Build a lightweight tabletop robot arm that rotates at the base, lifts at the shoulder and elbow, and opens a gripper. This beginner-friendly version uses an Arduino Uno or classic Nano, four hobby servos, four potentiometers, and a separate 5–6 V power supply for the motors.
It is an educational, light-duty robot—not an industrial arm. Reach, servo torque, link weight, rigidity, friction, and power quality determine whether it can lift an object. Start with a foam cube or ping-pong ball rather than assuming a particular payload.
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What you will build
The arm has four independently controlled movements, or degrees of freedom (DOF): base rotation, shoulder lift, elbow lift, and gripper opening. Three-DOF arms usually omit the elbow or combine movements; five- and six-DOF designs add wrist axes. More DOF does not automatically mean a better arm: every additional joint increases wiring, current demand, flex, calibration, and software complexity.
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Parts and tools
| Part | Quantity | Purpose |
|---|---|---|
| Arduino Uno Rev3 or classic Nano | 1 | Controller |
| Lightweight four-DOF frame | 1 | Base, links, brackets, and gripper |
| Hobby servos | 4 | Joint and gripper actuation |
| 10 kΩ potentiometers | 4 | Manual controls |
| Regulated 5–6 V servo supply | 1 | Motor power |
| Breadboard or terminal block, jumper wires, screws, and spacers | As needed | Assembly and prototyping |
| Large capacitor, limit switches, buttons, and emergency switch | Optional | Stability, safety, and future upgrades |
Use micro-servos for a gripper, wrist, or very short, lightly loaded arm. Shoulder and elbow joints often need higher-torque standard servos, especially when the links are long or carry downstream servos. Do not assume an SG90 or similar micro-servo can lift a specified mass without testing the exact geometry.
Choose the frame
- Cardboard or foam board: inexpensive and easy to modify, but flexible and less repeatable. Reinforce servo mounts so they do not tear out.
- Acrylic kit: quick to assemble with predictable holes, but thin plates can flex and acrylic can crack around screws. Included servos and power supplies vary.
- 3D-printed parts: customizable and upgradeable, but joints may need inserts, bearings, or reinforcement. Layer orientation and print tolerances affect strength and binding.
Keep heavy parts close to the base, make the upper arm and forearm light, space the shoulder supports widely, and use a broad or weighted base. A tiny plastic servo horn should not carry a large bending load without structural support.
Understand torque before adding a payload
A simple design rule is:
required torque ≈ force × distanceThe shoulder must support the links, elbow servo, gripper, and payload. The same object requires much more torque when held far from the shoulder. If a joint buzzes, stalls, overheats, or cannot hold position, shorten the reach, reduce the load, improve the structure, or use a stronger servo. Never solve a mechanical overload by simply increasing the software angle range.
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Assemble the mechanism
- Build a stable base and install the base-rotation servo.
- Attach the shoulder supports and keep the upper arm as light as practical.
- Install the elbow servo and forearm.
- Attach the gripper servo and confirm that its linkage moves freely.
- Leave linkages disconnected during the first electrical tests.
- Center each servo before permanently installing its horn, as described in the calibration section.
Wire the Arduino and servos safely
The Arduino supplies control signals; it should not be treated as the general-purpose power source for several loaded servos. Use this arrangement:
Rank #2
- Arduino Programming, Open Source: miniArm is built on the Atmega328 platform and is compatible with Arduino programming. The programs for miniArm are open-source, and learning tutorials and secondary development examples are available, making it easier for you to develop your robotic hand.
- High-Performance Hardware, Support Sensor Expansion: miniArm is equipped with a 6-channel knob controller, Bluetooth module, high-precision digital servos, and other high-performance hardware. Moreover, it provides multiple expansion ports for sensor integration, including ESP32 Cam, accelerometer, touch sensor, glowy ultrasonic sensor, etc., empowering users to engage in secondary development for sonic ranging and pose control capabilities.
- Versatile Control Options: miniArm supports app control, and users can utilize knob potentiometers for real-time knob control and offline action editing.
- Spark Your Creativity with miniArm: Expand the capabilities of miniArm with various sensors and unlock endless possibilities for your project.
- Starter Kit NO Glowing ultrasonic sensor, Touch sensor, Acceleration sensor, ESP32Cam Module.
External 5–6 V positive -> servo V+
External supply ground -> servo ground
Arduino GND -> external supply ground
Arduino signal pin -> servo signalConnect a master switch in the motor-power path so you can remove servo power quickly. Keep motor wires short and adequately sized. A capacitor across the servo supply can help with transients, but it does not compensate for an undersized supply.
Direct-servo pin plan
| Function | Servo pin | Potentiometer |
|---|---|---|
| Base | D5 | A0 |
| Shoulder | D6 | A1 |
| Elbow | D9 | A2 |
| Gripper | D10 | A3 |
Each potentiometer connects between 5 V and ground, with its wiper connected to the listed analog input. These pins are examples, not requirements. Avoid pins used for USB serial communication unless you understand the consequences.
When to use a PCA9685
For five or more servos, or for a cleaner expandable design, use an Adafruit PCA9685 16-channel PWM servo driver. It uses I2C—two signal lines—to provide 16 PWM channels, while a separate terminal supplies servo power:
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Arduino 5V -> PCA9685 VCC
Arduino GND -> PCA9685 GND
Arduino SDA -> PCA9685 SDA
Arduino SCL -> PCA9685 SCL
External 5–6 V -> PCA9685 servo-power terminal
Servos -> PCA9685 channelsThe PCA9685 does not solve an inadequate power supply. Its logic supply, servo supply, common ground, and I2C address must all be correct. Install the Adafruit PCA9685 library through Library Manager and follow the official wiring guidance.
Rank #3
- Arduino Programming, Open Source. miniArm is built on the Atmega328 platform and is compatible with Arduino programming. The programs for miniArm are open-source, and learning tutorials and secondary development examples are available, making it easier for you to develop your robotic hand.
- High-Performance Hardware, Support Sensor Expansion. miniArm is equipped with a 6-channel knob controller, Bluetooth module, high-precision digital servos, and other high-performance hardware. Moreover, it provides multiple expansion ports for sensor integration, including ESP32 Cam, accelerometer, touch sensor, glowy ultrasonic sensor, etc., empowering users to engage in secondary development for sonic ranging and pose control capabilities.
- Versatile Control Options. miniArm supports app control, and users can utilize knob potentiometers for real-time knob control and offline action editing.
- Spark Your Creativity with miniArm. Expand the capabilities of miniArm with various sensors and unlock endless possibilities for your project.
Install Arduino IDE and test one servo
Install the current Arduino IDE from Arduino’s software page. Connect an Uno with a USB-B cable or a classic Nano with a Mini-B cable. In Arduino IDE 2, select the detected board and port in the board selector, or use Tools > Board and Tools > Port. Install the AVR board package if prompted. Arduino’s upload guide covers this process.
Before assembling the arm, upload this conservative sweep:
#include <Servo.h>
Servo testServo;
void setup() {
testServo.attach(5);
testServo.write(90);
delay(1000);
}
void loop() {
for (int angle = 20; angle <= 160; angle++) {
testServo.write(angle);
delay(15);
}
for (int angle = 160; angle >= 20; angle--) {
testServo.write(angle);
delay(15);
}
}The expected result is smooth movement between approximately 20° and 160°. Do not begin with a full 0–180° sweep on an installed linkage; its safe range depends on the physical stops.
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#include <Servo.h>
Servo baseServo, shoulderServo, elbowServo, gripperServo;
const byte potPins[] = {A0, A1, A2, A3};
const byte servoPins[] = {5, 6, 9, 10};
// Replace these with calibrated, safe limits.
const int minAngle[] = {10, 20, 20, 35};
const int maxAngle[] = {170, 150, 160, 110};
int currentAngle[] = {90, 90, 90, 70};
int lastReading[] = {512, 512, 512, 512};
void setup() {
baseServo.attach(servoPins[0]);
shoulderServo.attach(servoPins[1]);
elbowServo.attach(servoPins[2]);
gripperServo.attach(servoPins[3]);
baseServo.write(currentAngle[0]);
shoulderServo.write(currentAngle[1]);
elbowServo.write(currentAngle[2]);
gripperServo.write(currentAngle[3]);
delay(500);
}
void loop() {
int target[4];
for (byte i = 0; i < 4; i++) {
int reading = analogRead(potPins[i]);
if (abs(reading - lastReading[i]) >= 4) {
lastReading[i] = reading;
}
target[i] = map(lastReading[i], 0, 1023,
minAngle[i], maxAngle[i]);
target[i] = constrain(target[i], minAngle[i], maxAngle[i]);
}
moveToward(baseServo, currentAngle[0], target[0]);
moveToward(shoulderServo, currentAngle[1], target[1]);
moveToward(elbowServo, currentAngle[2], target[2]);
moveToward(gripperServo, currentAngle[3], target[3]);
delay(15);
}
void moveToward(Servo &servo, int ¤t, int target) {
if (current < target) current++;
else if (current > target) current--;
servo.write(current);
}analogRead() returns the potentiometer position, map() converts it to a joint range, constrain() enforces the software limits, and the rate-limited movement prevents abrupt jumps. Smoothing reduces shock loads and input jitter; it cannot fix a weak power supply or overloaded joint.
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Calibrate every joint
- Remove each linkage from its servo horn.
- Move the servo to its midpoint with a test sketch.
- Switch off power and install the horn with the joint approximately centered.
- Reconnect the linkage and use conservative limits.
- Move slowly in both directions, stopping before a hard stop.
- Record a safe minimum and maximum for that joint.
Do not assume that a command of 90° is the physical center. Horns install at discrete positions, and linkages can reverse or amplify motion. If a control works backward, reverse its mapping:
int angle = map(value, 0, 1023, maxAngle, minAngle);Software limits are not a replacement for physical stops or an emergency power disconnect.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Try a pick-and-place task
Place a foam cube close to the base. Use the potentiometers to lower the gripper, close it gently, lift the object, rotate the base, and release it. Move one joint at a time at first. Increase reach only after the arm remains stable without buzzing, tipping, resetting, or overheating.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteThis open-loop system commands servo positions; it does not know the true joint angle, contact force, or object position. It can be repeatable enough for simple demonstrations, but it is not precision Cartesian robotics.
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- 4-in-1 Modular Robot Car for Endless Builds – Includes the base robot car (QD001), tank track expansion (QD004), and robotic arm kit (QD007), letting kids build multiple robot styles. Create a robotic arm car to grab and move objects, a tank robot for outdoor adventures, or combine both into a robotic arm tank. This versatile robotics kit for kids encourages creativity, hands-on STEM learning, and problem-solving—perfect for home learning, classrooms, and STEM training programs.
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Troubleshooting
| Symptom | Likely causes and recovery |
|---|---|
| Arduino repeatedly resets | Servo voltage dips, USB/Arduino power is overloaded, or ground wiring is poor. Disconnect servos, verify the sketch alone, then use a separate 5–6 V supply and reconnect one servo at a time. |
| Servo does not move | Check signal pin, common ground, external power, attach(), mechanical binding, and physical limits. Test without the linkage. |
| Servo chatters | Use a stronger, cleaner supply; tighten grounds and horns; add input deadband; reduce load; and avoid abrupt commands. |
| Servo becomes hot | It may be stalled, overloaded, blocked, or driven against a stop. Remove power and correct the geometry or limits. |
| Arm moves backward | Reverse the mapping, rotate the potentiometer, or reinstall the horn. |
| PCA9685 does not respond | Check SDA/SCL, I2C address, logic power, separate servo power, common ground, and the installed Adafruit library. |
| Arm tips over | Widen or weight the base, reduce reach, and keep heavy components low. |
| Upload fails | Try a data-capable USB cable, close Serial Monitor, select the correct board and port, install the board package, and check processor selection for a classic Nano clone. |
Useful upgrades
- PCA9685: add a wrist or second gripper without consuming many Arduino pins.
- Joystick: create compact two-axis controls.
- Buttons and memory: save and replay joint positions for repeatable demonstrations.
- Limit switches: detect travel boundaries independently of software.
- Better servos and structure: improve load handling, but reassess the power supply and mounts too.
- Encoders or smart servos: add feedback instead of relying only on commanded angles.
- Computer vision: use a more capable computer for vision and let the Arduino handle motor control. Arduino’s face-recognizing arm example illustrates the substantially more advanced architecture required.
Build, buy, or choose a commercial arm?
A scratch build is the lowest-cost learning route and teaches linkages, torque, calibration, and power distribution. An acrylic kit is faster if you want pre-cut parts, but verify that servos, a safe power supply, code, and replacement parts are included.
The official Arduino Braccio Bundle is a supported educational platform rather than a low-cost scratch build. Arduino’s listing states manufacturer specifications including a 400 g maximum load, 90 mm gripper width, and 180° rotation; treat those as product claims for the specified configuration, not as a prediction for this project. The European page showed €321.50 including VAT when accessed in August 2026, but price and availability vary by region and should be checked directly.
Braccio ++ is a different, more advanced platform using an Arduino Nano RP2040 Connect, RS485 communication, and smart servos. It is aimed at advanced secondary and university education, not as the default beginner alternative to four ordinary hobby servos.
For this build, start with four DOF, a light object, conservative limits, and properly separated motor power. The best next upgrade is usually stronger mechanical support or a PCA9685—not immediately adding three more joints.
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