From BEASTX Wiki
Maybe there is not enough movement or any movement at all on the rudder channel.
- Check servo throw and dual rate setting for the rudder channel in the transmitter and increase the throw.
- Receiver type "Standard": Check that the connector for the rudder channel (orange wire) is inserted correctly in the receiver.
- Is the correct stick moved? Check stick mode of transmitter and have a look at the servo monitor. Is there any movement on the channel that you have connected the orange wire for rudder function to (Receiver type "Standard")?
- Serial-wire receiver: Was the rudder channel assigned for rudder function at receiver setup menu?