Hardware Reference

All RoArm models (M2-S, M2-Pro, M3-S, M3-Pro) are built around the “General Driver for Robots” board — a custom ESP32-based controller designed by Waveshare for serial bus servo control, WiFi communication, and peripheral expansion. The M3 variant of the board adds an INA219 voltage/current monitor, AK09918C compass, QMI8658 6-axis IMU, and a TF card slot.

Driver Board Overview

Image: Waveshare

Key Components

Component	Description
ESP32-WROOM-32	Main MCU — dual-core 240MHz, WiFi + Bluetooth
CP2102 / CH340	USB-to-serial converter for programming and communication
9-DOF IMU	Onboard inertial measurement unit
0.91” OLED	Status display
Serial Bus Interface	Half-duplex UART for servo communication
12V Input	Barrel jack power input for servo and motor drive
5V Regulator	Steps down 12V to 5V for ESP32 and peripherals
Switched Outputs	Two 12V PWM channels (A and B) for external loads
LED	Controllable indicator LED
I2C Header	Expansion for sensors and displays
SPI Header	Expansion for high-speed peripherals

Power Architecture

graph TD
    A[12V DC Input] --> B[Servo Bus Power]
    A --> C[5V Regulator]
    A --> D[12V Switched Outputs]
    C --> E[ESP32]
    C --> F[USB-C 5V]
    B --> G[Servos ID 11-15/17]

Caution

The USB-C port provides 5V to the ESP32 for programming and serial communication, but it cannot power the servos. Always connect the 12V power supply for arm operation. Running the arm on USB power alone will cause erratic behavior or servo faults.

ESP32 Pinout

Image: Waveshare

Pin Assignments

Both M2 and M3 firmware share the same GPIO mapping. The underlying hardware (the “General Driver for Robots” board) uses identical pin assignments — the difference is in how the H-bridge channels are used: the M2 drives external accessories (lights, solenoids) via the switch module, while the M3 drives mobile base motors.

GPIO	Function	Notes
GPIO1 (TX)	Serial TX	Programming/debug UART
GPIO3 (RX)	Serial RX	Programming/debug UART
GPIO18	Servo Serial RXD	Half-duplex servo bus (Serial1)
GPIO19	Servo Serial TXD	Half-duplex servo bus (Serial1)
GPIO32	I2C SDA	OLED, INA219, sensors
GPIO33	I2C SCL	OLED, INA219, sensors
GPIO25	H-bridge A PWM	M2: switch channel A / M3: motor A
GPIO26	H-bridge B PWM	M2: switch channel B / M3: motor B
GPIO21	H-bridge AIN1	Direction control
GPIO17	H-bridge AIN2	Direction control
GPIO22	H-bridge BIN1	Direction control
GPIO23	H-bridge BIN2	Direction control
GPIO35	Encoder A ch.A	Motor/wheel encoder (input only)
GPIO34	Encoder A ch.B	Motor/wheel encoder (input only)
GPIO16	Encoder B ch.B	Motor/wheel encoder
GPIO27	Encoder B ch.A	Motor/wheel encoder

Note

Earlier versions of the Waveshare wiki listed GPIO 16/17 for servo UART and GPIO 21/22 for I2C on the M2. The current firmware (RoArm-M2_config.h and RoArm-M3_config.h) uses GPIO 18/19 and GPIO 32/33 respectively for both models. The GPIO 16/17/21/22 pins are H-bridge direction and encoder inputs. Always refer to the firmware config header for authoritative pin assignments.

Servo Bus

The arm uses serial bus servos connected on a daisy-chain bus. The “-S” models ship with ST3215 servos (plastic housing); the “-Pro” models use ST3235 servos (all-metal housing). Both share the same protocol, torque rating, and pinout — the metal construction provides better heat dissipation and more stable backlash over the servo’s lifetime.

M2 Servo Layout (5 servos)

Servo ID	Joint	Type
11	Base rotation	Single drive
12	Shoulder (driving)	Dual drive
13	Shoulder (driven)	Dual drive
14	Elbow	Single drive
15	Gripper / EoAT	Single drive

M3 Servo Layout (7 servos)

Servo ID	Joint	Type
11	Base rotation	Single drive
12	Shoulder (driving)	Dual drive
13	Shoulder (driven)	Dual drive
14	Elbow	Single drive
15	Wrist pitch	Single drive
16	Wrist rotation	Single drive
17	Gripper	Single drive

The M3 wrist adds pitch (servo 15) and rotation (servo 16) between the elbow and gripper. Image: Waveshare

Servo Specifications

Parameter	ST3215 (“-S” models)	ST3235 (“-Pro” models)
Protocol	Half-duplex TTL serial	Half-duplex TTL serial
Baud rate	1Mbps	1Mbps
Torque	30 kg.cm @ 12V	30 kg.cm @ 12V
Speed	40 rpm (no load)	40 rpm (no load)
Resolution	12-bit (4096 positions)	12-bit (4096 positions)
Encoder	12-bit magnetic (0.088°)	12-bit magnetic (0.088°)
Housing	Plastic	All-metal
Feedback	Position, speed, load, voltage, temperature, current, mode	Position, speed, load, voltage, temperature, current, mode

Tip

The dual-drive shoulder uses two servos (IDs 12 and 13) mechanically coupled to the same output shaft. The firmware synchronizes them automatically — you only need to control “shoulder” as a single joint. This design is shared across both M2 and M3 lines.

Electrical Specifications

Parameter	Value
Input Voltage	12V DC
Recommended PSU	12V / 5A
Battery Support	3S LiPo (11.1V nominal)
ESP32 Current	~250mA typical
Servo Stall Current	~1.5A per servo (peak)
Total Peak Current	~6A (all servos stalling)
Switched Outputs	12V, ±255 PWM, ~2A per channel
LED Max Current	~20mA

Mechanical Specifications

Parameter	M2-S	M2-Pro	M3-S	M3-Pro
Body Weight	826g ± 15g	873g ± 15g	973.5g ± 15g	1020.8g ± 15g
Clamp Weight	290g ± 10g	290g ± 10g	290g ± 10g	290g ± 10g
Horizontal Workspace	1090mm	1090mm	1120mm	1120mm
Vertical Reach	798mm	798mm	798mm	798mm
Repositioning Precision	≈ ±4mm	≈ ±4mm	≈ ±5mm	≈ ±5mm
Payload	0.5kg @ 500mm	0.5kg @ 500mm	0.2kg @ 500mm	0.2kg @ 500mm
Joint Ranges	Base 360°, Shoulder 180°, Elbow 180°, Hand 135°/270°	Same	Base 360°, Shoulder 180°, Elbow 225°, Wrist 180°+360°, Hand 180°	Same
Materials	Carbon fiber, 5052 aluminum	Carbon fiber, 5052 aluminum	Carbon fiber, 5052 aluminum	Carbon fiber, 5052 aluminum
Table Clamp	Supports edges up to 72mm	Supports edges up to 72mm	Supports edges up to 72mm	Supports edges up to 72mm

Expansion Options

The driver board provides headers for:

• I2C bus — Connect sensors (IMU, distance, force), displays, or additional controllers
• SPI bus — High-speed peripherals
• 12V switched outputs — Solenoids, pumps, additional motors (controlled via T:113)
• Servo bus — Additional serial bus servos can be daisy-chained

Image: Waveshare

The expansion plate on the arm’s forearm provides M3 mounting holes for custom end-effectors and sensors.

Image: Waveshare

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Hardware reference from the General Driver for Robots schematic, RoArm-M2-S Wiki, and RoArm-M3 Wiki. Images: Waveshare.