Stepper Robot Arm

A 6‑DOF robot arm that can pick up stuff. Most parts are 3D‑printed, an Arduino Mega + RAMPS 1.4 drives the motors, and a Raspberry Pi with a Pi Camera is used for the object detection.

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What this project is

• 6‑joint arm (6‑DOF) that can grab small objects
• Mostly 3D‑printed parts
• Steppers for the big joints, a large servo for one joint, and a tiny servo for the gripper
• Limit switches on the stepper joints for homing
• Raspberry Pi + Pi Camera does the vision, talks to the Arduino over serial
• Forward and inverse kinematics baked in
• Pick‑and‑place demos included

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Hardware (short version)

Mechanics

• Nearly everything is 3D‑printed.
• DIY ball bearings: BB pellets inside printed races (cheap and good enough).

Motors

• Mix of NEMA‑17 steppers.
• One 28‑BYJ48 unipolar stepper for a light joint.
• One larger servo for a joint.
• One micro servo for the gripper.

Control + Sensors

• Arduino Mega + RAMPS 1.4 for motors and limit switches.
• Raspberry Pi + Pi Camera for object detection.

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Software (short version)

• Arduino firmware handles steppers/servos and homing.
• Raspberry Pi runs the vision code (OpenCV / cv2) and sends target positions to the Arduino.
• You can pick a region in the camera image, the code deskews it, and maps pixels to the arm’s XY plane with a quick calibration.

Kinematics

The forward and inverse kinematics are adapted from this project (tuned for this arm’s links and joint directions):
https://github.com/glumb/robot-gui/blob/master/js/Kinematics.js

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Camera object detection

• Uses OpenCV to find objects in the selected area.
• Right now it doesn’t consider object width or in‑plane rotation (that’s on the roadmap).

Video demo — Click the image to watch on YouTube

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Pick the search area & map pixels to arm coordinates

• In the UI, pick four points to mark the area where the arm should look.
• The code deskews that patch to handle camera angle.
• Give the system two known points (with their arm‑frame coordinates, arm center is (0, 0)). From that, it scales/shifts so any pixel becomes an XY in the arm frame.

Mapping test video — Click the image to watch on YouTube

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Pick & place

A small example where the arm picks up a ball and drops it somewhere else.

Pick & place video — Click the image to watch on YouTube

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