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 / Total Mass (in grams) / Operating Voltage (in V) / Current Draw (in mA) / Power Consumption (in mW)Gyroscope / 0 / 3 / 7 / 21
GPS Reciever / 0 / 5 / 65 / 325
Infrared Camera / 148 / 5 / 200 / 1000
Regular Camera / 50 / 12 / 50 / 600
Ultrasonic Range Finder / 17.2 / 5 / 2 / 10
Data Storage Device/Socket / 25 / 0 / 0 / 0
Microcontroller / 175 / 0 / 0 / 0
Motors / 258 / 11 / 0
Propellers / 8 / 0 / 0 / 0
Battery / 103 / 11.1 / 0 / 0
Laser Scanner / 141 / 5 / 500 / 2500
Design 1 Totals: / 784 grams / 2 Watts
Design 2 Totals: / 908 grams / 4 Watts
, 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:
Where
When rearranged to calculate , the motor shaft power with propeller and motor efficiency considered is:
Propeller Width / 0.127 MetersThrust Design 1 / 7.691 Newtons
Thrust Design 2 / 8.905 Newtons
D1 Motor Power Requirements / 81 Watts / (Motor Efficiency Factored In)
D2 Motor Power Requirements / 101 Watts
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 / Total Mass (in grams) / Power Consumption (in mW)Gyroscope / 0 / 21
GPS Reciever / 0 / 325
Infrared Camera / 148 / 1000
Regular Camera / 50 / 600
Ultrasonic Range Finder / 17.2 / 10
Data Storage Device/Socket / 25 / 0
Microcontroller / 175 / 0
Motors / 258 / 0
Propellers / 8 / 0
Battery / 103 / 0
Laser Scanner / 141 / 2500
Design 1 Totals: / 784 grams / 83 Watts
Design 2 Totals: / 908 grams / 105 Watts
, where
D1 Max Runtime / 8.84 MinutesD2 Max Runtime / 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.