[maya] Tank rig expression sideways movement (Not my model)

m00k

I'm working on this tank rig for school and we have to, by way of expression limit the movement in logical ways. For instance when it moves sideways there should not be any movement. Which I'm kind of stumbling on at the moment there is just a simple Y angle analysis of the tank controller and that controls which way the tracks move.



I was wondering if it would be possible to do a vector analysis if the movement is 90d to the way the tank is facing then it would not move for instance. And it might be possible then to adapt that vector analysis to other situations to replace the rudimentary y angle check.

float $LbigWheelDia = 2.707961;
float $LbackWheelDia = 2.010008;
float $LfrontWheelDia = 1.545769;

float $trackLength = 18.3076935232;

global float $oldX = 0.0;
global float $oldY = 0.0;
global float $oldZ = 0.0;

float $changeX = tankRoot.translateX - $oldX;
float $changeY = tankRoot.translateY - $oldY;
float $changeZ = tankRoot.translateZ - $oldZ;


float $distance = sqrt( $changeX * $changeX + $changeY * $changeY + $changeZ * $changeZ);
float $angle = tankRoot.rotateY % 360;

int $switch = 1;
int $switch2 = 1;

if ($changeZ < 0)
  $switch = $switch * -1;

if (($angle == 90 || $angle == -270) && $changeX < 0)
  $switch = $switch * -1;

if ( ($angle == -90 || $angle == 270) && $changeX > 0)
  $switch = $switch * -1;

if ($angle > 90 && $angle < 270)
  $switch = $switch * -1; 

if ($angle < -90 && $angle > -270)
  $switch = $switch * -1; 

if ($changeX == 0 && $changeZ == 0)
  $switch2 = 0;
else
  $switch2 = 1;

L_GearWheel.rotateX = L_BigWheel.rotateX * -2 % 360;
L_FrontWheel.rotateX = L_BigWheel.rotateX * ($LbigWheelDia / $LfrontWheelDia) % 360;
L_BackWheel.rotateX = L_BigWheel.rotateX * ($LbigWheelDia / $LbackWheelDia) % 360;

tankRoot.LtrackMovement = L_BigWheel.rotateX * ((3.1415 * $LbigWheelDia) / $trackLength) / 360 * 21 ;

L_BigWheel.rotateX = L_BigWheel.rotateX + ($distance / (3.1415 * $LbigWheelDia) * 360 * $switch * $switch2)% 360;

$oldX = tankRoot.translateX;
$oldY = tankRoot.translateY;
$oldZ = tankRoot.translateZ;

m00k

Found this video! This is basically what I wanted

https://www.youtube.com/watch?v=QpDc93br3dM

m00k

Alright this is my expression now but I'm running into a new problem. At times when turning in place  the dot product becomes 0 and the track jitters.

m00k

The expression editor in maya is a little buggy. When I restarted maya it worked fine...