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I am making a rigid body physics simulation with Catapult supported by a Hinge. A Cube with a substantial mass drops on the catapult which also has substantial mass. I am expecting the catapult to rotate as the cube drops on it. But the catapult doesn't budge an inch! The Hinge does part of the job by holding itself & the catapult in place.

What am I doing wrong for the catapult to perform real physics ? Thank you for the help the Blender community stars may provide!

See-Saw (Catapult) With Hinge - Rigid Body Physics Simulation


Problem areas identified with the above animation: The Constraint Axis & Hinge physics configuration needed correction. Also, no object in the simulation is to be set as animated if physics has to take effect.

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    $\begingroup$ 1) Please at least embed images with question editor tools, so they're visible here. 2) are you sure you need those exact values? 3) why did you set "animated"? $\endgroup$ – m.ardito Mar 3 '18 at 8:02
  • $\begingroup$ Thank you for your comments. What Are question editor tools ? 1.) No I don't really need those mass values. They were given to give an idea that these objects have significant mass for physics simulation. 2. Well I set it to animated because i want it animated but guess it may not be required after all. $\endgroup$ – RKA Mar 3 '18 at 9:55
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    $\begingroup$ @m.ardito has a good point there... set to Animated tells it not to react to the rigid body world, allowing you to animate it instead. That would explain it not reacting. $\endgroup$ – Rich Sedman Mar 3 '18 at 10:01
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    $\begingroup$ For images meta.stackexchange.com/questions/75491/…, for files blend-exchange.giantcowfilms.com $\endgroup$ – Mr Zak Mar 3 '18 at 13:16
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    $\begingroup$ Please don't make us go to a link to understand the question. Please use the edit link at the bottom of your question (i.stack.imgur.com/lXFuK.png) and add the information as part of your post. $\endgroup$ – user1853 Mar 3 '18 at 18:58
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The Solution to the above and just about all catapult/see-saw type physics simulations lies in two important steps :

  1. Properly Set up the physics :

a.) Set the falling object/cube as "Active" Rigid body.

b.) Set the Catapult (or see-saw object) as "Active" Rigid body. Do NOT Set this as "animated" unless you want this simulation to be controlled through the animation system or key frames.

c.) Set the Hinge as a "PASSIVE" Rigid body.

  1. Set up Of the Catapult & Hinge constraint :

a.) Select The Hinge first, then shift select the catapult. This Will create an "empty object like Axis" which is the constraint. Set This constraint type to "Hinge". This can be selected on the Left Panels Menu by pressing "N" or under the "Constraint" Physics menu.

b). Set Up Proper Axis For The Hinge Constraint. An easy way to do this is to set all rotations of this constraint to zero. Then based on your object's orientation, select the proper axis for it to work. Trial & error may be required but with the above suggestions it should take not take more than a minute or two.

-- Thanks to @m.ardito for always trying to help and provide hints. Thanks To @Rich Sedman for providing a useful explanation. Thanks To @Mr Zak & @cegaton for providing help on question editor image tool.

enter image description here

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    $\begingroup$ Also to set shape on all elements to "mesh". $\endgroup$ – user1853 Mar 4 '18 at 6:38
  • $\begingroup$ TY! It's useful to set object's as meshes when you need the physics to react precisely to the mesh. For instance, a cube entering a hollow sphere or any such object will not be detected by a convex hull type shape. In this case, you will need objects as meshes. This is because convex hull type shapes calculates the physics maths on the surface. However, as you might reckon, mesh shapes consume a lot more resources than a convex hull type shapes. In my view, it's a trade off in some cases and sound judgement in others to decide whether you need objects as meshes or not in rigid body physics. $\endgroup$ – RKA Mar 4 '18 at 9:09

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