Animating ragdoll using armatures

[OSasuke]

Hello,

I would create a ragdoll which is animated using a blender armature.

The question is : how to animate a ragdoll using the informations of the animation ( rotations, tranlations ) ?

What are the diffirent ways to animate a ragdoll ?

Thanks, for any help.

[Erwin Coumans]

Usually a character is either purely animated, and under certain conditions it switched to fully simulation (without animation).

There are cases where you might want to blend between animation and simulation, in technology such as Natural Motion, is that what you want?
In that case, you can use motors to power the ragdoll simulation, and convert the animation data into velocity targets for the motor.

Given a timestep and a previous transform and current transform (both in world space) you can calculate the desired velocity,
See Bullet/LinearMath/btTransformUtil.h, the function btTransformUtil::calculateVelocity
and then set the motor target for that joint, see Bullet\Demos\DynamicControlDemo\MotorDemo.cpp how to set those motor velocity targets.

Hope this helps,
Erwin

[OSasuke]

Ah tank you Erwin.

I am good in mathematics, but I'm still young to know advanced things, I have only 16 years.

Heee An other things : Where can learn how to use quaternions, and understanding how it works.

Thanks again Erwin.

[OcelotV]

http://www.ogre3d.org/wiki/index.php/Qu ... ion_Primer
http://www.cprogramming.com/tutorial/3d ... nions.html

[OSasuke]

Hello,
After a year, i am returning to this thread, i am experiencing some problems :
First, Erwin : the function btTransformUtil::calculateVelocity doesn't seems to work correctly, this is a simplified version of my code :

Code: Select all

                    Ogre::TransformKeyFrame *target_tkf = desired key frame;
                    btTransform tA = myRigidBody->getCenterOfMassTransform();
                    btTransform tB;
                    tB.setIdentity();
                    tB.setRotation(Util::toBtQuaternion(bone->convertLocalToWorldOrientation(target_tkf->getRotation())));
                    tB.setOrigin(Util::toBtVector3(bone->convertLocalToWorldPosition(target_tkf->getTranslate())));

                    btTypedConstraint* tc = a constraint that join two bodies like : head to spine joint;
                    switch(tc->getConstraintType())
                    {
                        case HINGE_CONSTRAINT_TYPE:
                        {
                            //printf("HINGEVelCalc\n");
                            btHingeConstraint* hc = static_cast<btHingeConstraint*>(tc);

                            btVector3 lvel, avel;
                            btTransformUtil::calculateVelocity(tA, tB, 1, lvel, avel);

                            btScalar force = avel[0]+avel[1]+avel[2];
                            hc->enableAngularMotor(true, force, 100.f);
                        } break;
                        case CONETWIST_CONSTRAINT_TYPE:
                        {
                            //printf("CONETWISTVelCalc\n");
                            btConeTwistConstraint* ctc = static_cast<btConeTwistConstraint*>(tc);

                            ctc->setAngularOnly(true);
                            ctc->enableMotor(true);
                            ctc->setMotorTarget(tB.getRotation());
                            ctc->setMaxMotorImpulse(100.f);
                        } break;
                        case SLIDER_CONSTRAINT_TYPE:
                        {
                            //printf("SLIDERVelCalc\n");
                            btSliderConstraint* sc = static_cast<btSliderConstraint*>(tc);
                            btVector3 lvel, avel;
                            btTransformUtil::calculateVelocity(tA, tB, 1, lvel, avel);
                            sc->setPoweredLinMotor(true);
                            sc->setPoweredAngMotor(true);
                            sc->setTargetLinMotorVelocity(lvel[0]+lvel[1]+lvel[2]);
                            sc->setTargetAngMotorVelocity(avel[0]+avel[1]+avel[2]);
                            sc->setMaxAngMotorForce(100.f);
                            sc->setMaxLinMotorForce(100.f);
                        } break;
                        case D6_CONSTRAINT_TYPE:
                        {
                            printf("Generic6DOFVelCalc\n");
                            btGeneric6DofConstraint* g6dofc = static_cast<btGeneric6DofConstraint*>(tc);
                            btVector3 lvel, avel;
                            btTransformUtil::calculateVelocity(tA, tB, 1, lvel, avel);
                            //avel *= 60.f;
                            // Seting rotational motors
                            for(int i=0; i<3; i++)
                            {
                                btRotationalLimitMotor* rotLim = g6dofc->getRotationalLimitMotor(i);
                                rotLim->m_enableMotor = true;
                                rotLim->m_maxLimitForce = 99999.9f;
                                rotLim->m_maxMotorForce = 200.f;
                                rotLim->m_targetVelocity = avel[i];
                            }
                            // -> some debugging outputs ...
                        }

The problem i think is that the returned angular velocity is not enought to push the body to the desired state in both of Hinge and Generic6DOF constraint that i tested, the ConeTwist doesn't seem to have this problem but it has some precision and stability problem.
This is some debugging output where "A" is the rigid body rotation, "B" is the desired rotation and "V" is the angular velocity returned by the btTransformUtil::calculateVelocity function :
Note : In my exemple i'm only interesting in the Y axis so don't look to the others

Code: Select all

Generic6DOFVelCalc
**********************************
A=-0.658356;0.249826;-0.044969
B=4.914749;5.597017;-0.479366
**********************************
V=5.546857;5.361677;-0.235211
**********************************
Generic6DOFVelCalc
**********************************
A=-2.001161;0.402409;-0.340210
B=5.020587;13.020824;-1.132568
**********************************
V=6.900428;12.642287;-0.456080
**********************************
Generic6DOFVelCalc
**********************************
A=-1.601413;0.613351;-0.272982
B=5.220694;20.442895;-1.826346
**********************************
V=6.468188;19.877541;-0.908424
**********************************
Generic6DOFVelCalc
**********************************
A=-1.156978;0.944907;-0.205564
B=5.533372;27.843014;-2.589738
**********************************
V=5.967929;26.975901;-1.302698
**********************************
Generic6DOFVelCalc
**********************************
A=-0.676906;1.394787;-0.138891
B=5.992235;35.238317;-3.465508
**********************************
V=5.411608;33.958683;-1.632781
**********************************
Generic6DOFVelCalc
**********************************
A=-0.168283;1.961058;-0.073862
B=6.213282;38.018173;-3.836001
**********************************
V=4.860001;36.193870;-1.689451
**********************************
Generic6DOFVelCalc
**********************************
A=0.363377;2.564585;-0.010980
B=6.467050;40.796783;-4.235722
**********************************
V=4.283088;38.393085;-1.716395
**********************************
Generic6DOFVelCalc
**********************************
A=0.301682;3.204421;0.080141
B=6.387526;39.966607;-4.112976
**********************************
V=4.303945;36.922231;-1.816571
**********************************

As you can see the rotation of the body(A) is so far from the desired rotation(B) and applying "38" of velocity just moves the rotation by 1°

Can anyone tell me what's wrong ?

Thanks.

[OSasuke]

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