown in figure 5. The design
is intended to minimize the amount of vibrations while still holding the autopilot as stable
as possible during flight.
Autopilot Communications
Aircraft coordinate and altitude
telemetry is transmitted and received via a
pair of Aerocomm AC4490 900MHz
radio modems. The Ground Control
station consists of a notebook computer
and a device called the Commbox. The
Commbox is a small communications
hub. It contains the modem needed to
communicate with the Kestrel Autopilot
and the serial port connector to interface
with a notebook computer The notebook
computer along with the Virtual Cockpit
Figure 6: UAV in flight
UCCS 6
software from Procerus Technologies lets a user upload “waypoints”, tune PID gains,
calibrate sensors, and monitor the flight. Waypoints can be defined as latitude, longitude,
and altitude coordinates which are points in space through which the flight coordinator or
mission control operator wishes to fly the UAV to, or through.
Mission Control/ Navigation System for the autopilot
The mission control system
consists of a graphical user interface
(GUI) built into a software package
called the Virtual Cockpit. A basic
screen shot of the Virtual Cockpit is
shown in figure 7. The Virtual Cockpit
runs on a notebook PC and is designed to
command the autopilot to fly through a
predetermined waypoint sequence. The
commands are issued from the software
to the Commbox via a serial port and are
then transmitted to the autopilot. Mission
control also has the ability to accept and Figure 7: A screen shot of the Virtual Cockpit Software
submit a change in the waypoint
GUI. This software is responsible for the ground
sequence in mid-flight if a change in
control data management
mission objectives occurs in mid-flight.
Figure 8: The entire ground control station
including the Commbox and the Futaba RC
transmitter unit.
The Virtual Cockpit software
contains a GUI which makes
current altitude, attitude, and
elevation information immediately
available to the mission control
operator. The Virtual Cockpit’s
graphical display shows the
aircraft's ‘vital signs’ in an obvious
way so the flight coordinator and
backup pilot would be able to make
rapid decisions in the event an
emergency was to occur. The flight
telemetry data can then be saved to
a file and evaluated if needed.
UCCS 7
Platform Design
The platform for the UAV is the Sig Kadet LT-40
ARF. This model aircraft has proven to be an easy flier
for beginner RC pilots and is highly recommended as a
trainer by the RC community for its excellent stability.
An unmodified Sig Kadet LT-40 ARF is shown in figure
9. The entire platform with the payload is 8 lbs.
Figure 9: An unmodified
ARF SIG LT-40
Airframe Selection
The Kadet LT-40 has a large wing surface area of 900in2 with a wingspan of 70in.
The large wing surface lift area is a must for heavier payloads and uncompromised flight
stability. The standard airfoil design has a flat bottom with airfoil top side. The tricycle
style landing gear of the Kadet provides take-off and landing stability while also
remaining maneuverable on the ground.
Propulsion
Propulsion is provided by an O.S. 0.61 nitro RC engine. This is a 2 stroke engine
with a horsepower of 1.90 BHP at 16,000 RPMs. The engine was chosen for use in
combination with the Kadet LT-40 platform to allow enough power to sustain normal
flight with the increased payload weight of the autonomous flight electronics. The
altitude of UCCS is 6,300 ft. above sea level; the thinner atmosphere was a factor in
sizing the engine to an above average displacement.
Payload Placement
The payload must be carefully
distributed to maintain the center of gravity
within acceptable limits. The vehicle's center of
gravity is determined by payload placement,
engine size, location and weight among other
factors. It was determined that the center of
gravity must be kept a few inches behind the
airfoil's leading edge in order to keep the lift
vector and center of gravity as close together as
possible. Since the majority of the payload area
is located within the fuselage, re-balancing of
Figure 10: The target recognition (external)
loads lateral to the midline was unnecessary.
payload was placed directly under the
Figure 10 shows the placement of the
center of gravity to maintain stable flight
external payload. Special care was taken in the
dynamics.
design of this payload mount to ensure a
minimal amount of change occurred in the
flight dynamics of the platform. The weight of the payload is about 1.5lbs.
UCCS 8
Power System
Overall Power System Structure
Figure 11, below, shows the block diagram outline of the entire power system used
in the UAV.
Figure 11: Power Block Diagram
The UAV has two power sections, the first is on the onboard system and the
second is the ground station. As seen in figure 11, the laptop unit, video receiver, and the
Commbox for the Kestrel, will be powered using a separate DC to AC power inverter will
be powered by a 12V car battery. These are the three most critical devices outside of the
autopilot itself. The other devices are powered by their own internal batteries.
UCCS 9
On-board Power System
Figure 12 outlines the power system on-board the platform.
On­Board Power Supply System for UAV
Charge
Port 5V
4.8 V
700 mAH
Servo
Battery
11.1 V
Li­PO
2300 mAH
Kestrel
Battery
9.6 V
600 mAH
NiCd
Gimble
Battery
Charge
Port 12V
Charge
Port 10V
Servos
Switch 1
Kestrel
GPS
Switch 2
Gimble Power
Switch 3
Video
Transmitter
Camera
Gimble
Servo
Radio
Reciever
Figure 12: On-board Power Scheme Outline
The entire system is powered by three primary batteries: one Lithium Polymer
battery for the Kestrel Auto Pilot, and two NiCd batteries for the airplane servos and the
gimbal. These three batteries are attached to three switches which switch between a
charging supply and the component. An interface board with the three charge ports is
attached to one end of the switches along with the batteries. When the switches are in the
off position, the charge ports are attached directly to the batteries themselves. This allows
the batteries to charge without removing them from the platform, and allows for quick
voltage checks in the field.
The 4.8V NiCd for the servo control does not connect directly to the servos.
Rather, the connection is routed through the Kestrel unit, and multiplexed with the servo
controls on each channel. This is shown as a loop through in figure 11.
The 11.1V Li-PO is the most powerful battery, at 2300 mAH, used to power the
Kestrel unit itself. This also routes outward to power the GPS receiver unit, and the 900
MHz modem attachment.
Because of the volatile nature of the Li-PO, it is removable so it can be charged
separate of the platform. Figure 13 shows the way the three batteries are mounted inside
the platform. The 9.6V gimbal battery is mounted beneath the fuel tank, and the Velcro
strips outline where the Li-PO is mounted.
UCCS 10
Figure 13: Battery Mounts
The gimbal unit has a custom-built power supply system powered off of the 9.6V
NiCd. Figure 14 shows the power board schematics and board layout diagrams for the
main board. Figure 14 shows the schematic drawing of the power kill daughter board
(PKDB).
Figure 14: Gimbal Power Supply Main PCB Drawing
Figure 15: Schematic of the power supply with all components shown
UCCS 11
Figure 16: Power Kill Daughter Board
In Figure 15, JP2 is the 9.6V battery input. JP1 is the interface with the PKDB
seen in Figure 16. All other connectors on the board output 5V, which power the video
transmitter, the gimbal radio receiver, and the camera. Figure 17 shows the layout of the
PKDB, originally designed for use with the Li-PO battery in the earlier stages of the
project. IC1 is an Atmel TINY13S microcontroller, which senses the incoming voltage
from the battery. When the voltage drops below the programmed threshold voltage, it
disables the switching regulator on the main board. JP2 is a 3x2 header connector used to
program the part.
Ground Station Power
Most units on the ground are powered using internal batteries. A separate radio
transmitter, powered by a 9V internal battery array, controls the servo attached to the
camera on the gimbal, as seen in Figure 11. The Commbox unit has a12V rechargeable
battery inside. The vital importance of this unit and the laptop computer necessitates a
power inverter be used so the power loss issues will not be a factor. A 12V adapter
plugged into the inverter must power the video receiver. The Futaba radio transmitter does
not need external power supply unit.
UCCS 12
Target Recognition System Design
Image Recognition Design Overview
This system contains software that processes the images received from the plane
and has the sole purpose of finding target shapes/objects/colors in the pictures, and
determining their locations via the GPS information received from the plane at the time of
the photo being taken. The video processing software will give a signal to mission control
to take a picture. At the same time, the GPS coordinates and heading of the plane will be
sent to the image processing software. The GPS coordinates are needed as this allows
pictures to be matched up with the locations where they were taken. The process of
matching pictures with their GPS coordinates must have a low time delay, since longer the
time delays will introduce larger errors into the data.
Hardware Design
There are five main
components in the hardware
design; the components are the
camera, transmitter, servo, power
unit and receiver. First, the Black
Widow camera is responsible for
actually capturing the image.
Then, signal is digitized and sent
to the 2.4GHz Black Widow
transmitter. The receiver and
servo are connected so the camera
can be pointed in any given
Figure 17: The hardware for the imaging system.
direction along one axis. The
ability for the camera to turn
compensates for the image distortion which occurs as the plane rolls in a turn. The power
supply ties the unit together with a 9.8V power supply as mentioned above.
Software Design
Figure 18: The data flow upon clicking on a target
This section describes how the
data imaging software is
intended to work and describes
the data flow within the
software. First the target image
is received from a 2.4GHz
0.6Watt transmitter via a
2.4GHz video receiver and its
high gain 2.4GHz antenna.
Data is translated and stored to
an MPEG file using a video
capture device. The software
displays the video and when the
user sees a desirable target, the
user places a mouse cursor over
the target and clicks. The click's
UCCS 13
pixel coordinates are used by the software to identify the location of the target. Telemetry
from the UAV at the time of the video frame is matched up with the pixel coordinates and
the exact coordinates of the target are mathematically extrapolated. The program then
logs the information to a file for future reference. The data flow for this program is shown
in Figure 19.
Figure 19: Software Block Diagram
Procedures and General Safety
General Safety
UAV safety precautions fall under 5 stages: initial safety check, starting the engine, taking
off, flight and landing.
Aircraft Safety: Check/Walk around
• Walk Around
- Plug aileron and pitot tube** into designated attachments; attach wing and
secure wing bolts; ensure no wires hanging out.
- Check all hatches to confirm 4 screws attaching them to aircraft; tighten
any loose screws
- Rack all control surfaces gently; ensure no loose screws on control horn
attachments or broken hinges
- Gently shake aircraft and listen for loose parts tumbling around in aircraft;
remove any loose parts and confirm parts origination before continuing
- Turn all switches on and weight for ground controller sensor check,
COMM Check, RC COMM check, pressure check, altimeter check, and
zero all control surfaces check
- Throw all control surfaces in designated directions with manual control
unit to ensure they move in the correct direction; reverse any control surfaces that do not and confirm changes with ground controller
- Gain Clearance to begin engine startup procedures and proceed to next
section
** Pitot Tube – A tube used to measure air pressure due to forward velocity of an aircraft.
A pressure tube is routed from outside the aircraft to a pressure sensor.
Starting Engine
• Fuel Engine
UCCS 14
-
•
Command full throttle to open carburetor assembly.
Clear area within 6 feet diameter around aircraft; pilot plugs carburetor and
whorls prop until fuel drawn into engine and engine audibly starts.
- Command idle throttle setting.
- Confirm throttle cut closes carburetor assembly.
Start Engine
- Pilot assistant attaches glow clip to engine glow plug.
- Pilot announces “CLEAR PROP”.
- Clear bystanders from 15 feet on either side of line of prop (See Diagram
on following page.)
Airplane: Top View
Kill Zone
Red: DANGER ZONE: clear
bystanders from prop if prop
shatters during startup
No Standing
Figure 20: Diagram of danger zones for propeller safety
-
Apply electric starter and whorl engine until it runs
Move behind engine; pull glow clip off of engine and ensure engine runs
on its own
Announce full throttle; pilot assistant holds aircraft vertical to ensure RPM
stays constant; richen or lean engine as needed
Announce idle and prepare aircraft for taxing
Takeoff
• Gain clearance to takeoff from ground controller
- Pilot look both ways on Runway and ensure no obstacles/bystanders on
runway or tarmac; ground crew check also and confirm clearance status
- Announce “TAKING OFF” followed by “FULL THROTTLE”
- Allow aircraft to come up to sufficient airspeed for takeoff roll
- Fly aircraft to designated AGL and activate UAV systems when instructed
to do so by ground controller
Landing
• Gain clearance to land from ground controller
- Pilot glance both ways on runway to check for obstacles/bystanders on runway or tarmac; ground crew check also and confirm clearance status
- Pilot announce “LANDING” proceeded by “THROTTLING DOWN”
- Fly aircraft into landing pattern and announce “BASE LEG” followed by
“FINAL TURN INTO RUNWAY” followed by “FINAL APPROACH”
- Land aircraft gently within flight envelope
- Gain clearance to taxi on to tarmac and into pit area; shutdown engine
- Turn off all switches on aircraft and transmitter
- Move all equipment into competition impound area
UCCS 15
Failsafe
• The failsafe is designed to gently land plane in case of loss of transmission. The
following commands are executed in case of loss of transmission.
- Throttle Closed
- Elevator full up
- Full right rudder
- Full right aileron
Procedures
There are 4 initial flights before the system can be perfectly configured. These
procedures must be conducted after any change in platform or system. They are the
procedures recommend by Procerus for proper use of the Kestrel system.
Flight 1: Launch, flight, landing
The entire flight will be conducted in Manual Mode. In this mode, the control inputs on
the RC controller go directly to the control surfaces. Rate damping PID loops can be
enabled in this mode to make the aircraft easier to fly, however, because the rate loops
have not been tuned, they should be disabled for this flight. The goals for this flight are
trimming the aircraft and finding reasonable values for trim airspeed, trim throttle, and
trim angle of attack.
Flight 2: Tuning Rate Damping Servo PID loops
The purpose of the second flight is to tune the rate damping servo loops. The rate
damping PID loops damp the aircraft rotation around the pitch, roll, and yaw axis if the
aircraft has a rudder. Familiarity with the control algorithms of the autopilot is very
useful for this stage.
Flight 3: Tuning the inner attitude hold loops, the outer airspeed and altitude hold PID
loops
The purpose of the third flight is to tune the inner attitude hold loops and the outer
airspeed and altitude hold PID loops. Because the rate loops were tuned in Flight 2, the
pilot can now utilize rate damping in Manual Mode if desired. Again, keep the aircraft
close enough such that the pilot can easily switch to manual mode to save the aircraft.
Flight 4: Re-verification of waypoint navigation and proper loitering
The purpose of the fourth flight is to verify waypoint navigation and loiter work correctly.
At this point, it is assumed flights one, two, and three have been completed and the
aircraft is tuned to fly in Altitude and Speed Modes. Use the Failsafe Setup Screen to
enable the fail-safes. The user may also choose to enable the joystick or keyboard inputs
for roll and altitude control in Speed and Altitude modes.
UCCS 16
Conclusion
In conclusion, the target goals of designing a robust low cost UAV with a low
system complexity to minimize system malfunctions was met with great success. Test
flights confirm that the use of external charging ports, a small and efficient autopilot with
plug-and-play peripherals, and other equally effective systems has benefited in a low time
to flight and low incidence of operator errors. However, whether or not the NSUAV
design can meet AUVSI specifications and accomplish the mission goals is yet to be
determined.
UCCS 17
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