Hardware Development of a Low Cost Autopilot
for Small Surface Vehicles
Joe Banh
School of Aeronautical, Mechanical and Mechatronic Engineering
FACULTY OF ENGINEERING & INFORMATION TECHNOLOGIES
INTRODUCTION
AUTOPILOT HARDWARE
HARDWARE VALIDATION TESTING
There are many applications for surface
vehicles, particularly in marine sciences for
pollutant tracking, hydrographic surveys,
riverine and coastal observation and sea-air
interface measurements.
Functional Requirements Definition
GPS
Given the general mission nature of the lowcost autopilot in question, a number of
requirements were defined which drive the
components
selected:
• Truth value errors of approximately 0.002
seconds (Longitude and Latitude) for static
testing
Motivation
At the heart of any autonomous system is the
autopilot. However, the functionality of the
autopilot is dependent on the hardware. Many
commercial autopilots are feature rich but are
expensive. Open source autopilots are low
cost but often lack important features found in
commercial autopilots.
Objective
• Develop a low cost autopilot for use in a
small remote control boat by:
• Establishing metrics based on cost and
features of existing autopilots
• Selecting and integrating hardware for
the autopilot
CURRENT AUTOPILOTS
C
Commercial
i l
Functional Requirements
Required
Component
The autopilot shall be able to navigate GPS
through GPS waypoints
The autopilot shall be capable of Magnetometer
discerning its heading with respect to
magnetic north
The autopilot shall be able to log all sensor Datalogger
d t and
data
d the
th PWM outputs
t t to
t the
th motor
t
and servos, either from the user control or
from the autopilot itself
The pilot shall be able to switch from Remote
autonomous mode to user control mode Control Switch
and vice versa
The
autopilot
shall
be
able
to Wireless
communicate to a GCS in order to change Transceiver
mission and system parameters
Selected Hardware
Component
Part Selected
Rationale
Microcontroller Arduino Mega
Many I/O and
interfaces, Easy to
code and library rich
GPS
MediaTek
MT3329
Fast (10Hz) update
rate and low cost
IMU
Sparkfun Razor
IMU
Ease of use and
inclusion of quality
magnetometer for low
cost
• Sometimes not hardware rich but are high
cost due to robust mechanical and software
design (PICOPILOT-N)
Wireless
Transceiver
Xbee 900 Pro
Wire and RPSMA
No interferance with
2 4GHz devices and
2.4GHz
simple UART interface
Datalogger
OpenLog
Low cost and MicroSD
compatible
Open Source
Remote
Pololu RC Servo
Control Switch Multiplexer #721
• Generally designed for Unmanned Air
Vehicles but retrofitted to Unmanned
Surface Vehicles without the inner loop
stability algorithms
• Robust in terms of black-box design,
software
functionality
and
hardware
capabilities (CloudCap Piccolo II, Piccolo SL
and AUAV EZI-NAV)
• Costs can increase when additional
hardware and features are included (such
as IMU, Wireless and Datalogging) but are
still a low cost alternative to commercial
p
((ArduPilot Mega
g [[below])
])
autopilots
Ease of use and
COTS
INTEGRATION
Non-Functional Requirements Definition
A number of non-functional requirements were
d fi d which
defined
hi h iimpacted
d the
h iintegration
i off the
h
hardware:
Non-Functional
Requirements
Method of Compliance
The
autopilot Black-box design with only cables
should be easy to accessible by the user
use for the end
user
• Generalised design means that the autopilot
isn’t as easy to use or connect
• Software can be harder to use and may not
contain the features wanted or required
AUTOPILOT METRICS
The
autopilot Selection of a waterproof enclosure
should be housed and creation of a PCB to ensure fit
in an enclosure
Result
• Enclosed black-box autopilot with IP65
enclosure
Vehicle p
path ((blue)) g
generated from logged
gg GPS data
AUTOPILOT COMPARISON
Feature
Thesis
ArduPilot
AUAV
GPS
MT3329
MT3329
Garmin 18
IMU
Sparkfun
IMU
Yes with
HC5343
No
Wireless
Xbee 900
XBee
900MHz or
2.4GHz
Datalogger
OpenLog
((2GB))
Chip (16MB)
No
RCS
Pololu RCS
ATMega 328
Yes
Enclosure
Yes (IP65)
No
Yes
Ease of Use
Colour coded
and labeled
wires only
accessible to
user
Requires
user to know
where to
plug RC I/O
(unlabeled)
Colour coded
wires only
accessible to
user
Cost
$474.30AUD
$472AUD
$3800AUD
CONCLUSION
• The autopilot that was built met the majority
of
functional
and
non-functional
requirements. The next stage would be the
development of software that would be able
to rival the ArduPilot Mega and AUAV EZINAV.
• Although slightly expensive compared to the
ArduPilot Mega but there has been a
bridging of the gap due to the emphasis, not
on the hardware, but on the ergonomics and
ease of use for the end user.
The ArduPilot Mega (Open Source) and AUAV
EZI-NAV (Commercial) were found to be the
most feature rich and best designed autopilots
from both sides.
sides The aim is to bridge the gap
by designing an autopilot that has:
• The hardware capabilities of commercial
and open source autopilots and the robust,
black-box design of commercial autopilots
• Lower cost than both autopilots (ArduiPilot
Mega $472 and AUAV EZI-NAV $3800)
• Average of 7m error from truth path for
dynamic testing
Magnetometer
• Good static results with 0.03 degrees error
from truth bearing and 0.73 degrees
standard deviation
• Little effect from EMF generated by the
motor (1 degree error)
Integration Testing
• Results indicate ability for all hardware
components to work together (GPS, IMU,
Datalogger)
• Successful switchover from RC control to
preset control surface settings from the
remote control switch
THIS RESEARCH IS SP