ROBOLEG in the ADIDAS testing facility in Herzogenaurauch, Germany
Members of the FRC have been involved in the design and building of an experimental soccer- ball kicking robot for a large sports-shoe company in order to perform unbiased and repeatable experiments to improve upon shoe and soccer-ball designs. The leg was designed to approximate as close as possible the human kinematics and dynamics during the action of kicking a soccer ball. The purpose was to provide a consistent test-bed to remove the statistical variance associated with human testing and thus provide objective comparison criteria to judge and drive the design of new soccer-shoe prototypes. In addition, the developed system has the advantage of providing a highly visible, high-tech demonstration and show-piece for the sports-shoe company during trade-shows, press conferences and tournaments. The system was designed using early-century and the latest photographic and dynamic kicking data available, with the ultimate goal of being able to replicate and alter the leg trajectories, power and contact point and orientation during contact with the ball. Due to the large differences in mass between a human and a mechanical leg, it was decided to use the joint angle and-velocities as the driving goals for system performance and power. The robot consists of a vertical hollow post mounted on a steel-pallet, upon which are attached the power and control electronics, and supported by tension braces. The post houses the torso-rotation rotational module, to which are mounted two separate linear actuators to allow for controlling leg height and leg-sweep motions. The thigh rotation is actuated using an innovative spring-loaded rotational actuator, to enable the powerful swing of the thigh. A linear springloaded actuator is used to power the `snapping' swing of the shank. Both these actuator modules are innovative in that large power can be transferred to the thigh and shank in a short time period. The ankle is built around a mechanical replica of the achilles tendon by using a small linear actuator to enable toe up/down motions, and a compact rotary and bevel/rig-gearbox to allow for rotation of the toe. A test-shoe is mounted an a foot-lath and attached to the ankle using a simple spanner bolt. This allows the easy testing of different shoes with identical kicking conditions. The ball location is controlled with a translating linear stage which carries a passively pivoting three-prong support to hold the ball until the moment of impact, thus not affecting the impact nor take-off phases of the kick. The robot simulates a running kick through the use of the torso rotation and the spring-released thigh and shank `bones', while the toe is positioned to achieve different contact points and ball-spins. In order to achieve the high ball-speeds upon kicking (> 40 m/sec), the thigh and shank actuators were designed to be pre-loaded linear and rotary springs which are released via a clutch and then free-wheel to achieve leg-speeds comparable to a professional soccer player in a time-period of less than 0.25 sec., rotationally and linearly accelerating a torso/leg-mass of more than 125 kg and a leg-mass of 70kg to foot-tip speeds of more than 50 m/sec and transferring energy (momentum transfer via elastic collision) to the soccer ball over a contact period of no more than 0.01secs. in length. The main difference to a human kick is that the robot is only able to replicate a 1 m/sec running speed using the thigh-rotation, vs. a human with a top speed of around 5 m/sec. Translational speeds at the tip of the foot due to leg rotation is designed to reach between 30 and 45 m/sec. An IBM-compatible computer and motor controllers synchronize and coordinate all motions, while a graphical software user interface allows for easy kicking parameter adjustments by the operator. FRC team members have been collaborating with an industrial design firm (BALLY Design, Inc.) which was retained by an international sports equipment manufacturer (ADIDAS, Inc.) to develop the leg for research and promotional purposes. The leg will be used to introduce a revolutionary new soccer-shoe during a press conference at ADIDAS headquarters in Germany during early May 1994. Subsequently it will be shipped to be on display and operating during the 1994 World Cup in the USA (Chicago) to be held during the summer of 1994, after which it will be shipped to ADIDAS Research in Oregon, WA, to be used in their shoe and ball research and prototyping agenda.
