Gripper, left jaw
arm_gearThe left jaw of the gripper, with the gear that makes it close against the other.
MaterialPLA
2025
Servo Mini Arm
Every part below is clickable. Open one to see what it is and where it sits. The Servo Mini Arm is the simplest robot arm I could design that still does something useful: six printed parts, four 9 g servos, two servo extension cables, a few M3 and M2 screws and an Arduino. It was published on MakerWorld in April 2025 with a four-page assembly sheet, and updated twice after the comments of the people who built it: a mod that avoids cutting and soldering the servo cables, and a new base with a cover for the Arduino.
FilesFree on MakerWorld: the 3D files, a print profile and the assembly guide in PDF. The code is on GitHub.
Files and guide on MakerWorldmakerworld.com ↗Source code on GitHubgithub.com ↗4micro servos, one of them continuous
5 cmthe widest object the gripper takes
3.6klikes on MakerWorld
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Components
Every printed part, with its function and print settings.
Gripper, right jaw
arm_servo_gearThe right jaw, mounted on the gripper servo: turning, it moves the left one through the gears.
MaterialPLA
Base
baseThe ring-shaped foot, with four holes to fix it to the desk. The cross horn of the base servo is screwed into its centre.
MaterialPLA
Base mount
base_attachThe block on the base that holds two servos back to back: the one below turns the arm, the one above lifts the first arm.
MaterialPLA
Lower arm
first_armThe lower segment, an open frame with a servo horn screwed into each end: the shoulder servo below, the elbow servo above.
MaterialPLA
Micro servo
micro_servo_1 ×49 g digital servos with clutch protection: a continuous-rotation one in the base, three 180° positional ones at shoulder, elbow and gripper. The servo arms connect through two 200 mm extension cables.
ModelBambu Lab 9g servo, PG002 (360°) and PG001 (180°)
Product pageeu.store.bambulab.com
Upper arm
second_armThe upper segment: it holds the elbow servo at one end and the gripper servo at the other.
MaterialPLA
Gripper servo bracket
servo_attachThe bracket that holds the gripper servo on the second arm.
MaterialPLA
Servo horn
servo_horn_1 ×4The single-arm horns that come with the servos, screwed into both ends of the first arm.
Model9 g servo horn
Cross servo horn
servo_horn_crossThe cross horn that comes with the servo, screwed into the centre of the base: the base servo turns against it.
Model9 g servo horn
Electronics
Four servos and any Arduino.
Two servos sit back to back in the block on the base: the lower one, continuous-rotation, turns the whole arm against a cross horn screwed into the base; the upper one lifts the first arm. A third servo at the elbow moves the second arm, and a fourth closes the gripper through a pair of gears. For a first test every servo goes straight to the board: positives to Vin, negatives to GND, each signal to its own digital pin (3, 2, 4 and 5 in the example code). The full diagram powers the servos from an external supply through a 7805 regulator, with a capacitor that keeps the arm steady when several servos move at once. The diagram uses an Arduino Uno, the photos a Nano: any board with four free pins will do.
Software
Pick up a cube, put it down somewhere else.
The example sketch on GitHub runs one sequence at power-on: it opens the gripper, lowers the first arm onto a cube, closes, lifts, turns the base, reaches out with the second arm and lets the cube go, then goes back to rest. It is a few dozen lines with the standard Servo library, written to be changed. People who built it have driven it from a phone app over Bluetooth and from a web page served by an ESP32.
