9. A method for specifying an animatronics unit comprising: determining a force-based software model for the animatronics unit; determining a kinematics-based software model for the animatronics unit; receiving animation data for animating the kinematics-based software model, wherein the animation data comprises artistically determined motions by a user; animating the force-based software model in response to the animation data; displaying animation of the force-based software model determined in response to the animation data; and determining a physical implementation of the animatronics unit in response to animation of the kinematics-based software model, comprising: a) determining an initial physical implementation of the animatronics unit; and b) determining the physical implementation of the animatronics unit in response to animation of the kinematics-based software model and to the initial physical implementation; wherein the initial physical implementation comprises an initial implementation of a component of the animatronics unit consisting of a first material; wherein the physical implementation comprises an implementation of the component of the animatronics unit consisting of a second material instead of the first material; and wherein the first material has a density different from a density of the second material.
9. A method for specifying an animatronics unit comprising: determining a force-based software model for the animatronics unit; determining a kinematics-based software model for the animatronics unit; receiving animation data for animating the kinematics-based software model, wherein the animation data comprises artistically determined motions by a user; animating the force-based software model in response to the animation data; displaying animation of the force-based software model determined in response to the animation data; and determining a physical implementation of the animatronics unit in response to animation of the kinematics-based software model, comprising: a) determining an initial physical implementation of the animatronics unit; and b) determining the physical implementation of the animatronics unit in response to animation of the kinematics-based software model and to the initial physical implementation; wherein the initial physical implementation comprises an initial implementation of a component of the animatronics unit consisting of a first material; wherein the physical implementation comprises an implementation of the component of the animatronics unit consisting of a second material instead of the first material; and wherein the first material has a density different from a density of the second material. 12. The method of claim 9 wherein the initial physical implementation comprises an initial implementation of a joint of the animatronics unit having a first location; wherein the physical implementation comprises an implementation of the joint of the animatronics unit having a second location instead of the first location.