Open esc

Open-Source 3-Phase Sensorless ESC Firmware

This is an open-source firmware for controlling 3-phase sensorless BLDC motors using an ATmega88PA microcontroller running at 8 MHz (internal oscillator).
It is designed for small electric vehicles, drones, robotics, and DIY ESC applications.
The design uses 6 MOSFETs in a three-phase bridge configuration and includes back-EMF sensing for sensorless commutation.

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Features

• Sensorless 6-step (trapezoidal) commutation
• Automatic open-loop startup
• Zero-cross detection via ADC ISR
• Hardware timer-based phase PWM with dead-time
• RC PWM input for speed control
• Optional serial interface (UART) for speed setting
• Direction control and braking support
• Dead-time insertion to prevent MOSFET shoot-through
• Auto-calibrated ADC thresholds for zero-cross detection

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Schematic Overview

The system includes the following main blocks:

Microcontroller

• ATmega88PA, powered at 5V using AMS1117-3.3 regulator from +BATT
• Internal 8 MHz oscillator (no external crystal)
• Key pins used:
  • PD2 → PWM input (from RC receiver)
  • PD3/PD4/PD5 → High-side MOSFET gates (AH, BH, CH)
  • PB0/PB1/PB2 → Low-side PWM outputs (AL, BL, CL)
  • PC0/PC1/PC2 → ADC inputs for Phase A/B/C sensing (A0, A1, A2)

Power Stage

• 3-phase half-bridge using 6 MOSFETs (Q1–Q6)
• High-side: A03401A
• Low-side: IRLML0030
• Gate resistors to control switching speed and prevent ringing

Back-EMF Sensing

• Analog divider + DC blocking on each motor phase
• Inputs go to A0, A1, and A2
• Used for zero-cross detection in closed-loop mode

PWM Input

• Connected to D2 for RC signal input (standard 1–2 ms pulses)
• Used to control speed and direction
• Interrupt-based decoding for accurate readings

Serial Debug (optional)

• Via UART (TX/RX, PD0/PD1)
• Can be used to override speed or monitor state

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How to Use

1. Assemble the Hardware

• Follow the schematic to build the ESC on a PCB or breadboard
• Ensure proper power filtering (C2, C3–C6)
• Use heatsinks or airflow on the MOSFETs if under heavy load

2. Upload Firmware

• Connect AVR ISP programmer to the 6-pin header
• Use AVRDude or the Arduino IDE
• Ensure fuse bits are set for:
  • Internal 8 MHz clock
  • No clock division
• Upload the .ino firmware file

3. Calibrate Zero-Crossing (Auto)

• When powered, the firmware automatically calibrates ADC offset thresholds
• Ensure the motor is disconnected or not rotating for accurate calibration

4. Run

• Connect an RC receiver or PWM generator to D2
• Pulse width controls speed and direction:
  • < 1480 µs = reverse
  • 1480–1520 µs = brake
  • > 1520 µs = forward
• Motor will spin up in open-loop mode and switch to sensorless control

5. Serial Control (Optional)

• Connect USB-to-serial to TX/RX
• Open serial monitor at 115200 baud
• Send a value from 0–255 to manually set the speed (for testing/debug)

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Motor Braking and Reverse

• Controlled by PWM signal:
  • Brake mode: both high and low sides turned off briefly
  • Reverse: same commutation order but in reverse
• No position feedback required

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Dead-Time Handling

• Implemented in software by carefully disabling/enabling high/low MOSFETs with a short delay (a few µs)
• Prevents simultaneous conduction and shoot-through

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Files Included

• ESC_Firmware.ino – Full firmware with PWM control, ISR ADC, RC interface
• README.md – Project documentation
• Schematic (.png) – Visual hardware design

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Supported Microcontrollers

• ATmega88PA (default)
• Can be ported to ATmega328P with minimal changes

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Test Points

• TP1–TP3: Phase voltages for probing/debug
• TP6: PWM input
• TP5: GND
• TP4: +BATT

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Pictures

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Safety Notes

• Always test with low-voltage supply first
• Double-check gate drive signals with oscilloscope
• Use overcurrent and overtemperature protection externally if needed

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License

MIT License — You can freely use, modify, and distribute this project.

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Author

Created by [Your Name / GitHub Handle]
Feel free to fork, improve, and contribute via pull requests!