The Robonaut torso consists of a structural aluminum endoskeleton covered by a protective outer shell. The endoskeleton terminates in a mounting flange for each robot limb, providing convenient locations for three six-axis load cells used to measure external forces affecting the robot. When the distal end of the tail is held fixed, it becomes a leg capable of repositioning the body. In this configuration, the tail sensor measures external forces acting on the arms, the head, and the outer shell. When contact does occur, all three load cells may be used in concert to classify the collision as either internal or external and to estimate the contact force and location.
Traditionally, unintended physical contact between a robotic manipulator and its environment is treated as a failure and drastic measures are taken to limit the consequences. A robot is typically shut down when the controller detects a collision and then it waits helplessly for a human to resolve the problem. Humans, on the other hand, are adept at managing contact forces and routinely use them to great advantage, as when carrying bulky items.
Because Robonaut's manipulator workspaces overlap and because the robot will work in cluttered environments, frequent contact is expected and must be tolerated, even exploited through judicious use of the robot's various sensors. For added protection, the body is covered with a custom-fitted fabric skin designed to contain electrical wire harnesses while keeping foreign material out of the mechanical joints. The torso section also features a subcutaneous layer of foam padding designed to absorb impact energy while permitting contact forces to build up gradually. Future enhancements to the skin may include a force-sensing array capable of resolving the magnitude and location of an external force.The torso outer shell was produced in sections by first laying up dry carbon fiber fabric on a female mold and then injecting it with resin in a vacuum forming process. Both the torso and backpack are split into front and back halves to permit easy access to internal electronics.
The outer shell protects the robot in two ways. First, it hides fragile electronic components and wire bundles which would otherwise present a serious entanglement hazard. Second, it softens impact through a combination of a padded jacket and a floating suspension. Much like the human ribcage, the outer shell hangs from the backbone of the robot. In response to an external force, the shell deflects elastically while gradually building up reaction force until the controller responds.
In order to become a truly useful tool, Robonaut must achieve mobility. This goal is not unrealistic, considering the pace of miniaturization and the selection of wireless technologies available today. But making everything fit in a smaller, self-sustained package is only half the battle. Depending on the environment, moving around may involve operating in harsh conditions with poor lighting and limited fuel. EVA astronauts work in a microgravity environment that presents special challenges unfamiliar to most people. Future Robonaut body development work will address these mobility issues by incorporating the required capabilities and interfaces. The next generation backpack, for example, might have a grapple fixture compatible with the Space Shuttle arm, enabling the two robots to team up on spacewalks.
Robonaut's helmet is formed in a rapid-prototyping process to reduce fabrication costs. Unit A's helmet consists of a translucent, amber-colored resin that is hardened in a stereolithography process to build a three-dimensional object, one layer at a time. Unit B's helmet, formed using a different rapid-prototyping process and subsequently painted gold, is built up of sintered glass fibers and is opaque.
ChassisRobonaut's endoskeleton comprises hundreds of aluminum alloy parts machined to close tolerances from various stock geometries. Due to their geometrical complexity, the forearms and palms are cast and then post-machined to specified tolerances. Because of tight volumetric constraints, stainless steel is used extensively in the hands and wrists. To reduce complexity and fabrication costs, aluminum alloy and stainless steel sheet metal brackets are used to support various avionics and electrical power components throughout the body.Robonaut's torso section contains the system's CPU, a large electronic junction board, distributed power converters, and many exposed wires and connectors. These delicate components are protected by a black, rigid carbon fiber breastplate and backpack suspended from the robot's endoskeleton.
The robot's high-strength, gold-anodized aluminum alloy endoskeleton is covered with a white fabric spacesuit designed to soften collisions while keeping foreign materials out of the moving joints. The suit encloses all wire harnesses to prevent entanglement and presents an attractive, uncluttered exterior reminiscent of the spacesuit used by astronauts, called the External Mobility Unit (EMU). In fact, Robonaut's spacesuit consists mainly of Orthofabric, the same fabric forming the outermost layer of the EMU. It is a very flexible weave with high tensile strength, good abrasion resistance and fire retardant properties.