Hey @alesch ,
Yeah the rPlan does need that “offset” for the computation. Which means, the translation channel of the cube (body) and those spheres (foot) can not be Freeze (the same as their controller, if any).
As an additional resource, you may also want to have a look at this Crab rig (Ragdoll July Challenge - #14 by marcus), as an example of how it did work with locomotion.