The SCARA (Selective Compliance Assembly Robot Arm) is a type of robotic arm designed for tasks requiring high precision and speed, like assembly and pick-and-place operations. Its configuration allows for rigid vertical movement while maintaining flexibility in the horizontal plane.
This repository contains the design files, source code, and documentation for my SCARA robotic arm (forgive the redundancy). The arm is mostly 3d printed in order to offer a balance between affordability and functionality.
I wanted to build a simple robotic arm and found out the pyBot project that seemed to have a lot of potential and looked like a good starting point for further development. As I finished assembling the hardware according to the guide, the domain for the website hosting the project expired and was not renewed. At the time of writing this README, the site is still offline, meaning I no longer had access to the original code. The printable files are still available on Thingiverse here, and the Hackaday page is still accessible here.
Considering the situation, I decided to build my own robotic arm taking inspiration from this project. I redesigned everything from scratch in Fusion 360 to have precise control over the robot arm's parameters and to have accurate measurements for the inverse kinematics. The improvements with respect to the previous version include:
- tensioners for joint 2 and 3.
- endstops for each motor, essential for calibration and to recover from missed steps.
- heat set inserts to avoid screwing directly into the plastic.
- simplified assembly for joints 2 and 3.
- improved support for joints 2 and 3 from the
z_base, now consisting of two pieces. - control box for better organization, with optional fan to keep the stepper driver cool.
- universal tool mounting point (not limited to the previous servo motor insert).
- cleaner code with no external dependency (I wrote all the libraries I used), modular and easy to read and understand .
Below are two renders of the arm in Fusion 360; the left image shows it in the standard material and the right one has colored plastic components that match the actual arm I built.
* missing screws, nuts and heat set inserts
The original project utilized a DEVIA board, which is an Arduino Zero with built-in sockets for three A4988 stepper motor drivers and onboard drivers for four servos. I opted for an Arduino Uno paired with a CNC shield since it is more accessible and I happened to have the two lying around. This setup provides four sockets for stepper drivers and three pins that can be used for the endstops or the end-effector. I also added a 12V mini fan (used for 3d printers) to cool the stepper drivers.
TODO
Refer here for the Bill of Materials and some notes on what you will need.
- Design a universal mounting block to attach tools to the forearm
- Forget AccelStepper/MobaTools and write your own library to simultaneously control multiple steppers
- Add forearm calibration endstop
- Complete the BOM with the list of M3 screws needed
- Add schematics