10. Electronics Production-output

This week, I designed a PCB in KiCad and documented the full workflow, from library setup and schematic design to PCB layout, Gerber export, and PNG conversion for CNC milling. Although the design workflow is complete, our Snapmaker currently lacks a proper clamp/fixture for stable workholding, so precise in-house PCB milling is not reliable yet. For now, I completed the circuit design and prepared the manufacturing files. Circuit design in Circuit Designer

I also finished an output test circuit in Circuit Designer. When I press the button, the servo rotates by 10 degrees.

Test code:

/*
 * This Arduino Sketch controls a servo motor using a pushbutton. When the 
 * button connected to pin D2 is pressed, the servo connected to pin D5 
 * rotates by 10 degrees. The servo is powered by the 5V pin and grounded 
 * through the GND pin of the XIAO ESP32S3 microcontroller.
 */

#include 

Servo myServo;  // Create a Servo object

const int buttonPin = D2;  // Pin where the button is connected
const int servoPin = D5;   // Pin where the servo is connected

int buttonState = 0;       // Variable for reading the button status

void setup() {
  pinMode(buttonPin, INPUT);  // Set button pin as input
  myServo.attach(servoPin);   // Attach the servo to the servo pin
  myServo.write(0);           // Initialize servo position to 0 degrees
}

void loop() {
  buttonState = digitalRead(buttonPin);  // Read the state of the button

  if (buttonState == HIGH) {  // Check if the button is pressed
    myServo.write(10);        // Rotate servo to 10 degrees
    delay(500);               // Wait for half a second
  } else {
    myServo.write(0);         // Reset servo to 0 degrees
  }
}

Output -servo motor comparision

For a robotic arm, the “best” servo depends on where it sits on the arm.

A simple rule is:

Base / shoulder joints need the highest torque.
Elbow needs medium torque.
Wrist / gripper / lamp head can use smaller, lighter servos.

For a small desktop robotic arm, I compared these common options:

Servo	Typical size/class	Stall torque	Weight	Good for	Main limitation
SG90	micro	1.8 kg·cm @ 4.8V	9 g	tiny pointer, very light head	too weak for most arm joints
MG90S / MG90D	micro metal gear	1.8–2.4 kg·cm	13–13.4 g	wrist, light end-effector	still weak for shoulder/base on a real arm
SG92R	micro	2.5 kg·cm @ 4.8V	12 g	light wrist joint	still not ideal for heavy load joints
MG996R	standard servo	9.4 kg·cm @ 4.8V	55 g	base, shoulder, elbow on hobby arms	heavier, noisier, more current draw
Feetech STS3215 / SCS215	smart bus servo	16.5-19 kg·cm	55 g	better robotic arms, feedback and control	more expensive, needs bus setup

Finally, I decided to use the Feetech STS3215 because it offers the highest torque while keeping the weight low.

PCB Design

Step 1. Download and Install the Fab Academy Library

Before starting schematic design, I downloaded the Fab Academy KiCad library using:

git clone https://gitlab.fabcloud.org/pub/libraries/electronics/kicad.git

After downloading, I imported both symbol and footprint libraries in KiCad:

Manage Symbol Libraries: add Fab Academy symbol library
Manage Footprint Libraries: add Fab Academy footprint library

Then I opened Settings → Configure Paths and added a new path to the downloaded Fab library folder. This path setup is important, especially for correct 3D model display.

Step 2. Create the Schematic

I created the schematic in KiCad and added these components:

One main MCU
One LED (1206)
One switch
Two 6-pin socket headers from the Fab library

After placing all components, I connected them into a simple working circuit. I used a 499 ohm pull-down resistor with the switch to improve circuit stability and reduce the risk of short circuits or unexpected behavior. Schematic in KiCad

Step 4. Generate the PCB Layout

After finishing the schematic, I used Update Schematic to PCB to transfer the design to the PCB editor.

The PCB workflow was:

Adjust PCB design rules
Route all traces with the Route Tool
Add text and emoji graphics for personalization
Draw the board outline on the Edge.Cuts layer
Run DRC checks for design-rule and layout errors
Review the board in 3D Viewer

Step 5. Export Gerber Files

After confirming the board design, I exported Gerber files for fabrication and for the CNC toolpath workflow.

Step 6. Convert Gerber Files to PNG

To generate toolpaths in Mods, I converted Gerber files to PNG using an online tool (Gerber2PNG).

Uploaded files:

F_Cu.gbr
Edge_Cuts.gbr

Generated outputs:

One PNG for trace milling
One PNG for outline cutting

PCB Update

To better support PCB production requirements and Week 8 group assignment needs, I updated the design with the following improvements.

Step 7. Round the PCB Corners

I changed sharp corners to rounded corners (3 mm radius) on the Edge.Cuts layer to improve manufacturability and board appearance.

Step 8. Add Teardrops

I used Edit → Add Teardrops and adjusted the settings for CNC milling, to strengthen pad-trace connections.

Step 9. Add Copper Fill

I added a GND copper fill zone on the F.Cu layer, drew the fill around the board, and pressed B to refill all zones. I checked clearance to make sure the fill kept safe distance from signal traces.

Step 10. Export the Updated PCB Files

After these updates, I exported new Gerber files and converted updated F.Cu and Edge.Cuts files in Gerber2PNG again for Mods and CNC toolpath generation.

Current Fabrication Limitation

Although I completed the PCB design workflow, our Snapmaker currently does not have a proper clamp/fixture for stable workholding. Because of this, it may not guide or hold the PCB precisely during milling.

For now, I completed the circuit design in the circuit designer and prepared the manufacturing files, but I have not proceeded to precise in-house PCB milling yet.

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