RayCast vehicle - I think it's almost done

Dirso

23-09-2007 15:56:06

Hi,
I think I'm almost there, the suspension is working fine, and I also think I'm considering all forces, including the normals (since the wheels don't exist physicly, I add this force manually as the wheels were there applying this forces over the body - the point where the forces are applied is susAct, locally, and posSusAct, its global coordinates).

Anyway, this code, i think, should works fine, I'm killing lateral forces and when I steer the wheels I apply a perpendicular force to that wheels to kill that acceleration too and that way I think the car should make the turn, but it isn't and that's the reason of my post.
But that's not what happens

It actually starts "shaking" and making turns right then left then right again and so on not repecting my inputs, I think it might be a problem with the math, wrong angle calculation and velocity components.

Here is the main code, any help will be appreciated

Thanks,
Dirso

Ogre::Quaternion quat = getOrientation();

Ogre::Vector3 velocityVector(me->getVelocity());

Ogre::Real mass = _loader._carMass;

Ogre::Vector3 com = me->getCenterOfMass() + _loader._CoM;

// that's because Newton give me getCenterOfMass as an offset of the original CoM



// gravity force

Ogre::Vector3 Fg = Ogre::Vector3(0,-9.8, 0) * mass;

me->addForce(Fg);

// local vars

Ogre::Real deltaT = me->getWorld()->getTimeStep();



// for each wheel calculates all forces on each wheel

for(RayCastTireListIt it = _tires.begin(); it != _tires.end(); it++)

{

	// draw the rotation

	Quaternion WheelYaw((*it)->_steer * mSteerAngle, _worldOr);

	// suspension

	Ogre::Vector3 posSusAct((*it)->_wheelSusAct->getWorldPosition());

	Ogre::Real r = (*it)->_radius;

	Ogre::Real rayLength = r + (*it)->_susLength;

	Ogre::Vector3 uVector(quat*_worldOr);

	OgreNewt::BasicRaycast ray(mWorld, posSusAct, posSusAct - uVector*rayLength);

	OgreNewt::BasicRaycast::BasicRaycastInfo info = ray.getFirstHit();

	//

	Ogre::Vector3 susAct = (*it)->_wheelSusAct->getPosition();

	Ogre::Vector3 dWheel1 = (*it)->_wheelNode->getPosition();

	Ogre::Vector3 dWheel2;

	if(info.mBody)

	{

		// orientation vector

		Ogre::Vector3 rVector(quat*WheelYaw*(*it)->_pin);

		Ogre::Vector3 wheelVelocity(velocityVector + (susAct - com)*me->getOmega());

		Ogre::Vector3 wheelVelocityN(wheelVelocity);

		Ogre::Real velocityLen(wheelVelocityN.normalise());

		Ogre::Real cos1(rVector.dotProduct(wheelVelocityN)),

			cos2(uVector.dotProduct(wheelVelocityN)),

			sin1(Math::Sqrt(1 - cos1*cos1)),

			cosUp(uVector.dotProduct(_worldOr));

		if(cos2 < 0.0) sin1 = -sin1;

		// calculate the new position of the wheel

		dWheel2 = susAct - (info.mDistance*rayLength - r)*uVector;

		// calculate the suspension force

		Ogre::Real dist1 = MathHelperClass::getDistance(dWheel2, susAct),

			dist2 = MathHelperClass::getDistance(dWheel1, susAct);

		Ogre::Real Fs = (*it)->_susSpring*((*it)->_susLength - dist1),

			Fd = (dist2 - dist1)*(*it)->_susShock;

		Ogre::Vector3 Fn(-Fg*Math::Abs(cosUp)/4.0);

		Ogre::Vector3 Ft(Fn + quat*(Fd + Fs)*_worldOr);

		// drive force

		if(((*it)->_drive > 0.01) && (wheel_torque > 0.01))

		{

			Ogre::Vector3 driveForce(quat*_carAccelDir * 

				((*it)->_drive * wheel_torque / (*it)->_radius)	);

			Ft += driveForce;

		}

		// calculate the steering forces

		Ogre::Vector3 friction(velocityLen*sin1*rVector*mass/4.0);

		friction.y = 0.0f;

		Ft += friction;

		// set the final force

		me->addLocalForce(Ft, (*it)->_wheelSusAct->getPosition());

	}

	else

	{

		dWheel2 = susAct - uVector*(*it)->_susLength;

	}

	(*it)->_wheelNode->setPosition(dWheel2);

	(*it)->setOmega(getVelocity() / (*it)->_radius);



	mCurrRotZ += Ogre::Radian((*it)->getOmega()*deltaT);

	Quaternion WheelRotation(mCurrRotZ, (*it)->_pin);

	(*it)->_wheelNode->setOrientation(WheelYaw*WheelRotation); 

}

Dirso

29-10-2007 13:40:02

Hey there did you get this to work ? , im actually working on a raycast car myself and im having a lot of problems with the suspensions. i was wondering if you had any articles or tips of your own. we really need to get one up on the wiki.
I didn't get it working yet, but if you want, you can use the suspension part of this code, it works like a charm. I also will publish an OpenSource FrameWork (or Engine someday) by the weekend and all the code I've got so far will be there and I hope to get more contributions to finish this. It's a plugin based FrameWork, so the Raycast car will work with any physics system. Of course it's still the version 0.1

Best Regards,
Dirso