Stack Kame - Quadruped Robot Controller

A modified mini Kame quadruped robot accessory for Stack-Chan, running on Adafruit Feather ESP32-S3 (no PSRAM) with an 8-channel PWM servo wing. Could also just be a Lego-compatible platform for whatever.

Basically...

➕ 🟰

..but cute!

⚠️ THIS PROJECT IS A WORK IN PROGRESS ⚠️

🦿Hardware

• Microcontroller: Adafruit Feather ESP32-S3 (no PSRAM)
• Servo Controller: Adafruit 8-channel PWM Servo FeatherWing (PCA9685)
• Servos: 8x MG90S digital servos
• Battery Monitor: MAX17048 LiPo fuel gauge Not viable: will have to work out a setup with a simple voltage divider going to an analog pin on the feather
• Physical Design: Based on miniKame quadruped
  • 3D printed parts
  • M3 machine screws, nuts, and nylock nuts
  • F693ZZ flanged bearings
  • Lego Technic Pins (part # 2780)

I am redesigning the main body to:

• have a lego-compatible mount on top for StackChan
• allow the top cover to be opened without removing the legs
• provide enough space to use an adafruit 8ch PWM wing with right angle headers

Firmware

This project contains two PlatformIO firmware modules:

• firmware/legs-esp32s3 — gait controller for the quadruped body
• firmware/controller-cardputer — handheld remote for driving and testing

Each folder is a standalone PlatformIO project with its own platformio.ini.

Servo Configuration

Servo 0: Front Left Hip
Servo 1: Front Left Foot
Servo 2: Back Left Hip
Servo 3: Back Left Foot
Servo 4: Back Right Hip
Servo 5: Back Right Foot
Servo 6: Front Right Hip
Servo 7: Front Right Foot

Communication Protocols

1. ESP-NOW Wireless Control

• Format: 2-byte commands
• Controllers: M5Stack Cardputer, M5Stack Stack-Chan, or any ESP32 device
• Pairing: Auto-accepts commands from any sender (no MAC whitelist)
• Range: ~100m line-of-sight (typical ESP-NOW range)

Command Format:

• Byte 0: Command type (see command table below)
• Byte 1: Command value (typically number of steps)

Example (Arduino):

uint8_t command[2] = {0x02, 5};  // Walk forward 5 steps
esp_now_send(robotMAC, command, 2);

2. Serial Debugging (USB)

• Baud Rate: 115200
• Interactive Commands:
  • h - Move to home position
  • z - Zero all servos (90°)
  • w - Walk forward 3 steps
  • b - Walk backward 3 steps
  • t - Turn left
  • s - Emergency stop
  • r - Resume from emergency stop
  • c - Enter calibration mode
  • q - Show queue count

Command Protocol

Command	Type	Value	Description
Stop	0x01	0	Stop movement and return to home
Walk Forward	0x02	1-255	Walk forward N steps
Walk Backward	0x03	1-255	Walk backward N steps
Turn Left	0x04	1-255	Turn left N steps
Turn Right	0x05	1-255	Turn right N steps
Moonwalk Forward	0x06	1-255	Moonwalk forward N steps
Moonwalk Backward	0x07	1-255	Moonwalk backward N steps
Jump	0x08	0	Perform jump animation
Shuffle Left	0x09	1-255	Lateral shuffle left N steps
Shuffle Right	0x0A	1-255	Lateral shuffle right N steps
Emergency Stop	0xFF	0	Immediate stop all movements

Movement Library

The robot uses an oscillator-based movement system inspired by the original miniKame. Each servo is controlled by a sinusoidal oscillator with configurable:

• Amplitude: Range of motion in degrees
• Offset: Center position offset
• Phase: Phase shift for gait coordination
• Period: Time for one complete cycle

Available Gaits

1. Walk - Standard alternating tripod gait for forward/backward movement
2. Turn - In-place rotation using differential leg movement
3. Moonwalk - Smooth sliding motion (Michael Jackson style!)
4. Lateral Shuffle - Side-stepping movement
5. Jump - Quick up-down animation

Command Queue

• Queue Size: 16 commands
• Processing: First-come-first-served (fair arbitration)
• Priority: Emergency stop (0xFF) interrupts immediately

Battery Management - Not currently working (pun intended).

• Low Battery Threshold: 3.4V or 20% charge
• Behavior: Restricts movement commands when battery is low
• Monitoring: Checks every 10 seconds
• Status: Reported via serial output or can be polled from ESP-NOW

Servo Calibration

Trim values can be saved to non-volatile storage (Preferences):

// Trim values stored as:
preferences.putInt("trim0", value); // -50 to +50 typical range
...
preferences.putInt("trim7", value);

• numbers 0..7: select a servo
• +/-: jog servo forward or back
• p: print currently selected servo

TODO: Implement interactive calibration interface via serial

Building and Flashing

# Using PlatformIO
pio run -t upload

# Monitor serial output
pio device monitor

Example Usage

Example Usage

// From any ESP32 controller (Cardputer or Stack-Chan)
uint8_t command[2] = {0x02, 5}; // Walk forward 5 steps
esp_now_send(robotMAC, command, 2);

// Turn left 3 steps
uint8_t command[2] = {0x04, 3};
esp_now_send(robotMAC, command, 2);

// Jump
uint8_t command[2] = {0x08, 0};
esp_now_send(robotMAC, command, 2);

Safety Features

1. Emergency Stop: Stops all movements immediately
2. Low Battery Protection: Restricts movement on low battery Not yet implemented
3. Command Queue Overflow: Warns if queue is full
4. Servo Limits: PWM values clamped to safe range (204-410)

TODO / Future Enhancements

• Interactive calibration interface via serial
• MAC address whitelist for ESP-NOW security
• EEPROM-based movement sequence storage
• Sensor integration (IMU for balance, ultrasonic for obstacle detection)
• Smooth movement interpolation between gaits
• Custom choreographed dance sequences
• OTA (Over-The-Air) firmware updates
• New battery monitoring using voltage divider to analog pin

Credits

• Original miniKame design by Javier Isabel (JavierIH)
• Oscillator-based gait system inspired by Obijuan's work
• Hardware stack by Adafruit Industries

License

This project inherits the Creative Commons BY-SA license from the original miniKame project.