I want to animate an anchor being pulled in by a motor on the boat. The anchor is attached to some chains. I am having trouble with the physics. I am using the built in physics system, not the Blender Game Engine. On the boat I have a motor that is turning. Is is attached to the chain which is attached to the anchor. How can I use physics to animate the reeling in of an anchor?

blend file

The motor

enter image description here

The anchor

enter image description here

my attempt so far:

as you can see it's not working like it should.


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    $\begingroup$ I can't test now, but it looks like you are not using Mesh collision for the chain links, which is necessary for concave shapes. I would actually recommend using constraints instead, and disable collisions between linked links. I'll add an answer as soon as I can.. $\endgroup$ – gandalf3 Feb 23 '14 at 22:53
  • $\begingroup$ Mesh collision can be one of the problem. But there seem to be other problems however in this case. $\endgroup$ – Leon Cheung Feb 24 '14 at 1:34

There are several issues with your file:

  • The object origins are not centered. The origins are used to calculate the center of mass, which means that they can result in strange behavior if they are not correctly centered. Press CtrlShiftAltC> Origin to center of mass to snap the origin to the center of mass.

  • The intersecting concave links are using the Convex Hull collision shape. Because the hole in the middle of each link is a concave shape, the links then collide and fly apart. To the simulator it appears as if the links are inside one another. However, note for a chain I recommend using Constraints instead.

  • Some objects have unapplied transforms. In many cases applying the scale and rotation can improve the stability and behavior of a simulation. Just beware when applying transforms to animated objects.

  • Animated is not enabled on the capstan. Enabling this is important if you want to control rigid bodies with the animation system.

Setting up Constraints for a chain:

  1. Select all the links in the chain.

  2. Press Connect in 3D View > Tool Shelf > Physics > Rigid body tools, then set the constraint type to Point (sort of a ball joint) and the Connection Pattern to Chain by distance:

    enter image description here

By default the new constraints (added to the empties) will have Disable collisions enabled which disables collisions between objects constrained to each other. I recommend leaving this setting on, and keeping the collision shape on Convex Hull as nothing besides the links themselves are likely to try and pass through the hole.

enter image description here

(For Blender 2.8)

| improve this answer | |
  • $\begingroup$ The blend files are not available - death links. Too bad. The solution from gandalf3 looks like a really great anchor/chain example. $\endgroup$ – klwemu Jul 28 '19 at 19:25
  • $\begingroup$ @user1209926 Thanks for letting me know, I've re-made the example in Blender 2.8. In general I have copies of all the .blends I've uploaded so please don't hesitate to ask (this was an exception since it was actually a modified version of the .blend from the OP) $\endgroup$ – gandalf3 Jul 28 '19 at 23:45

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