***Human hopping experiment:
The hopping experiments involved six healthy young male subjects (age: 24.1 ± 3.3 years, mass: 73.5 ± 6.6 kg), as approved by the Technical University of Darmstadt's Ethical Committee in line with the Declaration of Helsinki guidelines. Subjects provided written consent before participating. Initially, subjects' preferred hopping frequency (PHF) was established at 2.5 ± 0.38 Hz through a 20-second self-selected frequency and height hopping task. Subsequently, they executed hopping trials at 75%, 100%, 125%, and 150% of their PHF, with six 20-second trials per frequency, guided by an acoustic metronome and spaced by at least two minutes of rest to minimize potential biases like muscle stiffness changes or fatigue.
Kinematics were tracked using 20 reflective markers placed on specific anatomical locations and captured by a 10-camera infrared system (Qualisys, 500 Hz, Sweden). Ground reaction force (GRF) and center of pressure (CoP) data were collected for each leg using two Kistler force plates (1 kHz, Switzerland). These data were processed using OpenSim's inverse kinematics and dynamics tools, with signals low-pass filtered at 50 Hz.
For analysis, 20 hops from three trials per subject and frequency were selected based on minimal variation in kinematic and kinetic data. The mean of these hops represented the trial's data.
For additional details, please refer to the corresponding paper.
*** EPA-Hopper-II hopping experiment:
The EPA-Hopper-II, a successor to previous hopper robots, is a unilegged robot engineered to mimic human-like hopping using a blend of electric and pneumatic actuation. Its design, featuring a 3-segment leg that parallels human leg structure, aims to explore how mechanical design and control contribute to replicating human hopping dynamics across various frequencies. The robot leverages electric motors for hip movement during flight phase adjustments and pneumatic artificial muscles (PAMs) for knee and ankle actuation, reflecting the shift from passive to active control seen in human motion. Constructed primarily from 3D printed materials and lightweight carbon fiber tubes, the robot weighs 3.75 kg and includes a compliant foot design for efficiency and shock absorption. It utilizes direct-drive mechanisms for precise control without needing force/torque sensors, powered by a high-capacity battery. While focusing on leg mechanics, the design omits hip actuation complexities, relying on fixed PAM pressures for simplicity. Ground reaction forces and joint angles are meticulously measured to study the robot's hopping behavior.
For additional details, please refer to the corresponding paper.
