The Happymodel Mobula7 is a 2S whoop class drone. I pre-ordered immediately after watching UAVfutures’ review. Stew described the Mobula7 as, “The most impressive whoop I’ve ever seen.” I think it would be hard to fake the enthusiasm in the video.

I bought the EU-LBT version of the Mobula7: EU-LBT Mobula7

LBT stands for listen before talk and is, according to Painless 360, mandated in the EU by ETSI EN 300 328 V1.8.1. Listen before talk is mechanism by which a transmitter first checks if a channel is in use before transmitting.

The EU-LBT receiver version of the Mobula7 currently costs 12% more than the other receiver versions, weighs more and has two extra antennas that increase drag. The extra cost and weight is due to an external Frsky XM+ receiver. According to the manufacturer, the XM+ receiver weighs 1.6 grams.

XM+ receiver in Mobula7: XM+ receiver in Mobula7 Mobula7

The EU-LBT and non-EU versions of the FrSky protocol use the same frequency band and hardware. The only difference is the firmware that runs on the transmitter and receiver.

The Mobula7 uses a Racerstar Crazybee F3 Pro Flight Controller which is available in three versions:

  • Compatible DSM2/DSMX Receiver
  • Compatible Flysky Receiver
  • Compatible Frsky Receiver (non-EU)

Non-EU Frsky support is provided by a TI CC2500 2.4 GHz RF Transceiver soldered directly on to the Crazybee F3 Pro.

The TI CC2500 transceiver chip is used both by FrSky and other transmitter manufacturers e.g. Futaba.

According to the Betaflight FrSky SPI documentation RX, FrSky protocol support has been added by a third party, midelic, who reverse engineered the FrSky protocol. This code is is part of Betaflight (but currently not INAV)

The Multiprotocol TX Module is another project that has reverse engineered the FrSky protocol. It also uses the TI CC2500 chip. The Multiprotocol TX Module supports both EU and non-EU versions of the FRSKYX aka D16 protocol which leads me to believe there is no reason why the Betaflight receiver could not also support the EU-LBT version FrSky protocol. The Frsky XM+ receiver was only added to the EU version of the Mobula7 because of missing software support in Betaflight.

I did not know any of this when the Mobula7 arrived. Transmitter binding instructions came in the box but they had fallen on the floor. The binding instructions I found on Youtube did not work for the EU-LBT version because you have to bind the external Frsky XM+ receiver not the receiver soldered onto the flight controller.

Maybe in the future, support for the EU-LBT FrSky protocol will be added to Betaflight. I raised a feature request.