11,515 research outputs found
Oncilla robot: a versatile open-source quadruped research robot with compliant pantograph legs
We present Oncilla robot, a novel mobile, quadruped legged locomotion
machine. This large-cat sized, 5.1 robot is one of a kind of a recent,
bioinspired legged robot class designed with the capability of model-free
locomotion control. Animal legged locomotion in rough terrain is clearly shaped
by sensor feedback systems. Results with Oncilla robot show that agile and
versatile locomotion is possible without sensory signals to some extend, and
tracking becomes robust when feedback control is added (Ajaoolleian 2015). By
incorporating mechanical and control blueprints inspired from animals, and by
observing the resulting robot locomotion characteristics, we aim to understand
the contribution of individual components. Legged robots have a wide mechanical
and control design parameter space, and a unique potential as research tools to
investigate principles of biomechanics and legged locomotion control. But the
hardware and controller design can be a steep initial hurdle for academic
research. To facilitate the easy start and development of legged robots,
Oncilla-robot's blueprints are available through open-source. [...
Body Lift and Drag for a Legged Millirobot in Compliant Beam Environment
Much current study of legged locomotion has rightly focused on foot traction
forces, including on granular media. Future legged millirobots will need to go
through terrain, such as brush or other vegetation, where the body contact
forces significantly affect locomotion. In this work, a (previously developed)
low-cost 6-axis force/torque sensing shell is used to measure the interaction
forces between a hexapedal millirobot and a set of compliant beams, which act
as a surrogate for a densely cluttered environment. Experiments with a
VelociRoACH robotic platform are used to measure lift and drag forces on the
tactile shell, where negative lift forces can increase traction, even while
drag forces increase. The drag energy and specific resistance required to pass
through dense terrains can be measured. Furthermore, some contact between the
robot and the compliant beams can lower specific resistance of locomotion. For
small, light-weight legged robots in the beam environment, the body motion
depends on both leg-ground and body-beam forces. A shell-shape which reduces
drag but increases negative lift, such as the half-ellipsoid used, is suggested
to be advantageous for robot locomotion in this type of environment.Comment: First three authors contributed equally. Accepted to ICRA 201
Robust Quadrupedal Locomotion via Risk-Averse Policy Learning
The robustness of legged locomotion is crucial for quadrupedal robots in
challenging terrains. Recently, Reinforcement Learning (RL) has shown promising
results in legged locomotion and various methods try to integrate privileged
distillation, scene modeling, and external sensors to improve the
generalization and robustness of locomotion policies. However, these methods
are hard to handle uncertain scenarios such as abrupt terrain changes or
unexpected external forces. In this paper, we consider a novel risk-sensitive
perspective to enhance the robustness of legged locomotion. Specifically, we
employ a distributional value function learned by quantile regression to model
the aleatoric uncertainty of environments, and perform risk-averse policy
learning by optimizing the worst-case scenarios via a risk distortion measure.
Extensive experiments in both simulation environments and a real Aliengo robot
demonstrate that our method is efficient in handling various external
disturbances, and the resulting policy exhibits improved robustness in harsh
and uncertain situations in legged locomotion. Videos are available at
https://risk-averse-locomotion.github.io/.Comment: 8 pages, 5 figure
Effective Viscous Damping Enables Morphological Computation in Legged Locomotion
Muscle models and animal observations suggest that physical damping is
beneficial for stabilization. Still, only a few implementations of mechanical
damping exist in compliant robotic legged locomotion. It remains unclear how
physical damping can be exploited for locomotion tasks, while its advantages as
sensor-free, adaptive force- and negative work-producing actuators are
promising. In a simplified numerical leg model, we studied the energy
dissipation from viscous and Coulomb damping during vertical drops with
ground-level perturbations. A parallel spring-damper is engaged between
touch-down and mid-stance, and its damper auto-disengages during mid-stance and
takeoff. Our simulations indicate that an adjustable and viscous damper is
desired. In hardware we explored effective viscous damping and adjustability
and quantified the dissipated energy. We tested two mechanical, leg-mounted
damping mechanisms; a commercial hydraulic damper, and a custom-made pneumatic
damper. The pneumatic damper exploits a rolling diaphragm with an adjustable
orifice, minimizing Coulomb damping effects while permitting adjustable
resistance. Experimental results show that the leg-mounted, hydraulic damper
exhibits the most effective viscous damping. Adjusting the orifice setting did
not result in substantial changes of dissipated energy per drop, unlike
adjusting damping parameters in the numerical model. Consequently, we also
emphasize the importance of characterizing physical dampers during real legged
impacts to evaluate their effectiveness for compliant legged locomotion
A Terradynamics of Legged Locomotion on Granular Media
The theories of aero- and hydrodynamics predict animal movement and device
design in air and water through the computation of lift, drag, and thrust
forces. Although models of terrestrial legged locomotion have focused on
interactions with solid ground, many animals move on substrates that flow in
response to intrusion. However, locomotor-ground interaction models on such
flowable ground are often unavailable. We developed a force model for
arbitrarily-shaped legs and bodies moving freely in granular media, and used
this "terradynamics" to predict a small legged robot's locomotion on granular
media using various leg shapes and stride frequencies. Our study reveals a
complex but generic dependence of stresses in granular media on intruder depth,
orientation, and movement direction and gives insight into the effects of leg
morphology and kinematics on movement
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