Happymodel has added another flight controller in their portfolio – Happymodel Pancake FC with integrated OpenSource VTX and ExpressLRS RX. It is rare to see video transmitter and radio receiver integrated on the single FC board, except highly integrated whoop/toothpick AIO boards. Happymodel Pancake is an interesting exception.
Happymodel Pancake is powered by STM32F411 MCU and has old trusty MPU6000 gyro. Flight controller can be powered from 2-6S battery directly and has only one 5V power out regulator on board.
The board has multiple (20x20mm and 30.5×30.5mm) mounting options. The FC itself is 20x20mm mount size with breakable tabs for mounting on the bigger 30.5×30.5mm stack.
Onboard video transmitter is based on the open source project Open VTX (https://github.com/OpenVTx/OpenVTx). It can output 0, 25, 100 and 400mW output power. OpenVTX firmware also has so called RCE (Race) mode. It will force pitmode on boot and only use 25mW.
Onboard ExpressLRS receiver is connected directly to the MCU via SPI interface. This means the ExpressLRS receiver firmware is embedded into the Betaflight source code. You cannot update the ExpressLRS firmware separately from the Betaflight firmware. New ExpressLRS firmware versions must be updated in the Betaflight code and we all know how rarely the new Betaflight versions are released (approximately once in a year). This is the biggest problem with integrated SPI RX. ExpressLRS receiver has ceramic antenna on the board, so you don’t need to worry where to place the receiver antenna. The range is somehow limited in comparison to the regular antenna, so this board is definitely not for the long range.