Two questions:

1. How do i create a spring (or any other motor that exists)?

2. How do would i do to cancel out force? If i have sent an object flying and want it to stop, how do i calculate how much force to apply to counter the current velocity (or torque)?

1. springs can be implemented by the user quite simply, search any physics page for spring formulas... but the basic formulas are:

F = -k * d
k is the spring constant (stiffness)
d is how far the spring is "stretched" from its neutral position.

you also may want to add damping to the equation like this:
F = (-k * d) + (d * v)
d is damping factor
v is relative velocity of the spring between head and tail.


2. to stop an object, you need to calculate the amount of force required to result in a new velocity of zero.

F = m*a
m is mass
a is acceleration.

so you need to know the acceleration to result in 0 velocity.
a = dv / dt
dv is change in velocity
dt is change in time.

so, you want to do this:

Ogre::Vector3 currentVel = mBody->getVelocity();
Ogre::Vector3 force = Ogre::Vector3::ZERO;

Ogre::Vector3 inertia;
Ogre::Real mass;

mBody->getMassMatrix( mass, inertia );

Ogre::Vector3 accel = (0.0f - currentVel) / mBody->getWorld()->getTimeStep();

force = accel * mass;

mBody->addForce( force );

Oh! I thought that newton had a function for springs :O

Anyway, thanks alot for the info

however you can motorize the built-in joints pretty simply.

also the custom joint system has a cool spring system built in as well, for making spring-loaded hinges, etc.

Is there any documentation on this subject? It would be really cool