Base shell
base_side_v2The drum everything stands on. It hides the UNO Q, the servo driver and the power converter, and carries the first servo, the one that turns the whole arm.
MaterialPETG HF
2026
A Robot Arm That Sees You
Like the Reflexes Machine, this project runs on both halves of the Arduino UNO Q at once. The Linux side watches the camera and decides who is standing there; the microcontroller side drives the servos over a serial bus and keeps the movements smooth. The interesting engineering is in between: a four-axis arm printed in pieces, a gripper on its own servo, and pressure sensors in the tray so the arm knows whether it actually picked something up.
FilesOpen source project: the files, the code and the assembly guide are published on Arduino Project Hub.
Files and guide on Arduino Project Hubprojecthub.arduino.cc ↗Source code on GitHubgithub.com ↗4axes, plus the gripper
0buttons to press
2processors, one board
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Components
Every printed part, with its function and print settings.
Base top
base_topCloses the drum and holds the ball bearing that takes the weight of the arm, so the base servo only has to turn it, not carry it.
MaterialPETG HF
Base bottom cover
base_cover_v2The plate under the drum. Unscrew it and the whole electronics bay is open.
MaterialPETG HF
Back cover
back_cover_v2Covers the opening at the back of the base where the power connector and the switch come out.
MaterialPETG HF
Bearing cover
bearing_coverThe ring on top of the base that keeps the bearing in place and hides it.
MaterialPETG HF
Bearing spacers
inner_spacer ×3Two thin rings, one inside and one outside the bearing, that centre it in the base top.
MaterialPETG HF
Base gear
first_arm_gearThe large gear under the arm: the base servo turns it through the smaller servo gear, and the whole arm turns with it.
MaterialPETG HF
Servo gear
servo_gearThe small gear on the base servo. Together with the base gear it gives the first axis its reduction.
MaterialPETG HF
Base servo support
servo_base_supportHolds the base servo inside the drum at the right distance from the big gear.
MaterialPETG HF
Servo support brace
servo_support_enforcerA small brace that stops the servo support from flexing when the gears push against each other.
MaterialPETG HF
USB collar
usb_collarOptional ring around the USB opening of the base, for a tidier cable exit.
MaterialPETG HF
Shoulder joint
first_arm_jointSits on the bearing and carries the shoulder servo. It is the piece that turns with the base and lifts the first arm.
MaterialPETG HF
First arm
first_armThe longest segment. It is printed in one piece and hollow, so the servo cables run inside it.
MaterialPETG HF
First arm cover
first_arm_coverCloses the cable channel of the first arm.
MaterialPETG HF
Second arm
second_armThe forearm: it carries the elbow and the wrist servo, and the head at its end.
MaterialPETG HF
Second arm cover
second_arm_coverCloses the cable channel of the second arm.
MaterialPETG HF
Joint covers
joint_cover ×7Six identical discs, two per joint, that cover the servo horns and the screws on both sides.
MaterialPETG HF
Head
third_armThe last segment is also the face: it holds the camera on top, the LED matrix in front and the gripper servo below.
MaterialPETG HF
Head cover
third_arm_coverThe back of the head, around the camera.
MaterialPETG HF
Gripper servo support
third_arm_gear_supportHolds the micro servo that opens and closes the gripper.
MaterialPETG HF
LED matrix frame
modulino_led_matrix_supportThe bezel that holds the Modulino LED Matrix in the head and sets how much of it shows.
MaterialPETG HF
Gripper fingers
servo_gripper ×3Two fingers: one is driven by the micro servo, the other is free and follows it.
MaterialPETG HF
Gripper pads
gripper_pen_threated_pad_dx ×3The two soft pads screwed to the fingertips. Printed in flexible TPU so a pen is held without slipping and without being crushed.
MaterialTPU 95A
Pen trays
pen_holder ×10Nine identical wedges that make up the fan in front of the base. Each one has a slot for a pen and a pressure sensor underneath, so the arm knows which pens are there.
MaterialPETG HF
Tray connector
holders_base_connectorJoins the fan of trays to the base so they stay aligned with the arm.
MaterialPETG HF
Tray joint
pen_holder_jointA small clip that locks two neighbouring trays together.
MaterialPETG HF
Arduino UNO Q
arduino_uno_qThe only board in the project. Its Linux side runs the camera and the face recognition; its microcontroller side drives the servos over a serial bus and reads the pressure sensors.
ModelArduino UNO Q, 4 GB
Product pagestore.arduino.cc
Servo driver board
servo_driverTurns the UNO Q serial port into the half-duplex bus the four STS3215 servos share, and feeds them 12 V.
ModelWaveshare Serial Bus Servo Driver Board
Product pageamazon.it
DC-DC converter
dc_converterSteps the 12 V of the power supply down to the 5 V that feed the UNO Q.
ModelDC-DC 12 V → 5 V, 3 A
Product pageamazon.it
Base servo
servo_baseThe first of four serial bus servos. It turns the whole arm through the pair of gears in the base.
ModelFeetech STS3215, ID 1
Product pageit.aliexpress.com
Shoulder servo
servo_shoulderLifts the first arm. It carries the most load of the four, which is why the arm is kept light and hollow.
ModelFeetech STS3215, ID 2
Product pageit.aliexpress.com
Elbow servo
servo_elbowMoves the second arm.
ModelFeetech STS3215, ID 3
Product pageit.aliexpress.com
Wrist servo
servo_wristTilts the head, so the camera and the gripper point where they need to.
ModelFeetech STS3215, ID 4
Product pageit.aliexpress.com
Gripper servo
micro_servoA small metal-gear PWM servo, driven directly from a pin of the UNO Q, that opens and closes the fingers.
ModelMG90 micro servo, metal gear, 90°
Product pageamazon.it
Ball bearing
bearingTakes the weight of the arm so the base servo only turns it.
ModelBall bearing 65 × 50 × 7 mm
Product pageit.aliexpress.com
Camera
cameraThe USB camera on top of the head. Its stream goes to the Linux side of the UNO Q, where the face recognition runs.
ModelUSB-C camera, on a powered USB-C hub
Product pageamazon.it
LED matrix
modulino_led_matrixThe face. A 12 × 8 LED matrix on the Modulino connector, which shows the eyes and reacts to who is in front of it.
ModelArduino Modulino LED Matrix
Product pagestore.arduino.cc
Electronics
Four servos on one wire.
The four joints are serial bus servos: they share a single half-duplex line and each answers to its own ID, so the wiring through the arm is one cable instead of four. A driver board sits between them and the Arduino; the gripper is a plain PWM servo on its own pin. Two pressure sensors in the trays tell the software whether an object is there before the arm reaches for it. Everything runs from a 12 V supply, stepped down to 5 V for the logic.
Software
It recognises you, then it moves.
On the Linux side a Python program reads the camera, runs face detection and keeps the state machine: waiting, someone recognised, pick, deliver, back to rest. On the microcontroller side a sketch talks to the servos and draws the face on the LED matrix. The two halves exchange short messages through the bridge library, so the arm never moves on a half-decided instruction.
