4,754 research outputs found
Dynamic Rolling for a Modular Loop Robot
Reconfigurable modular robots use different gaits and configurations to perform various tasks. A rolling gait is the fastest currently implemented gait available to a modular robot for traversal of level ground. In this work, we analyze and implement a sensor-based feedback controller to achieve dynamic rolling for a 10 module loop robot. The controller exploits the dynamics of the system to build up momentum in each step by specifying a desired global shape for the robot at touchdown. Energy is input into the system both by raising the height of the center of mass of the robot and moving the position of center of mass with respect to the ground to maximize the moment arm due to gravity. Using simulation and experimental results, we show how the desired shape can be varied to achieve higher terminal velocities. Through simulation, we also show rounder shapes have lower specific resistance and are thus more efficient
Control of Locomotion with Shape-Changing Wheels
We present a novel approach to controlling the locomotion of a wheel by changing its shape, leading to applications to the synthesis and closed-loop control of gaits for modular robots. A dynamic model of a planar, continuous deformable ellipse in contact with a ground surface is derived. We present two alternative approaches to controlling this system and a method for mapping the gaits to a discrete rolling polygon. Mathematical models and dynamic simulation of the continuous approximation and the discrete n-body system, and experimental results obtained from a physical modular robot system illustrate the accuracy of the dynamic models and the validity of the approach
Deep Reinforcement Learning for Tensegrity Robot Locomotion
Tensegrity robots, composed of rigid rods connected by elastic cables, have a
number of unique properties that make them appealing for use as planetary
exploration rovers. However, control of tensegrity robots remains a difficult
problem due to their unusual structures and complex dynamics. In this work, we
show how locomotion gaits can be learned automatically using a novel extension
of mirror descent guided policy search (MDGPS) applied to periodic locomotion
movements, and we demonstrate the effectiveness of our approach on tensegrity
robot locomotion. We evaluate our method with real-world and simulated
experiments on the SUPERball tensegrity robot, showing that the learned
policies generalize to changes in system parameters, unreliable sensor
measurements, and variation in environmental conditions, including varied
terrains and a range of different gravities. Our experiments demonstrate that
our method not only learns fast, power-efficient feedback policies for rolling
gaits, but that these policies can succeed with only the limited onboard
sensing provided by SUPERball's accelerometers. We compare the learned feedback
policies to learned open-loop policies and hand-engineered controllers, and
demonstrate that the learned policy enables the first continuous, reliable
locomotion gait for the real SUPERball robot. Our code and other supplementary
materials are available from http://rll.berkeley.edu/drl_tensegrityComment: International Conference on Robotics and Automation (ICRA), 2017.
Project website link is http://rll.berkeley.edu/drl_tensegrit
Design and optimal springs stiffness estimation of a Modular OmniCrawler in-pipe climbing Robot
This paper discusses the design of a novel compliant in-pipe climbing modular
robot for small diameter pipes. The robot consists of a kinematic chain of 3
OmniCrawler modules with a link connected in between 2 adjacent modules via
compliant joints. While the tank-like crawler mechanism provides good traction
on low friction surfaces, its circular cross-section makes it holonomic. The
holonomic motion assists it to re-align in a direction to avoid obstacles
during motion as well as overcome turns with a minimal energy posture.
Additionally, the modularity enables it to negotiate T-junction without motion
singularity. The compliance is realized using 4 torsion springs incorporated in
joints joining 3 modules with 2 links. For a desirable pipe diameter (\text{\O}
75mm), the springs' stiffness values are obtained by formulating a constraint
optimization problem which has been simulated in ADAMS MSC and further
validated on a real robot prototype. In order to negotiate smooth vertical
bends and friction coefficient variations in pipes, the design was later
modified by replacing springs with series elastic actuators (SEA) at 2 of the 4
joints.Comment: arXiv admin note: text overlap with arXiv:1704.0681
Inclined Surface Locomotion Strategies for Spherical Tensegrity Robots
This paper presents a new teleoperated spherical tensegrity robot capable of
performing locomotion on steep inclined surfaces. With a novel control scheme
centered around the simultaneous actuation of multiple cables, the robot
demonstrates robust climbing on inclined surfaces in hardware experiments and
speeds significantly faster than previous spherical tensegrity models. This
robot is an improvement over other iterations in the TT-series and the first
tensegrity to achieve reliable locomotion on inclined surfaces of up to
24\degree. We analyze locomotion in simulation and hardware under single and
multi-cable actuation, and introduce two novel multi-cable actuation policies,
suited for steep incline climbing and speed, respectively. We propose
compelling justifications for the increased dynamic ability of the robot and
motivate development of optimization algorithms able to take advantage of the
robot's increased control authority.Comment: 6 pages, 11 figures, IROS 201
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
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