Maya Script/rig For A Wheel

[fr-1]

hi there! i want to animate a bicycle and i have problems with the rotation of the wheel. i tried to script an expression but it's quiet hard. i can calculate the rotation-value of the wheel with the distance of the preverious x,z position-vector to the actual x,z by using pythagoras. but then i also have to take a look of the y-rotation of the wheel to know if a bigger x/z-value means a forward OR a backward rotation. does anyone know a script for that problem??? please help!

[joojaa]

Well i suggest you dont use a a incremental esxpression ,like this. while it can de done no bigger prpblem ist bad because its nota a determined answer. You can use path anim (path anim knows the exact distance traveled at all times scrub or no scrub) instead if you wish.

what you do is you take the cross product between your wheels plane normal and the velocity vector

anyway you can take the mag(corss(move amount, plane normal)) determine your trig function and the sign(dot(up, cross)) to determine direction

[dunkelzahn]

Sorry about my German, but I think you might be looking for something like this to determine the length of the translation for a full turn of your wheel for simplicities sake:

http://de.wikibooks.org/wiki/Formelsammlun...atik:\_Geometrie

An expression might look like:

translation axis character (length of path) = rotation axis wheel (one full turn)

You might think about adding a negative value for translation and rotation so you can move your character backward. The whole thing can also be done with a driven key, but I guess an expression is a cleaner solution (what do you say Joojaa?)

Viel Spa

[joojaa]

YEs second cleanest. BUt because its asim it carries a bit of problems that can arise at render/anim time because the expression dont evaluate when you jump around

[fr-1]

hey guys! if you want take a look on that expression i wrote. it works and that's all i wanted. but there a some problematic cases.

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

float $xAct; // the actual x-Value alias x2
float $zAct; // the actual z-Value alias z2
float $xPrev; // the preverious x-Value alias z1
float $zPrev; // the preverious z-Value alias z2
float $xDif; // Difference x1-x2
float $zDif; // Difference z1-z2
float $modYRot=control.rotateY; //modulo-value of the y-rotation-control-locator (wheel is attached to that)
float $xzDistance; //pythagoras for distance
float $WheelRadius = 1; // wheel-radius
int $reverse; //flag for rotation-direction 0 meens forward; 1 meens backwards

$xPrev = $xAct;$zPrev = $zAct;
$xAct = control.translateX;$zAct = control.translateZ;
$xDif = $xAct - $xPrev;$zDif = $zAct - $zPrev;

if($modYRot > 360){

while($modYRot>360){
	
	$modYRot=$modYRot-360;
}

}

if($modYRot < -360){

while($modYRot < -360){
	
	$modYRot=$modYRot+360;
}

}

if($modYRot == 0 || $modYRot == 360 || -360){

	if($zPrev < $zAct){
		$reverse = 0;
	}
					
	if($zPrev > $zAct){
		$reverse = 1;
	}

}
if(($modYRot > 0 && $modYRot < 90) || ($modYRot > -360 && $modYRot < -270)){

	if($xPrev < $xAct && $zPrev < $zAct){
		$reverse = 0;
	}

	if($xPrev > $xAct && $zPrev > $zAct){
		$reverse = 1;
	}

}

if($modYRot == 90 || $modYRot == -270){

	if($xPrev < $xAct){
		$reverse = 0;
	}
					
	if($xPrev > $xAct){
		$reverse = 1;
	}

}

if(($modYRot > 90 && $modYRot < 180) || ($modYRot > -270 && $modYRot < -180)){

	if($xPrev < $xAct && $zPrev > $zAct){
		$reverse = 0;
	}

	if($xPrev > $xAct && $zPrev < $zAct){
		$reverse = 1;
	}

}

if($modYRot == 180 || $modYRot == -180){

	if($zPrev > $zAct){
		$reverse = 0;
	}
					
	if($zPrev < $zAct){
		$reverse = 1;
	}

}

if(($modYRot > 180 && $modYRot < 270) || ($modYRot > -180 && $modYRot < -90)){

	if($xPrev > $xAct && $zPrev > $zAct){
		$reverse = 0;
	}

	if($xPrev < $xAct && $zPrev < $zAct){
		$reverse = 1;
	}

}

if($modYRot == 270 || $modYRot == -90){

	if($xPrev > $xAct){
		$reverse = 0;
	}
					
	if($xPrev < $xAct){
		$reverse = 1;
	}

}

if(($modYRot > 270 && $modYRot < 360) || ($modYRot > -90 && $modYRot < 0)){

	if($xPrev > $xAct && $zPrev < $zAct){
		$reverse = 0;
	}

	if($xPrev < $xAct && $zPrev > $zAct){
		$reverse = 1;
	}

}

$xzDistance = sqrt(($xDif)($xDif) + ($zDif)($zDif));

if ($reverse == 0){

wheel.rotateX = wheel.rotateX + $xzDistance*360/(2*3.1417*$WheelRadius);

}

if ($reverse == 1){

	wheel.rotateX = wheel.rotateX - $xzDistance*360/(2*3.1417*$WheelRadius);

}

//////////////////////////////////////////////////////////////////////////////////////////////////////////

http://www.frank-spalteholz.de/cinema/wheel\_test021.rar <- it's quick animated but it illustrates
that it works ... if you wnat please help me to simplify the script ... thanks for your atention and
helpful advises!

hank

[davvey]

Hi

I have recently put some scripts up on here to rig a vehicle for rotation etc using utility nodes. If you download them and look at the contents there is scripting top use utility nodes to calculate roation based on movement in X and Z planes. Also it takes account of rotation in Y plane to reverse direction automatically if vehicle is rotated more than +/-90 in Y plane. Also etc spin can be added if reuired based on time not movement.

The scripts are cirrently designed for setting up a four wheeled vehicle but if you edit the loops to only set up one or two loops it would set up a two wheeled vehicle.

If you want me to I will put up a set of modified scripts to do this.