S19: Hot Wheels

Self Driving Car

Project Title

Hot Wheels | Self Navigating RC car using CAN communication based on FreeRTOS.

Abstract

Embedded Systems take 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(bearing and 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

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	RC Car	Traxxas	1	$250.00
2	CAN Transceivers MCP2551-I/P	Microchip [2]	8	Free Samples
3	Graphics LCD module	1	From Preet
4	Bluetooth(HC-05)	1	HiLetgo	$9.00

Printed Circuit Board

PCB Schematics

PCB front side

PCB Back side

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 your DBC file [3]

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Sensor ECU

Sensor Selection

HC_SR04

Sonar_LV

Design & Implementation

Ultrasonic Sensor working

Ultrasonic Sensor calculation

Software Design

Algorithm

Init Sensor API

Update Sensor API

Update All Sensors

Motor Controller

Group Members

• Tahir Latif Rawn
  
• Kriti Hedau
  

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 [4].

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 [5]

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

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Geographical Controller

<Picture and link to Gitlab>

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:

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.>

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.

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 motors was causing the compass value to
   
   increment 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.
   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

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Communication Bridge Controller & LCD

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. The Android application also works as a display where it displays the recorded values of the ultrasonic sensors, the current latitude and longitude, the bearing angle, and the compass values for the car.

HC-05

connection diagram

The Hardware and the Software details are given below:

Hardware Design

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 communicated with the micro-controller through the Bluetooth module interfaced to it dedicated to receive the messages from the phone, parse those messages and convert them into 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

Software Design

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

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. 

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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.

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Master Module

<Picture and link to Gitlab>

Hardware Design

The Master controller only has the connections to the CAN bus apart from 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 is 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 destination is provided by the GEO control. The App control provides the start and stop command.
• 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

<Bullet points and discussion>

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
• Traxxas - RC Car & Forum