Furuta pendulum controller

This is the controller I use for my Furuta pendulum: a Teensy 4.1 reads the pendulum encoder, commands an ODrive S1 over UART, and runs the balance and swing-up state machine. A local Web Serial dashboard handles setup, telemetry, logging, and supervised tuning.

The project is still an experimental controls platform, not a finished or safety-rated machine. Automatic swing-up remains disabled in the default configuration while I validate guarded trials on the hardware.

System

• Controller: Teensy 4.1 at a 200 Hz control rate
• Motor drive: ODrive S1 in torque control over isolated 115200-baud UART
• Pendulum sensor: AS5048A absolute encoder over SPI
• Interface: local browser dashboard over USB Web Serial
• Tooling: PlatformIO, native C++ tests, and Python log-analysis tools

The firmware starts disarmed and requires an explicit zero reference before motion. Motor-active modes also require a focused-page Spacebar dead man. Travel, speed, current, stale-feedback, watchdog, and control-deadline checks can stop a run independently.

What is implemented

• full-state upright feedback with measured mechanism parameters;
• guarded energy-shaping swing-up with automatic arm centering;
• checksummed ODrive UART feedback and AS5048A diagnostic checks;
• live telemetry, CSV capture, runtime gain selection, and a hardware-free demo;
• native tests for control math, protocol parsing, limits, and timing logic;
• a command-line tool for capturing and comparing supervised swing-up trials.

Build and test

Install PlatformIO, then run:

pio test -e native
pio run -e teensy41

Upload to a connected Teensy 4.1 with:

pio run -e teensy41 -t upload

Dashboard

Start the dependency-free local server:

python web/serve.py

Open http://localhost:8765 in Chrome or Edge and choose Connect Teensy. Add ?demo=1 to the URL to explore the dashboard without hardware. The server binds to 127.0.0.1 and the page loads no cloud resources.

Hardware connections

Power everything off before changing wiring. Teensy 4.1 pins are not 5 V tolerant.

Teensy 4.1	ODrive S1 isolated I/O
pin 0 / RX1	isolated UART TX / G06
pin 1 / TX1	isolated UART RX / G07
3.3V	isolated I/O supply
GND	isolated I/O ground

Teensy 4.1	AS5048A
pin 10	CSn
pin 11	MOSI
pin 12	MISO
pin 13	SCK
3.3V and GND	sensor power and ground

The ODrive must be calibrated separately and configured for UART before the firmware can communicate with it. Review every hardware value in include/config.hpp, especially direction, travel, current, and bus-voltage limits, before allowing motion.

Repository map

Path	Purpose
src/main.cpp	firmware state machine, control loop, and safety paths
include/config.hpp	measured plant values and commissioning limits
include/control_math.hpp	testable control and protocol math
web/	Web Serial dashboard and local server
test/	native PlatformIO tests
tools/	LQR reproduction and swing-up log analysis

The measured mechanism values are recorded in MECHANISM_DATA.md, and the controller derivation is in BALANCING_REVIEW.md. CAD assumptions behind the rotary inertia estimate are in CAD_MASS_PROPERTIES.md.

Current engineering values

Quantity	Value
Pendulum mass	0.159 kg
Small-angle period	0.7327 s
Pivot-to-COM estimate	0.05379 m
Pendulum pivot inertia	0.001141 kg m^2
Motor-axis to pendulum pivot	0.1815 m
Upright yaw inertia estimate	0.00561 kg m^2
Default balance gain	[-0.0700, 1.6000, -0.0692, 0.0900]

These values describe my current mechanism and should not be copied to a different build without re-measuring it.