Simplified - External High-Power Motor Driver Using RC ESC Output PWM Relay Polarity Swap

This circuit allows an RC receiver’s brushed-motor output (8.4 V PWM with polarity reversal) to control a separate high-power motor using any external supply voltage. Instead of building a full MOSFET H-bridge with high-side N-channel issues, this design uses: 1. Relay-Based Polarity Reversal Two SPDT relays form a simple mechanical H-bridge. When the ESC output polarity is “forward,” the relays stay in their NC position, feeding the motor normally. When the ESC output polarity reverses, the relay coils energize and flip to NO, swapping the motor leads. This gives full forward/reverse control with minimal parts. 2. Single-Direction PWM Power MOSFET The motor’s actual power does NOT come from the ESC. Instead: The ESC’s PWM signal (from the positive lead during forward and from the negative lead during reverse) is rectified and level-shifted to produce a clean gate-drive PWM. That PWM drives a single N-channel MOSFET (or several in parallel) on the low side of your own power supply. This avoids high-side complexity completely. 3. Flyback Protection Because the relays and motor are inductive loads: Each relay coil gets a flyback diode (1N4148 or 1N4007). The motor supply MOSFET gets a fast diode (Schottky or UF diode) across the motor. 4. Gate Protection and Stability To prevent ringing and ensure clean switching: Add a gate resistor (10–47 Ω) Add a 10 kΩ gate-pulldown Add a TVS or RC snubber across the motor if using high voltage 5. MOSFET Paralleling For higher current, multiple identical MOSFETs may be paralleled: Use individual small gate resistors per MOSFET Tie sources and drains together

published 5 months ago