Autonomous Search and Rescue VehiclesAutonomous Search and Rescue VehiclesPop MihneaPop MihneaTătar AlexTătar Alex

Petru Maior University of Târgu MureșPetru Maior University of Târgu MureșMay 16May 16thth 2015 2015

Short introductionShort introduction

This project represents an application for the 11-th (2015) edition of Digilent’s Design Contest, and consists of two mobile platforms. The controlling unit is powered by a Nexys4DDR development board based on the Xilinx Artix-7 XC7A100T Field Programmable Gate Array (FPGA).

The first (main) platform will autonomously traverse a obstacle-filled area (the “search” phase) to find the target (“victim” – a hands warmer). Once the target has been found the direct route from the starting point will be calculated and then traversed by the second platform, without any sensory aid. Once it too will reach the target, it will physically pick-up the target (the “rescue” phase).

Rotary Encoders

Nexys4DDR

UltrasoundDistance

Measurement Devices

Infrared thermomet

er

Magnetometer

LCD screen

RF antenna

First platformFirst platform

RF transmitt

er

Motors driver

Level converter

s

Power resistors

Batteries holder

Step-down SMPS

Step-upSMPS

First platformFirst platform

1. Nexys4DDR:This board is used as the main controller in the project.On-board peripherals (buttons, switches, seven segment displays) were also

implemented.2. Mobile platforms:Both platforms were acquired as a kit, and includes the main Plexiglas support

board, two DC motors-driven wheels (with fixing brackets), and a third passive wheel.The multi-layer structure was obtained using PCB cooper boards.3. LCD screen:HannStar HSD043I9W1 TFT LCD, 4.3 (16:9) inch diagonally, 480 horizontal by 272

vertical pixels. RGB data is inputted via parallel 24-bit (8-bit per colour) and sync (control) signals are: DataEnable high when the display is in the active area, DataClock at 10MHz.

4. Infrared thermometer:A household-usage contactless infrared ear and ambient thermometer,

repurposed as a surface temperature measurement device. Digital interface appears to be SPI-like.

5. Ultrasonic sensor:The HC-SR04 Ultrasonic ranging module provides 2cm - 400cm non-contact

distance measurement function, and includes an ultrasonic transmitter, receiver and control circuit.

6. Magnetometer:In order to eliminate drift while the first platform moves forward or backward, and

also enable precise angle of rotation while the platform turn left, right or 180 degrees, an HMC5883L 3-axis magnetometer (digital compass) was integrated in the design.

By measuring the magnetic field strength on the X and Y axis, and applying an arctan2() operation, an magnetic north heading can be calculated.

7. RF transmitter and receiver:A pair of unbranded 2.4GHz one-way transmitter/receiver devices, which were

removed from a radio-controlled toy car. The transmitter accepts an asynchronous serial signal composed of multiple pulses.

The entire pulse train inputted at the transmitter and each individual signal outputted by the receiver is repeated at a rate of 50Hz (20mSecs), allowing the control of any standard, analogue servos and ESCs (electronic speed controllers).

8. Dual DC motor driver:This dual bidirectional motor driver is based on the L298 Dual H-Bridge Motor

Driver Integrated Circuit.The circuit allows the state and direction control of two DC motors. An 10Ohm, 5W

power resistor limits the current sourced by the driver.

9. Logic level converter:The JY-MCU is a 4-way bi-directional MOS-FET-based level converter, and allow

interfacing 5V-level devices to the 3.3V-only FPGA board.10. Rotary Encoder:Standard 24-steps per revolution passive rotary encoder, used to provide the

number of full or partial rotation of the wheels, allowing a measurement of distance travelled on the ground by each wheel.

11. Step-up, Step-down Switching mode power supply:Powered by an XLSemi XL6009 400kHz 60V 4A Boost DC-DC converter, this module

supplies the required 19V voltage rail for the LCD’s LED backlight.Powered by an TI LM2596 150kHz 40V 3A Buck DC-DC converter, this module

supplies the required 5V voltage rail for the Nexys4 board, ultrasound modules, motor driver logic and RF transmitter.

ESC

Motors driver

StretcherServos

RF receiver

Power resistors

Second platformSecond platform

RF antenna

Step-downSMPS

Batteries holder

Second platformSecond platform

1. ESC:This is a standardized, hobby-level, microcontroller-powered, ESC (electronic speed

controller) that convert two 50Hz PWM signals (correspondent to throttle and direction) into the six signals necessary for the L298 motor driver.

2. RF Receiver:This receiver converts the signal received into four separate channels, each

compliant to the standard, 50Hz, 1~2ms high time PWM.3. Servomotors:The two PWM-commanded servos allow us to modify the angle of the make-shift

stretcher in order to pick-up the “victim” (the hands warmer).

SoftwareSoftware

To map the trace done (the movement the first platform does inside the area) and obstacles detected, we used two uni-dimensional block-RAMs.

RAM1 has 272*480 positions , equivalent to the LCD screen resolution, for faster ‘drawing’ and displaying.

RAM2 is used to represent the working area in blocks (addresses) equivalent to 25-by-25cm real-world area, resulting in 10*18 positions.

Although both are implemented using one-dimensional addressing, access and location interpretation are accomplished by a process that converts two dimensions (vertical, horizontal), to one dimension (RAM address).

For example, for RAM2, to go to a next line, it adds 18 to the address, subtracts 18 to go to previous. To go to a next column it adds 1, to previous it subtracts 1.

179 178 177 176 175 174 173 172 171 170 169 168 167 166 165 164 163 162

161 160 159 158 157 156 155 154 153 152 151 150 149 148 147 146 145 144

143 142 141 140 139 138 137 136 135 134 133 132 131 130 129 128 127 126

125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108

107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90

89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72

71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54

53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36

35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18

17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

LogicalBoundari

es

Each RAM position is

equivalent to 25x25cm

physical space

Although the RAM addressing is 1-

dimensional, interpretation is made in

2-dimensions (18 horizontal by 10 vertical)

Starting position

272

cm

480 cm

11 c

m

15 cm

Physicaldimensio

nsCurrent position

Current heading

Obstacle in front?

Obstacle on right?

Obstacle on left?

Obstacle behind?

A. Check for obstacles

Read RAM for position in front

No obstacle previously

found

Obstacle previously

found

Check for obstacle using

Ultrasound sensors

No obstacle found

Go to step B

Obstacle found

Turn to next direction

B. Check for traces

Read RAM for 1 position in front

No trace found

Write to RAM

Go forwards

Check for target

Write to RAM Target found

Go to “reposition”

state

Target not found

Go to step A

Trace found

Read RAM for 2 positions in

front

Trace found

Turn to next direction

No trace or obstacle

found

Check for obstacle using

Ultrasound sensors

Obstacle not found

Obstacle found

Write to RAMGo forwards

Phase 1- SearchPhase 1- Search

TARGET

179 178 177 176 175 174 173 172 171 170 169 168 167 166 165 164 163 162

161 160 159 158 157 156 155 154 153 152 151 150 149 148 147 146 145 144

143 142 141 140 139 138 137 136 135 134 133 132 131 130 129 128 127 126

125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108

107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90

89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72

71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54

53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36

35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18

17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Phase 2 and 3- Reposition and RescuePhase 2 and 3- Reposition and Rescue

TARGET

TARGET

TARGET

Second Vehicle

ConclusionsConclusions

By using RAM-based mapping technique, the time it take for the platform to search is considerably shorter, as it stops and measures distance (for obstacle detection) only in positions where it has not previously been or detected obstacles.

Although multiple corrections are made to assure precise movement (rotary encoders, magnetometer heading), the first platform still presents errors due to its construction (two active wheels, one passive wheel). Also, as the second platform, by design, lacks any feedback/corrections mechanisms, it will too occasionally have unpredictable behavior.

Thank you for your Thank you for your attention.attention.

For more information, contact us at pop_mihnea_vlad@yahoo.comFor more information, contact us at pop_mihnea_vlad@yahoo.com