Servo Robot Arm

A simple robot arm built with SG90 servos and an ESP32, designed to pick up ping pong balls and move with inverse kinematics.

What this project is

This project is a compact servo-based robot arm controlled by an ESP32. It can pick up ping pong balls and move its end effector using inverse kinematics, which makes the motion feel much more natural than simple fixed-angle positioning.

What makes it a little different is that it is designed to be cheap, approachable, and easy to build from common parts. It uses SG90 servos, an ESP32, and USB power, so it stays accessible while still being capable of some interesting motion.

Why I made it

I have wanted to make a robot arm for a long time. I have seen many people build one, and I wanted to try it myself.

The goal was to make something practical, small, and affordable rather than overcomplicated. I also wanted to explore inverse kinematics in a real build, because it opens the door to more natural movement and future upgrades. For example, with a custom grip or tool head, the arm could be adapted into a simple drawing bot later on.

Features

• Picks up ping pong balls and similar small objects
• Uses inverse kinematics for smoother arm movement
• Controlled from a phone using a serial Bluetooth app
• Built with widely available and low-cost parts

Hardware

• ESP32
• SG90 servos
• USB power supply
• 3D printed parts
• Bluetooth control from a phone

How to use it

1. Power the robot arm through USB.
2. Upload the micropython code to the ESP32.
3. Pair your phone with the ESP32 over Bluetooth.
4. Open your serial Bluetooth app.
5. Send control commands from the app to move the arm. * TODO: make controlls overview *

The arm is controlled through the phone app, so movement is handled by serial Bluetooth communication rather than physical buttons or a separate controller.

Build notes

The robot arm is designed around SG90 servos, so the structure and movement range are matched to small hobby servos. The inverse kinematics system allows the arm to move to positions in space instead of requiring you to control every joint manually.

The current version is focused on object pickup. There is no pen holder yet, but the arm already has a mounting point that could support future attachments.

Future improvements

• Add a pen holder
• Add a better user interface for mobile control

Notes

This project is still a work in progress, but it already demonstrates a functional small robot arm with Bluetooth control and inverse kinematics.