Homework 7
Search and Rescue
Copter
Group Members:
Karim Gilani
Jaydeep Patel
Patrick Fakhir
“We pledge my honor that we have abided by the Stevens Honor
System”
Design #1 Hardware Realization Block Diagram:
Design 1 focuses on using the echolocation approach to the obstacle evasion problem to
the autonomous copter. This approach uses the ultrasonic range finder mounted top, bottom,
front left, and front right.
Common Components:
The Gyroscope:
The gyroscope provides data about the current
x, y, and z axis orientation of the copter. This data is essential
to the movement of the copter. If the copter is tilted forward,
thrust from the motors will drive the copter forward. If the
copter is tilted sideways, the copter will move sideways. The
copter relies on its angular orientation to achieve movement
in various directions.
The particular gyroscope the group chose for the copter is a dual axis gyroscope. The
copter is concerned with only with angular orientation with respect to the x and y axis for
movement. The gyroscope model consumes approximately 7 milliamperes of current at 3 volts.
The weight of the gyroscope is very negligible – and unfortunately not even provided under the
physical description in the datasheet.
The GPS receiver:
While the gyroscope provides angular
orientation, the GPS provides coordinate location of
the copter. The user will determine where the copter
needs to go. GPS is how the copter will know that it
has reached its goal.
This Parallax GPS receiver module can be
queried via serial i/o commands for latitude,
longitude, altitude, speed, and direction/heading.
This satisfies the position and power alertness
functionality previously discussed. In addition, the
PMB-648 based module also supports querying for altitude as well as tracking of up to
20 satellites. An additional specification important to note is the acquisition time. On
cold and warm starts, the chip requires 42 and 38 seconds respectively. The module
consumes approximately 65 milliamperes of current at 5 volts. The weight of the
gyroscope is also negligible and surprisingly not provided under the physical description
in the datasheet.
The Infrared Camera:
The infrared image data is vital to the
clients of this product. When tracking people,
infrared heat emitted from people is better
contrasted against environmental surroundings.
Operators of the search and rescue copter can thus
spend more time rescuing than searching for a
person in a regular photo.
The ICI 7320 Pro infrared camera is the most expensive part of design 1. Though
the exact price must be quoted from the supplier, similar products are prices at one
thousand dollars. Though the price is high, this camera comes equipped with 320/240
resolution alongside an auto-tracking feature. Though software is provided alongside
the camera, it would be sufficient to make use of the C++ software development kit
provided with the product for interfacing with the Arduino Mega microcontroller. The
infrared camera consumes 1 watt of power via USB connection. This is equivalent to 200
milliamperes of current at 5 volts operation. The camera weighs 148 grams total
including the lens.
The Camera/Video device:
Though the infrared sensor provides an
excellent means for which to search for someone, a
more accurate visual on the status of the victim would
be appreciable. Depending on the economic concerns of
the project, a video device may not be worth the extra
capital and power costs incurred to the search and
rescue copter. A camera taking pictures at interval time increments would suffice.
The group chose a small camera with minimal weight: the CM-26N/P CMOS
Camera Module. The camera has a 640 by 480 resolution and operating range of 5 to 15
volts with 50 milliampere current consumption at 12 volts.
The Ultrasonic Range Finder:
The ultrasonic range finder is capable of
detecting objects within a 6.45 meter range. It consumes 2
milliamperes of current with a variable operating range of 2.5
volts to 5.5 volts, with improved performance at 5.5 volt
operation. Readings can be taken at a rate of 20 Hz; every 50
milliseconds. With 4 range finders mounted on the copter
weighing 4.3 grams a piece, the total weight contribution to
the copter comes out to 17.2 grams.
The Data Storage Device:
The microcontroller
has a limited amount of memory;
much of it will be used in computing
motor power from gyroscope data
and in buffering image results from
the infrared sensors and audio/video
devices. If the data from these
sensors is stored into volatile
memory, a failure of the search and rescue copter would
mean loss of this important information. Thus a high
capacity data storage device such as an SD card with SD
card reader/writer is essential to success of the copter. This
data can be stored into the card in a format that would be
recognized by the corresponding application on the
operator’s laptop.
The Search and Rescue Copter Data Viewer Application:
The data written to the SD card by the copter could easily be viewed as images
but an application would allow for possible future expansion of the project to include
other features. These features may require additional processing of the data before
meaningful results can be properly displayed to the user. The application would act as
an organized base from which behavior of the copter can be programmed and the data
retrieved from the copter viewed.
The Microcontroller:
The microcontroller is
the main component of the
project and is responsible for a
number of functions. It has to
interpret data retrieved from
the dual-axis gyroscope to
achieve the desired
orientation. In determining the
desired orientation, the
controller must take into
consideration obstacles sensed
by the ultrasonic sensors. The final changes in power delivered to the motors will
produce thrust in the desired direction. The controller will also save the data obtained
from the infrared sensors and image device.
Given the number of components involved with the project, it is necessary that
the microcontroller have sufficient input/output pins with sufficient power supply to
each. The microcontroller does not have enough memory to buffer the image data but is
able to buffer some data; which can be written to the SD card allowing the next packet
of data to be written.
Calculating Motor Requirements:
In order to calculate the motor requirements, the weight of the copter must be
known. In order for the weight to be known, the motor weight must be known. Using
assumptions about the motor weight, approximated to 64.5 grams each, the assumed
total weight of the copter allows us to calculate the minimum amount of thrust need for
an idle state. This thrust can be calculated by Newton’s first law: F = ma. From this
thrust and known propeller radius, the shaft power required (with motor efficiency
factored in) can be calculated. These calculations are made from aforementioned data
about each component as shown below.
Component
Gyroscope
GPS Reciever
Infrared Camera
Regular Camera
Ultrasonic Range Finder
Data Storage
Device/Socket
Microcontroller
Motors
Propellers
Battery
Laser Scanner
Total Mass
(in grams)
0
0
148
50
17.2
25
175
258
8
103
141
Operating
Voltage (in V)
3
5
5
12
5
0
0
11
0
11.1
5
Current
Draw (in mA)
7
65
200
50
2
0
0
0
0
500
Power Consumption
(in mW)
21
325
1000
600
10
0
0
0
0
0
2500
Design 1 Totals:
784 grams
2 Watts
Design 2 Totals:
908 grams
4 Watts
T  mcopter *( g  a )
Tidle  mcopter g , since a = 0 in an idle state.
Where the mass of the copter is in kilograms and g is the acceleration due to gravity = 9.807 m/s2.
The power requirements were calculated using the following equation:
T  (( P) 2 *  * r 2 *  )1/3
Where
T = Thrust
η = propeller hover efficiency (typically 0.7-0.8)
P = motor shaft power
r = propeller radius
kg
  air density = 1.22 3
m
When rearranged to calculate
 P , the motor shaft power with propeller and motor efficiency
considered is:
T3
P 
 *r2 * 
Propeller Width
Thrust Design 1
Thrust Design 2
D1 Motor Power
Requirements
D2 Motor Power
Requirements
0.127 Meters
7.691 Newtons
8.905 Newtons
81 Watts
101 Watts
(Motor Efficiency
Factored In)
The Motors:
The TP2410-09 brushless motor provides a max power of 104 watts. Given that these
motors become inefficient when operated at the limit of their maximum ratings, four of these
motors should efficiently be able to counter the weight of the copter.
The Propellers:
These propellers were suggested to be used with the motors above, fit the shaft, and
have a radius of 0.254 meters.
The Battery:
The battery is the limiting factor for the
search and rescue copter. Every component
adds weight to the copter, which must be
countered with thrust from the motor thus
constantly draining power even in a constant
floating position. A high energy density ratio is
needed for the battery. Lithium ion is currently a very feasible option.
Calculation of operating time:
Component
Gyroscope
GPS Reciever
Infrared Camera
Regular Camera
Ultrasonic Range Finder
Data Storage Device/Socket
Microcontroller
Motors
Propellers
Battery
Laser Scanner
Design 1 Totals:
Design 2 Totals:
Total Mass
(in grams)
0
0
148
50
17.2
25
175
258
8
103
141
784 grams
908 grams
Power
Consumption (in
mW)
21
325
1000
600
10
0
0
0
0
0
2500
83 Watts
105 Watts
T  Max Flight Time in minutes
60* R 60* R
R = Battery Energy Capacity Rating in Amp-Hours


,
where
I
(P / V )
P = Power Consumed by Copter
max
Tmax
V = Battery Voltage
D1 Max Runtime
D2 Max Runtime
8.84 Minutes
6.96 Minutes
With Design 1, the copter can run for approximately an additional 1.88 minutes. Of course this is
only the maximum runtime of the copter at steady state. The copter will require additional power due to
acceleration and deceleration towards the destination. If the battery is replaced with a more powerful
battery, the runtime can be increased considerably.
Design #2 Hardware Realization Block Diagram:
The Laser Scanner:
The laser scanner is the alternative to
echolocation that uses the same approach but with the
speed of light alternative. This alternative is very costly.
The Hokuyo R283 laser scanner costs approximately
2,300 dollars. It can perform a laser scan in
approximately 100 milliseconds. It operates at 5 volts
and consumes 500 milliamperes of current – 800
milliamperes rush.
It operates on
serial protocol.