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Seven — 3-DOF Arduino Robotic Arm

⚠️ Safety Warning: This project features a custom power supply setup. Please proceed at your own risk. I am not responsible for any damage to your components, your board, or yourself. Work carefully, and stay safe.

A 3-DOF (Degrees of Freedom) robotic arm built with 3D-printed parts and SG90 servo motors, controlled via an Arduino Uno over serial communication. Seven supports manual joint control, inverse kinematics, gripper control, waypoint list programming, and external software integration via a handshake protocol.

Assembly Guide

The assembly guide YouTube video is here: https://youtu.be/ZC04lUFtJYI?si=HDjUfc8iGIEtEkAY

Features

Manual Control — Set individual joint angles directly
Inverse Kinematics — Move the end effector to any (X, Y, Z) coordinate in 3D space
Directional Movement — Move up/down/left/right/forward/backward by a set amount in cm
Gripper Control — Open/close gripper, with calibration for custom open/close angles
Waypoint Programming — Record up to 25 positions and replay them in a loop
Handshake Protocol — Integrate with external software by synchronizing over serial
EEPROM Calibration — Calibration offsets persist across power cycles
Adjustable Speed — Control angular speed between 30–90 degrees/second

Hardware Requirements

Component	Details
Arduino Uno	Or equivalent board
SG90 Servo Motor	× 4
Large Breadboard	For power distribution
Jumper Wires	Male-to-Male
2mm × 10mm Screws	For frame assembly
USB-A Cable (stripped)	Custom power delivery
USB-A to USB-C Adapter	For power supply connection
USB Wall Adapter	5V DC, 3.0A minimum (see below)

Photos

_{SG90 Servo + Screws}

_{2mm × 10mm Frame Screws}

_{Stripped USB-A Cable}

_{USB-A to USB-C Adapter}

_{Samsung 25W PD Adapter}

Power Supply Notes

Voltage: 5V DC (Stable)
Current: 3.0A minimum (2.5A if running fewer servos)
Power Rating: 15W – 25W
Recommended: Samsung 25W PD Adapter (EP-TA800) or equivalent high-quality branded charger

⚠️ Do not use cheap, unbranded "knock-off" adapters. Quality adapters include Short Circuit Protection (SCP) and Overcurrent Protection (OCP), which are vital when using a custom-stripped USB cable.

💡 Voltage Stability: Ensure the adapter defaults to 5V. While many "Fast Chargers" can output 9V or 12V, they will only do so if they detect a compatible device. A basic stripped USB cable will naturally pull the default 5V, which is safe for SG90 servos.

🔌 Common Ground: You must connect the negative (GND) wire from the adapter to the Arduino GND pin to ensure a common reference point for control signals.

3D Printing

All STL files are in the STL_files/ folder. Recommended filament: Hyper PLA.

File	Supports	Infill
`base_large.stl`	Tree (auto) · Tree Hybrid · Top Z: 0.25	Default
`base_slim.stl`	Tree (auto) · Tree Hybrid · Top Z: 0.25	Default
`base_rotation.stl`	Tree (auto) · Default · Top Z: 0.25	Default
`lower_arm.stl`	None	Gyroid
`upper_arm.stl`	Tree (auto) · Tree Hybrid · Top Z: 0.25	Gyroid
`gripper_upper_arm.stl`	Tree (auto) · Tree Hybrid · Top Z: 0.25	Gyroid
`gripper.stl`	Tree (auto) · Tree Hybrid · Top Z: 0.25	Gyroid

Wiring & Circuit

Servo	Arduino PWM Pin
Base	Digital Pin 6
Shoulder	Digital Pin 9
Elbow	Digital Pin 10
Gripper	Digital Pin 11

Servo power (5V & GND) wires are routed through the breadboard, which is powered by the external USB adapter.
The USB adapter's negative (GND) wire must be connected to an Arduino GND pin to establish a common ground.
Servo signal wires connect directly to the corresponding Arduino digital pins.

Testing

A dedicated test sketch is provided in code/test/test.ino to help with servo assembly and verification.

How to use:

Upload code/test/test.ino to the Arduino.
Open the Serial Monitor at 115200 baud rate.
Send one of the following characters to select a servo to test:

Input	Servo
`B`	Base (Pin 6)
`S`	Shoulder (Pin 9)
`E`	Elbow (Pin 10)
`G`	Gripper (Pin 11)

After selecting a servo, enter a numeric angle value (within that servo's min/max range) to move it.
When powered, every servo automatically center it to 90°.

Software Setup

Open code/main/main.ino in the Arduino IDE.
Upload the sketch to your Arduino Uno.
Open the Serial Monitor at 115200 baud rate.
Send commands as described in the Command Reference below.

Configuration (`config.h`)

Key constants that govern the arm's behavior:

Constant	Value	Description
`REST_ANGLE`	90°	Default resting angle for all joints
`DEFAULT_ANGULAR_SPEED`	60°/s	Default movement speed
`MIN_ANGULAR_SPEED`	30°/s	Minimum allowed speed
`MAX_ANGULAR_SPEED`	90°/s	Maximum allowed speed
`DEFAULT_MOVE_AMOUNT`	5 cm	Default step for directional moves
`MAX_VECTOR_ARR_SIZE`	25	Maximum number of waypoints
`LENGTH_SHOULDER_ELBOW`	12 cm	Upper arm segment length
`LENGTH_ELBOW_GRIPPER`	12 cm	Forearm segment length

These are tuned for the default arm geometry. Only modify them if you alter the physical build.

Command Reference

All commands are case-insensitive. Send them via the Serial Monitor at 115200 baud.

Calibration Commands

Command	Description
`-C`	Calibrate and save current angles to EEPROM
`-R`	Reset all calibration and gripper angles to 0 and save
`-GO(ANGLE)`	Set and save the gripper open angle (e.g. `-GO(45)`)
`-GC(ANGLE)`	Set and save the gripper close angle (e.g. `-GC(0)`)

Movement Commands

Command	Description
`S(SPEED)`	Set angular speed in degrees/second (e.g. `S(75)`)
`A(X Y Z)`	Inverse Kinematics — move end effector to (X, Y, Z) in cm
`M(BASE SHOULDER ELBOW)`	Manual — set angles for each joint directly
`G(ANGLE)`	Set current gripper angle
`GO`	Open gripper
`GC`	Close gripper
`O`	Reset arm to rest position (90°, 90°, 90°)

Directional Movement

Move the end effector in 3D space by a given distance in cm. Omitting the amount moves by the default 5 cm.

Command	Description
`U(x)` / `U`	Move up x cm (default 5 cm)
`D(x)` / `D`	Move down x cm
`L(x)` / `L`	Move left x cm
`R(x)` / `R`	Move right x cm
`F(x)` / `F`	Move forward x cm
`B(x)` / `B`	Move backward x cm

Waypoint List Commands

Command	Description
`+S`	Create a new list and save current position as the start point
`+W`	Save current position and gripper state as a waypoint
`+E`	Save current position as the end point and close the list
`+M`	Begin looping through the waypoint list

Handshake Commands

Command	Description
`HA`	Activate handshake mode
`HD`	Deactivate handshake mode

Calibration

Due to physical mounting variation, servo joints may not align perfectly at their true 90° position. Calibration corrects this offset and stores it to EEPROM so it persists across power cycles.

How to calibrate:

Use the M(BASE SHOULDER ELBOW) command to manually adjust each joint until each one points exactly at its physical 90° rest position.
Once satisfied, send -C to save the calibration to EEPROM.

Gripper calibration:

Use G(ANGLE) to find a good open angle (typically ~45°) and close angle (typically ~0°).
Save them with -GO(45) and -GC(0).

Reset calibration:

Send -R to wipe all calibration values (joints and gripper) back to zero.

Coordinate System

The shoulder servo's pivot point is the origin (0, 0, 0). All coordinates are in centimeters.

Axis	Direction
X	Forward
Y	Left / Right
Z	Up / Down

Example: A(10 0 5) moves the gripper to a point 10 cm forward and 5 cm up from the shoulder pivot.

Reach limits:

Minimum X: 1 cm
Minimum Z: −6 cm
Maximum reach: ~24 cm (sum of both arm segments)

Waypoint Lists

Waypoints let you record a sequence of positions and replay them continuously in a loop. The list can hold up to 25 waypoints.

Workflow (always in this order):

+S  →  (move arm)  →  +W  →  (move arm)  →  +W  →  ...  →  +E  →  +M

Send +S to start a new list and record the current position as the start.
Move the arm to the next desired position, then send +W to record it as a waypoint.
Repeat step 2 for as many waypoints as needed (up to 25).
Send +E to record the final end position and close the list.
Send +M to start looping through the list.

Note: All serial commands are blocked while the arm is executing a waypoint list. Waypoint commands (+S, +W, +E, +M) and calibration (-C) are disabled while handshake is active.

External Software Integration (Handshake)

Seven can be controlled from any external application over serial.

Send HA to activate handshake mode.
In handshake mode, the Arduino prints "K" to the serial port after every update cycle.
Your application should wait for "K" before sending the next command — this ensures commands are processed in sync with the arm's update loop.
Send HD to deactivate handshake mode.

While handshake is active, calibration (-C) and waypoint list commands (+S, +W, +E, +M) are disabled.

Project Structure

seven_github/
├── code/
│   ├── main/
│   │   ├── main.ino            # Main Arduino sketch
│   │   ├── roboticArm.h/.cpp   # Core arm logic, IK, commands, EEPROM
│   │   ├── servoConfig.h/.cpp  # Servo wrapper with rotation direction & limits
│   │   ├── vector3.h/.cpp      # 3D vector math (magnitude, normalize, distance)
│   │   ├── fixedVector.h       # Fixed-size array for waypoint storage
│   │   └── config.h            # Global constants (speeds, angles, limits)
│   └── test/
│       ├── test.ino            # Servo testing sketch
│       ├── roboticArmTester.h  # Tester class header
│       ├── roboticArmTest.cpp  # Tester class implementation
│       ├── servoConfig.h/.cpp  # Servo config for test environment
│       └── config.h            # Constants for test environment
├── STL_files/
│   ├── base_large.stl
│   ├── base_slim.stl
│   ├── base_rotation.stl
│   ├── lower_arm.stl
│   ├── upper_arm.stl
│   ├── gripper_upper_arm.stl
│   └── gripper.stl
└── photos/
    ├── robotic_arm(seven).jpg
    ├── circuit.png
    ├── parts.png
    └── ...

Author: T. Selçuk Yüksel

Name		Name	Last commit message	Last commit date
STL_files		STL_files
code		code
photos		photos
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
README.md		README.md

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Seven — 3-DOF Arduino Robotic Arm

Assembly Guide

Table of Contents

Features

Hardware Requirements

Photos

Power Supply Notes

3D Printing

Wiring & Circuit

Testing

Software Setup

Configuration (`config.h`)

Command Reference

Calibration Commands

Movement Commands

Directional Movement

Waypoint List Commands

Handshake Commands

Calibration

Coordinate System

Waypoint Lists

External Software Integration (Handshake)

Project Structure

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Supported by

Seven — 3-DOF Arduino Robotic Arm

Assembly Guide

Table of Contents

Features

Hardware Requirements

Photos

Power Supply Notes

3D Printing

Wiring & Circuit

Testing

Software Setup

Configuration (config.h)

Command Reference

Calibration Commands

Movement Commands

Directional Movement

Waypoint List Commands

Handshake Commands

Calibration

Coordinate System

Waypoint Lists

External Software Integration (Handshake)

Project Structure

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Configuration (`config.h`)