# [SOLVED] Quaternion Rigidbody Torque rotation

Hi everyone, after a lot of time away I finally found time to continue my game project
However Iām directly stuck again at the issue I had last.

Iām trying to rotate a rigidbody to a target quaternion using torque, but I do not manage to wrap my head around the math required

I kinda know the idea behind hit, but do not manage to get it into code.
As far as I understand,
a) I calculate the deltaQuaternion between current and targetrotation
b) I convert this via toAngles into Euler angles
c) I clamp the angles based on my maximum rotationAcceleation
d) I convert this into a torque vector
e) predict how long untill target rotation, and determine if acceleration on axis is wanted?

I kinda hope that someone already solved this or a similar problem, as I kinda hit a brickwall here

``````	Quaternion currentRotation = rigidBody.getPhysicsRotation();
Quaternion deltaOrientation = targetRotation.mult(currentRotation.inverse());
Quaternion rotatedDeltaOrient = currentRotation.inverse().mult(deltaOrientation);
float[] deltaEulerRaw  = new float[3];
rotatedDeltaOrient.toAngles(deltaEulerRaw);
//do I risk a gimbal lock here?
Vector3f deltaEuler = new Vector3f(deltaEulerRaw[0],deltaEulerRaw[1],deltaEulerRaw[2]);

//Clamping for now simulated by scaling it to a probably low speed? use maxis.getTurnSpeedLimit() instead later
System.out.println(deltaEuler);
Vector3f deltaEulerMin = deltaEuler.mult(0.01f);

//instead of just the mass probably use the inertia also for correction of this?
//somehow incorporate the current angularVelocity and break before reaching target, can this be calculated for each axis if in local space of rigidbody?
rigidBody.applyTorque(deltaEulerMin.mult(rigidBody.getMass()));``````
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i kinda have gone in something like that , but i think far more simpler , which is `RocksPlotterSystem` , it was using rocks & gravity only to draw 2d maths functions in jme world :

`````` public static abstract class Simulate2dQuadratic extends AbstractControl{

private final float zDirection;
private final float[] xPoints;
private final float equationConstant;
private final float timeToGenerate;
private float generatorTime;

private int xPosition=0;

private final Vector3f coffecientVector;
/**
* Simulate Square/Quadratic equation using Formula : f(x)=y=[((x*coffecientX)^2)+C*signC] * coffecientY based upon f(x)=y=(+/-)x^2 (+/-) C
*
* use Right Hand Rule (RHR) to provide yourself with adequate coordinate system orientation in JME world :
*
* where : - thumb is the +ve y-axis going up
*         - Index is the +ve z-axis going into the screen
*         - The other fingers represent the direction of +ve x-axis
*
* so , ++++CoffecientZ -> ++++++in the domain of the function :-))
*
*    , +++++CoffecientY -> +++++++in function Height or peak
*
*    , +++++CoffecientX -> +++++++in function wide & height/peak
*
* warning : timeToGenerate should be >= 0.5f because this algorithum simulates the 2d Exponential function using Gravitional Acceleration
*
* @param coffecientVector the starting point of applying gravity produces coffecientX & coffecientY & coffecientZ
* @param zDirection the direction on z-axis takes in : SAME_TAIL , REVERSED_TAIL , ORIGIN_TAIL
* @param xPoints the points on x-axis to find thier f(x)=y
* @param equationConstant the equation constant C or the function peak
* @param timeToGenerate time required by fps to regenerate rocks
*/
public Simulate2dQuadratic(Vector3f coffecientVector,float zDirection,float[] xPoints,float equationConstant,float timeToGenerate){
this.coffecientVector=coffecientVector;
this.zDirection=zDirection;
this.xPoints=xPoints;
this.equationConstant=equationConstant;
this.timeToGenerate=timeToGenerate;
}
/**
* Simulate Exponential equation using Formula : f(x)=y=[sign*((x*startingPointX)^2)+C*signC] * startingPointY based upon f(x)=y=(+/-)x^2 (+/-) C
* @param xPosition the current X to be substituted to find the f(x) respectively
*/
rigidRocks.setGravity(new Vector3f(
coffecientVector.getX()*xPoints[xPosition],
coffecientVector.getY()*((FastMath.pow(xPoints[xPosition], 2)*coffecientVector.getX())+equationConstant),
coffecientVector.getZ()*zDirection));
}

@Override
protected void controlUpdate(float tpf) {
generatorTime+=tpf;
if(generatorTime > timeToGenerate){
if(xPosition<xPoints.length-1){
}else{
xPosition=0;
afterRockDecays();
}
generatorTime=0f;
}
}
/**
* controls what to do after x ends substitution
*/
public abstract void afterRockDecays();

@Override
protected void controlRender(RenderManager arg0, ViewPort arg1) {

}

}
``````

I have made `QuadraticPlotter` , `CubicPlotter` ,`AbsolutePlotter`, `ModuluoPlotter`,LinearPlotter`,`Reciprocal`&`Radical``` ,

i was trying to handle & wrap the Circle equation in gravity to create a circular motion by some (x,z) co-ordinates , but i am still trying , you can try using `Gravity` because `applyTorque` sometimes gives bad behavour .

`EDIT`: so circle equation is basically nothing but Pythagras theory , if you can do (x,z) points based on the object that you try to rotate around , you will get the answer using gravity only.

https://www.mathsisfun.com/algebra/circle-equations.html

Ok that helped, the simple case seems to work for now

``````  Quaternion currentRotation = rigidBody.getPhysicsRotation();
Quaternion deltaOrientation = targetRotation.inverse().mult(currentRotation);
float[] deltaEulerRaw  = new float[3];
//do I risk a gimbal lock here?
deltaOrientation.toAngles(deltaEulerRaw);

Vector3f deltaEuler = new Vector3f(-deltaEulerRaw[0],-deltaEulerRaw[1],-deltaEulerRaw[2]);
System.out.println(deltaEuler);

Vector3f local = new Vector3f(deltaEuler);
local = currentRotation.mult(local);
rigidBody.applyTorqueMassless(local);

//instead of just the mass probably use the inertia also for correction of this?
//somehow incorporate the current angularVelocity and break before reaching target, can this be calculated for each axis if in local space of rigidbody?
//simple stabilizing for now
rigidBody.setAngularDamping(0.9f);
``````

The important information was, that bullet seems to do torque in world space

Now I need to think about incorporating the current angular velocity in a way so I can reduce the angular dampening by a lot (as that causes a lot of strange effects when colliding)

2 Likes