Rigid Body animation: How to apply springy / dampen effect

Question

I'm trying to create a Wheel of Fortune animation, see the image below.

I also have a movie that makes the issue a lot more clear: Wheel of Fortune movie

I've got it somewhat working using the Rigid Body system. The issue I'm having is that once the wheel stops spinning, the flippers just keep swinging from side to side way too long. I'm looking for some way to make them come to a halt a lot faster. Preferably I'd like the flipper to behave as if it's attached with a sort of spring, forcing it back to it's center position.

I'll explain the current setup for the upper flipper / outer ring (blender file attached below). There are 3 objects:

• The wheel itself
• The flipper
• The axle for the flipper to rotate around

The wheel

The wheel is just normally animated using keyframes. It rotates around it's Y axis. It has Rigid Body physics enabled, Active and animated so it won't fall down. Shape is set to mesh.

The flipper Also Rigid body enabled, Type: active, Animated: No, Shape: mesh

The axle Rigid Body enabled, Type: active, Animated: Yes, Shape: mesh

The Axle and the flipper are connected with a constraint set to Hinge with a -45 degree to 45 degree limit on the Z-axis. The constrain has been rotated so the z-axis faces the correct direction and it all works.

In order to get this damping / springy effect I'm looking for I figured I use the Friction parameter. This doesn't seem to work. Any changes I make to this parameter doesn't seem to have any effect whatsoever. I've also tried increasing the margins to make sure the margin of the flipper and the axis overlap. Still no luck. I'm guessing this is because I'm using a hinge constraint.

Sorry for the long text, I'm just trying to explain my question as good as I can. Here's the blend file I'm using: Wheel of Fortune blend file

Thanks in advance!

Answer 1

The main problem you're encountering is with the center of gravity of your flippers. With Blender's rigid body physics, this is defined by the object origin. But for those objects, the object origin is way, way outside of the mesh. This creates the difference between swinging a small hammer vs. taping it to a twenty-foot long pole and swinging it-- the collisions create a lot more momentum than they should. For mesh-type collision objects, like the flippers, it's wise to set the origin of the objects to center of mass (volume). For the top flipper, this should be just slightly below the hinge constraint, so that gravity will keep them it downward. (You could fudge the origin of the bottom flipper if you want, or you could use a spring, detailed below.)

That alone should help, but there are other options as well. The easiest way to create damping is in properties/physics/rigid body/dynamics, which gives you options to damp the translation and/or rotation of objects. There's nothing particularly realistic about these settings, but they're easy to tune, and usually the first thing you should go to in order to tune damping. (Here, I would recommend increasing rotational damping to, maybe, 0.7 or so.)

Your other option is create a different or additional rigid body constraint. A hinge, on its own, doesn't create any damping. But you can use a generic spring constraint to create a springy hinge, just by giving it 0-0 linear limits and 0-0 XY angular limits. You can enable Z-angle springs on this constraint, creating force (via "stiffness") that drives the flipper back to its rest (frame 1) position; you can create damping on this force to prevent it from oscillating forever. Note that two objects can be joined by two different constraints just fine! So you can combine a spring with low force and broad limits with a hinge with perfect force and narrow limits.