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Final Project

Slide 2020

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Presentation 2020

DIL E-scooter by Ashot Margaryan is licensed under CC BY-NC 4.0

2020 Final project presentation My presentation starts at 1:18min

Research

During my 2020 Fab Academy, I successfully accomplished and presented my final project. At the start of my Fab Academy journey, I didn’t have a clear understanding of what I wanted to do for my final project. My first idea was an automatic dog or cat feeder. I sketched an approximate design and even did 3D modeling of the feeder during the second week (Computer-aided design).

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From week 2 to week 7, I hadn’t developed a better idea for my final project until, during the “Make Something Big” week, I decided to create a 1:1 wooden replica of an Italian Vespa scooter. After a few discussions with my instructor, Babken Chugazsyan, I realized that this would be my final project. It had to be drivable. I fully understood that it couldn’t become a product itself, but the process of making something big and drivable with electric motors and batteries was a huge experience for me and our Fab Lab. We understood that it was fun, but we are not going to try it again.

3D Modeling

As it was required for the “Make Something Big” week, the project had to be large with joints, such as a table or chair. In my case, I wanted to design a wooden scooter that had to be drivable, so the frame needed to be strong enough to carry an adult. I started designing the plywood frame of my scooter using Fusion 360 and described the entire process of designing and CNC machining in my week 7 documentation (please check week 7).

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The main challenge in making the wooden frame of the scooter was COVID-19. Our lab, along with the entire country, went into lockdown exactly during the 2020 “Make Something Big” week, which was a disaster for me. During that week, I managed to cut only 2 parts out of the needed 25 and used only one sheet of plywood out of the required 6. I continued the cutting and assembly process for my assignment and final project only after the lockdown, during the summer of 2020.

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Drivetrain

Another major problem with this project was the drivetrain(The drivetrain is comprised of a collection of components in a vehicle that transfer power from the transmission to the wheels). As I mentioned before, it was going to be electric, so I needed to install an electric motor and batteries on the scooter, do the wiring, and find a controller to manage the motor. The main issue was that this was happening during the post-pandemic period, and all supply chains worldwide were not functioning well. As a result, I couldn’t order the desired motor and had to use what I could find.

First, I had to choose a motor, and based on its parameters, select other components such as the controller and wire thickness. Eventually, I chose a vehicle engine starter as the motor.

The next step was the power transmission, which was going to be a chain drive. The DC motor operates at high RPMs, which was not suitable for my needs, so I needed to put a small sprocket gear on the DC motor and a larger one on the wheel. Unfortunately, we couldn’t do metalwork at our lab, so I had to outsource that. Fortunately, I work in a place where I could solve that problem.

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The first step was to attach the small gear to the motor. For that, I needed a specific part, which was machined on a manual lathe (turning machine). After machining, we fixed it by welding.

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The second step was to attach the larger gear to the wheel. This was easier because the only thing we needed to do was enlarge the hole of the sprocket from 20 mm to 34 mm. This operation was also done on the lathe. It was difficult because the sprocket is thin and made of strong steel, but we managed it. Afterward, it was welded to the shaft of the wheel. The third step was fixing the motor. Overall, we achieved a strong construction that can be used.

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3D printing

Additionally, I needed some lighting on the bike, (Also, I had to have some input and output on the final project). so I designed and printed a headlight with classic styling. It has a simple design and looks pretty nice. After I did 3D printing on the Makerbot Replicator 2, the case of the lamp was black. I found transparent filament in the lab and printed the ‘glass part’.

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Electronic

The light will be automatically controlled with an LDR sensor and a board, which I designed with the help of Azniv Hovhannisyan. The LED light operates from a 9V battery. Both the battery and the board are hidden inside the headlight, making it fully autonomous and usable not only on the bike.

Light dependent resistors (LDRs), or photoresistors, are electronic components used to detect light and change the operation of a circuit based on the light levels. I used KiCad to design my board. Sketched the board. Do the schematic design of the board (traces), then soldered the board.

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// Define the pins
const int ldrPin = A0; // Analog pin connected to LDR
const int ledPin = PA1; // Digital pin connected to LED

// Define a threshold for light detection
const int threshold = 500;

void setup() {
  // Set LED pin as an output
  pinMode(ledPin, OUTPUT);

  // Initialize the serial communication for debugging (optional)
  Serial.begin(9600);
}

void loop() {
  // Read the value from the LDR
  int ldrValue = analogRead(ldrPin);

  // Print the LDR value to the serial monitor (optional)
  Serial.println(ldrValue);

  // Check if the LDR value is above or below the threshold
  if (ldrValue < threshold) {
    // If below threshold, turn the LED on
    digitalWrite(ledPin, HIGH);
  } else {
    // If above threshold, turn the LED off
    digitalWrite(ledPin, LOW);
  }

  // Add a small delay for stability
  delay(100);
}

After assembling it looks like this;

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Batteries and shield

A PWM (Pulse Width Modulation) shield is an add-on board used with microcontrollers like Arduino to control devices that need variable power, such as motors, LEDs, and servos.

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How it works:

PWM Signal: It creates a PWM signal, which is a series of on-off pulses. The speed or brightness is controlled by changing the width of these pulses (how long they stay on vs. off). Control: By adjusting the pulse width, you can control the amount of power delivered to the device without changing the voltage.

What it does:

  • Motor Control: Adjusts motor speed smoothly.
  • LED Brightness: Dims or brightens LEDs.
  • Servo Positioning: Controls the position of servo motors precisely.

The shield makes it easy to connect and control multiple devices without needing complex wiring or programming. Tests showed that the PWM shield we were using was operating at its maximum capacity, and the transistors were getting too hot. Fortunately, during testing, we didn’t burn it out. To solve this problem, I decided to put an electric fan on the board. Additionally, I needed a prepared casing for the shield, so I designed a box with a cover. Inside the box, I placed the shield, and on the cover, I installed the electric fan.

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To get 24 volts from four 12-volt batteries by connecting each pair in series and then connecting the two pairs in parallel, I followed these steps:

Pairing Batteries in Series - Connect the positive terminal of the first battery to the negative terminal of the second battery. This is your first series pair. - Connect the positive terminal of the third battery to the negative terminal of the fourth battery. This is your second series pair.

**Connecting Pairs in Parallel**
  • Connect the negative terminal of the first series pair to the negative terminal of the second series pair.
  • Connect the positive terminal of the first series pair to the positive terminal of the second series pair.

Here’s a step-by-step guide:

  • First Series Pair: Connect Battery 1 (positive) to Battery 2 (negative).

  • Second Series Pair: Connect Battery 3 (positive) to Battery 4 (negative).

  • Parallel Connection: Connect the negative terminal of Battery 1 to the negative terminal of Battery 3. Connect the positive terminal of Battery 2 to the positive terminal of Battery 4.

The connections look like this:

Battery 1 (positive) -----> Battery 2 (negative)
Battery 3 (positive) -----> Battery 4 (negative)

Negative terminal of Battery 1 -----> Negative terminal of Battery 3
Positive terminal of Battery 2 -----> Positive terminal of Battery 4

Result: This setup creates two series pairs, each generating 24 volts. The parallel connection ensures you have a combined output of 24 volts with increased capacity (amp-hours).

By connecting the batteries this way, you will get a total output voltage of 24 volts with the combined energy storage capacity of both pairs. Also By connecting the batteries this way, I reduce the amperage needed to make the motor rotate, which is easier on your shield, ensuring it can handle the current.

For packing the batteries together, I made a box using a laser cutter. It was a simple box without joints. I glued the walls together and packed the batteries inside with wiring. I soldered all the wiring and connectors; it took me all day.

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When all the wiring was done and everything was packed into its place, the result looked like this:

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Materials

Qty Description Price per unit Link Notes
1 PWM 10-50V 60A 3000W DC Motor Speed Controller Board 22.00 $ https://www.droking.com/Motor-Speed-Control-Board-DC-Controller-DC10-50V-3000W-60A-Speed-Controller-DC-Motor-Control-Board-light-dimmer-heater-Controller-PWM-Regulator Order many
1 24 volt 6 cm fan 4.00 $ https://www.alibaba.com/product-detail/Pc-Cooling-Fan-80mm-Pc-Fan_1600259732511.html?spm=a2700.7735675.0.0.6ee2auu7auu7MK&s=p
4 7 Ah 12 Volt Scooter Battery 29.99 $ https://www.monsterscooterparts.com/trsc/rec-categories/12vo7amphoba.html
6 plywood sheets 1525 x 1525 18mm 19.00 $ local shop link
1 filament 400g 12 $ local shop link
2 LED 3 $
1 switch 1 $
2 LED 3 $
2 LED 3 $
5 XT 60 conector set 9 $ XT60 amazon link
2 LDR sensor 0.5 $
## Conclusion

My Fab Academy project journey began with an idea for an automatic pet feeder but evolved into creating a drivable, wooden Vespa scooter replica. This project, accomplished amidst the challenges of the COVID-19 pandemic, required substantial effort in 3D modeling, CNC machining, and electronics.

Starting with the plywood frame design in Fusion 360, the project faced a major hurdle when the pandemic lockdown halted progress. Once restrictions were lifted, I resumed the project, focusing on the drivetrain, which involved using a vehicle starter motor and a chain drive system. This required precise machining and welding, which I was able to accomplish with the help of my workplace resources.

I incorporated 3D printing for the scooter’s lighting, creating a headlight with an LDR sensor for automatic control. Additionally, I designed a PWM shield with a cooling fan to manage motor speed, ensuring it could handle the current without overheating. To power the scooter, I connected four 12-volt batteries in a series-parallel configuration, achieving the necessary 24 volts while reducing the amperage strain on the shield.

Despite supply chain disruptions and the challenges posed by the pandemic, I successfully completed the project, creating a functional and drivable wooden scooter. The entire process provided valuable experience in various fabrication techniques and problem-solving under constrained conditions.

Files

Wooden scooter Fusion360 file

head light traces

head light outcut

DIL E-scooter by Ashot Margaryan is licensed under CC BY-NC 4.0