[TD912]

The joysticks return values between -1 and +1 for both the X and Y axes, And these values are then used to generate a signal for the speed controller. You can "curve" the output however you want. Normally, moving the joystick 50% forward would send a 0.5 signal to the contoller. Squaring it should give you finer control at lower speeds (moving the joystick 50% forward would result in a 0.25 signal being sent), while getting the square root would do the opposite (50% forward would end up sending a 0.71 signal instead!). In either case, you could still achieve full speed by moving the joysticks all the way forward. You should experiment to see what works best for you, and be sure to program in a way to keep your positive values positive, and negative values negative when squaring.

Just remember that the motors will still need to be able to produce enough force to move the robot, Plus there are things like deadband to deal with, so very low values like .1 might not appear to do anything.

Edit: By the time I typed this up, all these people replied already! Sorry if I repeated what was already said.