The BAC855 from Accelerated Systems Inc. (ASI) is a high-performance Field-Oriented Control (FOC) motor controller designed for brushless DC (BLDC) and permanent magnet synchronous motors (PMSM), widely used in e-bikes, scooters, and light EVs. It’s a favorite among e-bike enthusiasts for upgrading stock controllers (e.g., Bafang’s trapezoidal units) due to its efficiency, torque boost, and programmability.