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I first wanted to make a medical device like the automatic syringe for its use in a hospital setting. However, after the computer-controlled machining week, where I made an OSD mini car, I changed my project to make a drivable car. (I'll make medical devices in a different class :) )

As of 10/20/22, I am very excited to develop the engineering acumen necessary to prototype an RC car.

SET FINAL PROJECT IDEA: wireless, remote controlled car!

The car's motor will be controlled by a joystick. The process goes as this:

Joystick -> SAMD21 (microcontroller) Tx -> RN4871 (1) Tx/Rx -> RN4871 (2) Tx/Rx -> SAMD21 (microcontroller) Rx -> 2 motors' speed (A schematic of the process/car is shown below)

I resketched the car during my wildcard week to make it compatible with the material: steel metal sheet.

Initially, I was planning to 3D print my car, but after learning about the wildcard week where I got to learn about various metal works (Fablight laser cut, water jet, spot welding, etc.), I decided to create a steel-based car. The actual design and building of the car were completed in week 14, where I used steel sheet metal and welding to construct an approximately 6.5" x 11" car. Then, John helped me with sandblasting the surface, and I coated the car with clear antioxidant spray paint.

I wanted to purchase RC car wheels, but nothing was suitable for my car, so I decided to CAD my wheels. The rim and core of the wheel were 3D printed with PLA to provide stiffness. Then, I used TPU filament (flexible) to print my tire. Unfortunately, I ran through numerous hardware challenges because the Prusa 3D printer wasn't working as intended (an example is shown below for the car joints). The fact that some parts were small contributed to the difficulty in 3D printing. In the end, I became familiar with using 3D printers and adjusting settings accordingly (i.e. adding brims, supports).

During my week11 (Networking and Communications) week, I created two RN4871 Bluetooth PCBs. Although it took many trials-and-errors to make my board functional, using two breakout boards (Neil's design), I was able make both of them work.

1. Serial Passthrough: I ensured that both of my Bluetooth PCBs worked separately using the BLE scanner app and Arduino's Serial monitor as shown below (steps are also written in week11)



2. Controller & Car PCB Communication: these two Bluetooth devices needed to talk to each other.
   I referred to RN4871's datasheet (4.3 Module-to-Module connection) to establish two RN4871's communication.
   The steps are:
   1. Upload the code to begin the Serial
   2. Enter "$$$" in the No line ending mode
   3. Enter "+" and then "SS,C0" in the Carriage return mode
   4. Find both Bluetooth devices's MAC addresses by typing "D" (Mine was controller:44B7D0642065 AND car: 44B7D064205F)
   5. Enter "C,0,*Mac address (substitute)*" in the No line ending mode
   6. Connection should be established and communication should be enabled (refer to the video below)
   
   
   


3. Sending information from the joystick to motors:
   I established communication between my car and the control's Bluetooth devices. The video shows how the potentiometer readout is being sent from COM12(controller) to COM5(car). On the screen, "2000" indicates that the button is being pressed. By including the lines of command from step 2 into the Arduino setup(), I no longer have to call these codes into the Serial Monitor (I only needed the car's MAC address because the joystick was making a connection with the car).
   ** I faced frequent challenges with the unreliable connection between the two Bluetooth devices, where it worked one time and didn't the other. Neil recommended substituting RN4871 with the simpler nRF24L01+ (2.4 GHz ISM), which uses radio frequency to transmit/receive information within a channel. Fortunately, Quentin helped me discover a copper flake that was disrupting the PCB connection, and the communication has been fairly consistent since then.

In order to work modular (as recommended by Neil), I decided to create a separate motherboard for my two DC motors and RN4871 Bluetooth device. The diagram below shows the schematic and design of the board using Fusion 360 electronics.

I will use two motors, one for the left and one for the right, to control the direction of the car. The PCB schematic and board design is shown below.

I soldered components on the motor board and connected them to the motherboard and motors to test if these motors moved as expected. I used an external power supply at 9V and specified the state of the motors for commanding movements like forward, reverse, and gradually increasing or decreasing speed.

Initially, I used digitalWrite() to indicate the state of the motors, but I changed to analogWrite() for more flexibility. I knew how to gradually move forward and backward as well as turn left and right at the maximum speed (for instance, when turning right, the left motor would move at a maximum speed and the right motor would be stopped). However, coding to allow turning left and right at an in-between speed was confusing. Quentin and Anthony kindly helped me code for this issue (Code to control the car after receiving the joystick data).

Despite the coding change, the motors' and potentiometer's manufacturing flaws led to the difficulty in maneuvering the car as easily as I hoped. Nonetheless, I'm very glad that my car works wirelessly!

Finally, I implemented an external speaker that can make a honking noise based on the button state of the joystick. I used a frequency of 1000 Hz because this was within the range of usual car honks. The code was easily done via the use of if statements (when the "input == 2000") and Arduino's "tone()" function.

On Friday night (12/16/2022 @10:00 PM), I accidentally fried my computer. I was tired from being in the lab and accidentally connected an external 18V battery to my 3.3V breakout pin, which burned my voltage regulator, microcontroller, and computer. My computer was completely shut, and this was not the happiest moment of my life.

Fortunately, Guillaume (a fellow student in the EECS section, also an expert!!) helped me detach my SSD drive and store the data into a hard drive, and Anthony set up a desktop for me to use in the lab. After this chaotic hour, we put the SSD drive back into my computer, and "MAGIC!" my computer turned back on! Instantly, that day changed to a cheerful day.

Moreover, I must not forget to honorably mention Yuval, who made me a wonderful meme. I thank him for his creativity, time, and effort :)

Assembling everything was challenging but exciting. I wanted to see the parts all coherently functioning together and especially as a bioengineer, this final project was very meaningful to go out of my comfort zone. I started by building the joystick and testing on Arduino that the connection was still reliable. I also used the bandsaw to cut acrylic and a laser cutter to fill the void with wood (which I didn't use in the end). I joined some parts using a glue gun and others by tight-fitting joints.

I used various lab resources (3D printed parts, hot glue, hot air gun, double-sided tape, soldering iron, wires, heat shrink, acrylic, nuts & bolts, etc.) to assemble the car. I approximate the entire cost of the materials to be around $65 to $85 (~$20 for steel sheet, ~$20-40 PCBs (including ones I had to remake), ~$10 for 3D print filaments, and ~$15 for others, including motors, OLED, glue gun, wires, acrylic, etc.)