Difference between revisions of "S20: Bucephalus"

Schedule

Parts List & Cost

Hardware Integration:- Printed Circuit Board

We Initially started with a very basic design of mounting all the hardware on a cardboard sheet for our first round of Integrated hardware testing.

First Prototype Board

Challenges:- The wires were an entire mess and the car could not navigate properly due to the wiring issues as all the wires were entangling and few had connectivity issues. Hence we decided to go for a basic dot matrix Design before finalizing our final PCB Design as a Prototype board for testing if anything goes haywire.

The Prototype Board just before the actual PCB board was created on a dot matrix PCB along with all the hardware components for the Intermediate Integrated testing phase is as follows:

Prototype board 1

Prototype board 2

Prototype board 3

1) To avoid all the above challenges We designed the custom PCB using EasyEDA in which we implemented connections for all the controller modules(SJTwo Board LPC4078) all communicating/sending data via CAN bus. The data is sent by individual sensors to the respective controllers. GPS and Compass are connected to Geographical Controller. RPM sensor, DC and Servo Motors are connected to Motor Controller.
2) Ultrasonic are connected to Bridge and Sensor Controller. LCD is connected to Driver Controller. Bluetooth is connected to Bridge and Sensor Controller. CAN Bus is implemented using CAN Transceivers SN65HVD230 terminated by 120 Ohms; with PCAN for monitoring CAN Debug Messages and Data. Some Components need 5V while some sensors worked on 3.3V power supply. Also it was difficult to use separate USB's to power up all boards.Hence we used CorpCo breadboard power supply 3.3V/5V.
3) 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 GPS sensor and Compass sensor. We implemented rectangular header connector for SJTwo boards, RPM sensor, DC & Servo Motor on the bottom layer. There were 2 iterations of this board.
4) Challenges :-We also need to change the header for LCD since it was having different pitch.

DESIGNING:-

Top Layer development

Bottom Layer development

AFTER DELIVERY:-

Top Layer development

Bottom Layer development

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

DBC File

Bridge and Sensor Controller

<Picture and link to Gitlab>

Hardware Design

Software Design

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

Technical Challenges

< List of problems and their detailed resolutions>

Motor Controller

The Motor Controller SJ2-Board is mainly responsible for RC-Car’s steering and speed to move the car towards the destination. The RC-Car we are using is 2 Wheel Drive which means the front wheels are used for steering which is controlled by servo motor and the rear wheels are used for car’s forward and reverse movements which are controlled by DC Motor through ESC.

Hardware Design

<Motor_Module_Schematic.png>

Bucephalus Logo

ESC & DC Motor

<esc.jpg> <motor.jpg>

The ESC(Electronic Speed Control, Traxxas ESC XL-05) and DC Motor we used were provided with the RC car. The DC motor is controlled by ESC using PWM signals provided by the motor controller for forward and reverse movements. We used the 7.4v LiPo battery to power up the ESC. The DC motor is powered by the ESC which has a dc-to-dc converter which converts 7.4v to 6v. ESC can provide high current to the power-hungry DC motor running at faster speeds. ESC has an LED and a button which is used for calibration and setting different modes for the car.

The car can be operated in the following 3 modes: Sport mode(100% Forward, 100% Brakes, 100% Reverse) Racing mode(100% Forward, 100% Brakes, No Reverse) Training mode(50% Forward, 100% Brakes, 50% Reverse)

As we needed more than 50% speed for steep ramps, we used Sport mode. The frequency of the PWM signal fed to the servo motor is 100Hz. Based on the duty cycle set by the user, the car will go forward, reverse, or neutral. 10% - 20% duty cycle for reverse. 15% duty cycle for neutral. 15%-20% duty cycle for the forward motion.

SERVO

<servo.jpg>

The servo motor we used is Traxxas 2075 which was provided with the car and it is responsible for steering the car. It takes the 6V power directly from ESC. The servo motor is controlled directly from the SJ2 micro-controller board. The PWM signal fed to the servo motor is of frequency 100Hz. Based on the duty cycle of the signal sent to the servo, it rotates in the left / right direction. 10% - 20% duty cycle for left. 15% duty cycle for straight. 15%-20% duty cycle for right.

RPM SENSOR

<rpm_sensor.jpg> <trigger_magnet.jpg>

There are two parts to the RPM sensor - one is the trigger magnet and the other is the sensor. The RPM sensor is used as an input to maintain a constant speed of the vehicle. The sensor mounts on the inside of the gear cover, the trigger magnet mounts on the DC motor shaft. The gear cover and motor shaft need to be removed using the toolkit provided along with the RC car. The procedure is similar to this video, but note that the car used in the video is a 4WD RC car by Traxxas. We made use of the trigger magnet attached to the spur gear to trigger a pulse on the sensor for every rotation of the spur gear. These pulses are then read by the SJ2 board to calculate rotations in a second and later convert it to RPM and MPH. The RPM sensor has 3 wires, the white wire is the output wire that provides the pulses to the SJ2 Board, and the other wires are Supply(6V) and GND. We also used a Pull Down 1K Resistor between Supply and RPM output wires.

Software Design

Periodic Callbacks:

Periodic Init: CAN, PWM(Servo and Motor), and Interrupts(RPM Sensor and Test button) were initialized in this function.

10Hz function: CAN messages were transmitted in this function. Also, Cleared wheel rotations every 500ms.

100Hz function: Used this function to run at 20Hz. When the test button is pressed, Motor tests are performed else the car will follow driver commands.

<Periodic_Callbacks_Flowchart.PNG>

Servo Motor:

The PWM signal fed to the servo motor is of frequency 100Hz. The motor controller receives steer controls from the driver controller and it sends corresponding PWM value to the servo motor.

<Steering_Flowchart.PNG>

DC Motor:

The PWM signal fed to the DC motor is of frequency 100Hz. The motor controller receives speed controls from the driver controller and it sends corresponding PWM value to the ESC which controls the DC motor.

<DC_Motor_Flowchart.PNG>

RPM Sensor:

RPM Sensor gives one pulse for each wheel rotation and the software calculates speed in mph using the no. of rotations. We are re-calculating the speed, every 500ms to maintain the speed of the motor while the car is going uphill or downhill.

<RPM_Sensor_Flowchart.PNG>

Technical Challenges

Car Reverse Movement

Problem: The RC car sometimes wouldn’t go reverse and this used to happen randomly.

Solution: We checked the code and were giving the correct PWM values for the car to go reverse but the car wouldn’t do it sometimes. Then, we read the ESC manual and figured out that the wheels need to stop before giving the reverse command. For us, using these Commands (FULL REVERSE and STOP) before giving reverse PWM values for the reverse movement worked well. Also, we had to use current speed in combination with these FULL REVERSE commands to make sure that these reverse commands are given only when the car is moving forward.

Car downhill movement

Problem: The car would move too fast while downhill even though the feedback loop for the speed control is reducing the PWM.

Solution: The feedback loop to maintain the speed of the car was working fine while the car was going uphill, but while downhill the car would go too fast. To resolve this, we applied brakes(FULL REVERSE commands) to the car whenever the speed crosses a certain limit.

Mounting the RPM Sensor

Problem: We had a hard time figuring out where to mount the rpm sensor, as the documentation provided by Traxxas was for 4WD and ours was a 2WD RC car.

Solution: We figured out the place to mount the sensor by chance, using common sense. It was mounted on the inside of the gear cover, where a tiny hidden place was provided.

Geographical Controller

<Picture and link to Gitlab>

Hardware Design

Software Design

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

Technical Challenges

< List of problems and their detailed resolutions>

Driver Module

<Picture and link to Gitlab>

Hardware Design

Software Design

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

Technical Challenges

< List of problems and their detailed resolutions>

Mobile Application

<Picture and link to Gitlab>

Hardware Design

Software Design

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

Technical Challenges

< List of problems and their detailed resolutions>

Conclusion

This project taught us how to work with so many people with same goal but different working patterns to come together and execute their ideas together in tandem to accomplish the team goal. We developed an autonomously navigating RC car. Each team member brought unique skills, passions and personalities to the project. Some team people were skilled with designing and placing components on the PCB Board, while others were skilled in firmware development, project management, catching bugs, organizing meetings etc. Some people had the ability to lighten the mood on disappointing demo days, while others had the management skill to keep the team focused and making the car its best version than the day before, while avoiding burning the team out at each other. When these different minds and their skills came together, it resulted in the final product that we all are extremely proud of, as well as one that performed well on the final demo day. The shelter in place brought more challenges in coordination as we couldn't meet much for in person meetings and everyone needed the hardware for testing their code. It was difficult for a single person who had all the hardware to always test with few members or alone and to explain others where exactly their code was failing.

It wasn't always fun and lively though. We experienced soaring highs, during few of our progress demos, where we hit almost all of our specs. We also experienced devastating lows, when we were not able to demo properly as there were coordination issues offline at the start. While we look back fondly on our project, the reality is that it was the result of 7 graduate students spending almost every day of the semester developing and fine tuning the final product. We failed and succeeded together as a team. The goal was too important. Blame fell on the team as a whole and so did success and praise. We succeeded because we failed together. We succeeded because we didn't let failure break us and instead worked harder to fine tune and improve our test cases so that no case in the testing is left unexplored and the car worked exceptionally well.

There was so much to learn. Always something new, it felt like. We developed a clean and best working PCB, to integrate all of our subsystems together with least number of wires needed and visible on the car, even though none of us had experience developing a board that complex before. We also approached new challenges such as developing an Android Mobile Application, even though none of us knew JAVA or knew Android Studio beforehand. We never stopped learning. We learned the value of investing in quality components. We honed our unit testing skills, trying to write firmware that was as high quality as our hardware. We learned about CANbus on an intimate level and applied all of the knowledge. Testing at residential area gave us a tough time especially with the GPS module and the ultrasonic sensors as the google maps did not give us the exact co-ordinates of internal society roads. while the ultrasonic sensors faced difficulty in detecting low height sidewalks.

Working on this project was a difficult yet ultimately rewarding experience. It taught us how to make use of unit tests so that we don't need hardware at all and this helped alot in online coordination with team members. We can't stress enough how important is to start the project as early as possible in the semester and to keep pushing until the final demo. Each of contributed roughly 20 hours a week to work on the project. As a result, we were exhausted by the end of it, but we also never had to pull nights sometimes to meet the deadlines. We had excellent leadership from our team lead, Mohit Ingale, as well as our mentors, Preet and ISA members Aakash, Vignesh. We also had excellent peers in CMPE 243 and are proud of what they achieved as well. Overall, we were happy to be part of this class and we hope that our project will inspire future students to develop electric vehicles.

Project Video

Project Source Code

Advise for Future Students