S20: Tesla Model RC
Contents
- 1 Tesla Model RC
- 2 Abstract
- 3 Schedule
- 4 Parts List & Cost
- 5 Printed Circuit Board
- 6 3D Printed Parts
- 7 CAN Communication
- 8 Bridge Sensor ECU
- 9 Motor ECU
- 10 Geographical ECU
- 11 Driver Controller & LCD
- 12 Mobile Application
- 13 Conclusion
Tesla Model RC
Abstract
Tesla Model RC is an electric, battery-powered, self-navigating RC car. The aim is to navigate to the destination set on the Android application by utilizing GPS navigation. The car combines the data received from multiple sensors to perceive its surroundings to avoid obstacles in its path.
Introduction
The project was divided into 5 modules:
- Bridge and Sensor Controller
- Motor Controller
- Geographical Controller
- Driver and LCD controller
- Android Application
Team Members & Responsibilities
- Salvatore Nicosia Gitlab
- Motor Controller
- Geographical Controller
- System Integration and Testing
- RC Car Design: 3D Printing
<Member picture>
- Nickolas Schiffer
- Motor Controller
- Geographical Controller
- Danny Nuch Gitlab
- Bridge Sensor Controller
<Member picture here>
- Ayesha Siddiqua
- Driver & LCD Controller
<Member picture here>
- Andrew Kwon
- Android Application
- Review Team
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Parts List & Cost
| Item# | Part Desciption | Vendor | Qty | Cost |
|---|---|---|---|---|
| 1 | RC Car 1/10 Scale | Redcat Racing [1] | 1 | $99.99 + Tax |
| 2 | CAN Transceivers TJA1050 | LIVISN [2] | 5 | $6.39 + Tax |
| 3 | GPS Module Built-in Compass | Readytosky [3] | 1 | $28.89 + Tax |
| 4 | HC-SR04 Ultrasonic Module | ELEGOO [4] | 5 | $9.98 + Tax |
| 5 | HC-020K Wheel Encoder Module | Hilitchi [5] | 1 | $9.99 + Tax |
| 6 | ESP8266 WiFi Module | DIYmall [6] | 1 | $6.55 + Tax |
| 7 | Extra 7.2V 5000mAh NiMH battery | Melasta [7] | 1 | $29.99 + Tax |
| 8 | Micro-USB to USB cable | Walmart [8] | 4 | $4.00 + Tax |
| 9 | EL-CP-004 120pcs Multicolored Dupont Wire | ELEGOO [9] | 1 pack | $6.98 + Tax |
| 10 | SJTwo Microcontroller | SCE at SJSU [10] | 4 | $40 |
| 11 | Black PLA Filament | Hatchbox [11] | 1 | $22.99 + Tax |
| 12 | 120 Ω Resistor | Excess Solutions | 2 | $0.30 |
| 13 | 1 MΩ Resistor | Excess Solutions | 1 | $0.15 |
| 13 | 100 kΩ Resistor | Excess Solutions | 1 | $0.15 |
| 14 | DB9 Female Connector Right Angle Mount | Excess Solutions | 1 | $0.30 |
| 15 | 2.54 Male Header Strip 36 Pin | Excess Solutions [12] | 1 | $0.36 |
| 16 | 5x7cm Prototype Board | uxcell [13] | 3 | $7.09 + Tax |
| 17 | 2.54mm JST-XHP 2 Pin Housing with 2.54mm JST XH Female Connector | QLOUNI [14] | 8 | |
| 18 | 12mm Waterproof Push Button Momentary On Off Switch | PP-NEST [15] | 1 | |
| 19 | #22 Gauge Wire | Elenco [16] | As needed | |
| 20 | LM2596 Buck Converter DC to DC | D-PLANET [17] | 1 | $5.95 + Tax |
| 21 | 11 in. x 14 in. x .093 in. Acrylic Sheet | The Home Depot [18] | 1 | $6.67 + Tax |
| 22 | 20x4 LCD Display Module | [19] | 1 | $ |
| 23 | 6-32 Brass Motherboard Standoffs | Hantof [20] | 36 | $14.58 + Tax |
| 24 | Metallic Aluminium Spray Paint | Walmart [21] | 1 | $3.96 + Tax |
| 25 | Metallic Dark Metal Spray Paint | Walmart [22] | 1 | $4.96 + Tax |
| 26 | Plastidip Black Spray Paint | Walmart [23] | 1 | $5.82 + Tax |
Printed Circuit Board
<Picture and information, including links to your PCB>
3D Printed Parts
Cybertruck 3D Model
This 3D model was modified and rescaled to fit the chassis of our car. Credit goes to the designer of the model in which can be found on thingiverse at this link.
Shell Supports
These supports were designed to allow the shell to sit in place on the chassis by using 6 small magnets for each of the four corners. 4 magnets are inserted in in each of these supports and 2 are attached in each corner to the plexiglass surface where the boards are mounted.
Ultrasonic Sensor Supports
The ultrasonic support 3D model was slightly resized to fit the HC-SR04 sensor. Credit goes to the designer of the model which can be found on thigiverse at this link.
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> High Level Hardware Diagram
DBC File
https://gitlab.com/tesla-model-rc/sjtwo-c/-/blob/dev/dbc/tesla_model_rc.dbc
Bridge Sensor ECU
https://gitlab.com/tesla-model-rc/sjtwo-c/-/tree/dev/projects/sensor
https://gitlab.com/tesla-model-rc/esp8266-coap-server
Hardware Design
| SJTwo Board | Module | Description | Protocol/Bus |
|---|---|---|---|
| P4.28 (TX3) | RX (ESP8266) | ESP8266 Rx data line | UART 3 |
| P4.29 (RX3) | TX (ESP8266) | ESP8266 Tx data line | UART 3 |
| P0.6 | Trigger (Ultrasonic) | Front sensor | |
| P2.0 | Echo (Ultrasonic) | Front sensor | |
| P0.7 | Trigger (Ultrasonic) | Rear sensor | |
| P2.1 | Echo (Ultrasonic) | Rear sensor | |
| P0.8 | Trigger (Ultrasonic) | Left sensor | |
| P2.2 | Echo (Ultrasonic) | Left sensor | |
| P0.9 | Trigger (Ultrasonic) | Right sensor | |
| P2.4 | Echo (Ultrasonic) | Right sensor | |
| P0.25 (ADC2) | Voltage reading (S) | Output of voltage divider | |
| P0.1 (SCL1) | CAN transceiver (Tx) | CAN transmit | CAN |
| P0.0 (SDA1) | CAN transceiver (Rx) | CAN receive | CAN |
| 5V (Ultrasonics) | Vcc | ||
| GND | GND | Ground |
Software Design
Bridge and Sensor Node
The Bridge and Sensor node interfaces with four ultrasonic sensors (front, back, left, and right) and the ESP8266 Wifi module for bridging connection with a mobile application to control the car and display ultrasonic ranging diagnostics.
Sensor Node and CAN Bus Periodics Handler module
The CAN bus handler has periodicially running functions specific to a task and is called in the Periodics module. Debug messages that may be enabled are sent at 1Hz. The handler of all incoming messages (including Wifi messages) is parsed in 10Hz, along with MIA management and the transmission of CAN messages. Unique to this node is the 100Hz functions that initiates and records Ultrasonic sensor rangings at this rate along with the Wifi character parser which fills the message buffer. This module wraps the Sensor Node module.
The Sensor Node module creates the sensing messages that are sent over the CAN bus. These messages include battery voltage level and all four ultrasonic ranging distances. Furthermore, the GPS longitude and latitude value and start/stop state changes parsed from Wifi transmissions are sent as well. This module handles MIA messages of the Driver node's heartbeat message. On not receiving the Driver node's heartbeat message, this module will not send messages over CAN bus and brighten LED0 indicating the node is not synchronized with the Driver node.
Wifi module
The Wifi module initializes UART channel 3 peripheral and the line buffer module. The line buffer module is used for parsing and handling Wifi messages transmitted over UART from the ESP8266. The Wifi line buffer has 128 bytes of allocated space and is filled at a rate of 100Hz from the UART queue. Then, at 10Hz the Wifi line buffer handler parses all lines found in the line buffer based upon the identifier found from a new-line delimiter sequence of messages. These messages are specified in the ESP8266 section and set variables received from the mobile application to messages over CAN bus. The Wifi module also sends all four ultrasonic ranging values to the ESP8266 over UART allowing the mobile application to query ultrasonic diagnostics.
Battery Tracking module
The Battery Tracking module is simply an ADC that receives the battery output as input. The ADC has a voltage reference of 3.3V and has a 12 bit resolution. Thus, the ADC conversion is 3.3V / 4095. The voltage divider set for the receiving battery voltage is a divider where R1 = 1M ohm and R2 = 100k ohm. Thus, the received ADC value along with the ADC conversion value and the voltage multiplier gives the current battery voltage and is set over the CAN bus.
Ultrasonics and GPIO Interrupts module
ultrasonic initialization
GPIO interrupts initialization
ultrasonic initiate ranging from setting trigger pin for 10 microseconds
Sample time until falling edge of interrupt on echo pin
time of flight calculation to inches
Average Buffer module
Ultrasonic smoothing by averaging
low pass filter of zeroed values from receiving ultrasonic values too quickly as soon as a trigger occurred from scattered reflection of other ultrasonics
ESP8266
Bridging between ESP8266 and mobile application is done through the creation of an access point on the ESP8266. Furthermore, the ESP8266 opens a server socket through CoAP allowing other CoAP clients to transmit or receive data from a created resource (/topics). The mobile application serves as the CoAP client and currently performs:
(GET) /heartbeat will receive string: "tmrc:heartbeat"
(GET) /getRadars will receive string: "aa,bb,cc,dd" where a is front radar, b is left radar, c is right radar, and d is back radar
(PUT) /setStatus will send string - either "$stop\n" or "$start\n"
(PUT) /setCoordinates will send coordinates as string - i.e. "#Sxxx.xxxxxx,Syyy.yyyyyy\n" where S is the sign and x is latitude and y is longitude
/getRadars resource will update through UART from a microcontroller. The string must follow the format: "^%02,%02,%02,%02" where '^' is the identifier for setting this resource. This length is also fixed where each radar data must have a width of no more than 2.
/setStatus resource has an identifier of '$', while /setCoordinates resource has an identifier of '#'. Both resources require appending a new line character at the end of string. This is essential for parsing strings on microcontroller side as the ESP8266 echoes received data over UART.
Project Setup
This project is built with ESP8266 RTOS SDK for programming the ESP8266. FreeRTOS, UART, Wifi with CoAP libraries are fully utilized in this project.
See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
Wifi Access Point module
ESP8266 opens an access point for other wireless devices to connect too. This access point follows adaptation of this example:
https://github.com/espressif/ESP8266_RTOS_SDK/tree/master/examples/wifi/getting_started/softAP.
UART Configuration module
UART is simply transmitted over UART0 TX/RX pins. This example is integrated.
CoAP Server module
CoAP server would startup a daemon task, create resources and receive data from CoAP clients and transmit data to CoAP clients. This server follows adaptation of a couple examples:
https://github.com/espressif/ESP8266_RTOS_SDK/tree/master/examples/protocols/coap_server
https://github.com/obgm/libcoap-minimal/blob/master/server.cc
https://github.com/obgm/libcoap/blob/develop/examples/coap-server.c
The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained networks in the Internet of Things.
The protocol is designed for machine-to-machine (M2M) applications such as smart energy and building automation.
Please refer to RFC7252 for more details.
Technical Challenges
Ultrasonic Sensors Smoothing and Filtering
The average buffer module had to be implemented as ultrasonics ranging values from a fixed distance had varying values. The average buffer module smoothed out ranging values by using an average sliding window of the last 10 ranges as the value sent over the CAN bus. In parallel to this average buffer, a low-pass filter is implemented where a value of zero would be replaced by the average of the sliding window buffer. This further smoothed the ultrasonic ranges by removing values that occurred upon reception of a radar wave right after a range is initiated through the trigger pin.
ESP8266 Flashing
When flashing the ESP8266 be extremely observant about which mode the SPI should be configured. Different vendors will have SPI flash modes.
Motor ECU
https://gitlab.com/tesla-model-rc/sjtwo-c/-/tree/dev/projects/motor_node
Hardware Design
| SJTwo Board | Module | Description | Protocol/Bus |
|---|---|---|---|
| P2.0 (PWM1) | Motor (S) | Control signal for motor speed | |
| P2.4 (PWM5) | Servo (S) | Control signal for servo steering | |
| P0.22 (PWM1) | Wheel encoder (Out) | Output signal of wheel encoder | |
| P0.1 (SCL1) | CAN transceiver (Tx) | CAN transmit | CAN |
| P0.0 (SDA1) | CAN transceiver (Rx) | CAN receive | CAN |
| 6V Motor and Servo | Vcc | ||
| 5V Wheel encoder | Vcc | ||
| GND | GND | Ground |
Wheel Encoder
Software Design
<List the code modules that are being called periodically.>
Technical Challenges
< List of problems and their detailed resolutions>
Geographical ECU
https://gitlab.com/tesla-model-rc/sjtwo-c/-/tree/dev/projects/geo_node
Hardware Design
The geographical controller is interfaced to the readytosky GPS with built-in compass and a CAN transceiver as shown in figure #. The readytosky module uses the Ublox NEO-M8N GPS which provides great accuracy and customization. In addition, it uses the 3-Axis compass HMC5883L magnetometer which provides an 1 to 2 degrees compass heading accuracy. The Ublox GPS module communicates with SJTwo board via UART whereas the HMC5883L communicates with the SJTwo board via I2C. The CAN transceiver is interfaced to the CAN Bus and allows reception and sending of CAN messages via the CAN pins on the SJTwo board.
| SJTwo Board | GPS/Compass Module | Description | Protocol/Bus |
|---|---|---|---|
| P4.28 (TX3) | RX (Yellow Wire) | Ublox M8N Rx data line | UART 3 |
| P4.29 (RX3) | TX (Green Wire) | Ublox M8N Tx data line | UART 3 |
| P0.10 (SDA2) | SDA (White wire) | HCM5883L SDA | I2C 2 |
| P0.10 (SCL2) | SCL (Orange wire) | HCM5883L SCL | I2C 2 |
| P0.1 (SCL1) | CAN transceiver (Tx) | CAN transmit | CAN |
| P0.0 (SDA1) | CAN transceiver (Rx) | CAN receive | CAN |
| Vcc 3.3V | Vcc (Red wire) | Vcc | |
| GND | GND (Black wire) | Ground |
Software Design
Overview
The geographical node calls periodically the following code modules:
- gps.c
- compass.c
- checkpoint.c
- geological.c
- can_bus_message_handler.c
These modules, calculate compass heading degree, bearing, parse GPS coordinates, calculate the checkpoints the RC car has to go trough when navigating to a destination, send distance to destination to driver node, and handle messages received on the CAN bus.
- The period_callbacks__initialize() function calls the following functions:
- can_bus_initializer__init(): initializes the CAN bus to handle MIA and messages.
- geological__init(): initializes the GPS, compass, and checkpoint algorithm.
- The period_callbacks__1Hz() function calls the following function:
- can_bus_initializer__handle_bus_off()
- The period_callbacks__10Hz() function calls the following functions:
- can_bus_message_handler__manage_mia_10Hz() to manage MIA signals.
- can_bus_meesage_handler__handle_all_incoming_messages_10Hz() to handle messages on the CAN bus (e.g. destination coordinates from Bridge sensor node).
GPS
Initialization
In the initialization process of the GPS, the line buffer module is configured to parse the GPS messages, the GPIOs P4.28(Tx) and P4.29(Rx) are configured, UART interrupt queues enabled, and the UART is configured at a baudrate of 9600.
Configuration
In the gps__run_once_10Hz() the GPS is initially configured once to disable all NMEA messages except GNGGA which is message chosen to parse the coordinates and GPS lock.
Parsing NMEA GNGGA messages
The GPS module constantly transmits NMEA GNGGA messages over UART to the SJTwo MCU. These messages which come in the form of a string are stored character by character in the line buffer until a new line character which indicates the end of string. The stored string is then extracted from the line buffer and the checksum is verified to ensure that the message is not corrupted. The extracted line is then tokenized to parse the latitude, latitude direction, longitude, longitude direction, and fix quality. South and West directions are also properly handle to make the latitude and longitude negative values.
GPS lock
The GPS lock is a function in the gps.c module that has the job to set a bool flag and blink an LED when the fix quality is either 1 or 2 in the GNGGA message. When the fix quality is one of those values it means the GPS has acquired a good connection to the satellites and the data received is valid. The LED blinking functionality was used for debugging purposes indicating the GPS has a lock. Whereas the bool flag was used as a condition to calculate calculate the bearing and checkpoints only when the GPS had a lock and thus the current coordinates were valid.
Compass
Initialization
The compass initialization configures the HMC5883L magnetometer registers over I2C bus to default settings using a gain of 1090 and single mode.
Heading degree computation
The compass heading degree is computed by using the tilt compensation algorithm and pitch and roll values calculated from the SJTwo accelerometer. The tilt compensation algorithm ensures that the values of the compass heading are precise within an error 1 to 2 degrees when the compass is tilted in all directions. Shown below are the formulas used to compute the heading degree referenced from this link.
Pitch and Roll:
pitch = asin(-accelerometer_x_axis)
roll = asin(accelerometer_y_axis / cos(pitch)
Tilt compensated magnetic sensor values for x and y:
Mx_c = (Mx - offset_x_axis) * cos(pitch) + Mz * sin(pitch)
My_c = (Mx - offset_x_axis) * sin(roll) * sin(pitch) + (My - offset_y) * cos(roll) - Mz * sin(roll) cos(pitch)
- where:
- Mx_c = Magnetometer x-axis tilt compensated
- My_c = Magnetometer y-axis tilt compensated
- Mx = Magnetometer x-axis value
- My = Magnetometer y-axis value
- Mz = Magnetometer z-axis value
The offset values for x and y are calculated during calibration to reduce soft-iron and hard-iron distortions. Soft-iron distortions are generally caused by nearby metals such nickel and iron in which distorts the existing magnetic field of the compass depending in which direction the field acts. Hard-iron distortions are produced by objects that generate a magnetic field such as the motor of the RC car causing a permanent bias in the compass sensor if not corrected.
To calculate the scale factors for x and y for soft-iron distortion the following equations were used:
a = (max_y - min_y) / (max_x - min_x)
b = (max_x - min_x) / (max_y - min_y)
x_scale = a > 1.0 ? a : 1.0;
y_scale = b > 1.0 ? b : 1.0;
To calculate the offset for x and y for hard-iron distortion the following equations were used:
offset_x = ((max_x + min_x) / 2.0) * x_scale
offset_y = ((max_y + min_y) / 2.0) * y_scale
Heading angle
heading = azimuth = atan2(magnetometer_x_axis / magnetomer_y_axis) - π + 0.23
To the heading is also added the declination angle which is based on location and in our case it is 0.23. This heading is calculated in radians since atan2 returns a value between -π and +π. Therefore, before converting the heading into degrees the value needs to be normalized to put it in the range from 0 to 360 degrees.
Geological.c module
Initialization
The geological.c module initializes the gps and compass with configurations explained before.
Run once at 10Hz
Every 10Hz the geological_run_once() function periodically calls the gps module, gets the parsed coordinates, gets the compass heading degree, sets the current and destination coordinates, send the calculated bearing degree to the driver node, and runs the checkpoint algorithm.
Bearing Angle computation
The bearing which is the angle towards our desired destination is computed using the formulas below referenced at this link.
X = cos θb * sin ∆L Y = cos θa * sin θb – sin θa * cos θb * cos ∆L
β = atan2(X,Y)
- where:
- θa = current latitude
- θb = destination latitude
- ∆L = destination longitude - current longitude
- β = heading degree in radians
The bearing is also calculated in radians since atan2 returns a value between -π and +π. Therefore, before converting the heading into degrees the value needs to be normalized to put it in the range from 0 to 360 degrees. The calculated bearing is then sent to the driver node which use the compass heading degree and the bearing to align the car toward the target destination.
Checkpoints Algorithm
The checkpoint algorithm depicted below uses a simple algorithm in which chooses the next point to navigate to if the checkpoint is the closest to the car while at the same time the closest to the destination. For the testing of our car navigation system, we choose the top floor of the north garage at San Jose State University as it provides a great open space and best signal for the GPS. In the figure shown below, five checkpoints were chosen in which the car can navigate to depending on where the destination is set to. Having fewer points rather then having too many reduces the amount of checkpoints the car has to move to and allows to reach the destination quicker while at the same time avoid areas such as the ramp in which the car should not go to.
Technical Challenges
GPS (Ublox Neo-M8N)
- Problem:The enabled 2-stop bits in uart.c were causing communication problems between the SJTwo MCU and the Ublox M8N GPS module.
- Solution:To solve the 2 stop bits configuration was disabled in uart.c in the uart__init() function as shown in figure # and issue was solved.
- Problem:GPS module did not retain configurations and were lost after being powered off for many hours going back back to default settings. This problem was crucial since it was causing the SJ2 to parse the latitude and longitude incorrectly from other messages other than NMEA GNGGA.
- Solution: To solve this configuration problem u-center which is an interface for the GPS Ublox module was used to read which strings the program sends over UART to configure the GPS module. This solution was implemented in the gps.c module creating a function called gps__private_configure_for_nmea_gngga() in which holds a char array with the hex representation of the configurations needed to disable all of the NMEA messages except GNGGA. This function then sends this configuration values back to the GPS module over UART and the GPS module responds back with an ACK message (8μ.......) from every configuration message meaning that the configurations were successfully applied as shown in figure #. The function gps__private_configure_for_nmea_gngga() could not be called in the periodic_callbacks__initialize() function has it required more time to properly configure the GPS. As a solution, a bool flag indicating that the configuration was done was used along with calling gps__private_configure_for_nmea_gngga() in the gps_run_once_10Hz() to allow it properly configure the GPS module.
Compass (HMC5883L 3-Axis Magnetometer)
- Problem:SJTwo MCU could not detect the slave address of the HMC5883L magnetometer on the I2C Bus 2.
- Solution:Upon reading the HMC5883L datasheet it was mentioned that it works at 400KHz. However, this was not the case as changing the speed in peripherals__init.c module from 400KHz to 100KHz solved the issue and the SJTwo board successfully detected the HMC5883L 3-Axis Magnetometer. In Figure # is shown the function a long with change it was made. In addition, changing the speed did not affect the other modules using I2C Bus 2.
- Problem:Compass heading degree true north was off by about 90 degree when compared to the compass of smart phone. This problem was due the fact the compass had to be completely flat to show proper values. In addition, the default calibration seemed also to be a problem in providing an accurate heading degree a long with hard iron and soft iron interferences.
- Solution:To solve these problems a function to calibrate the compass was implemented in which calculates offset and scale correcting for hard iron and soft iron interferences respectively. The process to calibrate consisted in turning the compass at different angles to collect as many sample points as possible and store offsets values of x and y axes in const variables which were then used in the equations to compute the heading degree. Although this corrected some of the imprecision problems, not having the compass completely flat still provided results that were not precise. To solve this issue the compass was compensated for tilt by using the built-in accelerometer of the SJTwo board which provides roll and pitch and the tilt compensation algorithm described at this link. The challenge in making this work properly was that the axes of the magnetometer and the axes of the accelerometer need to be perfectly aligned. However, after finalizing the place of the compass on the RC car it was fairly easy to align the axes. The tilt compensation system for the compass is shown in figure #. After including the tilt compensation algorithm the compass heading degree was off by 1-2 degrees when tilted in all directions drastically improving the accuracy from non-compensated in which the heading was off by 60-90 degrees when the compass was not held flat.
- Problem:Compass heading degree was decreasing when turning clock-wise rather then increasing.
- Solution:To solve this problem, the Azimuth rather then being calculated as atan2(Y / X) was calculated as atan2(X / Y). This fixed the Azimuth orientation however, North degree was shown as 180 degrees which was incorrect. Finally to compensate for this, π was subtracted from the Azimuth = atan2(X / Y) - π to show the correct decimal degree for true North which is 0 degrees.
Driver Controller & LCD
https://gitlab.com/tesla-model-rc/sjtwo-c/-/tree/dev/projects/driver_controller_node
Hardware Design
| SJTwo Board | LCD Module | Description | Protocol/Bus |
|---|---|---|---|
| P4.28 (TX3) | RX | LCD Rx data line | UART 3 |
| P4.29 (RX3) | TX | LCD Tx data line | UART 3 |
| P0.1 (SCL1) | CAN transceiver (Tx) | CAN transmit | CAN |
| P0.0 (SDA1) | CAN transceiver (Rx) | CAN receive | CAN |
| Vcc 3.3V | Vcc (Red wire) | Vcc | |
| GND | GND (Black wire) | Ground |
Software Design
<List the code modules that are being called periodically.>
Technical Challenges
< List of problems and their detailed resolutions>
Mobile Application
https://gitlab.com/tesla-model-rc/mobile-app-CoAP-client
<Insert screenshots of app here>
Application Communication
Our App communicates with the Bridge/Sensor node through WiFi using the Constrained Application Protocol (CoAP). CoAP protocol has the benefits of transmitting smaller message packets since its underlying transport is UDP. CoAP works extremely well for point to point communication and doesn't require the full feature sets from TCP transportation.
Because our App was written in Java, requirements were set such that the CoAP library to be imported must also be written in Java to be compatible with the App. After days of research we found several Java candidates of this protocol. Californium is a library that is constantly being updated and has the most documentation and most active community. WS4D was also a strong candidate because of its simple interface design. We chose WS4D over Californium because WS4D provides an interface for a CoAP Client that gave us the most flexibility on how we connect to end points and send/receive data.
Pros and Cons
The ESP8266 WiFi module was able to communicate with the App over very long distances. We were able to send POST messages from approximately 50 meters away. However power consumption on the App from the frequent message requests were draining the battery on the phone faster than normal. Bluetooth and Bluetooth LE has the advantage of being able to drain less power and run for longer periods of time on the App as well as the RC car.
The length of the payload, or response to a GET request, has a maximum length of 16 bits. Any string data before being decoded, must fit this requirement. If a message fails to reach its destined end point, CoAP protocol will attempt to resend the message three times, before sending a failure response. One problem that arose was sending GET requests without verifying connection to the ESP8266 server. The buffer of unsent messages overflowed causing the Bridge node to receive unintentional error messages.
One cool feature was that up to 3 phones could connect to the car at the same time and each send "start","stop", or send GPS coordinates.
Application Design
Three fragments were created. Main Fragment, Sensor Fragment, and Map Fragment. The Sensor and Map fragment were embedded inside the Main Fragment. The design decision behind this was so that the Main fragment could easily access any layout resource defined in the .xml files of the Map fragment and Sensor Fragment. A TabLayout was used to switch between the Map fragment and Sensor Fragment. Each fragment had an Activity associated with its respective fragment. In the background, a Service is running. A Service must be bound to an application, in our case it was bound to the MainActivity and starts running when the app is opened. Its sole function is to obtain the CoAP Client instance and send GET requests to the /getRadars resource and /heartbeat resource at a frequency of 10hz.
Software Design
Technical Challenges
I had no prior experience programming an Android App, let alone having any experience in dealing with network applications. The main challenges I had were not realizing the difference between a Fragment and an Activity. I had created my Fragments without realizing they needed to exist within an Activity, so when my onClick methods for buttons weren't registering, it was because there was no underlying Activity attached with the Fragment. I would suggest to have a getInstance method for all the Fragments so that different Fragments can access or call different methods.
I also had a problem with the Progress bars not updating based off the sensor values from the Sensor node. Solution was to update the Progress bars inside a handler that accessed the main UI thread.
There was a problem with the App not functioning properly on different Android Devices. Some buttons would not show up. I realized there are some button attributes in the layout file that caused this bug.
Stackoverflow will be your best friend and make sure to consider every single answer, even the ones wit 0 upvotes.
Future Advice
Before even touching any Android Studio code, read the following documents:
- https://developer.android.com/guide/components/fragments
- https://developer.android.com/guide/components/activities/intro-activities
If the App requires a periodic task such as sending GET requests, I recommend to use a Service. It doesn't instantiate a new thread and runs off the main thread.
You can verify that you can query POST/GET messages by creating a Server on the main thread and a Client on another thread within the same App. The very first time I connected to the ESP8266, communication worked perfectly because I was able to verify it beforehand.
Conclusion
<Organized summary of the project>
<What did you learn?>
Project Video
Project Source Code
- Git Project Link: Tesla Model RC
Advise for Future Students
- Communication is key. Every member should know the progress of every other member. What they are working on, how they are doing, and progress updates in general. Bi-Weekly meetings of at least 10 minutes between all group members would be extremely beneficial. Be proactive and ask your teammates for advice on any implementation detail. All members should know the basic functionality of all the modules. If you think you are done with your part, you aren't. There is always room for improvements and don't stop there. Ask other members if they need assistance.
