Query: cheetah robot

title: Design Principles for Energy Efficient Legged Locomotion and Implementation on the MIT Cheetah Robot
abstract: This paper presents the design principles for highly efficient legged robots, the implementation of the principles in the design of the MIT Cheetah, and the analysis of the high speed trotting experimental results. The design principles were derived by analyzing three major energy loss mechanisms in locomotion: heat losses from the actuators, friction losses in transmission, and the interaction losses caused by the interface between the system and the environment. Four design principles that minimize these losses are discussed: employment of high torque density motors, energy regenerative electronic system, low loss transmission, and a low leg inertia. These principles were implemented in the design of the MIT Cheetah; the major design features are large gap diameter motors, regenerative electric motor drivers, single stage low gear transmission, dual coaxial motors with composite legs, and the differential actuated spine. The experimental results of fast trotting are presented; the 33 kg robot runs at 22 km/h (6 m/s) The total power consumption from the battery pack was 973 W and resulted in a total cost of transport of 0.5, which rivals running animals' at the same scale. 76% of the total energy consumption is attributed to heat loss from the motor, and the remaining 24% is used in mechanical work, which is dissipated as interaction loss as well as friction losses at the joint and transmission.

title: MIT Cheetah 3: Design and Control of a Robust, Dynamic Quadruped Robot
abstract: This paper introduces a new robust, dynamic quadruped, the MIT Cheetah 3. Like its predecessor, the Cheetah 3 exploits tailored mechanical design to enable simple control strategies for dynamic locomotion and features high bandwidth proprioceptive actuators to manage physical interaction with the environment. A new leg design is presented that includes proprioceptive actuation on the abduction/adduction degrees of freedom in addition to an expanded range of motion on the hips and knees. To make full use of these new capabilities, general balance and locomotion controllers for Cheetah 3 are presented. These controllers are embedded into a modular control architecture that allows the robot to handle unexpected terrain disturbances through reactive gait modification and without the need for external sensors or prior environment knowledge. The efficiency of the robot is demonstrated by a low Cost of Transport (CoT) over multiple gaits at moderate speeds, with the lowest CoT of 0.45 found during trotting. Experiments showcase the ability to blindly climb up stairs as a result of the full system integration. These results collectively represent a promising step toward a platform capable of generalized dynamic legged locomotion.

title: Cheetah cub S: Steering of a quadruped robot using trunk motion
abstract: A reliable concept for steering was realized by integrating a spine like structure with one DoF into a quadruped robot Cheetah cub S. We increased maneuverability dramatically compared to a robot with rigid spine, while keeping controlling effort low. The robot weights 1160 g at 0.1 m (height) 0.105 m (width) and 0.205 m (length) Based on qualitative tests, it is able to run 0.36 m/s and turn within a radius of 0.51 m (equivalent to 2.48 body lengths) at 0.31 m/s (equivalent to 34deg/s) We could steer the quadruped around three objects in a 7.13 m (23 s 0.31 m/s) slalom within our test area. Due to its modularity, Cheetah cub S is a versatile mobile platform and components such as the spine segment, legs, motors or steering mechanism can be exchanged, leading to easier development of even higher performing robot versions.

title: Towards dynamic trot gait locomotion: Design, control, and experiments with Cheetah cub, a compliant quadruped robot
abstract: We present the design of a novel compliant quadruped robot, called Cheetah cub, and a series of locomotion experiments with fast trotting gaits. The robot's leg configuration is based on a spring loaded, pantograph mechanism with multiple segments. A dedicated open loop locomotion controller was derived and implemented. Experiments were run in simulation and in hardware on flat terrain and with a step down, demonstrating the robot's self stabilizing properties. The robot reached a running trot with short flight phases with a maximum Froude number of FR 1.30, or 6.9 body lengths per second. Morphological parameters such as the leg design also played a role. By adding distal in series elasticity, self stability and maximum robot speed improved. Our robot has several advantages, especially when compared with larger and stiffer quadruped robot designs. (1) It is, to the best of the authors' knowledge, the fastest of all quadruped robots below 30kg (in terms of Froude number and body lengths per second) (2) It shows self stabilizing behavior over a large range of speeds with open loop control. (3) It is lightweight, compact, and electrically powered. (4) It is cheap, easy to reproduce, robust, and safe to handle. This makes it an excellent tool for research of multi segment legs in quadruped robots.

title: Realization of three dimensional walking of a cheetah modeled bio inspired quadruped robot
abstract: Adaptability of quadruped animals is not solely reached by brain control, but by the interaction between its body, environment, and control. Especially, morphology of the body is supposed to contribute largely to the adaptability. We have tried to understand quadrupedal locomotion by building a bio inspired quadruped robot named "Pneupard" which has a feline like muscular skeletal structure. In our previous study, we successfully realized alternative gait of hindlimbs by reflex control based on the sole touch information, which is called an unloading rule, and that of forelimbs as well. In this paper, we finally connect forelimbs and hindlimbs by a rigid spine, and conduct 3D walking experiments only with the simple unloading rule. Through several preliminary experiments, we realize that the touch information on the sole is the most critical for stable 3D walking.

title: Stable reflex based walking of forelimbs of a bio inspired quadruped robot modeled cheetah
abstract: In contrast to the high movement adaptability of quadruped animals in many environmental conditions, it is hard for conventional quadruped robots to operate in complex environment conditions. We investigate the adaptability of animals' musculo skeletal systems, by building a bio inspired quadruped robot named "Pneupard" which duplicates a feline musculo skeletal system. In this study, we built Pneupard's forelimb which has 14 active muscles, 4 passive muscles and 8 degrees of freedom (DOF) We propose sole reflex based control and verify its effectiveness by conducting walking experiments, in which the robot performed stable walking with a two dimensional restriction.

title: Geometrical synthesis method and parametric optimization of galloping robot leg mechanism
abstract: Subject of Research. The paper presents geometrical synthesis results of kinematic schemes for a femur and a whole leg mechanisms of a cheetah robot, which is able to jump in place and run at various speed. We substantiate the topology of mechanisms, describe their operation principles, characteristics and distinctive features, involving the controlled reconfiguration of mechanisms for changing the trajectory of the ground contact point, and the use of flexible elements and links with variable length to ensure energy efficient locomotion.  A structure scheme of the whole cheetah robot leg was obtained by attaching four movable links to the femur mechanism, imitating large and small tibial bones, metatarsus and sartorius muscle. The obtained structure was decomposed into three mechanism components: a "minitaur" two rocker four bar lambda mechanism and a rocker slider mechanism. The kinematic schemes of the above mentioned mechanisms were synthesized by the method of extreme discrete positions with the result that the kinematic scheme of the whole leg with intermediate positions was obtained. The parametric optimization algorithm was described and the minitaur objective function was given using mathematical programming.  The kinematic scheme of the whole cheetah robot leg is obtained in the first approximation without taking into account the robot dynamics, location of flexible elements and their resonance necessary for the resonance behavior in order to achieve energy efficient movement. Modeling results of the robot dynamics according to the synthesized scheme are given. Stable behavior is obtained both while jumping in place and running.  The study is carried out for the development of an energy efficient four legged galloping cheetah robot performing energy recovery with the help of flexible elements. The synthesized kinematic scheme is applicable for detailed analyzes of dynamics, kinetostatics, energy recovery and losses upon impact with the ground surface, and for the robot prototype design.

title: Joint variable stiffness of musculoskeletal leg mechanism for quadruped robot
abstract: When the quadruped robot is in locomotion such as jumping and running with higher speed, there is non continuous contact force between the foot and the environment inevitably. In order to achieve the flexible force interaction of the bionic legs with the environment, it is necessary to analyze the joint angular stiffness of the bionic leg. In this article, based on the designing principles of the bionics, light weighted, and flexible, a kind of musculoskeletal bionic leg mechanism driven by pneumatic artificial muscles is presented by inspiring from the biological cheetah anatomy and physiology muscle distribution. The kinematics of the bionic leg is analyzed to obtain the Jacobian matrix. In order to achieve high speed jumping and soft landing of the bionic leg, a kind of foot stiffness model is presented by analyzing the foot elastic potential energy caused by the contact force. The mapping relationship between the joint stiffness matrix and the foot stiffness matrix is obtained by the Jacobian matrix. Then, the dynamics of the bionic leg is analyzed to determine the relationship between the joint angular stiffness and the pneumatic artificial muscle gas pressure. Finally, the experiment on controlling the pneumatic artificial muscles gas pressure for tracking the joint angular stiffness of the bionic leg is conducted. By regulating the pneumatic artificial muscle gas pressure, the needed pneumatic artificial muscle gas pressure that could meet the desired foot stiffness ellipse model can be determined. The study will pay a theoretical foundation for controlling the pneumatic artificial muscles to achieve the high speed locomotion of the bionic leg.

title: On the dynamics of a quadruped robot model with impedance control: Self stabilizing high speed trot running and period doubling bifurcations
abstract: The MIT Cheetah demonstrated a stable 6 m/s trot gait in the sagittal plane utilizing the self stable characteristics of locomotion. This paper presents a numerical analysis of the behavior of a quadruped robot model with the proposed controller. We first demonstrate the existence of periodic trot gaits at various speeds and examine local orbital stability of each trajectory using Poincar`e map analysis. Beyond the local stability, we additionally demonstrate the stability of the model against large initial perturbations. Stability of trot gaits at a wide range of speed enables gradual acceleration demonstrated in this paper and a real machine. This simulation study also suggests the upper limit of the command speed that ensures stable steady state running. As we increase the command speed, we observe series of period doubling bifurcations, which suggests presence of chaotic dynamics beyond a certain level of command speed. Extension of this simulation analysis will provide useful guidelines for searching control parameters to further improve the system performance.

title: Pneupard: A biomimetic musculoskeletal approach for a feline inspired quadruped robot
abstract: Feline locomotion combines great acrobatic proficiency, unparalleled balance and higher accelerations than other animals. Capable of accelerating from 0 to 100 km h 1 in three seconds, the cheetah (Acinonyx jubatus) is still a mystery which intrigues scientists. Aiming for a better understanding of the source of such higher speeds, we develop a biomimetic platform, where musculoskeletal parameters (range of motion and moment arms) from the biological system can be evaluated with air muscles within a lightweight robotic structure. We performed experiments validating the muscular structure during a treadmill walk, successfully reproducing animal locomotion while adopting an EMG based control method.