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: Cheetahcub, 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 to larger and stiffer quadruped robot designs. 1) It is, to the best of our knowledge, the fastest of all quadruped robots below 30 kg (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, 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.

Horse-like walking, trotting, and galloping derived from kinematic Motion Primitives (kMPs) and their application to walk/trot transitions in a compliant quadruped robot

“…RC Fig. 4 The compliant quadruped robot used for experimentation (rendered image), developed at Biorobotics laboratory, EPFL, Switzerland (Spröwitz et al, 2012). Snapshots of the real robot during walking and trotting are provided in Fig.…”

“…In Section 2 the kMPs extracted from walking, trotting, and galloping are analyzed. The compliant quadruped robot (Spröwitz et al, 2012) that was used to test the horse-like trajectories synthesized is introduced in Section 3. Next, in Section 4, the method used to generate these trajectories by reconstruction from kMPs is presented.…”

Continuous Static Gait with Twisting Trunk of a Metamorphic Quadruped Robot

“…Works have been carried out in the field in recent years, such as LittleDog (Kolter and Ng, 2011), BigDog (Raibert et al, 2008), HyQ (Boaventura et al, 2013), Tekken (Fukuoka et al, 2003), Cheetahcub (Spröwitz et al, 2013), LS3 (Bloss, 2012) [7], Baby Elephant , MIT Cheetah (Hyun et al, 2014) and so on. Conventionally, trunks of quadruped robots are all designed as a single rigid body or with a passive compliant joint.…”

Comparing trotting and turning strategies on the quadrupedal oncilla robot

“…Part of the previous research for this class of small compliant quadrupedal robots showed interest in slow but robust movement over very rough terrain, using techniques to find optimal foot placement [6]. Other research focussed on running in a bounding gait [8], [9], and more recently, trotting gaits have been developed for small compliant robots as well, e.g., for the Reservoir Dog [10] and the Cheetah-cub robot [11], two direct predecessors of the Oncilla. The purpose of our research on the Oncilla is to continue this trend, but with more and improved actuators that enable us to develop faster movement and dynamical gaits, as well as more realistic turning behaviors.…”