Skystars F4 HD2 + KO55 3–6S BLHeli_S 4-in-1 ESC 30×30 Stack

The Skystars F4 HD2 + KO55 55A stack is a heavy-duty, digital-HD-ready electronic control stack engineered for 5-inch freestyle quads, aggressive racing rigs, and 6- to 7-inch long-range builds. Powered by the STM32F405 processor and paired with a 55A BLHeli_S 4-in-1 ESC, this 30.5x30.5mm stack handles 3-6S LiPo power configurations while providing dedicated hardware support for modern digital video transmitters and demanding flight characteristics.

Key features

• STM32F405RGT6 microcontroller: Runs at 168MHz with 6 full hardware UARTs for simultaneous connection of GPS receivers, RC links, telemetry, and HD digital air units.
• Dual high-output BECs: Features a clean 5V/3A rail for flight controller peripherals and a dedicated 10V/2A rail optimized for powering DJI O3 Air Units, Caddx Vista, and Walksnail systems without external regulators.
• KO55 55A 4-in-1 ESC: Delivers 55A of continuous current per channel (65A burst for 10 seconds), equipped with onboard TVS diode surge protection and a CNC-machined aluminium heatsink shield for thermal dissipation.
• Bluejay compatible BLHeli_S: Ships with BLHeli_S firmware that supports DShot300 and DShot600, ready to be flashed with Bluejay for full bidirectional DShot and RPM filtering capabilities.
• Plug-and-play digital HD port: Includes a dedicated 6-pin connector for direct, solder-free wiring to digital HD VTX transmitters, alongside reinforced solder pads for custom wiring schemes.

Specifications

• FC Processor: STM32F405RGT6 (168MHz)
• IMU / Gyro: BMI270
• Input Voltage: 3-6S LiPo (11.1 V – 22.2 V)
• ESC Continuous Current: 55 A (65 A burst, 10 seconds)
• BEC Output: 5 V / 3 A, 10 V / 2 A
• Blackbox Storage: 16 MB Flash
• Hardware UARTs: 6
• ESC Firmware: BLHeli_S (DShot300 / DShot600)
• Supported Firmware: Betaflight, INAV
• Mounting Size: 30.5x30.5 mm (M3 hardware)

The standard 30.5x30.5mm mounting pattern fits seamlessly into most mid-to-large multirotor frames. The stack kit comes complete with vibration-damping silicone grommets, XT60 power lead components, and interconnecting harnesses to ensure a clean, interference-free installation.