VESC HFI Guide: Improving Low-Speed Sensorless Accuracy

HFI helps VESC estimate rotor position more accurately at low speed for sensorless motors. It doesn’t dramatically change overall performance, but it improves low‑speed precision and can provide an advantage at race starts.

Reference video

Cautions when using HFI

• There are basic HFI and Silent modes (45 Deg/Coupled), and both produce continuous ultrasonic noise while active.
• Because very high‑frequency current is injected, keeping HFI active too long can overheat the motor, potentially deforming mounts or damaging the chassis.
• Noise and heat can be significant during setup, so test briefly and monitor temperature.
• When tuned well, low‑speed performance reaches about 95% of sensored motors, but you may still see occasional stutter (roughly 1 in 10 starts).
• Avoid long low‑speed runs with HFI enabled. Even without driving, continuous joystick signals (auto‑repeat) can keep HFI active and stress the motor and chassis.

VESC Silent HFI

Wrap-up

HFI is a useful tool for improving low‑speed sensorless control, but heat and noise are real concerns. Use short tests, watch for overheating, and stop immediately if abnormal heat or vibration appears.