public void setDynamicChain(PhysicsLink startLink, int chainLength,
            Vector3f uniformAcceleration) {
        if (chainLength == 0) {
            return;
        }
        verifyAddedToSpatial("change modes");

        if (startLink instanceof BoneLink) {
            BoneLink boneLink = (BoneLink) startLink;
            boneLink.setDynamic(uniformAcceleration);
        }

        PhysicsLink parent = startLink.getParent();
        if (parent != null && chainLength > 1) {
            setDynamicChain(parent, chainLength - 1, uniformAcceleration);
        }
    }
Immediately put the specified link and all its ancestors (excluding the
torso) into dynamic mode. Note: recursive!
<p>
Allowed only when the control IS added to a spatial.

@param startLink the start of the chain to modify (not null)
@param chainLength the maximum number of links to modify (&ge;0)
@param uniformAcceleration the uniform acceleration vector (in
physics-space coordinates, not null, unaffected)
jme3-jbullet/src/main/java/com/jme3/bullet/animation/DynamicAnimControl.java