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Robot Introduction

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					Robot Introduction
The robot is the final component of the system. It receives the instructions to complete the maze through
the wireless communication and then executes them. As the robot transverses the maze, it will send a
heartbeat signal to the base station after the execution of each instruction. Finally, it will notify the base
station when it has arrived at finish point. The robot uses four opto-reflector sensors to track its
movement through the maze, detecting the path and intersections. In the event of an error, for example
the robot cannot find the designated path, the robot will send distress signal to the base station, which
can take corrective action. The robot will also have overrides that can be received from the base station
or from onboard switches and executed.


In order to accomplish its designated purpose the robot must meet the following requirements.
     Physical
             o Must be less than 1 foot in length
             o Must be able to have microcontroller, battery(s), motors, sensors, and other electronics
                mounted on it
     Electronics
             o Must be able to execute maze-solving commands and overrides
             o Must process input from several devices (sensors, switches/buttons)
             o Must communicate with Mote
             o Must output control signals to motors
             o Must output status to LEDs
     Movement/Motors
             o Must be able to move fully loaded robot (carrying microcontroller, RF devices, antennas,
                batteries, misc. electronics)
                     Minimum required speed 2.0 in/s
                     Maximum desired speed 12.0 in/s
             o Must be able to make approximately 90 degree turns in place
     Feedback/Sensors
             o Must be able to detect a path
                     Path – two inch wide reflective tape
             o Must be able to detect intersections
                     Intersection – two inch by four inch cross over path

For this project, the team has decided to use a robot designed and constructed by a previous
multidisciplinary team. Dr. Yang of the RIT Computer Engineering department was the advisor for this
team and offered the robot to the team. This robot consists of a chassis, battery, voltage regulator,
microprocessor, a motor drive system, and a few sensors. Details are given below.
   Chassis
        o Custom small, low weight design
        o Two powered wheels for movement (sides)
        o Two ball bearing castor wheels for stability (front and rear)
        o Multiple platforms
                 Includes mast for compass sensor
   Battery
        o Rechargeable NiMh
        o 9.6 V
        o 1600mAhr
   Voltage Regulator
        o LM317T
                 1.2-37 V output range (configured for 5V)
                 1.5 A load current
   Microprocessor
        o Microchip® PIC18F4320
                 36 I/O ports
                 8 MHz frequency
                 8kB memory storage
                 512 bytes RAM
   Motor drive system
        o Two stepper motors
                 9.6 V
                 1.8-degree steps
        o Four UC3770AN motor drivers
                 Allow 1 Amp
                 Built-in current limiting feature
   Sensors
        o Sonar sensors (Not intended to be used in this project)
                 Devantech SRF04 Ranger
                        Highly accurate
                           Linear output
                           45-degree sensing arc, most sensitive in central 15-degrees
            o   Compass sensor (Not intended to be used in this project)
                    R117-COMPASS
                           0.1 degree resolution
                           Requires calibration


Chassis:
        The chassis was custom designed to provide enough room for all the components with minimum
weight, while still allowing room for additional components to be added later if necessary.

Battery and Voltage Regulator:
         The battery provides power for both the motors and the electronic components. The battery
provides power directly to the motor while a voltage regulator device is used to condition the voltage to
the proper voltage level (5 V) for the electronic components. The schematic of the implementation used
for the robot is shown below.




                                    Voltage Regulator Circuit Schematic

There is an additional voltage regulator setup to provide 3.3V (using different resistor values) required for
some of the electrical components.

Motors:
         The robot includes two stepper motors, one for each of the wheels. Stepper motors are highly
accurate in their movement, allowing precision 1.8 degree movements. This is ideal for the robot since it
allows it to move in near perfect straight lines forward or backward and rotate in place to with high
precision.

Motor Drivers:
         The motor driver devices are used to isolate the motors from the microprocessor and provide
sufficient current to the motors. Two of these devices are required to control each of the stepper motors.
The schematic of the motor control implementation used in the robot is shown below. The motor is
controlled by driving the phase pins of the two motor drivers. The expected signal on each is a square
wave. If the phases of the two square waves are the same, the motor moves in one direction. If the
phases are opposite, the motor moves in the other direction.
         An additional feature of the motor driver device is that its current draw can be limited. For most
similar devices, high current is required all the time, which uses a significant amount of power. However,
the UC3770AN device allows the current to be decreased when the motor is idle. This will allow the robot
to save power while idle and thereby extend battery life.
                                                 Motor Driver Circuit



Sensors:
There are several sensors already on the robot. Unfortunately, these do not help meet the requirements
of this project. They will simply remain on the robot unused.


Additional Components:
        In order to meet the requirements of the system, several components will need to be added to the
robot. These include positional feedback sensors, switches/buttons, and LEDs.

Sensors:
In order to provide feedback of the robot’s positioning in the maze, four opto-reflectors sensors will be
mounted on the robot. Two will be mounted slightly off-center in the front of the robot, and two will be
mounted 1.5 inches from the center along the front curve of the robot. The middle two sensors will be
used to detect the path the robot is following, and the outside sensors will be used to detect intersections.
                                  Opto-Reflector Sensor Mount Locations


The opto-reflectors used will be QRB1113, Phototransistor reflective object sensor, from Fairchild
Semiconductor. The output of the phototransistor will be passed through a Schmitt-trigger inverter to
eliminate noise and ensure a strong logic signal output.




                                        Single Opto-Reflector Circuit

Switches/Buttons:
Several switches or buttons will be added to the robot to allow the user to interact directly with the robot in
a limited way. These will be mounted in the rear of the robot on the top level. The use for the switches is
discussed below in the User Interface section. The schematic for the switches/ buttons is shown below.




                                          Switch/Button Schematic

LEDs:
Several LEDs will be added in order to indicate the status of the robot. Their usage is discussed in the
user interface section. The schematic for the Power On LED and the other status LED outputs are shown
here.




                                                                        LED output schematic


           Power on LED Schematic

The complete robot system block diagram is shown below.



       9.6 V Battery




       5V Regulator                Microcontroller         2 Motor Controllers       Stepper Motor
         LM317T                     PIC18F4320                UC3770AN




                       Sensors

                                                           2 Motor Controllers       Stepper Motor
                                                              UC3770AN


                           LEDs       Switches
                                                           Mica2Dot Mote




                                           Robot Block Diagram




Functionality:
The robot has three main functional elements, communicating with the base station via the mote,
executing maze solving instructions, and executing overrides.

Communication:
Communication details are handled within the mote, so the microcontroller will simply need to transmit
and receive the data and instructions from the mote using the UART protocol.
Commands:
The commands sent from the base station to solve the maze are send these commands cause the robot
to move in different ways. A table of the commands and their meanings is shown below.
With these commands, the robot will be able to move through the maze in any desired path.

                   Command                                    Description
             Move Forward          Move forward one intersection
             Turn Left             Turn 90-degrees counter-clockwise in place
             Turn Right            Turn 90-degrees clockwise in place
             End                   Signifies that the maze has been solved

These are high level commands and experimentation and testing will determine the exact algorithms for
executing each of the commands.

Overrides:
There are several overrides available to the user both on the robot and at the base station. Executing
these overrides will interrupt the robot from an idle state or during it’s execution of maze solving
commands.

           Override       Description
           Forward        Pause execution and move forward one 'step', approximately one
                          inch
           Backward       Pause execution and move back one 'step', approximately one inch
           Left           Pause execution and rotate left one 'step', approximately ten degrees
           Right          Pause execution and rotate right one 'step', approximately ten
                          degrees
           Stop           Pause execution of maze solving commands
           Resume         Resume execution of maze solving commands (if not finished)
           Reset          Reset the robot to the idle state

The basic flow of the functionality of the robot is captured in the following diagram.
                                                Power on




                                                  Idle




                                              Receive Maze                   Receive and
                                               Instructions                Execute Overrides




                      Send Distress   Error   Execute Maze
                         Signal                Instructions


                                                         Finished


                                              Send Finished
                                                 Signal



                                              Robot Flowchart

Robot User Interface:
As mentioned above, there will be several status LEDs and switches/buttons to allow the user to interact
with the robot. The LEDs will show different status information about the robot as indicated in the table.
The switches/buttons will allow all the overrides available to be executed.
Additionally, there is an switch already on the robot that turns power on and off.


        Status Name         Description
        Power               This LED simply indicates that the system is powered on.
        Communicating       When this LED is on, the base station and the robot are transmitting
                            and receiving packets
         Distress           When this LED is on, the robot is in distress, i.e. has lost the path.
                            Overrides must be manually issued to get the robot back on track.
         Finished           When this LED is on, the robot has finished traversing the maze.
         Stopped            When this LED is on, the robot is not autonomously traversing the
                            maze – the system is in a halted state and more overrides must be
                            issued for continuing operation.
The LEDs and switches will be mounted on a small box exposing only the necessary elements while
hiding the electronics inside. The box will be placed in an easy to access location on the robot near the
top rear.
                                          User Interface Layout


Testing Strategy:
Programming and testing of the robot will be done in an incremental manner. The first elements to
undergo testing will be the additional components. The sensors are the must be tested to make sure that
they can detect the paths and intersections. The next subsystem that will be implementing and tested is
the onboard override system. This will test the robots maneuverability and the user interface. Then the
robot will be programmed to follow maze-solving commands that are hard coded into the program. The
final step will be to test the communication to and integration of the mote into the robot.

Costs:
Dr. Yang is lending the robot to the team so there is no cost to the team for its components. The cost of
the robot to the original team with and without the unused components is totaled below. The additional
components added to the robot for this project and the combined cost are also included.

                                      Starting Robot Components
                   Component                Price      Quantity            Cost
                   Devantech SRF04          $36.00     2                   $72.00
                   Ranger
                   R117-COMPASS             $51.00     1                   $51.00
                   UC3770 Motor             $5.56      4                   $22.24
                   Controller
                   PIC18F4320               $8.17      1                   $8.17
                   Tires                    $5.99      2                   $11.98
                   Stepper Motors           $6.49      2                   $12.98
                   9.6V Rechargeable        $8.99      2 (1 Backup)        $17.98
                   Battery
                   Battery Charger          $26.99     1                   $26.99
                   Acrylite FF sheets       $9.99      1                   $9.99
                   Ball Bearings            $9.99      1                   $9.99
                   Total                                                   $243.33
                   Cost of unused components                               $123.00
                   Total Cost – Cost of unused components                  $120.32


                                      Additional Robot Components
                  Component                Price               Quantity        Cost
                  LEDs, Switches,          $10.00 (estimated)  1               $10.00
                  misc electrons
                  QRB1113 Sensors          $1.50                   4           $6.00
                  Total                                                        $16.00

                                            Total Robot Costs
Robot – Unused Components Cost   $120.32
Additional Components            $16.00
Total                            $130.32

				
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