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I have a very simple hinged paddle: there's a rigid, passive side that stays still, and there's an active 'paddle' side that can rotate from 0 to -45 Z around the hinge.

enter image description here

Right now, a ball drops from above directly onto the paddle, the paddle rotates down around Z like it should, the ball deflects off the paddle and keeps falling like it should, the paddle eventually rotates to -45 then bounces off that constraint and then flops around a bit till it loses momentum. Just basic rigid body stuff.

What I want is for the paddle to reach that -45 angle and then quickly rotate back to 0, deflecting the ball upwards. In other words: I want the paddle to actively swat the ball away.

I'd rather not do this by moving things manually with keyframes because A) I doubt I could get the physics to look right and B) this is something that needs to happen hundreds of times.

I'm very new to Blender. But I assume this is possible, somehow.

Can someone recommend an approach?

ETA: The idea here is that I will have four of these paddles arranged at 90 deg to each other (paddles at the center), and they will all be bouncing the same large beach-ball up and down.I'm just trying to get the mechanics of one working, first.

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  • $\begingroup$ Have you tried using a rigid body spring constraint? $\endgroup$ Nov 5, 2021 at 16:35
  • $\begingroup$ @MartyFouts - I've played around with springs, but they don't seem to be able to put enough energy into the rebound for what I need. I need something that can give back at least as much energy as it takes in, but springs absorb too much energy, even with damping at 0. $\endgroup$
    – cleek
    Nov 5, 2021 at 16:51
  • $\begingroup$ Would you mind sharing your blend file? $\endgroup$
    – Chris
    Nov 5, 2021 at 17:06
  • $\begingroup$ blend file is at ok-cleek.com/stuff/yetagain.blend. This doesn't have a spring on it (I discarded my attempts). $\endgroup$
    – cleek
    Nov 5, 2021 at 17:58

1 Answer 1

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You can do it with a rigid body constraint.

Add an empty here:

enter image description here

Type: generic spring

Choose these settings:

enter image description here

Note: The orientation of the empty is important, else it won't work.

I took the freedom to change the mass of your ball to 10 kg.

result:

enter image description here

result with 400000 stiffness:

enter image description here

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  • $\begingroup$ OK, that looks promising. I had tried springs, but not with stiffness values anywhere close to that high. Thanks! $\endgroup$
    – cleek
    Nov 6, 2021 at 13:09
  • $\begingroup$ you are welcome. If my answer helped you, please check the checkmark left to my answer. Thank you. $\endgroup$
    – Chris
    Nov 6, 2021 at 13:21

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