People have been looking into using PCTx to have the PC talk directly to their transmitter. Yes, for this setup you will still a transmitter.
You can use an Xbee to talk directly to the copter, but 1. I don't think direct control via Xbee is supported by the software, and 2. I don't know if the data rate over an Xbee will be fast enough.
Personally, I've only been able to work with the default mode which sends an ASCII character per packet... but that's at least 8-times slower than what could be done if the packets where raw numerical data.
Will the PCTx work with the Turnigy 9x Controller?
If it has a trainer port, then it should.
I don't have any new or working transmitters with me. :( But I did see at least one that had a DIN socket, which should be the trainer port.
You will need an RC transmitter and receiver to operate the ArduCopter, if only to arm the motors and perform certain tuning functions and auto-trim. You can get a cheap transmitter and receiver for about $60. You should also really have the transmitter available as your failsafe method of controlling the copter, even if you fly from a joystick. You might lose xbee connectivity during the flight, and you might even have time to switch over to the RC controller (maybe)
There are a few members here who operate mainly with joysticks, I have no experience with flying by joystick so I cannot offer any advice.
If you code, it is possible to code around the RC transmitter requirement, but you will be patching throughout the releases.
The PC communicates with the copter over either USB or via its 3rd TTL port. The Xbee adaptor on the copter is normally attached to the "telemetry port", which is Serial3, the 3rd TTL port. If you get the Xbee telemetry kit (and have a soldering iron) you'll have what you need to communicate wireless to the copter while in flight. The 900Mhz is useful in the US, but uses frequencies not permitted in all countries. You didn't list your location, so I will not spend time guessing.
Under windows, you will need to download and install the FTDI driver to use the Xbee adaptor. Instructions are in the manual for setting up the Xbee. Follow the instructions carefully.
Well first, thank you so much for the detailed responses. That helps me a ton. As for the 3rd TTL port, are you saying i have to choose either telemetry or remote control? Can i not have both? PCTx looks like a good solution too.
also, with the control and telemtry data, could i still use the 900mhz band to send video. I am in the US.
Yes, the xbee uses spread spectrum. Unless your video transmitter steps on the entire band, you can use both at the same time. You might get some interference, depending on how bad your inter mod or VSWR is.
Telemetry is via the MAVlink protocol. This is sent to/from Serial3, the most common method is attaching an Xbee radio and adaptor to this TTL.
"Remote Control" comes in two forms, via the RC receiver, and via the ground control station. If the ground control allows joystick input, like Mission Planner, then that data is also sent over the MAVlink link (which may be over xbee to the Serial3/TTL, or may be over USB to the USB/Serial0 port, or it may be to either Serial0 or Serial3 via some other medium of your choose.