The Vex Cortex 2.0 controller was working fine with the wireless keys and the controllers before I changed it to radio controlled. Now the Vexnet light on the Cortex is not blinking anymore and I tried redownloading the firmware and everything but nothing seems to be working. How do I switch it back to vexnet?

Hi Henry -

I'm assuming that you unplugged the RX receiver from the Cortex completely?

One thing you might check is what your "VEX Cortex Download Method" is set to in ROBOTC. Go to Robot > VEX Cortex Download Method, and choose "Download using VEXnet or USB".

If this was not selected, you will need to redownload your program once you select it. Afterward, you may also need to power cycle the Cortex before it takes effect.

Yes I did unplug the Rx receivers. I tried power cycling and redownloading firmwares multiple times on both the microcontroller and the joystick but the Vexnet light is not blinking at all. And I do have the download method on "Download using VEXnet or USB" in robotc. What else might be the problem?
And just another question, is the cortex controller more radio senstive? Because when I first tried it with the radio controllers, the robot glitches and moves even when the controllers' buttons are not pressed. Is that a common problem? If so, how can I fix it? It seems very unreliable and that's why I gave up using radio control and use the new joysticks instead and now our team must order another of the new joysticks.
Thanks.

Another thing you might try is to manually re-link your Cortex and VEXnet Joysticks. We have instructions on how to do that here: http://www.education.rec.ri.cmu.edu/products/teaching_robotc_cortex/reference/VEXnet_setup_guide.pdf

The Cortex shouldn't be any more or less sensitive than the PIC radio-wise. What may be happening is that the joysticks on the Radio Transmitter are sending non-zero values, even when they're centered. This tends to happen after the Radio Transmitter has had a decent amount of use. You can adjust the trim on the joysticks to ignore some of the small non-zero values. Instructions here: http://content.vexrobotics.com/docs/inventors-guide/main-2008/06-control-06272008.pdf

The other possibility is that there is another piece of equipment nearby that is operating on the same or a very similar frequency as the Transmitter, causing interference and false values to be sent to the robot.