1. As has been said, you can't control a Jaguar, Victor, or Talon directly with a potentiometer.
2. There are other COTS speed controllers (not FIRST-legal) that accept analog input. I've used the Sabertooth series in personal projects before and have been happy with them. Some models from this series accept analog input, and there are models that can switch up to 60A per motor channel. You can get them on
Trossen Robotics or
Robot Shop
3. If you want a remote-controlled system that requires no programming, that's entirely possible. The PWM signal that Jaguars, Victors, and Talons accept is a standard signal type outputted by many (if not most) hobby RC systems.
4. If you're looking to easily test your speed controllers without the need for a microcontroller, AndyMark has a
product for that, or you can build your own version, as has been said.
__________________
FRC 2046, 2007-2008, Student member
FRC 1708, 2009-2012, College mentor; 2013-2014, Mentor
FRC 766, 2015-, Mentor