How can one make a box2d body move in a spiral motion? I believe it will require applying some force but I am not sure how. I would appreciate any assistance.
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You can chain joints together using intermediate invisible bodies. Pin a body at the center to the ground with a revolute joint, and a prismatic from that body to the real one. Two joints = two motors = two controllable degrees of freedom.
MrWaqasAhmed
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I would really appreciate it if you could explain this further, possibly with a code sample. Thanks. – oopology Apr 17 '13 at 07:05
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You'll have two forces, a tangential force, and a radial force.
The tangential force accelerates the body around the center.
The radial force accelerates the body towards or away from the center.
radialVector = (objectPosition - spiralCenter).normalize();
tangentialVector = radialVector.perpendicularVector();
forceTangential = tangentialForceMagnitude * tangentialVector;
forceRadial = radialForceMagnitude * radialVector;
force = forceTangential + forceRadial;
object.applyForce(force);
The specific values for your force magnitudes will determine the behaviour of the spiral; things like wether it's an inward or outward motion, and how fast.
I answered a related question about making a whirlpool/vortex: SO: How to create whirlpool/vortex effect?
