Raycast vehicle tilts when turning right or left

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razer
Posts: 82
Joined: Sun Apr 04, 2010 10:08 pm

Raycast vehicle tilts when turning right or left

Post by razer » Fri Apr 09, 2010 1:09 pm

I coded demo program with RaycastVehicle based on Demo project from bullet.

It uses Z as up.

When I drive car and press left then car turns left as it should and tilts left like bike or bicycle but car must tilt right instead of left.

How tilt controlled?

Thanks

ola
Posts: 169
Joined: Sun Jan 14, 2007 7:56 pm
Location: Norway
Contact:

Re: Raycast vehicle tilts when turning right or left

Post by ola » Fri Apr 09, 2010 6:37 pm

Your center of gravity is set too low (it's below the ground). Move it up and you will get the effect you want.

In the vehicle demo VehicleDemo.cpp, this happens on line 310:

Code: Select all

	
//localTrans effectively shifts the center of mass with respect to the chassis
	localTrans.setOrigin(btVector3(0,0,1));
Cheers,
Ola

razer
Posts: 82
Joined: Sun Apr 04, 2010 10:08 pm

Re: Raycast vehicle tilts when turning right or left

Post by razer » Fri Apr 09, 2010 7:14 pm

Thank You! But it does not help.

I made it
localTrans.setOrigin(btVector3(0,0,2.0f));
localTrans.setOrigin(btVector3(0,0,5.0f));
localTrans.setOrigin(btVector3(0,0,10.0f));

It always tilts as before.

razer
Posts: 82
Joined: Sun Apr 04, 2010 10:08 pm

Re: Raycast vehicle tilts when turning right or left

Post by razer » Fri Apr 09, 2010 11:41 pm

I have to change

float connectionHeight = 1.2f;
to
float connectionHeight = 1.2f / 2;
from Vehicle demo used to add Wheel
m_vehicle->addWheel


It moved box and it tilts as it should.

I thought smaller connectionHeight should move center mass down.
It works not good as it should but it is progress.

Thanks

ola
Posts: 169
Joined: Sun Jan 14, 2007 7:56 pm
Location: Norway
Contact:

Re: Raycast vehicle tilts when turning right or left

Post by ola » Sun Apr 11, 2010 9:47 am

razer wrote:Thank You! But it does not help.

I made it
localTrans.setOrigin(btVector3(0,0,2.0f));
localTrans.setOrigin(btVector3(0,0,5.0f));
localTrans.setOrigin(btVector3(0,0,10.0f));

It always tilts as before.
The z-axis is positive downwards, so you need to try 0.0 or a negative value. The 1.0 value sets the center of gravity one meter below.

Cheers,
Ola

razer
Posts: 82
Joined: Sun Apr 04, 2010 10:08 pm

Re: Raycast vehicle tilts when turning right or left

Post by razer » Sun Apr 11, 2010 3:33 pm

ola wrote: The z-axis is positive downwards, so you need to try 0.0 or a negative value. The 1.0 value sets the center of gravity one meter below.

Cheers,
Ola
I have Z axis as up. When I set Y then I got bad result. Negative value was also not what I was expecting.

BTW I have a bit upgraded my car and set convex cast instead of ray cast %)

Code: Select all

class btConvexVehicleRaycaster : public btVehicleRaycaster
{
	btDynamicsWorld*	m_dynamicsWorld;
	btConvexShape*		m_convexShape;
	btScalar m_wheelRadius;
public:
	btConvexVehicleRaycaster(btDynamicsWorld* world, btConvexShape* convexShape, btScalar wheelRadius)
		:m_dynamicsWorld(world), m_convexShape(convexShape), m_wheelRadius(wheelRadius)
	{
	}

	virtual void* castRay(const btVector3& from,const btVector3& to, btVehicleRaycasterResult& result);

};void* btConvexVehicleRaycaster::castRay(const btVector3& from,const btVector3& to, btVehicleRaycasterResult& result)
{
//	RayResultCallback& resultCallback;


	btVector3 v1 = to - from;
	btScalar length = v1.length();
	length -= m_wheelRadius;
	v1.normalize();
	v1 *= length;
	btVector3 to1 = from + v1;


	btCollisionWorld::ClosestConvexResultCallback convexCallback(from,to1);

	btTransform trFrom; trFrom.setIdentity(); trFrom.setOrigin(from);
	btTransform trTo; trTo.setIdentity(); trTo.setOrigin(to1);


	m_dynamicsWorld->convexSweepTest(m_convexShape, trFrom, trTo, convexCallback);
	

	if (convexCallback.hasHit())
	{
		
		btRigidBody* body = btRigidBody::upcast(convexCallback.m_hitCollisionObject);
        if (body && body->hasContactResponse())
		{
			result.m_hitPointInWorld = convexCallback.m_hitPointWorld;
			result.m_hitNormalInWorld = convexCallback.m_hitNormalWorld;
			result.m_hitNormalInWorld.normalize();
			result.m_distFraction = convexCallback.m_closestHitFraction;
			return body;
		}
	}
	return 0;
}
wheelRadius is wheelWidth / 2.0 (wheelRadius must be called radius. That name is my mistake)

It was advised in Google Document written by Kester Maddock to use convex. (I use sphere instead of torus.)

Ray may fall in cracks.

May car was stumbling and jumping at some point unpredictably. (It happens rare but is happens)

Convex does not fix that for me.

Damp helps but in general springs are not reliable for high speeds.

May be there should be added another force that will compensate such erroneous outbursts. Not sure how to formalize them.

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