Re: robot with mecanum wheels
It is possible to wire each of the four motors to one of four different channels on your RC system. However, this probably won't give you the control scheme you're looking for.
The standard way to control a mecanum drive is to have one joystick that moves the robot forward, backward, left and right, and a second joystick that controls the robot's turning. All RC systems that I've ever seen have at most what's usually called "V-tail mixing" between two channels at a time, but don't support the more complex arrangement of combining three three input channels (forward/back, strafe left/right, and turn) to generate four output channels.
There is, however, an off-the-shelf modular product that performs the appropriate mixing for a mecanum drive: http://www.robotmarketplace.com/products/RL-MECANUM.html
. You can also, of course, use a programmable controller to do the appropriate mixing operations as well.