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Koobazaur

Calculating direction of angular velocity?

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Hmm, I just can't figure this one out... basically, I calculate my angular velocity doing Torque's Magnitude/Moment of Inertia but there is a problem... it doesn't tell you whether this angular velocity is clockwise or counterclockwise! I came up with an idea on how to solve this - let's assume our force is made of two points: A (point at which interacts) and B (point A + magnitude, end of the force). Now if I draw a line from body's center of mass to A, then if B is to the right, it'll rotate clockwise, otherwise, counterclockwise (and of course, if B is on the line, it wont rotate at all). However, I found calcuating this really tricky... so how do I determine if a point is to the left or right of a line! Also, keep in mind that if the point goes "below center of mass" then the direction of rotation flips: if our CenterOfMass - A line goes straight up then if point B is to the right and above CM, it'll rotate clockwise, but if it is below CM - counterclockwise... so how do you determine that? or is there a better way to determine the direction of angular velocity??? EDIT: I'm speaking 2D here... EDIT2: THe only thing I came up with, is to rotate points A and B around the CM so that A is directly above CM. Then, checking this is quite easy... [edited by - Koobazaur on June 3, 2004 3:03:27 AM]

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so, you have torques and moment, translating into angular velocity, translating into an orientation, or angle of the object. You should not have to worry about that at all. It''s just a standard integration.


void CBody::Update(float dt)
{
m_xPosition += m_xVelocity * dt;
m_fOrientation += m_fAngVelocity * dt;

m_xVelocity += m_xNetForce * (m_fInvMass * dt);
m_fAngVelocity += m_fNetTorque * (m_fInvInertia * dt);

m_xNetForce = Vector(0.0f, 0.0f);
m_fNetTorque = 0.0f;
}

void CBody::AddForce(const Vector& F, const Vector& P)
{
m_xNetForce += F;
m_fNetTorque += (P - m_xPosition) ^ F;
}

''^'' is a vector cross product. in 2D, it returns a float

inline float operator^(const Vector &V) const { return (x * V.y) - (y * V.x); }


if you don''t undestand what I''m talking about, I suggest you read Chris Hecker''s physics articles.

you can see a demo of that stuff here.

http://uk.geocities.com/olivier_rebellion/box.zip
(or at http://uk.geocities.com/olivier_rebellion/ "2D box contact calculations" if the link is broken).

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