Reaction Wheel - 775

Reaction Wheel Balancing Robot — Flywheel & Hub

Self-balancing inverted pendulum robot controlled by a reaction wheel. The flywheel spins up to 4600 RPM, generating gyroscopic torque to keep the robot upright — no wheels, no legs, just angular momentum

With proper PID tuning and desaturation algorithm the robot achieves indefinite balance for the entire battery runtime. The desaturation system continuously prevents wheel speed saturation by applying subtle setpoint corrections, keeping the reaction wheel in its effective operating range at all times.

Safety warning: At 4600 RPM the flywheel rim reaches ~37 m/s (133 km/h). A structural failure at this speed is extremely dangerous — flywheel fragments become high-velocity projectiles. Never use damaged, delaminated, or incorrectly printed parts. Always inspect the flywheel before each session. Do not exceed rated RPM. Keep bystanders away during first spin-up tests. The author takes no responsibility for any injury or damage resulting from improper use or print quality.

Safety analysis — verified telemetry

From a representative 15.6-second stable balancing session, sampled at ~428 Hz, using default configuration (pidPower 70%, motorPower 65.4%, 12V battery).

The regulator operates conservatively. In stable balancing, the controller uses only about 13% of available motor power on average, with brief excursions to 50% during disturbance recovery. The firmware PWM cap of 70% is never reached in normal operation, providing a comfortable margin against motor and driver limits.

The reaction wheel never approaches the motor's no-load speed. Maximum observed wheel speed is roughly half of the theoretical maximum, and typical operation runs at about 13% of that limit. This means the controller keeps the wheel well within its active-torque regime, where reaction wheel control is effective. Wheel saturation, the primary failure mode of reaction wheel pendulums, does not occur under default settings.

Pendulum stability is tight and deterministic. The controller maintains the pendulum within ±1° of vertical for 99.5% of the time, with a standard deviation of just 0.31°. The robot does not exhibit large oscillations, runaway behavior, or unstable limit cycles within the verified envelope.

Wheel speed values are estimated from PWM duty cycle and motor specifications (775 brushed motor, ~950 RPM/V no-load), not directly measured. Actual wheel speed may differ by ±20% depending on bearing friction, aerodynamic drag, and motor unit-to-unit variation. For precise measurements, install a tachometer or enable current-sense-based speed estimation (csEn=true in firmware config).

These values apply to the specific hardware configuration documented in the BOM. Changing the motor, battery voltage, wheel mass, or removing software limits will invalidate this characterization. Builders who modify the hardware should re-characterize their own system before assuming similar safe operation.

Firmware driver, webui app and blackbox debugger  - TBD