How to make non-sensored BLDC Motor?

Here's how to approach creating the sensorless control system:

Phase 1: Hardware Design (The Sensorless ESC)

1. Microcontroller (MCU):

   • Choose an MCU with sufficient speed, ADC channels, PWM outputs, and timers (e.g., STM32, ATmega, ESP32, PIC, TI C2000).

   • Needs fast ADC sampling for Back-EMF detection.

2. Power Stage (Inverter):

   • MOSFETs: Select N-channel MOSFETs with low Rds(on), appropriate voltage/current ratings, and fast switching. Often 6 MOSFETs in a 3-phase bridge configuration.

   • Gate Drivers: ICs to boost MCU PWM signals to drive MOSFET gates quickly and safely (e.g., IR2101, IR2184, DRV830x).

3. Back-EMF Sensing Circuit:

   • Voltage Dividers: Resistor networks to scale motor phase voltages (which can be high) down to the MCU's ADC input range (e.g., 0-3.3V).

   • Low-Pass Filtering (Optional): Small capacitors to reduce high-frequency switching noise from PWM.

   • Isolation (Critical for High Voltage): Use operational amplifiers in differential configuration or isolated voltage sensors for safety and accurate measurement if the DC bus voltage is high (>60V).

4. DC Power Input:

   • Capacitors (bulk and decoupling) to smooth input voltage and handle current ripple.

5. Current Sensing (Optional but Highly Recommended):

   • Shunt resistors + amplifiers for phase/bus current measurement. Essential for advanced control, over-current protection, and torque control.

6. Communication/Interface (Optional):

   • UART, CAN, I2C for configuration/speed commands.

   • Basic PWM input for RC-style speed control.

Phase 2: Firmware Development (The Sensorless Algorithm)

This is the complex core. Key steps:

1. Initialization & Setup:

   • Configure PWM channels (Complementary, Dead-Time insertion), ADC (timed/synchronized sampling), timers, interrupts.

2. Motor Startup (The Biggest Challenge):

   • Align: Apply a fixed pattern to phases (e.g., energize A-B phases) briefly to "lock" rotor to a known position.

   • Open-Loop Acceleration: Gradually ramp up PWM duty cycle and commutate phases at a predetermined sequence/timing, ignoring position feedback. This builds enough speed to generate measurable Back-EMF.

   • Advanced Start Methods: "Initial Position Detection" (IPD) using inductance variation or "High-Frequency Injection" (HFI) can provide smoother starts but are more complex.

3. Back-EMF Zero-Crossing Detection (ZCD):

   • Sample Floating Phase: During commutation, one phase is floating. Continuously sample its voltage via ADC.

   • Virtual Neutral Point: Calculate the expected neutral point voltage (Vbus / 2) or measure it.

   • Detect Zero-Crossing: Compare the floating phase voltage to the virtual neutral point. When they cross, a ZC event occurs.

   • Timing: A ZC event typically indicates the rotor is 30 electrical degrees past the ideal commutation point. The controller must wait 30 degrees (based on current speed) before commutating.

4. Commutation Control:

   • Based on ZC timing and calculated speed, trigger the next commutation step in the 6-step sequence.

   • Adjust PWM duty cycle to control speed/torque.

5. Speed Estimation:

   • Measure the time between consecutive ZC events. Since 6 commutations = 1 electrical revolution, speed can be calculated.

6. Closed-Loop Control (PID):

   • Use speed error (desired vs. estimated) to adjust PWM duty cycle via a PID controller.

7. Protection & Diagnostics:

   • Over-current, over-voltage, under-voltage, over-temperature, stall detection.

Phase 3: Implementation & Debugging

1. Prototype: Build the ESC hardware on a development board or custom PCB.

2. Connect Motor & Power: Use a current-limited bench power supply initially! Connect the 3 motor phases.

3. Firmware Flashing & Basic Testing:

   • Test PWM outputs, ADC readings (phase voltages, currents), MOSFET switching.

4. Startup Tuning:

   • Crucial and tricky. Adjust open-loop acceleration ramp rate/duration. Use an oscilloscope to monitor phase voltages and detect ZC events.

5. Running Tuning:

   • Fine-tune the ZC detection filtering and timing offset (the 30-degree delay).

   • Tune PID gains for speed control.

6. Load Testing: Gradually apply load and observe performance/stability.

Key Challenges & Tips

• Startup Reliability: This is the hardest part. Expect lots of trial and error. Advanced techniques (IPD, HFI) significantly help but increase complexity.

• Low-Speed Operation: Back-EMF is weak. Requires excellent signal conditioning and filtering. May need current sensing for commutation.

• Noise: PWM switching creates massive electrical noise. Careful PCB layout (star grounding, short gate drive paths, shielded sensing) and analog filtering are critical.

• MCU Performance: Needs fast ADC sampling (often synchronized with PWM center) and computation for real-time control.

• Debugging Tools: An oscilloscope is essential. Logic analyzer helps with commutation sequence. Serial debug output is useful.

Starting Points for Hobbyists

1. Open-Source Firmware: Study and modify existing code:

   • SimpleFOC: Excellent Arduino-compatible library (supports sensorless).

   • VESC Project: Advanced open-source ESC platform.

   • BLHeli_S / Bluejay: Firmware for drone ESCs (highly optimized sensorless).

2. Development Kits: Use kits from TI (DRV830x), ST (STM32 PMSM FOC SDK), Infineon, Microchip. These include hardware and example code.

3. Pre-Built ESCs: Buy a cheap sensorless drone ESC (e.g., 30A BLHeli_S) to experiment with motor behavior before designing your own.

In essence: You "make" a sensorless BLDC motor system by combining a standard 3-phase BLDC motor (without Hall sensors) with a custom or modified Electronic Speed Controller (ESC) that implements a sensorless control algorithm based on Back-EMF zero-crossing detection. The complexity lies almost entirely in designing and programming the ESC. Start simple, use existing resources, and expect a significant learning curve!