BLHeli_S ESC firmware

BLHeli_S is a new custom ESC firmware based on the most popular BLHeli firmware – it is an improved version. Here is an overview of the new features and which ESCs support the new BLHeli_S firmware.


  • Very smooth throttle response
  • Generally does startup better than base BLHeli
  • Only damped light mode
  • Synchronous motor PWM to the MCU master clock
  • Very small throttle steps
  • Very high motor speeds – up to 500k erpm
  • OneShot 42, MultiShot

Most of the new BLHeli_S ESCs have the Silabs BusyBee 2 MCU – EFM8BB21F16. It runs at 48Mhz and just like the Silabs F39x MCU, it´s an 8bit MCU. The main factor for the smooth throttle response as well as for the synchronous motor PWM is the hardware generated PWM signal by that MCU.

The new BLHeli_S firmware is not available for F330 or F39x ESC (for now). I doubt these MCUs will be supported in the feature, cause of hardware limitations. They do support hardware generated PWM, but “can not get symmetrical deadtimes for PWM on and PWM off when you have a H/L type driver” as sskaug mentioned in the RCGroups thread.

Because of the synchronous motor PWM to the MCU master clock, the motor is very silent now. I was really amazed! It should also remove some micro vibrations, which are the multirotors worst problem.

BLHeli_S support regular 1-2ms input signal, OneShot125, OneShot42 and MultiShot. I have tested MultiShot on my XRotor 10A (F396 MC) in the last month and throttle was very smooth compared to “normal” OneShot 125. So far the only ESC, that I know to support OneShot42 was the KISS24A. Will be interested to see how the new BLHeli_S ESC will perform with my KISS FC.

Just like the standard BLHeli ESCs, you can easy flash and setup your new BLHeli_S based ESC through your flight controller using the passthrough protocol.

BLHeli_S supported ESC:

  • DYS XS 20A & DYS XS 30A
  • EMAX Lightning_S 35A
  • Maytech MT25A-OPTO-BK2 &  MT30A-OPTO-BK2
  • Maytech MT20A-OPTO-BK1 & MT30A-OPTO-BK1
  • LittleBee 20A-S
  • Racerstar 30A
  • Racerstar MS 15A, 25A, 35A / ZTW Polaris
  • Flycolor Raptor BLS

Summary: Personally I think, that the new BLHeli_S firmware and supported ESCs will massively improve your flight experience. Throttle smoothness and response are essential for a precise flight and you get these with the BLHeli_S firmware. The available ESCs are not much for now, but it is just a matter of time.

Thanks to ZTW I got some ZTW Flash 30A ESCs for tests. I am going to publish the review soon, so make sure you get the latest news by liking the Facebook page.

Update: Review, thrust and efficiency data of almost all listed BLHeli_S can be found here.

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