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Lightweight robots described by low weight, low payload capabilities and high motion dynamics

The challenge of autonomous walking with lightweight robots with a low payload capability is a sophisticated dynamic problem. All sensor and actuator components as well as the onboard computer have to selected carefully.

The low additional payload causes all on board components to be well selected with respect to small mass and as less as possible additional energy supply to reduce the mass of the required batteries. Our legged robots - humanoid and four-legged - are designed in a lightweight manner.

The lightweight aspect here refers to software and components for sensory, which runs with a good performance on a robot with usually small payload, but a sophisticated dynamic behavior. Typical robots beside our legged robots are air vehicles. They all have a tailored hardware as a light on board computer, often with low computational power, and inertial sensory as gyroscopes and accelerometers.

The mass in the robot, mainly caused by the motors, is reduced as much as possible. Our humanoid robot is equipped with altogether 21 non-redundant servo motors, 6 arranged in each legs, 3 in each arms, 1 in the upper body and two in the head. The motors are tailored for the challenge of fast walking: The knees, which are highly stressed, are equipped with the high-torque motors, the other motors are the conventional servo motors for humanoid robots.

The robot is extended with two off-the-shelf CCD cameras with different lenses. The cameras come with a plastic cover, which is robust and lightweight. Further on a three axes accelerometer and three one axis gyroscopes are attached as inertial sensors with 100 Hz for stabilization during walking motions by correction movements mainly in the arms. The control software is executed on a off-the-shelf Pocket PC with integrated power supply. The robot is powered by Lithium Polymer batteries, which have a good capacity-mass-rate. The motor batteries are placed in the feet to lower the center of mass of the robot. The whole body stabilization is increased, whereas the rules concerning the foot area with respect to the height of the center of mass are are still fulfilled. The robot frame partly consists of aluminum in the legs, arm, and head holder, partly on carbon fiber reinforced plastic in the upper body. The metal was chosen to give a basic stability, whereas the plastic reduces the weight in less stressed parts.

Our four-legged robots are constructed in a similar way. They have an on board computer, light servo motors and inertial sensors. The software is adapted to the limited computational power.