Hardware¶

PI Plus Robot

Overview¶

Mini Pi+ is a 27-DOF full humanoid robot platform evolved from Mini Pi.

The system follows a modular design:

Leg modules are fully reused from Mini Pi
Upper body (waist, arms, head) is added via quick-release interfaces
No modification to leg control strategy or driver layer is required

This design enables rapid iteration and extensibility.

Mechanical Structure¶

Robot Structure

The robot consists of:

Legs (fully reused)
Waist (1 DOF)
Arms (6 DOF × 2)
Head (2 DOF)

Key properties:

Height: ~75 cm
Mass: ~13.84 kg

The modular structure enables rapid hardware extension without redesigning the core system.

Actuation System¶

Joint Module

The platform uses integrated joint modules:

HTDW-5036 (legs)
HTCP-5031 (waist)
HTDW-4438 (arms)
HTDW-3536 (arms/head)

Key features:

Integrated motor, gearbox, driver, and dual encoders
Two-stage planetary reduction
CAN FD communication (up to 1 kHz control loop)

Typical performance:

Leg module peak torque: 21 N·m
Arm module peak torque: 10 N·m
Head module peak torque: 3 N·m

System Architecture¶

System Architecture

The system adopts a distributed control architecture:

Central controller (RK3588 / Jetson platform)
Multi-channel CAN FD communication
Independent bus per subsystem

Each subsystem (legs, arms, waist, head) is connected via isolated CAN FD channels.

Main Control Unit¶

Main Control Box

The main control unit integrates:

RK3588 computing platform
IMU
Power management
Communication interfaces

Specifications:

16 GB RAM + 128 GB storage
Supports motion control, perception, and planning
WiFi / Ethernet connectivity
OTA update support

Control Panel¶

Control Panel

The robot provides a physical control panel for system operation and status monitoring.

Components¶

Module Power Switch Controls power to joint modules
Main Control Computer Power Switch Controls the onboard computing system
Mode Lever Used to switch display information (e.g., IP address, system status)
Screen Displays system information and status

Power Operation¶

Module Power

Power on: short press → modules powered
Power off: short press → modules powered down

Main Control Computer

Power on: press > 2 seconds
Power off: press > 2 seconds

Status Indication¶

Battery Indicator

The LED bar indicates battery level
Each segment represents approximately 25% capacity

Notes¶

Always power on the main control system before sending commands
Ensure battery level is sufficient before operation

Communication Architecture¶

6 independent CAN FD buses
Fault isolation between subsystems
High-frequency multi-motor coordination

Advantages:

Easier debugging
Higher reliability
Strong scalability

Power System¶

Battery¶

6S lithium battery
Nominal voltage: 21.6 V
Energy: ~97 Wh
Endurance: ~55–65 minutes

Power Management¶

Multi-branch power distribution
Overcurrent / undervoltage / thermal protection
Real-time monitoring via CAN

Sensors and Expansion¶

Built-in Sensors¶

IMU
Joint encoders

External Interfaces¶

USB 2.0 / 3.0
GPIO
I²C / SPI / UART

Supports plug-and-play devices such as:

Intel RealSense
ZED Mini

System Characteristics¶

Modularity¶

Quick-release hardware design
Upper body can be upgraded independently

Reliability¶

Multi-bus CAN FD isolation
Integrated protection mechanisms

Performance¶

Verified torque margins
Stable thermal performance (< 55 °C in long-duration tests)

Notes¶

Hardware modules are reused across configurations
Driver layer remains consistent during upgrades