Difference between revisions of "F15: Minion"

Revision as of 14:09, 9 December 2015

Grading Criteria

Minion

Abstract

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Objectives & Introduction

Show list of your objectives. This section includes the high level details of your project. You can write about the various sensors or peripherals you used to get your project completed.

Team Members & Responsibilities

Sensor Controller:-

• Bhupendra Naphade
  

Motor & I/0 Controller:-

• Sudheer Doddapaneni
  
• Keerthanaa Alagudurai
  

Communication Bridge & Android Controller:-

• Akshay Kanchar
• Asmita Deshpande

Geographical Controller:-

• Amit Pachore
  
• Sindhuja Gopalakrishnan Elango

Master Controller:-

• Gaurao Chaudhari
  
• Akshay Dabholkar

Tester:-

• Bhupendra Naphade
  

Treasurer:-

• Keerthanaa Alagudurai

Hardware:-

• Amit Pachore
• Gaurao Chaudhari
• Bhupendra Naphade

Release:-

• Akshay Kanchar

Schedule

Common Schedule

Sensor Controller Schedule

Motor & I/0 Controller Schedule

Geographical Controller Schedule

Master Controller Schedule

Communication Bridge & Android Controller Schedule

Parts List & Cost

DBC Implementation

   VERSION ""


   NS_ :	 
        NS_DESC_
        CM_
        BA_DEF_
        BA_
        VAL_
        CAT_DEF_
        CAT_
        FILTER
        BA_DEF_DEF_
        EV_DATA_
        ENVVAR_DATA_
        SGTYPE_
        SGTYPE_VAL_
        BA_DEF_SGTYPE_
        BA_SGTYPE_
        SIG_TYPE_REF_
        VAL_TABLE_
        SIG_GROUP_
        SIG_VALTYPE_
        SIGTYPE_VALTYPE_
        BO_TX_BU_
        BA_DEF_REL_
        BA_REL_
        BA_DEF_DEF_REL_
        BU_SG_REL_
        BU_EV_REL_
        BU_BO_REL_
        SG_MUL_VAL_


BS_:
BU_: NOONE SENSOR MASTER MOTORIO ANDROID GEO

BO_ 220 MOTORIO_CMD: 4 MASTER
 SG_ MOTORIO_CMD_LeftRightdirection : 0|8@1+ (1,0) [0|2] "" MOTORIO
 SG_ MOTORIO_CMD_LevelOfDirection : 8|8@1+ (1,0) [0|5] "" MOTORIO
 SG_ MOTORIO_CMD_FrontBackDirection : 16|8@1+ (1,0) [0|2] "" MOTORIO
 SG_ MOTORIO_CMD_LevelOfSpeed : 24|8@1+ (1,0) [0|5] "" MOTORIO

BO_ 010 KILL_REQUEST: 0 ANDROID
 SG_ KILL_REQUEST : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 020 KILL_MESSAGE: 0 MASTER
 SG_ KILL_REQUEST : 0|0@1+ (1,0) [0|0] "" MOTORIO,SENSOR,GEO,ANDROID

BO_ 030 STOP_REQUEST: 0 ANDROID
 SG_ STOP_REQUEST : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 040 STOP_COMMAND: 0 MASTER
 SG_ ANDROID_HEARTBEAT_cmd : 0|0@1+ (1,0) [0|0] "" MOTOR

BO_ 210 SONARS: 4 SENSOR
 SG_ SENSOR_SONARS_FrontDistance : 0|8@1+ (1,0) [0|0] "" MASTER,MOTORIO
 SG_ SENSOR_SONARS_LeftDistance : 8|8@1+ (1,0) [0|0] "" MASTER,MOTORIO
 SG_ SENSOR_SONARS_RightDistance : 16|8@1+ (1,0) [0|0] "" MASTER,MOTORIO
 SG_ SENSOR_SONARS_RearDistance : 24|12@1+ (1,0) [0|0] "" MASTER,MOTORIO

BO_ 230 TOTAL_DISTANCE_TO_TRAVEL: 4 ANDROID
 SG_ TOTAL_DISTANCE_TO_TRAVEL: 0|16@1+ (1,0) [0|0] "" GEO

BO_ 240 SEND_CHECKPOINTS: 8 ANDROID
 SG_ SEND_CHECKPOINTS_Latitude: 0|32@1+ (1,0) [0|0] "" GEO
 SG_ SEND_CHECKPOINTS_Longitude: 32|64@1+ (1,0) [0|0] "" GEO

BO_ 250 DISTANCE: 4 GEO
 SG_ DISTANCE_FinalDistance : 0|16@1+ (1,0) [0|0] "" MASTER
 SG_ DISTANCE_CheckpointDistance : 16|16@1+ (1,0) [0|0] "" MASTER

BO_ 260 TURN_ANGLE_DIRECTION: 2 GEO
 SG_ TURN_ANGLE_DIRECTION_TurnAngle : 0|8@1+ (1,0) [0|0] "" MASTER
 SG_ TURN_ANGLE_DIRECTION_TurnDirection : 8|8@1+ (1,0) [0|0] "" MASTER

BO_ 270 RUN_PAUSE: 0 ANDROID
 SG_ RUN_PAUSE : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 280 HEARTBEAT_: 0 MOTORIO
 SG_ MOTORIO_HEARTBEAT_cmd : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 281 HEARTBEAT: 0 GEO
 SG_ GEO_HEARTBEAT_cmd : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 282 HEARTBEAT: 0 ANDROID
 SG_ ANDROID_HEARTBEAT_cmd : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 283 HEARTBEAT: 0 SENSOR
 SG_ SENSOR_HEARTBEAT_cmd : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 410 DESTINATION_REACHED: 0 MASTER
 SG_ SENSOR_HEARTBEAT_cmd : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 420 BATTERY_STATUS: 1 SENSOR
 SG_ BATTERY_STATUS_VALUE : 0|0@1+ (1,0) [0|0] "" MASTER,MOTORIO

BO_ 610 BOOT_REQUEST: 0 MASTER
 SG_ BATTERY_STATUS_VALUE : 0|0@1+ (1,0) [0|0] "" MOTORIO,SENSOR,ANDROID,GEO

BO_ 620 BOOT_REPLY_MOTORIO: 0 MOTORIO
 SG_ BOOT_REPLY_MOTORIO : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 621 BOOT_REPLY_SENSOR: 0 SENSOR
 SG_ BOOT_REPLY_SENSOR : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 622 BOOT_REPLY_GEO: 0 GEO
 SG_ BOOT_REPLY_GEO : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 623 BOOT_REPLY_ANDROID: 0 ANDROID
 SG_ BOOT_REPLY_ANDROID : 0|0@1+ (1,0) [0|0] "" MASTER

BO_ 630 BOOT_STATUS: 0 MASTER
 SG_ BOOT_STATUS : 0|0@1+ (1,0) [0|0] "" MOTORIO,ANDROID

BO_ 650 SOURCE_COORDINATE: 8 GEO
 SG_ SOURCE_COORDINATE_LATITUDE : 0|32@1+ (1,0) [0|0] "" ANDROID
 SG_ SOURCE_COORDINATE_LONGITUDE : 32|32@1+ (1,0) [0|0] "" ANDROID

CM_ BU_ NOONE "No node, used to indicate if it's a debug message going to no one.";
CM_ BU_ MASTER "The Master controller driving the car.";
CM_ BU_ SENSOR "The Sensor controller of the car.";
CM_ BU_ MOTORIO "The Motor-IO controller of the car.";
CM_ BU_ ANDROID "The Android controller of the car.";
CM_ BU_ GEO "The Geo controller of the car.";
CM_ BO_ 100 "Sync message used to synchronize the controllers";

BA_DEF_  "BusType" STRING ;
BA_DEF_ SG_ "FieldType" STRING ;
BA_DEF_ BO_ "GenMsgCycleTime" INT 0 0;

BA_DEF_DEF_ "BusType" "CAN";
BA_DEF_DEF_ "FieldType" "";

BA_ "GenMsgCycleTime" BO_ 220 10;
BA_ "GenMsgCycleTime" BO_ 210 10;
BA_ "GenMsgCycleTime" BO_ 250 10;
BA_ "GenMsgCycleTime" BO_ 260 10;
BA_ "GenMsgCycleTime" BO_ 280 1;
BA_ "GenMsgCycleTime" BO_ 281 1;
BA_ "GenMsgCycleTime" BO_ 282 1;
BA_ "GenMsgCycleTime" BO_ 283 1;
BA_ "GenMsgCycleTime" BO_ 420 1;

VAL_ 100 MASTER_HEARTBEAT_cmd 0 "MASTER_HEARTBEAT_cmd_NOOP" 1 "MASTER_HEARTBEAT_cmd_SYNC" 2 "MASTER_HEARTBEAT_cmd_REBOOT";

Design & Implementation

CAN Communication Table

Car Framework and Components

The RC car, Traxxas Stampede, in its raw form consists of a Titan 12T 550 Brushed DC motor, a Servo motor, an XL-5 ESC (Electronic Speed Control) unit, battery and a pre-programmed wireless receiver and controller. The Battery used in the RC car is an 8.4 V, 3000 NiMH from Traxxas. The wireless receiver gets commands from the remote control and drives the motors accordingly, but the DC motor can be controlled only through ESC.

The ESC (Electronic Speed Control) unit is an electronic module, which receives PWM signals from the controller and varies speed and direction of the DC motor and also acts as dynamic brakes. ESCs are often used in RC models. The ESC has the capability to provide dynamic braking depending on the mode in which it is being operated.

Motor and I/O Controller

Hardware Design

Motor Module

The motor module comprises of a servo motor for the direction control and a DC motor for speed control. The servo motor helps the car in turning left and right where as the DC motor on the other hand helps the car move forward and backward. The DC motor used in the project is a brushed motor. Conventionally, brushless motors are faster and more efficient than brushed motors. But, the reason for selecting a brushed motor over a brushless motor is that we employ a dedicated battery for the motor such that we do not have any issues with power and efficiency. Moreover, we need not operate the car at high speeds.

The initial task in the motor module is to find the operating ranges of the motor so that we get to know the output signal range and frequency from the SJONE board which would be replacing the pre-programmed controller. The simplest way to find the operating ranges of the motor is to tap and analyze PWM signal that is being supplied to the motor over an oscilloscope. The results as shown in the below pictures indicate that the operating duty cycle of both the motors lie between 10% to 20% and the frequencies at which the motors operate is 100Hz.

The hardware interface of the Motors and SJONE board includes the following connections.

The Motor controller receives the commands from the Master controller which guides it to navigate the car based on the information from the Sensors and GPS. While it does so, it also needs to get feedback from the DC motor and control the motor independently in order to ensure that the car is moving with the speed requested by the Master. This requires increasing or decreasing the actual speed level that is being provided to the Motor in case of movement along uphill, downhill, glass and high friction tracks.

The feedback is achieved through a shaft encoder which works based on Hall-effect. The installation of the speed sensor was pretty easy as we went with the one from Traxass, the same manufacturer as our RC car. It involves removing the DC motor casing, placing the sensor over the spur gear and the magnet holder. The sensor would sense the rotation of the axle. It produces a pulse when the magnet comes into the line of the sensor, which is then detected by the Motor controller.

IO Module

The IO module Consists of a 4 line * 20 characters serial LCD. Data from GPS and sensor module is displayed continuously by refreshing it every second. SJ one board communicates with LCD through UART. GPS data :-

• Latitude
• Longitude
• Final distance remaining

Sensor data:-

• Left sensor reading
• Right sensor reading
• Front sensor reading
• Rear sensor reading

Additionally, IO module controls lighting up headlights/taillights based on the direction of the car movement.

Hardware Interface

LCD unit requires 5V power supply for its working. The VCC and Ground pins are connected to common power supply lines that is used to power up all the boards. The Rx pin of LCD is connected to TXD2 (p2.8) pin on SJ one board. Two of the GPIO pins p2.6 and p2.7 controls the headlights LED’S and taillights LED’S respectively.

Software Design

Motor/IO Module

The controller on boot up initializes the CAN communication, UART and also the PWM for initialization pulse required for the motor to run. The inter-controller communication is done over CAN bus. It is configured to receive and transmit messages at 100K baud-rate. The type of CAN ID is Standard. Later these are accomplished at run time using the periodic scheduler task.

LCD communicates with SJ one board through UART. The UART port is configured to operate at the default baud rate of 9600 bps. “FO” character is sent to initialize the UART port after a delay of 100 ms, upon powering up the board. The display unit responds after 100 ms. Now the LCD module is configured and can receive further messages to display on it. Data from modules such as GPS and sensor are received continuously through CAN. It is decoded, converted into proper format and displayed on the LCD periodically.

The Motor controller, after sending the initialization pulse to the DC motor, waits for a start command from the Master over CAN and then controls the motors in order to reach the destination with required levels of speed and direction. The control algorithm for the Motor operation is as shown below.

Software Implementation

“Can receive” function is called in periodic scheduler 100 Hz task. This function lets the Motor/IO module receive CAN messages from other modules connected to it. CAN set up filter function has been used to accept only essential messages required by this module. Based on the CAN message identifier, corresponding action is performed. These are the CAN messages required by the motor/IO module.

CAN MESSAGE ID:-

• 0x210 – Sensor data
• 0x220 – motor control message from master
• 0x240 , 0x250 – GPS data

Data from sensor and GPS modules are stored in global message buffers. Sensor data is 8 bit whereas GPS data ranges between 16-32 bits. These integer values are converted into character type and then sent to LCD through UART. LCD display function is called in 1Hz periodic scheduler task. Thus Sensor and GPS data get displayed on the LCD every sec.

The 3D design used as a support for mounting the LCD is shown below:

3D design for LCD mounting

Motor Control On receiving the CAN message(0x220) from the Master, the data is extracted and and used for specific functions as shown below.

          *Byte0 – Servo Direction
          *Byte1 – Servo Level
          *Byte2 - DC Direction
          *Byte3 - DC Level

Based on this data, the first two bytes decide the direction(left/right) and the level(angle), respectively in which the car should turn using the Servo motor. Similaly, the next two bytes decide the direction(forward/backward) and the level(speed) in which the car has to move.

To implement all the motor related functions, we have employed a dedicated task. Initially, the pre-scaled PWM values are fed to the motors based on the direction and level from the Master. We have a bit robust algorithm to obtain these PWM values which has offsets and level multipliers. The advantage of this is we can change the code to function for multiple levels with minimum effort.

Motor Feedback After feeding the motors with the required levels, we have to check if the car is actually moving at that speed. This is ensured through feedback and control based on that. The feedback is obtained through the speed sensor collaborated with the DC motor, which triggers a pulse on every rotation and this is recorded by a rising edge based interrupt. The interrupt callback function increments the number of pulses. A separate logic is used to calculate and then compare the actual and required(from Master) speed levels. The corrective measures are enforced to achieve the desired speed.

The transmit messages, except Heart beat message(sent every one second), are transmitted once every 100ms. The Motor/IO controller, on receiving a boot request from Master controller, transmits a boot reply message in order to let the Master know that it has booted successfully. The heart beat message is transmitted continuously to indicate that the controller is active and this will be acknowledged by the Master.

Master Controller

As the name suggests, it is main controller on the car which interacts with all other controllers over the CAN Bus to achieve real-time functionality. Basic function of the Master Controller is to receive data from Android, Geo and Sensor Modules and develop the algorithm to drive the car autonomously based on the received data through the Motor Controller.

Hardware Design

• RC car was the basic infrastructure that was required to implement the project.
• CAN Bus with five SJone controller boards was integrated on General purpose Printed Circuit Board (PCB).
• Sufficient power-supply ports and external pins were provided to each controllers.
• Flat Ribbon Cables were used to reduce circuit complexity arising from external connecting wires.

Software Design

Algorithm

• Master Controller uses FreeRTOS environment to achieve its functionality.
• It uses Periodic Scheduler Task provided by Preet at its core to communicate with all other controllers.
• The functions of the Periodic Scheduler Task were used in a customized manner to transmit/receive the messages at specific intervals of 1Hz,10Hz,100Hz and 1000Hz.
• File logger function was used to log the real-time data onto SD card which was used for debugging purpose.
• Can Message structure of 11-bit id was implemented to send and receive CAN messages over the CAN Bus.
• CAN acceptance filter was set-up to receive messages specific to Master Controller from the CAN Bus, since it is the broadcast Bus.

Geo-Based :

• Step 1: Check if there is no obstruction. If there is no obstruction proceed to step2, otherwise proceed to step7.
• Step 2: Check if distance towards next check-point is greater than 30. If distance towards next check-point is greater than 30, proceed to step3, otherwise go to Step 6.
• Step 3: Check if turning angle is greater than 10. If turning angle is greater than 10, proceed to step4, otherwise go straight go to step7.
• Step 4: Check if turning angle is greater than or equal to 90. If turning angle is greater than or equal to 90, turn left or right according to the turning bit with level of direction 3 go to step7, otherwise proceed to step5.
• Step 5: Check if turning angle is greater than or equal to 45 and less than 90. If turning angle is greater than or equal to 45 and less than 90, turn left or right according to the turning bit with level of direction 2, otherwise turn left or right according to the turning bit with level of direction 1 go to step7.
• Step 6: Check if distance towards next check-point is less than 10.If the distance is less than 10, stop the car, otherwise move slowly with level of speed 1.
• Step 7: End.

Software Implementation

• Master Controller starts with initialization of CAN Bus and setting up reception filter from the main() function.
• The Periodic Scheduler Task then takes over to implement the actual functionality of the Master Controller.
• CAN_is_busoff() was used at an interval of 10Hz through periodic scheduler task to check if CAN bus was working continuously.
• The basic flow of control is as follows:

Sensor Controller

Sensor controller consists of sonar and ultrasonic sensors that are inter-connected to the SJOne board and CAN bus. The sensors detect if there is any obstacle around the car and report the distance of obstacle.

Hardware Design

MB1010 LV MaxSonar EZ1 Sensor

MB1010 Sensor

Working of sensor

Hardware design consists of four sensors connected to ports of LPC1758. The sensors in front, right and left direction are MB1010 sensors while the one at back is HCSR04. The sensors are connected to +5V to achieve the highest beam pattern that is available. The LV MaxSonar EZ detects objects from 0 inches to 254 inches and provides sonar range from 6 to 254 inches with 1 inch resolution. Objects from 0 to 6 inches are reported as 6 inches. Sensor operates at 42KHz. The sensor reports output formats in from of pulse width output, analog voltage output, and RS232 serial output. We have selected pulse width output.The sensor will continually measure range and output if RX data is left unconnected or held high. If held low the sensor will stop ranging. We have commanded a range reading by triggering high for 20uS. Below are the timing diagrams for the sensor

Timing Diagram for LV MaxSonar EZ Sensor

HCSR-04 sensor

HCSR-04 Sensor

HCSR-04 sensor is a ultrasonic ranging module which detects obstacle from 0 to 400 cm. It is a four pin module – Vcc, trig, echo and Gnd. It includes transmitter, receiver and control circuit. The sensor operates at 40 KHz.It Requires 5V 15mA power supply. When a short 10uS pulse is provided to the trigger input, the sensor will transmit out 8 cycle of ultrasonic burst at 40kHz and makes the echo pin high.The Echo pin is lowered to logic low when the ultrasound burst is reflected off a distant object.To obtain the distance, measure the width (Ton) of Echo pin. Time = Width of Echo pulse, in uS (micro second) Distance in centimeters = Time / 58 Distance in inches = Time / 148 Or you can utilize the speed of sound, which is 340m/s

Working-of-HC-SR04-Ultrasonic-Sensor

The 3D design used as a support for mounting the sensors is shown below:

3D Design for Sensor mounting

Software Design

Geographical Controller

Geographical Controller consists of GPS and Compass module. GPS module is used to track current position of car, find bearing angle of destination with respect to north and compass module used to know heading of car with respect to north. Difference between heading and bearing gives us turn angle which car have to take to reach destination from current position.

Hardware Design

Schematic

Schematic

SparkFun Venus GPS with SMA Connector
SparkFun Venus GPS uses Skytraq VENUS634FLPx IC. The Venus638FLPx outputs standard NMEA-0183 or SkyTraq Binary sentences at a default rate of 9600 bps which is adjustable to 115200 bps, with update rates up to 20Hz. We configured this module with update rate of 10Hz and 38400 bps UART rate. Module outputs GGA, GSA, GSV, GLL, RMC, VTG, ZDA NMEA standard messages which can be configures to as per our requirements. We configured it to give only GGA messages. GGA message format is shown below.
For configuring GPS modules to UART rate 38400 bps, 10Hz update rate and only GGA message at output, below binary commands are used.

GGA Message Format

Binary Configuration Commands

SparkFun Venus GPS with SMA Connector and Antenna

HMC5883L

HMC5883L

Software Design

The GPS communicates with the SJOne board through the UART and the Compass communicates with the SJOne board through the I2C

I2C Communication

The HMC5883L IC communicates to the SJOne Board through the I2C bus.
SJONE board -Master device
HMC5883L - Slave device
The I2C rate is controlled by the master and can be upto maximum 400 KHz. We have configured the rate as 100 KHz.

Master Transmitter Mode:
In this mode, the master writes to the slave registers.
The compass IC has a set of 8 bit registers to be initially configured for parameters such as device output rate, number of samples, device gain and operating mode. By identifying the device write address and register address, the values can be written by the SJONE board to the compass registers.

Master Receive Mode:
In this mode, the master reads from the slave registers.
The X,Y,Z registers of the compass can be then read by the SJOne board one by one knowing the device read address and register address.The register pointer will be incremented by 1 automatically after the current register has been successfully read.

Android Communication Bridge Controller

Hardware Design

The Communication bridge consists of establishing connection between car and the android phone which is established with the help of bluetooth module HC-05 connected to UART peripheral of SJOne Board. The UART pins on board are connected to bluetooth module in the manner shown in diagram. Once the connection is established between the car and the android phone and signals like 'Start','Stop' and 'Kill' are sent from android phone then they are received by the bluetooth and sent to SJOne board to be further broadcasted over CAN bus.

Communication Bridge

HC-05 Bluetooth Module

Software Design

Android Application

Software Design

Testing

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Accuracy of GPS Module

GPS Module Coordinates on Google Maps

Accuracy of GPS module was tested by recording/logging coordinates received by module using LOG_INFO() function and plotting them on Google maps GPS Module Coordinates on Google Maps. GPS module was very much accurate we did not needed to calibrate it. It is observed that more number of satellite locks with module, greater the accuracy of coordinate readings.

Calibration of Compass

As any instrument has instrument error, so has the compass IC. The compass needs to be calibrated for accuracy. We undertook two levels of calibration.
1. Level 1 calibration was done without mounting the compass on car. The compass was rotated in its axis for 360 degrees and the error was identified for every 15 degrees (totally 24 zones) with the setup shown by the image in the left.
2. Level 2 calibration was done after mounting the compass on car.The car setup by itself had some tilt and we compensated it by means of adjusting the hardware mounting. Next, the motor’s EMI caused some magnetic deviation and the motor's influence was taken into account too. The car was rotated in its axis ( its axis being parallel to the compass axis) for 360 degrees with the deviation measured for every 15 degrees(totally 24 zones) with the setup depicted by the image in the right.

Set up for Compass Calibration before mounting on Car

Set up for Compass Calibration on Car

The deviation was not uniform for every zone. Using linear regression analysis technique, the relationship between the predictor variable - degrees and the response variable - radians was found in an ideal environment and the same was repeated several times for accuracy. The average of several such readings was taken as the final calibration value.

Before Calibration

After Calibration

Motor and Feedback

The motor operation is initially tested for its accuracy with different direction and levels such as forward, reverse, left, right. After ensuring everything is as expected, we went for refining it. Later, with the speed sensor installed, the functioning of it and the control based on it has to be checked properly. For this, we have tested the car by running it over ramp-up, ramp-down, grassy and rough paths. Then we have refined it. Finally, we made sure that the car gets back to the required speed when it deviates from the same.

Technical Challenges

Configuring GPS Module

We faced difficulty in configuring GPS module to sending only $GGA messages, 10Hz Position update rate and updating baud rate to 38400. Initially we were trying to configure GPS module via writing program for SJ One board and we were unable to do it. Later on we completed configuring by connecting GPS module directly to serial port and using GPS Viewer software. Through it we can directly configure GPS module without worrying about binary messages and checksum calculation.

Compass and Calibration

1. Initially the compass was mounted and tested on breadboard with its upper face downwards as the connecting strips are on the upper side. This made the compass produce incorrect values.
2. While reading the registers in compass HMC5883L, only x and y register values are needed. Hence we tried to read only those registers from the device. But it so happened that z register is in between the x and y registers and the read pointer did not advance after the x register was read and remained in the z register. This led to compass producing constant values.
3. While calibrating, the compass should be rotated on a horizontal plane with its axis of rotation fixed. Shifting the axis may result in incorrect values.
4. Having a robust hardware that does not cause any or very less tilt, will reduce the efforts of calibration as HMC5883L IC is not tilt compensated.
5. Calibration should be done in an environment which does not have iron , magnetic particles etc as those may cause magnetic deviation. As the motor module influences the compass with the generated EMI, mount the compass far away from the motor and calibrate with the motor ON to take account of the EMI generated.

Motor Feedback

The major difficulty with motor speed feedback was getting enough number of pulses from the speed sensor in order to calculate the current speed. When we run at very low speeds, we get pulses as low as 2 0r 3 at even 10Hz. If the same value is multiplied by required factor(say 600 in 10Hz) to get the rpm, then we have a couple of issues.

i) Firstly, we cannot get intermediate speed values as we get only in multiples of the the factor which will be very high.

ii) Secondly, we may have some issues, at very low speeds, like we don't get a pulse every 100ms or 10ms, which means the motor is at rest but which actually is not.

Solution: Never try to implement in terms of "rpm". Instead go for "rps" or "m/s". This will eliminate the first issue. And to solve the second problem, we may think of aggregating the pulse count for a greater time interval. But this will lead to a delayed feedback which in turn leads to an undesired behavior. Hence we have a trade-off between the two.

Motor Control

1) The first hurdle one would face with the Motor control through an ESC is starting the motor. This requires an initialization pulse, which would have been sent by the transmitter earlier. We have to realize the required pattern or PWM value for the achieving this. 2) The second difficulty with the motor comes into picture when with backward movement of the car. Due to the presence of the ESC and the resudual momentum in forward direction, we cannot alter the direction of the motor suddenly. We have to manually discover the pattern required for this forward to reverse transition which takes a bit of time unless one is aware of it.

Conclusion

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Project Video

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Project Source Code

• Git Repository
  

References

Acknowledgement

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References Used

• GPS Binary Command Set
  
• GPS Logging Application Note
  
• Haversine Calculations
  

Appendix

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