Apply torque on angular acceleration

Ronan Guinot · 2014-10-16T12:14:23

I'm working on a game project about a top down car game in 2d. I want to manage all the physics by myself. Im working with this book : http://www.amazon.fr/Game-Physics-Engine-Development-Commercial-Grade/dp/0123819768 to implement the physics. From now my physic engine can handle force on the different cardinal axes. But I have some issues to implement a correct simulation of rotation. Im trying to implement some torque to find angular acceleration. So I implemented an inertia tensor matrix : setMass(400.f); Matrix3 it; it.setBlockInertiaTensor(Vector3(2, 1, 1), 400); setInertiaTensor(it); void setBlockInertiaTensor(const Vector3 &halfSizes, float mass) { Vector3 squares = halfSizes.componentProduct(halfSizes); setInertiaTensorCoeffs(0.3f*mass*(squares.y + squares.z), 0.3f*mass*(squares.x + squares.z), 0.3f*mass*(squares.x + squares.y)); } To apply torque I apply a force on a body point of my car and I find the torque by a cross product : The meaning of this is to simulate the steering : player->addForceAtBodyPoint(Vector3(-2000, 1000, 0), Vector3(0, 100, 0)); void AObject::addForceAtBodyPoint(const Vector3 &force, const Vector3 &point) { Vector3 pt = getPointInWorldSpace(point); addForceAtPoint(force, pt); } void AObject::addForceAtPoint(const Vector3 &force, const Vector3 &point) { // Convert to coordinates relative to center of mass. Vector3 pt = point; pt -= _position; _forceAccumulate += force; _torqueAccumulate += pt % force; //std::cout << "torque x " << pt.x << " y " << pt.y << " z "<< pt.z << std::endl; } Vector3 Vector3::operator%(const Vector3 &vector) const { return Vector3(y*vector.z - z*vector.y, z*vector.x - x*vector.z, x*vector.y - y*vector.x); } The overload of modulo is the cross product And finally I do the integration of all the physics data (forces and torques) void Player::integrate(float deltaTime) { addForce(_velocity * -150.0f); // Calculate linear acceleration from force inputs. _lastFrameAcceleration = _acceleration; _lastFrameAcceleration.addScaledVector(_forceAccumulate, _inverseMass); // Calculate angular acceleration from torque inputs. Vector3 angularAcceleration = _inverseInertiaTensorWorld.transform(_torqueAccumulate); // Update linear velocity from acceleration . _velocity.addScaledVector(_lastFrameAcceleration, deltaTime); // Update angular velocity from acceleration . _rotation.addScaledVector(angularAcceleration, deltaTime); // Impose drag. _velocity *= pow(_linearDamping, deltaTime); _rotation *= pow(_angularDamping, deltaTime); // Update linear position. _position.addScaledVector(_velocity, deltaTime); _position.z = 0; // Update angular position _orientation.addScaledVector(_rotation, deltaTime); // Normalise the orientation, and update the matrice calculateWorldLocalData(); // Clear accumulators. clearAccumulator(); } And the orientation is not working at all. Im not that good with physics stuff, so I think that im misunderstanding the physic implementation of torque with inertia tensor... Thank you for your help.