Motor PID Control

Objective: Designed and implemented a closed-loop motor control system using a PIC32 microcontroller, with a Python interface for real-time interaction and data visualization.

Requirements: Develop current and position control using nested PID loops, communicate with a brushed DC motor via UART, and achieve reliable motion control with tunable gains and trajectory tracking.

Top Skills: embedded C (PIC32), Python UI, control systems (PID), UART communication, real-time motor feedback, system integration

Overview

This three-week Intro to Mechatronics project focused on creating a closed-loop motor control system from the ground up. I programmed the PIC32 microcontroller in C to control a brushed DC motor through a DRV8835 H-bridge, with sensor feedback from an encoder and a MAX9918 current amplifier. A Python client communicated with the board via UART, allowing real-time interaction, gain tuning, and trajectory execution. This project gave me hands-on experience with low-level embedded systems, real-time control, and hardware-software integration.

System Architecture

• Microcontroller: PIC32MX170F256B via NU32 board

• Motor: Brushed DC motor with quadrature encoder

• Current Sensing: MAX9918 amplifier with 15 mΩ shunt resistor

• Actuation: DRV8835 H-bridge circuit controlled via PWM

• Control Loops:

  • Inner current loop (PI) @ 5 kHz

  • Outer position loop (PID) @ 200 Hz

• Communication: UART over USB to Python interface

• Power: 6V battery pack

Feature Implementation

• ✅ Encoder interface for count and angle (degrees) with reset option

• ✅ Current sensor reading in both ADC counts and calibrated mA

• ✅ PWM control with user-specified duty cycle

• ✅ Set/Get PID gains for both current and position control

• ✅ Interactive UI (Python) with a menu of 20+ real-time commands

• ✅ Current loop test (ITEST) with error calculation and plotting

• ✅ Angle hold mode for precise position control

• ✅ Trajectory loading (step or cubic) using genRef()

• ✅ Trajectory execution and plotting of actual vs. reference angles

Sample Outputs

• Current Control ITEST Example:

  • ±200 mA square wave reference

  • Achieved avg. error: ~32 mA with tuned PI gains

• Step Trajectory Tracking:

  • 0° → 180° → −90° → 0° → 45°

  • Held within ±5° of target

• Cubic Trajectory:

  • Smooth reference transitions

  • Minimal overshoot with PD tuning

The videos for these demonstrations are shown below:

Key Takeaways

This was my first time building a fully functional embedded motor control system with real-time feedback. I gained hands-on experience writing ISR-based control loops, developing UART communication protocols, and integrating hardware with software. Tuning nested PID loops gave me a deeper understanding of control dynamics, and writing modular C code for embedded systems taught me good design practices for scalability and debugging.