I just wanted to give a shout out here to the fantastic work that MikeB has been doing over at openrc forums with firmware for the Turnigy 9XR Pro transmitter. You can pick up one of these transmitters (sans module) for about $50 from HobbyKing, and you get something that, once you’ve added the open source ersky9xr firmware, can…
…can support at least 16 channels (depending on your tx module)
…has firmware support for the “serial” mode on the multiprotocol modules, so you can perform protocol selection et al via the menu interface
…can be connected to your computer as a USB joystick (great for simulators!)
…has native support for FrSky telemetry (including Ardupilot-specific telemetry)
…and so much more!
I have been very happy using my 9xr pro with Ardupilot.