Kinematics basic question

Troubleshooting General Help
1

i m facing too many difficulties with physics simulation like kinematics,collision, bouncing etc.



is there a detailed theoretical documentation available which can help me in understanding what basically goes behind the scenes?



i have a basic question:

i have made a platform and set it to 0 mass.



new RigidBodyControl(0.0f);



so it doesn’t fall under gravity.



similarly i have a ball above platform, and if i set its mass to zero then it just hangs in air, otherwise it falls…all as expected.



now if i let ball fall by giving it mass then it collides with platform and rest upon it after some collision behabiour like bouncing etc…but ball falls only if i haven’t set kinematics to true.

if i do like this

((RigidBodyControl)ball.getControl(RigidBodyControl.class)).setKinematic(true);



then ball just hangs in mid air.



why such behaviour?



moreover,i have given user inputs which can tilt the platform so that ball rolls accordingly.

now if i set kinematics for platform to true:

((RigidBodyControl)platform.getControl(RigidBodyControl.class)).setKinematic(true);



only then ball rolls on platform…if i comment this code then ball has no rolling behaviour even if i tilt platform and it remains still.



can somone throw some light here?



in hellophysics tutorial, there is nothing like kinematics related code…and all collision, bouncing etc works fine.

2

Yes the physics tutorials do explain this.

3

You could also take a look at the Bullet Manual, although the classes and structs won’t match exactly. This document might also help.

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4

thanks survivor.



i read somewhere that meshing of colliding bodies also may cause unexpecte collision behaviour. is it true?

5

I don’t know. I’m a beginner, too. I try and modify until it works. :smiley:


now if i let ball fall by giving it mass then it collides with platform and rest upon it after some collision behabiour like bouncing etc…but ball falls only if i haven’t set kinematics to true.

This is called a dynamic object. Please take a look at the Bullet Manual, page 22, or in the jme3 wiki here at the section "Kinematic vs Dynamic vs Static".

if i do like this
((RigidBodyControl)ball.getControl(RigidBodyControl.class)).setKinematic(true);

then ball just hangs in mid air.

why such behaviour? [...]


I answered this here. Kinematic objects are animated by you (directly by calling i.e. physicsRigidBody.setPhysicsLocation(vector3f) or indirectly by the scene graph).
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