Physics and gravity question with maya

[shapiro500]

Hey, I have a question about the physics and gravity in maya.

I want to make an animation where i juggle a ridiculous amount of balls. I would do this by filming me with my hands throwing invisible balls and then add the balls in with maya.

This is what i would like to do, and I am wondering if it is possible:
put in the direction of the ball
put in the end location of the ball
put in the gravity as 9.8
have maya fill in the ball's trajectory

is this possible? basically i just want to set where the ball starts and ends and how fast it is going, and then have maya fill in the direction of the ball so i can get the look of realistic physics. How would i do this?

[failure]

If you know start, end and velocity then the whole motion is defined. Nothing to fill in.

[shapiro500]

How do I do this in maya? If i have a sphere and i put it in the starting position and add a gravity field, it just acts under the field and falls. I can set an initial velocity but it looks like i have to specify in which direction. And if i keyframe a postion of the sphere then it doesnt have the effect of gravity any more.

[failure]

Yes, you've got the logic right. If you know the positions and/or velocities you just need to key them. If you don't know the behavior you need to input the initial conditions and forces into simulation and let it solve the movement.

In your case I suggest you just go and try to keyframe the animation. That way you have direct control over movement which may be important for believable blending into live footage.

[joojaa]

actualy the entire animation is fully known by knowing the initial position velocity and initial acceleration, the destination does come into count the physics will compute the destinatiion form that info and theres not much you can do about that.

If however we asume the acceleration is unknown you can offcourse solve the equation, but as said its simpler just to keyframe it. Maya as such is not a equation solver so using a physics simulator to do this means you need top solve or atleast do the expression for initial velocity for yourself (as such there are no real autosolver applications around or well there is its called mathematics and physics, yes thats why we learn the tools in school). but hey whay not use a aexpression instead then(atleast its not lolved by iteration wich is much better from usability standpoint)

//paste into empty scene So no nameclash occours
//Asuming 1 unit = meter (no dont change the unit setting thinkof maya as unitless)
sphere -p 0 0 0
-ax 0 1 01
-ssw 0
-esw 360
-r 1 -d 3
-ut 0 -tol 0.01
-s 8 -nsp 4 -ch 1
-name ballToShoot;
gravity -pos 0 0 0 -m 9.81
-att 0 -dx 0 -dy -1
-dz 0 -mxd -1
-vsh none -vex 0
-vof 0 0 0 -vsw 360 -tsr 0.5
-name gravityInMeters;
connectDynamic -f gravityInMeters ballToShoot;
setAttr "rigidBody1.centerOfMassX" 0;
setAttr "rigidBody1.initialVelocityY" 10;//10 meters per second upward
setAttr "rigidBody1.initialVelocityX" 1;// meter/sec in xoffcourse if you want to later add forces to the object animate impulse.

[jonathan161]

Hey,
I had to solve a similar problem where i needed to write a MEL tool to simulate arrows(projectiles). I came up with this procedure below to calculate the initial velocity of an object to get it from point A to point B reaching a height H with gravity G. This may not be the solution to your problem, but may give you a more accurate way to calculation the projectile motion of the balls.

//----------------------------------------------------------------
//
// Compute the velocity to launch a projectile from p0 to p1
// with a parabola height of h
//
global proc vector ComputeInitialVelocity( vector $p0, vector $p1, float $h, float $g )
{
vector $vel;
// Find the position and direction we want to jump in
vector $dir = <>; // jump direction
float $R = sqrt($dir.x*$dir.x + $dir.z*$dir.z); // horizontal distance
float $b = $dir.y; // vertical distance

	float $theta;
	float $cosA;
	float $v0;

// If h is too small to make the jump (i.e. the sqrt if -ve)
// then clamp it to abs([img]http://www.highend3d.com/boards/style_emoticons/<#EMO_DIR#>/cool.gif[/img] (an angle big enough to make the jump)

$h = max($h, abs($[img]http://www.highend3d.com/boards/style_emoticons/<#EMO_DIR#>/cool.gif[/img]);

// Compute the initial angle

$theta = atan(2*($h+sqrt($h*($h+$[img]http://www.highend3d.com/boards/style_emoticons/<#EMO_DIR#>/cool.gif[/img]))/$R);
	$cosA = cos($theta);

// Compute the velocity

	$v0 = sqrt( 0.5 * $g * $R * $R / ($cosA*$cosA*($R * tan($theta) - $[img]http://www.highend3d.com/boards/style_emoticons/<#EMO_DIR#>/cool.gif[/img]) );

// Find the amount we need to rotate around the Y
// axis to face the target

float $yrot = atan2( -$dir.z, $dir.x );

// Compute the velocity vector in XY plane

	float $velx = $v0 * $cosA;
	float $vely = $v0 * sin($theta);

// Rotate around y

	float $velz  = $velx * -sin($yrot);
	$velx *= cos($yrot);

$vel = << $velx, $vely, $velz>>;

return $vel;

}

//Example of use
vector $InitialVelocity = ComputeInitialVelocity( <>, <>, 8, 9.8 )
//----------------------------------------------------------------

To test out the procedure just create 2 locators in different positions, create a sphere and add a gravity field to it. Run the procedure with the locators positions as p0 and p1, choose a height for the projectile, and set the gravity to the same gravity as your gravity field magnitude. The procedure will return a vector whihc u can apply to the initial velocity attribute of your sphere(rigidbody).

On playback the sphere should be shot from locator A to locator B at the height you specified!

hope some of this helps..

[joojaa]

Why would you do this with dynamics? you know the fully correct physical behaivour so if you know where it ends you could jsut generate keys directly instead. This would have benefits when scrubbing the thing as well as rendering because theres no need to calc the next position and the next and the next because you can do a lookup directly form a curve (vic is physicaly correct).

If however theres something else going on in the way or its a bunc of particles then thats a noyther issuue alltogether.