Re: Using USB Sensors?
 

Beta testing team here. The RoboRIO has *some* support for USB<->Serial devices, like the Arduino and other FTDI devices. You should not need an ethernet shield to do this. Be careful about powering the Arduino over the USB on the RoboRIO though. I don't think it will let you pull more than 500mA (USB Spec) so no massively long blinky LED chains.

Re: Using USB Sensors?
 

You can install additional drivers on the RoboRIO (provided it supports Linux) so software is generally not an issue. For USB, National Instruments does have a "durable" USB cable they were showing at St. Louis this year.

http://sine.ni.com/nips/cds/view/p/lang/en/nid/210962

Additionally, you could try using direct RS-232 or I2C with the arduino.

Re: Using USB Sensors?
 

You could always attempt something similar using a camera pointed at the floor. NI provides some pretty easy to use optical flow VIs.

Re: Using USB Sensors?
 

Alas a standard webcam won't have nearly the frame rate necessary to keep up with a robot moving at 15ft/s. That's why mice have always been interesting since the new gaming mice have some pretty significant specialized processing power on-board. It is the case that some optics magic will need to take place in order to not have the mouse dragging on the carpet.

Re: Using USB Sensors?
 

500 mA is the USB 2.0 spec'd max current for Vbus. You should not generally expect more than that from that standard.

That said, the roboRIO is designed to be able to operate with USB 3.0 cameras (at USB 2.0 data rates), but that means roboRIO can source 900 mA per host port so that those cameras function reliably.