nrf24l01 + old aritronics + L298N need a little help.

Using Arduino Programming Questions
17

I still need an answer to the above question, but I have something to add to it.

If I do this;

  leftAdcVal = joystick[0];           // range 0 to 1032
  leftMotorVal = leftAdcVal - 513;    // range -511 to +510
  // subtracting 513 (rather than 512) ensures that no later value will exceed 255
  Serial.print("LMotor = ");
  Serial.println(leftMotorVal);

My serial monitor spits out values I would expect given my joystick max and min limits.

LMotor min is -98 LMotor max is 91.

If I change that snippet to this;

  leftAdcVal = joystick[0];           // range 319 to 567
  leftMotorVal = leftAdcVal - 64;    // range -64 to +64
  // subtracting 513 (rather than 512) ensures that no later value will exceed 255
  Serial.print("LMotor = ");
  Serial.println(leftMotorVal);

The serial output falls back to giving a max reading of 540 and min of 352.

I may just be a very slow school teacher trying to learn how to code, but to me math is math and should give me predictable results. What's up with that?