Robot Electrical Architecture (36 DoF)

System Overview

This robot is a 36 DoF humanoid platform powered by a 12.6V (3S4P) battery system.
The design separates high-current servo power from logic + sensor control, using an ESP32 + Raspberry Pi hybrid architecture.

Degrees of Freedom

DoF Distribution

• Legs: 4 DoF × 2 = 8

• Arms: 4 DoF × 2 = 8

• Hands: 8 DoF × 2 = 16

• Neck: 2 DoF

• Torso: 2 DoF

Total: 36 DoF

Power Distribution

Main Flow

• Battery (12.6V) → XT60 → Fuse → Split

Then:

• → Buck (8V) → Legs + Arms

• → Buck (5V) → Hands + Neck

• → Direct 12V → Torso servos

PCB and Wiring Design

Board Layout

The custom PCB is designed to handle power distribution, signal routing, and component integration within a single compact system.

The layout is divided into:

• controller regions

• sensor interfaces

• servo driver connections

• power distribution paths

Controllers

The system uses a dual-layer control architecture:

• Raspberry Pi 5

  • Handles AI processing, vision, and high-level decision-making

• ESP32 Microcontrollers

  • Handle real-time control

  • Read sensor data

  • Manage fast I/O operations

Communication between controllers is handled over UART.

Servo Control System

Servo actuation is managed using multiple PCA9685 PWM driver boards, connected via I2C.

• Generates precise PWM signals for all 36 servos

• Allows scalable expansion without overloading the main controller

I2C Expansion

An I2C multiplexer (TCA) is used to manage multiple devices on the same bus.

This enables:

• simultaneous communication with multiple PCA boards

• integration of sensors with overlapping I2C addresses

Sensor Integration

IMU

An inertial measurement unit provides:

• orientation data

• balance feedback for walking and stabilization

FSR Sensors

Force-sensitive resistors are placed in the feet to detect:

• ground contact

• weight distribution

Each FSR is implemented using a voltage divider circuit and read through ESP32 analog inputs.

Signal Flow

Sensor data is processed and converted into actuation commands through the following pipeline:

Sensors → ESP32 → Raspberry Pi → PCA9685 → Servos

Design Highlights

• Separation of high-level processing and real-time control

• Scalable servo architecture using PWM driver boards

• Robust I2C communication with multiplexer support

• Dedicated sensor processing for stability and interaction

• Multi-voltage power system optimized for performance and reliability

Summary

The system is designed as a high-current, modular electrical architecture for a full humanoid robot.
It supports 36 degrees of freedom, distributed control, and stable operation across multiple voltage domains while maintaining scalability for future expansion.