Thanks for the help Paul!
PaulS:
You got that right.The simplest solution for your problem is the use the X value to determine the speed for both motors, assuming you want to move straight ahead at some speed. Then use the Y value to determine how much to increase the speed of one motor and decrease the speed of the other.
Suppose that you read 800 from X and 600 from Y. The 800 value is greater than the midpoint, so you want to go forward. It's beyond halfway to maximum, so you want to go just over half the maximum speed forward.
The 600 value is greater than the midpoint, so you want to steer to the right. It's only a little to the right of the midpoint, so you want the left motor to spin just a little faster, and the right motor to spin just a little slower. How much faster and slower will be something you experiment with.
Suppose that you read 600 from X and 1000 from Y. Now, you don't want to be traveling very fast, but you want a large difference between the left (faster) and right (slower) motors.
If you read 800 and 400, the turn is to the left, so the right motor goes faster (a little) and the left motor goes slower (a little).
Well, the problem with that is, say you're pointing the stick at between 2 and 3 o'clock. Because the speed is measured in the Y axis, both motors would be going pretty slow, when what wold be more practical is that when you're pushing the stick to that in between 2 and 3, the left motor would be going quite strong and the right one quite weak.
PaulS:
Do you really expect that mapping the same value to the same ranges might result in different values?
That was actually intentional of my part, I knew it was redundant. Not too useful though so I'll delete it.