S19: Hot Wheels

Hot Wheels

Hot Wheels

Self Navigating RC car using CAN communication based on FreeRTOS.

Abstract

Hot Wheels is Self Navigating RC car using CAN communication based on FreeRTOS. While navigating to the destination, if car sees any kind of obstacle, it avoids that too. The RC car takes real time inputs and covert it into the data that can be processed to monitor and control to meet the desired requirements. In this project, we aim to design and develop a self-driving car that autonomously navigates from the current location to the destination which is selected through an Android application, avoiding all the obstacles in the path. The car comprises of 5 control units communicating with each other over the CAN Bus, each having a specific functionality that helps the car to navigate to its destination successfully.

Introduction

The project was divided into 5 modules:

Sensor Controller	This module detects obstacles in the driving path with the help of ultrasonic sensors.
Motor Controller	This controller drives the DC motor and Servo in the car and controls the speed of the car.
Geographical Controller	This module assists the car in navigating to a destination with the help of location details provided by GPS and the orientation(heading angle) provided by the compass.
Android Application	Application developed on Android-based phones to communicate with car. Destination coordinates,Start and Stop signals are send to car using this application.The Application also displays sensor values in real time for debugging purposes.
Bluetooth Controller	The controller uses Bluetooth to communicate with an Android application on the Android phone. Destination coordinates are provided by this module. The Bluetooth module also displays important data like Ultrasonic sensor values and GPS coordinates on the app and LCD.
Master Controller	This module collects inputs from all other modules and controls the motor. It is responsible for system health monitoring, Obstacle avoidance and navigation to the destination.

Team Members & Responsibilities

Hot Wheels-Team Photo

Gitlab Project Link - [1]

• Master Controller
  • Kailash Chakravarty

• Sensor Controller
  • Rishabh Sheth

• Motor Controller
  • Kriti Hedau
  • Tahir Rawn

• Geographical Controller
  • Harmeen Joshi
  • Nandini Shankar

• Communication Bridge Controller & Android Application
  • Swanand Sapre
  • Aquib Mulani

• Code Review & Commit Approvers
  • Rishabh Sheth
  • Nandini Shankar
  • Kailash Chakravarty

Legend

Color	Component
Red	Master Controller
Blue	Geographical Controller
Purple	Communication Controller (Bridge)
Green	Motor/IO Controller
Clouds	Sensor Controller
Teal	Android App
Brown	QA

Schedule

Week#	Start Date	End Date	Task	Status
1	02/26/2019	03/05/2019	Read previous projects, gather information and discuss among the group members. Assign team responsibilities for each module. Analysis of component required for each module	Completed Completed Completed
2	03/05/2019	03/12/2019	Project plans and timelines discussed Finalize Components and order them Set-up GIT and Slack	Completed Completed Completed
3	03/12/2019	03/19/2019	Master Controller: Discuss with other Modules about how Master shall expect and send the data between have. Work on having common DBC. GEO Controller: Make Initial GEO code push on GIT Android Application: Start taking tutorial to build basic app Bridge Controller: Initial Bridge code push on GIT Motor Controller: Push Initial Motor Code on GIT Sensor Controller: Initial Sensor code push on GIT	Completed Completed Completed Completed Completed
4	03/19/2019	03/26/2019	Android: Get access tokens for Google API to enable maps in the application GPS Controller: Get raw values from MPU9150 IMU sensor Bridge Controller:Implementation of mDNS protocol for discovery of device on local subnet Motor Controller: Tap into the servo motor controlling the steering	Completed Completed Completed Completed
5	03/26/2019	04/02/2019	Android: Embed Google maps onto the Android App and add the project to the git repository GPS Controller: Implement driver to get filtered values from the IMU GEO Controller: Implementation of software interface to communicate with CMPS14 Bridge Controller: Implementation of local MQTT Broker on ESP8266 and Cloud broker on EC2 Instance Pin Layouts from all groups Motor Controller: Tap into the in-built ESC and overclock	Completed Completed Completed Completed
6	04/02/2019	04/09/2019	GPS Controller: Send and receive coordinates and other parameters between Car and application GEO Controller: Calibration of CMPS14 module PCB layout 1st Iteration Bridge Controller: Configure ESP8266 (as Wifi-to-serial bridge) to receiver data over Wifi and push it on UART Motor Controller: Find suitable Motor Driver Module and place an order Sensor Controller: Experiment with the different sensors to check for which type works best for the RC Car	Completed Completed Completed Completed
7	04/09/2019	04/16/2019	GPS Controller: Send and receive coordinates and other parameters between Car and appS GEO Controller: Implementation of dedicated switches and 7-segment display for CMPS14 calibration Bridge Controller: Program for MQTT Client to UART link on ESP8266 module Motor Controller: Find optimal Frequency and PWM values to drive Steering and Rear Wheels Sensor Controller: Obstacle detection with SJ One board	Completed Completed Completed Completed
8	04/16/2019	04/23/2019	Android: Read the current position and get user input for the destination GPS Controller: Get GPS and COMPASS readings and parse them GEO Controller: Implementation of offset addition to raw compass values on switch press Bridge Controller: MQTT to UART to CAN Bus Link and Bridge Controller MQTT to Android application Connection Link Master Controller: Define and acquire DBC messages intended for master Motor Controller: Implementation of basic maneuvering of the RC car Sensor Controller: Integration with the RC Car and distance calculation	Completed Completed Completed Completed Completed Completed
9	04/23/2019	04/30/2019	Android: Configure the UI elements for live monitoring in the app. GPS Controller: Get the destination and waypoints from the Bridge Controller GEO Controller: Transmit heading angle and CMPS14 debug messages to master and mobile app through CAN bus Bridge Controller: Define messages and MQTT topics for bridge to app communication Master Controller: Create a simple program to instruct motor ECU to drive and acquire sensor values to send stop instruction to motor ECU Motor Controller: Implementation of RPM Sensor and integration with CAN Bus Sensor Controller: Final Testing	Completed Completed Completed Completed Completed Completed
10	04/30/2019	05/07/2019	Android: Define the message parameters and packing format for communication between car and app and plot the waypoints for the given coordinates GPS Controller: Calculate Bearing and send navigation instructions to the Master Bridge Controller: Encapsulation and parsing the data from MQTT payload Master Controller: Receive navigation instructions from the GPS Controller and move the car accordingly Motor Controller: Fine tuning of Speed Control and Steering control using PWM duty cycle levels	Completed Completed Completed Completed Completed
11	05/07/2019	05/14/2019	Android: Send coordinates to Car GPS Controller: Mount on the car and start testing on the field and make final changes accordingly Bridge Controller: Update debug messages Master Controller: Implement algorithm and avoid obstacles while maintaining bearing angles as provided by Geo Controller Motor Controller: Optimize control by accelerating / decelerating as instructed by Master Controller	Completed Completed Completed Completed Completed
12	05/14/2019	05/21/2019	Android: Add additional commands to the app (stop, reset, reroute) GPS Controller: Final system testing Bridge Controller: Display interfacing and final Testing Master Controller: Final testing and handling of corner cases Motor Controller: Final Testing	Completed Completed Completed Completed Completed
13	05/22/2019		FINAL DEMO	Completed

Schedule

Week#	Date	Task	Status	Completion Date
1	02/12/19	Form Teams	Completed	02/12/19
2	02/17/19	Setup a Slack workspace for the team. Setup private channel on Slack workspace	Completed Completed	02/17/19 02/17/19
3	02/26/19	Create a Gitlab project and add all team members as well as Preet Order CAN transcievers All team members get familiar with the Gitlab environment and make their initial commit.	Completed Completed Completed	02/26/19 02/26/19 02/26/19
4	03/05/19	Research previous projects wiki page and gather useful information. Identify and discuss individual modules within the project and finalize roles of each team member. Demo CAN Communication	Completed Completed Completed	03/07/19 03/07/19 03/07/19
5	03/12/19	Each team member review their corresponding module hardware requirements. Study data sheets of sensors used in each module. Pick PCB design platform and begin work on PCB design/schematic.	Completed Completed Completed	03/12/19 03/12/19 03/12/19
6	03/19/19	Finish ordering required components. Finalize PCB design/order by end of week. Each team member start work on implementing individually working modules.	Completed Completed Completed
7	03/26/19	Demo a "Hello World" program implementation by each module. Study android app development environment. Start implementing android app.	Completed Completed Completed
8	04/02/19	--- SPRING BREAK ---
9	04/09/19	Demo Android app basic prototype	Completed
10	04/16/19	Finish implementing individual working modules.	Completed
11	04/23/19	Work on integrating individual modules into the final testing. Identify test cases for the integrated prototype model. Start integration testing.	Completed Completed Completed
12	04/30/19	Finish integration testing. Finalize Wiki page documentation.	In Progress In Progress
13	05/07/19	--- BUFFER WEEK ---
14	05/14/19	Final Exam Preparation
15	05/22/19	Final Demo

Parts List & Cost

Item#	Part Desciption	Vendor	Qty	Cost
1	Traxxas Slash 4x4 [2]	Traxxas	1	$239.00
2	Traxxas 5800mAh 7.4v 2-Cell 25C LiPo Battery [3]	Traxxas	1	$69.99
2	Traxxas Battery Charger [4]	Traxxas	1	$69.99
2	Traxxas RPM Sensor 6522 [5]	Traxxas	1	$12.00
2	Traxxas Magnet Holder, Magnet and Spur Cover 6538 [6]	Traxxas	1	$5.11
2	Traxxas Gear Cover 6537 [7]	Traxxas	1	$5.13
3	CAN Transceivers MCP2551-I/P	Microchip [8]	8	Free Samples
4	Graphics LCD module		1	From Preet
5	Bluetooth(HC-05)	HiLetgo	1	$9.00

Printed Circuit Board

Design

The project requires to connect five ECUs (SJOne Boards) via CAN modules, Sensors, GPS, Compass, LCD, and lots of other connections for controlling RC Car. Initially, we used a general purpose board to connect all these modules together. Though due to the small size of the board ( 10mm x 30mm ), there were lots of congestion and wiring. The arrangement helped us to start initially testing. Though lots of wiring was a headache and was a hurdle to get consistent output so we decided to design PCB to get consistent output and also reduce wirings.

We designed the PCB using EGAL PCB Design Software. In our previous project (CMPE 244) we used KiCAD for PCB design. KiCAD is opensource software and features nicer and simpler UI, shortcut keys for fast development ( It was a really nice and nice to have a feature ) and inbuilt 3D PCB view. Though the problem with KiCAD was lack of library support, unorganized components library, and manual matching of the component with the footprint was a pain so we looked for other options. AutoCAD offers a free EGAL's license to students and hobbyists. EGAL is more organized compared to KiCAD and has good support of the component library. Bad UI and lack of shortcut keys slowed down our development process though it was trading. We can use Fusion 360 software from Auto CAD to visualize a 3D model of PCB.

We designed FRC connectors for each ECUs. Along with that we also populated 17x2 male header to incorporate any new changes in the future. Other major things were onboard CAN IC for each ECUs, connectors for four sensors, GPS, Compass and Bluetooth. We also provided support for the DB9 connector and onboard steady power supply.

PCB Schematics

Power Supply

We decided to go with a single power supply i.e. power from a LiPo battery of Traxxas RC car. Based on battery specification it is sufficient to provide require current, though one concern was during speed increase in the motor it can bring down overall voltage significant down below 5V which can cause to shut down or restart of SJOne board. To overcome this issue we used Buck-Boost convert. The S7V7F5 switching step-up/step-down regulator efficiently produces 5 V from input voltages between 2.7 V and 11.8 V. Its ability to convert both higher and lower input voltages makes it useful for applications where the power supply voltage can vary greatly, as with batteries that start above but discharge below 5 V.

5V Step-Up/Step-Down Voltage Regulator

Traxass ESC gives 6V output which we provided to Buck-Boost which then provides regulated 5V to all required components. Instead of designing a separate power supply for 3.3V we used the 3.3V output from SJOne Board which is working well.

Fabrication

PCB was sent to fabrication to JLCPCB China which provided PCB with MOQ of 5 with the lead time of 1 week. We implemented 2 layers of PCB with most of the parts in top layer. This time we decided to go with all SMD components due to the freedom it gives in terms of space. Also, our CAN IC was not available in DIP package. Soldering of SMD components is intimidating in the first place but after try on a few samples, it was very easy.

PCB front side

PCB Back side

Challenges

PCB designing was there on our agenda but due to delay in sensor selection and prioritizing other tasks, PCB designing was delayed. We believe that PCB greatly improved car's robustness. So every team should finalize components in early stage and try to integrate PCB in design as soon as possible.

After receiving first order we came to know about a few bugs in PCB design. One of the major bugs was we accidentally swapped CAN high low pins, which we corrected by using external CAN trance receiver instead of onboard CAN IC. Due to lack of communication and rigorous PCB review instead of swapping UART Tx-Rx pins for GPS and Bluetooth we connected them directly as it is So we need to use wires for those modules. Still, PCB design helped us a lot to reduce our wire count.

Bill Of Materials

HARDWARE INTEGRATION PCB
PART NAME	PART MODEL	QUANTITY	COST PER UNIT (USD)
CAN Transceiver	SN65HVD230DR	10	$2.38
5V Step-Up/Step-Down Voltage Regulator	S7V7F5	1	$8.99
Header Connectors Kit	LED-0603	2	$9.99
Diode	Diode	1	$0.32
0.1uF Capacitor	SMD 0805 0.1uF Capacitor	10	$0.23
0 ohm Resistor	SMD 0805 0 ohm Resistor	25	$0.1
120 ohm Resistor	SMD 0805 0 ohm Resistor	10	$0.44
IDC Extension Flat Ribbon Cable	uxcell 34P 34 Way 2.54mm Pitch F/F IDC cable	6	$9.0

Mounting Mechanism

Mount mechanism

This is one of the first things which we did ones we received our RC car. The mounting board is an essential part of the hardware design. This will provide support to all ECUs, sensor, and PCB. We used Acrylic glass Sheet for this purpose. We used MakerSpace (located in ground floor SJSU egineerring building) to cut the sheet in required shape and make holes for mounting. To mount sensor we order some readymade sensor stand from Amazon.

CAN Communication

<Talk about your message IDs or communication strategy, such as periodic transmission, MIA management etc.>

Hardware Design

<Show your CAN bus hardware design>

DBC File

Gitlab link to DBC file [9]

VERSION ""

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

BS_:

BU_: MASTER GEO APP MOTOR SENSOR DBG

BO_ 1 START_STOP: 1 APP
 SG_ BRIDGE_START_STOP : 0|8@1+ (1,0) [0|1] "cmd" MASTER
 
BO_ 2 MOTOR_COMMANDS: 1 MASTER
 SG_ MOTOR_COMMANDS_stsp : 0|8@1+ (1,0) [0|1] "" MOTOR

BO_ 36 APP_HEARTBEAT: 1 APP
 SG_ APP_HEARTBEAT_signal : 0|8@1+ (1,0) [0|255] "" MASTER
 
BO_ 37 GEO_HEARTBEAT: 1 GEO
 SG_ GEO_HEARTBEAT_signal : 0|8@1+ (1,0) [0|255] "" MASTER
 
BO_ 38 MOTOR_HEARTBEAT: 1 MOTOR
 SG_ MOTOR_HEARTBEAT_cmd : 0|8@1+ (1,0) [0|0] "" MASTER

BO_ 17 MASTER_SPEED_STEER_VAL: 3 MASTER
 SG_ MASTER_SPEED_STEER_VAL_speed : 0|8@1+ (0.1,0) [0.0|2.0] "m/s" MOTOR
 SG_ MASTER_SPEED_STEER_VAL_steer : 8|8@1+ (0.1,0) [10.0|20.0] "%dc" MOTOR
 SG_ MASTER_SPEED_STEER_VAL_dir : 16|8@1+ (1,0) [0|2] "" MOTOR
 
BO_ 108 BLUETOOTH_LAT_LONG: 8 APP
 SG_ GPS_Latitude : 0|31@1+ (0.000001,-90.000000) [-90|90] "degrees" GEO,MASTER
 SG_ GPS_Longitude : 32|32@1+ (0.000001,-180.000000) [-180|180] "degrees" GEO,MASTER
 
BO_ 39 ULTRA_CMD: 5 SENSOR
 SG_ ULTRA_CMD_Front_Left : 0|9@1+ (1,0) [2|400] "" MASTER,APP
 SG_ ULTRA_CMD_Front_Center : 9|9@1+ (1,0) [2|400] "" MASTER,APP
 SG_ ULTRA_CMD_Front_Right : 18|9@1+ (1,0) [2|400] "" MASTER,APP
 SG_ ULTRA_CMD_Back_Center : 27|9@1+ (1,0) [2|400] "" MASTER,APP
 

BO_ 195 GEO_NAV_DATA: 6 GEO
 SG_ GEO_TELECOMPASS_compass : 0|13@1+ (0.1,0) [0|365.0] "" MASTER,APP
 SG_ GEO_TELECOMPASS_bearing_angle : 13|12@1+ (0.1,0) [0|360.0] "" MASTER,APP
 SG_ GEO_TELECOMPASS_distance : 25|12@1+ (0.1,0) [0|0] "" MASTER,APP
 SG_ GEO_TELECOMPASS_destination_reached : 37|1@1+ (1,0) [0|1] "" MASTER,APP

BO_ 214 GEO_CURRENT_COORD: 8 GEO
 SG_ GEO_CURRENT_COORD_LAT : 0|32@1+ (0.000001,0) [36.000000|38.000000] "degrees" MASTER,APP
 SG_ GEO_CURRENT_COORD_LONG : 32|32@1+ (0.000001,-123) [-123.000000|-120.000000] "degrees" MASTER,APP

BO_ 517 MOTOR_SPEED_STEER_DBG: 3 MOTOR
 SG_ DBG_STEER_VAL_speed : 0|8@1+ (0.1,0) [13.5|16.5] "%dc" MASTER,DBG
 SG_ DBG_SPEED_STEER_VAL_steer : 8|8@1+ (0.1,0) [10.0|20.0] "%dc" MASTER,DBG
 SG_ DBG_SPEED_STEER_VAL_dir : 16|8@1+ (1,0) [0|1] "" MASTER,DBG

BO_ 505 GEO_DEBUG_CMPS_CALIB_STATUS: 1 GEO
 SG_ GEO_DEBUG_CMPS_CALIB_STATUS_System : 0|2@1+ (1,0) [0|3] "" 
 SG_ GEO_DEBUG_CMPS_CALIB_STATUS_Magneto : 2|2@1+ (1,0) [0|3] "" 
 SG_ GEO_DEBUG_CMPS_CALIB_STATUS_Accelero : 4|2@1+ (1,0) [0|3] "" 
 SG_ GEO_DEBUG_CMPS_CALIB_STATUS_Gyro : 6|2@1+ (1,0) [0|3] "" 

BO_ 508 GEO_DEBUG_DEST_COORD: 8 GEO
 SG_ GEO_DEBUG_DEST_COORD_Latitude : 0|31@1+ (0.000001,-90.000000) [-90|90] "degrees" 
 SG_ GEO_DEBUG_DEST_COORD_Longitude : 32|32@1+ (0.000001,-180.000000) [-180|180] "degrees"

CM_ BU_ DRIVER "The driver controller driving the car";
CM_ BU_ MOTOR "The motor controller of the car";
CM_ BU_ SENSOR "The sensor controller of the car";
CM_ BO_ 100 "Sync message used to synchronize the controllers";

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

BA_DEF_DEF_ "BusType" "CAN";
BA_DEF_DEF_ "FieldType" "";
BA_DEF_DEF_ "GenMsgCycleTime" 0;

BA_ "GenMsgCycleTime" BO_ 100 1000;
BA_ "GenMsgCycleTime" BO_ 500 100;
BA_ "GenMsgCycleTime" BO_ 101 100;
BA_ "GenMsgCycleTime" BO_ 400 100;
BA_ "GenMsgCycleTime" BO_ 200 100;
BA_ "FieldType" SG_ 100 DRIVER_HEARTBEAT_cmd "DRIVER_HEARTBEAT_cmd";
BA_ "FieldType" SG_ 500 IO_DEBUG_test_enum "IO_DEBUG_test_enum";


VAL_ 100 DRIVER_HEARTBEAT_cmd 2 "DRIVER_HEARTBEAT_cmd_REBOOT" 1 "DRIVER_HEARTBEAT_cmd_SYNC" 0 "DRIVER_HEARTBEAT_cmd_NOOP" ;
VAL_ 500 IO_DEBUG_test_enum 2 "IO_DEBUG_test2_enum_two" 1 "IO_DEBUG_test2_enum_one" ;

---

Sensor ECU

Group Member

• Rishabh Sheth
  

Sensor Selection

HC_SR04

Sonar_LV

Selecting the correct sensor for applicating is very important. For this project, the sensor should be able to responsive, accurate, able to work in the outdoor environment and it should provide long-range obstetrical detection. Though there are lots of option available for distance, we can divide them into three main categories 1) Lidar 2) Ultrasonic and 3) IR sensor. We choose to go with the ultrasonic sensor due to it is proven and easy to implement compared to Lidar and IR sensor, moreover, it is cheaper than both other option. We specifically selected SparkFun Ultrasonic Sensor - HC-SR04 to measure the distance from the back, left and right of the robot while we used MaxBotix Inc. Ultrasonic Distance Sensor MB1240-000 XL-MaxSonar-EZ4 as the center sensor. MaxSonar-EZ4 is able to detect obstetrical in 700cm range while HC-SR04 can detect obstetrical in the 300-400cm range. MaxSonar-EZ4 uses more narrow beam and more accurate than HC-SR04, though it is five times costlier than HC-SR04.

Design & Implementation

Ultrasonic Sensor calculation

Hardware Design

We ordered the HC-SR04 sensor's mounting bracket from Amazon. We printed 3D mounting bracket for MaxSonar-EZ4 sensor from SCE lab.

The HC-SR04 Ultrasonic Module has 4 pins, Ground, VCC, Trig and Echo. The Ground and the VCC pins of the module needs to be connected to the Ground and the 5 volts pins on the Board respectively and the trig and echo pins to any I/O pin on the SJOne Board. In order to generate the ultrasound, you need to set the Trig on a High State for 10 µs. That will send out an 8 cycle sonic burst which will travel at the speed sound and it will be received in the Echo pin. The Echo pin will output the time in microseconds the sound wave traveled.

For example, if the object is 10 cm away from the sensor, and the speed of the sound is 340 m/s or 0.034 cm/µs the sound wave will need to travel about 294 u seconds. But what we will get from the Echo pin will be double that number because the sound wave needs to travel forward and bounce backward. So in order to get the distance in cm we need to multiply the received travel time value from the echo pin by 0.034 and divide it by 2.

Software Design

We designed APIs in generalize manner and tried to avoid hard-coding any pin configuration in API itself. To make API 100% testable we used dependency injection concept. All sensors we initialize before stating periodic task. We used the 10Hz periodic task to update sensor value.

In beganing, using periodic take do any work was a mandatory/ requirement of the project. Though the way in which sensor works it takes more than or almost 100ms so we ran into task overrun issue. This we overcome by just measuring only any two sensor value in a single iteration. This helped us to reduce interference and also it made the code more robust. Though this logic reduced the speed at which sensor update its value.

Instead of using inbuilt timer interrupt or polling GPIO we used the fixed delay to get a response from echo pin, which made our code more deterministic.

Algorithm

Init Sensor API

Update Sensor API

Update All Sensors

Motor Controller

Group Members

• Tahir Latif Rawn
  
• Kriti Hedau
  

Design & Implementation

Hardware Design

Motor Module Schematic

SJOne Pin Connections

Pin Number	Pin Function
P0.0	CAN RX
P0.1	CAN TX
P2.0	Servo Motor
P2.1	Electronic Speed Controller (ESC)
P2.5	RPM Sensor

Hardware Specifications

ESC and DC Motor

ESC and DC Motor

The Traxass Slash 4x4 has XL-5 Electronic Speed Controller (ESC) and Titan 12T DC Motor installed in it. The ESC is powered by LiPo Battery which further controls the DC motor. The ESC comes with the feature of calibrating the DC motor using the EZ set button that is present on ESC. It comes with three modes

• Sport mode (100% Forward, 100% Brakes, 100% Reverse)
• Training mode (100% Forward, 100% Brakes, No Reverse)
• Racing mode (50% Forward, 100% Brakes, 50% Reverse)

For our project we used Sport mode because we needed full capability of the motor for uphills and rough terrains. Also we used our ESC in Low-Voltage Detection activated mode. In order to know more about ESC profiles, Battery modes and how to calibrate them, refer to Traxxas official link here [10].

DC Motor Pin Connection

Wires on (ESC)	Description	Wire Color Code
(+)ve	Positive Terminal	RED
(-)ve	Negative terminal	BLACK

ESC Pin Connection

Wires on (ESC)	Description	Wire Color Code
(+)ve	Connects to (+)ve of DC Motor	RED
(-)ve	Connects to (-)ve of DC Motor	BLACK
(+)ve	Connects to (+)ve of Battery	RED
(-)ve	Connects to (-)ve of Battery	BLACK
P2.0 (PWM1)	PWM Signal From SJOne	WHITE
VCC	6 Volts (OUTPUT)	RED
GND	Ground	BLACK

Servo Motor

Traxxas Servo Motor

Servo Motor is responsible for steering the car. Traxxas Slash 4x4 has Servo Motor 2075 pre-installed in it. It controls the front two tires of the car.

Servo Motor Pin Connection

Pin No. (SJOne Board)	Function	Wire Color Code
P2.1 (PWM2)	PWM Signal	WHITE
VCC	5V (INPUT)	RED
GND	Ground	BLACK

RPM Sensor

Traxxas RPM Sensor

RPM sensor is used to calculate speed of the car. A magnet is placed inside the spur gear with the help of magnet holder and every time a tire completes one rotation, RPM sensor detects a pulse. RPM sensor it self is placed in the gear cover. In order get the RPM Sensor working, following Telemetry items from Traxxas are required

• Traxxas RPM Sensor 6522
• Traxxas Magnet Holder 6538
• Traxxas Gear Cover 6537

To install these, there is very detailed step by step tutorial by Steve Jones (Cstoneav) on Youtube which can be found here [11]

RPM Sensor Pin Connection

Pin No. (SJOne Board)	Description	Wire Color Code
P2.5 (PWM6)	GPIO (INPUT)	WHITE
VCC	5V (INPUT)	RED
GND	Ground	BLACK

Software Design

For Motor Controller module, we made a singleton class for it. Some groups from our batch and from previous batches faced an issue that PWM object was going out of scope and they weren't able to get it run. We adapted this implementation from start, learning from experiences of our seniors of this course and never faced any issue regarding this. This class would only have one object, which initializes PWM objects for both Servo and DC in it's constructor.

In Periodic Init function, CAN1 is initialized at baudrate 100bps and TX/RX queues of size 10. In same function, to detect RPM rotation, an interrupt is enabled at port 2.5 at rising edge. In 1Hz Task, we check is bus is off, then we just reset it if it's off. Similarly, in 10Hz Task, we are detecting the speed of the car and driving the car. Then in 100Hz Task, we are sending heartbeat to the Master along with actual speed and debug messages on CAN. In same task we are receiving the values of direction, speed and steer from the Master on CAN and storing them in our global variables.

ESC and DC Motor

Servo Motor

---

Geographical Controller

Group Members

• Nandini Shankar
  
• Harmeen Joshi
  

Hardware Design:

Module Interface:

The GEO module primarily consists of two independent hardware modules: the GPS module and the compass module. The GPS module provides the current location of the car as it moves and the compass module provides the heading angle of the car with respect to true north. For the GPS module, we are using Adafruit's "Ultimate GPS Breakout V3" and for the compass module, we are using "CMPS14" module from Robotshop. CMPS14 module uses I2C interface to connect with the SJ-One board whereas, the GPS module is interfaced to SJ-One using UART.

Module Selection:

Selecting the appropriate module for both the compass and the GPS sensing were difficult decisions. We initially ordered "GPS - Readytosky Ublox NEO-M8N GPS Module" from Amazon as it came with a stand and an inbuilt compass module. This would have been cheaper as we would save money on the compass module. However, we later found out that the inbuilt compass values were not reliable enough and the GPS in this module was not original Ublox. Original Ublox GPS has an inbuilt flash memory to update its firmware for GPS calibration. We would thus have to rely on the factory calibration for the GPS. After considering all this, we decided to move to better modules as navigation was key for our project's success.

Compass modules are very sensitive to magnetic interference. We selected CMPS14 module as our compass as it has commands to dynamically check the calibration status of the module at runtime. We mapped this calibration status value to the 7-segment display on the SJ-one board which proved to be very useful in detecting magnetic interference across the campus and take decisions accordingly. Note however that CMPS14 does not return the current gyro calibration status. This is a bug which is mentioned in its data sheet. For the GPS module, we went with Adafruit's Ultimate GPS breakout module as it is known for its reliable GPS values.

CMPS14 Commands:

CMPS14 Start Calibration Process

To start the compass calibration, write the following to the command register 0x98, 0x95, 0x99 with a 20 millisecond delay after each byte. You can then send the setup byte to the command register. It takes the form:

Switch 1 dedicated for this purpose.

CMPS14 End Calibration Process

To end the calibration and store the updated calibration profile in CMPS14, write the following byte sequence to the command register with a 20 millisecond delay after each of the three bytes: 0xF0, 0xF5, 0xF6. Switch 4 dedicated for this purpose.

CMPS14 Erase Calibration Profile

To erase the stored calibration profile in CMPS14, write the following byte sequence to the command regiester with a 20 millisecond delay: 0xE0, 0xE5, 0xE2. Switch 3 dedicated for this purpose.

Software Design

<List the code modules that are being called periodically.>

Technical Challenges and Solutions

1. Calibrating Compass Module

   The compass module was not giving stable values on default calibration.
   
   The compass north changed every time the module powered off.
   
   The compass value would change after a full 360-degree rotation.
   
   The compass value moved up on tilting the module.

Solution:

   Step 1: Keep the compass stable on the ground to calibrate the gyro sensor.
   
   Step 2: Now, randomly move the module to calibrate the magnetometer.
   
   Step 3: After this, tilt the compass module in all directions and slowly move the module 360-degrees clockwise and anti-clockwise
           to calibrate the accelerometer.
   
   Make sure the calibration status of the respective in-built sensor reaches the maximum value of 3 on each of the above steps.
   
   Note: Compass is best calibrated in a non-magnetic environment. To check the magnetism in any area, use a mechanical (magnetic)compass.
   
   Note: There are underground electrical lines spread throughout the university which cause magnetic interference in the compass module.
         We found 10th street parking, 6th floor to be a good spot for testing and calibrating compass and GPS module.

2. Compass Calibration Unreliable

   After calibrating the compass, the calibration status was changing at runtime due to magnetic interference from the ground and shaking of the car.

Solution:

   Mapped system calibration status to on-board 7-segment display to keep track of the compass calibration at run-time and provided dedicated switches
   to start calibration, end calibration and erase calibration profile. This allowed us to perform instant re-calibration of the compass
   if the calibration is affected.
   
   Also provided dedicated switch to add offset to the compass value.
   This enabled us to set true North according to the mechanical compass in high magnetic interference areas.

3. Magnetic Interference from Motor

   Unlike interference from the ground and underground electrical lines, interference from car's DC motor was causing the compass value to
   
   increment constantly even when the car was not moving. This interference increased as the car speed increased.

Solution:

   To avoid this interference, we magnetically shielded the car's DC motor. To achieve this, we simply covered the motor with aluminum foil.
   Aluminum is magnetic and absorbs magnetism. This significantly reduced the magnetic interference to the compass from the motor.
   
   Note: There is no known material that blocks magnetic fields without itself being attracted to the magnetic force. Magnetic fields can only be redirected,
   not created or removed. The magnetic field cannot be completely blocked. Magnetic shielding can be done by any material which absorbs magnetism.
   
   Note: Shielding the compass module would block the earth's magnetic field from reaching it which is why we cannot cover the compass module with foil.

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Communication Bridge Controller

Group Members

• Swanand Sapre
  
• Aquib Mulani
  

The user communicates with the car through the Communication Bridge Controller. This module consists of the LPC1758 communicating with the Android application on the phone via Bluetooth. The user selects the final destination on the google map to which the car should navigate, through an android application. LCD is used to display the recorded values of the ultrasonic sensors, the current latitude, and longitude values from GPS, bearing and heading angle from the compass for the car. Along with that, these values can be seen on Android application as well.

HC-05

connection diagram

Hardware Design

Bluetooth

The HC-05 Bluetooth module was used to communicate the Android application in the Android phone with the car. This module is based on the Cambridge Silicon Radio BC417 2.4 GHz Bluetooth Radio chip. This is a complex chip which uses an external 8 Mbit flash memory. It includes the Radio and Memory chips, 26 MHz crystal, antenna, and RF matching network. The right section of the Bluetooth Board has connection pins for power and signals as well as a 5V to 3.3V Regulator, LED, and level shifting. The Bluetooth from mobile phone communicates with the microcontroller through the Bluetooth module interfaced to it dedicated to receiving the messages from the phone, parse those messages and convert them into an appropriate data type that was transmitted to the expected receiver through the CAN Bus.

• HC-05 PinOut :

• • EN: In case brought HIGH before power is applied, forces AT Command Setup Mode
  • VCC: +3.3V Power
  • GND: Ground
  • TXD: Serial Transmit pin connected to RXD2 of SJOne board
  • RXD: Serial Receive pin connected to TXD2 of SJOne board
  • STATE: States if connected or not

• LED Blinking signals:
  • if flashing RED fast: ready to pair
  • if flashing RED slow: paired and connected

Liquid Crystal Display

A 20x4 LCD(CM 204-1) with LCD driver by SJValley Engineering is used for accessing the LCD through UART. The driver and LCD are soldered directly to avoid any loose connection. To power up, LCD 5V supply is given from common 5V source which is coming from ESC (6V) and converting it to 5V using buck-boost. As soon as the LCD is powered on, it is initialized to a baud rate of 38500 and 0xF0 command is sent. After 0xF0 is sent, the data can be transmitted using UART. Before that two commands are sent to set brightness level and clear screen. If you are getting some junk values, make sure that the baud rate is set correctly and check the soldering.

Bluetooth

A special format for the strings received was used to make extracting of the important aspects such as start/stop command, latitude and longitude of the destination. Similarly, we also kept a specific format for the string that was to be transmitted to the mobile application which made data parsing and displaying in the android application easy . The specific formats that we chose are as shown below:

• Format for the string received from android application: ~start/stop@latitude!longitude#

 ~ denotes the start of the string and also the start of the start/stop variable
 @ denotes the start of latitude value
 ! denotes the start of longitude and the end of latitude values
 # denotes the end of the entire string
 example: ~1@37.337897!-121.885623# 

• Format for the string transmitted to android application: ~Sensor values@latitude!longitudeCcompass_value^bearing angle$distance#

 ~ denotes start of the string 
 @ denotes start of latitude
 ! denotes start of longitude
 C denotes start of the compass_values
 ^ denotes start of bearing angle
 $ denotes start of distance
 # denotes end of the string  
 example: ~L300R200F150B200@37.337897!-121.885623C140.12^310.87$26#

Keeping such dedicated formats made data parsing convenient and easy to convert and process the data further ahead.

Communication Process Flow Diagram

Liquid Crystal Display

On boot up, LCD is initialized at baud rate 38400 and 0xF0 is sent through UART. Then Brightness is set and the screen is clear. This is done only for the first time. After this Ultrasonic sensor values are displayed on LCD through UART and our screen is getting updated after every 1 second and this value will continue for a total of 3 seconds and then GPS coordinates and Compass values are shown similarly by clearing the screen and in this way, it goes on continuously until power off. By default, the cursor value is at first row and the first column, to jump to the next column we send the desired column and row through GOTO command. We implemented the LCD driver such that all this is handled in one function call.

LCD Flow Diagram

LCD Commands

Command	Description
$BLIGHT:100	To set brightness to 100(full)
$CLR_SCR	To clear screen
$GOTO:3:4	To move cursor to particular position (col:row)

Technical Challenges

• Connection between Application and Module is not stable. Over a medium-long range, the application gets disconnected with HC-05 module.

Solution: We used "Reconnect Button" on our Android application to re-establish Bluetooth socket connection instead of re-opening the application.

• When multiple cars are around and if they are using the same HC-05 module since the pairing password for the HC-05 module is same for everyone, the application ceased to connect to the Bluetooth due to interference from Bluetooth of other Android applications.

Solution: Change the password of the Bluetooth module using the AT commands using an Arduino. 

• Getting junk values when LCD is power ON and only 2 lines were displaying.

Solution: Soldering issue possibly or driver also, so better test it before soldering to get a clear idea. In our project, we change our LCD and the second one works well.

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Android Application

User Communicates with the car using Android application.We have three modes on application namely
1.Self-Drive Mode
2.Obstacle Detection Mode
3.Communication mode.

UI of Application

Technical Challenges

• Connection between Application and Module is not stable. Over a medium-long range, the application gets disconnected with HC-05 module.

Solution: We used "Reconnect Button" on our Android application to re-establish Bluetooth socket connection instead of re-opening the application.

References for Android Application

• Git Code
• Bluetooth
• Map Fragment

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Master Module

Group Member

• Kailash Chakravarty
  

Hardware Design

The Master controller only has the connections to the CAN bus apart from the power supply. Below diagram describes the connections.

Software Design

• The Master control unit is the heart of the Self-driving car as it takes all the critical decisions based on inputs it receives from the other control units like App, Sensor, Geo and drives outputs which are the Motor control Unit.
• The Master control unit mainly performs Navigation of the car to the selected destination and Obstacle avoidance as and when they come in the car's way.
• For navigation to the destination through numerous checkpoints, the bearing angle, heading angle and the distance to the destination is provided by the GEO control. The App control provides the start and stop commands.
• The Sensor control unit provides the ultrasonic sensor values of the 4 sensors regarding obstacle avoidance.
• The Master control unit algorithms - Navigation and Obstacle avoidance are run @25Hz. The detailed flowcharts are shown below.

Master control Algorithm

Obstacle avoidance Algorithm

Navigation Algorithm

Technical Challenges

Improper Unit Testing

Problem : It was tedious to tune the proximity thresholds for the 4 sensors for proper obstacle avoidance, because it involved changing them, build them, flash them and test again and again till we get fine tuned results. This was time and effort consuming.

Resolution : I placed a CAN debug message in the code to write directly into the threshold variables, via PCAN dongle and bussmaster whenever I want. So basically I change the thresholds anytime within seconds and immediately test.

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Conclusion

We were able to navigate our RC car from current destination of the car to the destination chosen through the android application successfully . The car was also able to avoid obstacles in its path throughout the journey to the marked destination.The project helped us gain a working knowledge of CAN bus and communication, interfacing various components such as motors, GPS, Bluetooth and ultrasonic sensors along with some knowledge regarding pulse width modulation (PWM), UART, I2C. This course and project also gave us a deep understanding of FreeRTOS, Android, Unit testing and Git. It taught us the important aspect of team work, coordination and surely taught us the importance of proper planning and hard work.Overall, it was a superb experience enriched with knowledge and hands on experience that molded us into better than we were before.

Project Video

Team Hotwheels Project Video

Advise for Future Students

• Do thorough research on all the sensors before ordering them. We had previously ordered some cheap sensors but had to replace them with good quality sensors.
• Achieving steady readings and calibration for compass is tricky, so start with the compass module as soon as possible. The navigation algorithm depends upon the compass module.
• Do not rely on compass applications while calibrating your compass, use a mechanical compass for calibration.
• For Android application design remember to close the mchat sockets and disable bluetooth adapter before exiting the application or changing the intent

Acknowledgement

We would like to thank our professr, Preetpal Kang for designing such an amazing course and including the project of self-navigating car in the coursework. He was always there to guide and push us to achieve our goal of implementing a self-navigating car successfully. We would also like to thank the ISA member,Pratap for providing his insights and feedback after demos and motivating us to do well. We would also like to thank all the members of the other teams who selflessly coordinated and helped us,forgetting all their differences when in need.

References

• Professor Preetpal Kangs lecture notes and slides of CMPE 243, Computer Engineering, San Jose State University
• HC-05 Datasheet
• CMPS14 Datasheet
• A Guide to Magnetic Shielding
• Traxxas - RC Car & Forum