When you have a Skinned Mesh that is moving in tracks that are visually parallel to each other, the Parent Constraint will strictly follow the track’s orientation independently from the other track. This results in a object sliding in a rigid way.

However, you may want to make that Skinned Mesh depend on the movement of the other parallel track.

Using Aim Constraints, you can make an object of a track orient itself to an object of another track. Redefine the Parent Constraint sources of the Bones to children of the Proxies that have Aim Constraints on them.

The Aim Constraint has the advantage of having the “Object Rotation Up” option that lets you aim on another object while keeping the upwards orientation influence from the Proxy moving on the track. This will keep the aiming generally lined up with the direction of the track.

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How to

Create the Aim Constraint:

• Create a GameObject as a child of your Proxy.
• Add an Aim Constraint in that new GameObject.
• Set the Aim Constraint to “World Up Type” to Object Rotation Up.
• Add another GameObject inside your Proxy.
• Set the “World Up Object” to be that new GameObject.
  • The orientation of this object may need to be tweaked.
• In the Constraint Sources, select the target of your Aim Constraint.
• Activate your Aim Constraint.

Redefine the sources of the Parent Constraint:

• Select your Bone.
• Uncheck “Active”.
• In the Constraint Sources, replace the Proxy with the child of your Proxy which has the Aim Constraint.
• Activate the Parent Constraint of the Bone.

Demonstration

In the following video, you can see this process being done to the leg group.

At the end of the video, notice how the three cubes are nicely rotating with each other in an axis that traverses the two tracks.