PID Motor Control

Closed-loop PID motor controller on STM32 Nucleo-F411RE with real-time IMU feedback. Live tuning via UART CLI, step response capture to CSV for plotting.

Hardware

Architecture

TIM3_CH1 (20 kHz PWM) --> TB6612FNG --> DC Motor
                                          |
MPU-6050 (I2C, 14-byte burst read) <-----+
    |                                  (physical coupling)
    v
Complementary Filter (alpha=0.98)
    |
    v
PID Controller (1 kHz, TIM2 ISR)
    |  - Derivative on measurement
    |  - Low-pass filter on D term (N=10)
    |  - Integral clamping anti-windup
    v
Motor effort (-1.0 to +1.0) --> sign-magnitude drive

Control Design

The PID loop runs at 1 kHz in TIM2’s update ISR. Three techniques keep the output clean:

Derivative on measurement – the D term differentiates the process variable, not the error signal. This eliminates the derivative kick that occurs when the setpoint changes abruptly.

Low-pass filter on D term – a first-order filter with N=10 smooths high-frequency noise from the IMU without adding significant phase lag at the control bandwidth.

Integral anti-windup – the integrator is clamped to the output range. When the motor saturates, the integrator stops accumulating, preventing overshoot on recovery.

UART CLI

The main loop runs a serial command interface for live tuning:

Step response data streams as CSV over UART for offline plotting with scripts/plot_step_response.py.

Build

mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
make

Flash via ST-Link SWD.