116 research outputs found
Tail-Assisted Rigid and Compliant Legged Leaping
This paper explores the design space of simple legged robots capable of leaping culminating in new behaviors for the Penn Jerboa, an underactuated, dynamically dexterous robot. Using a combination of formal reasoning and physical intuition, we analyze and test successively more capable leaping behaviors through successively more complicated body mechanics. The final version of this machine studied here bounds up a ledge 1.5 times its hip height and crosses a gap 2 times its body length, exceeding in this last regard the mark set by the far more mature RHex hexapod. Theoretical contributions include a non-existence proof of a useful class of leaps for a stripped-down initial version of the new machine, setting in motion the sequence of improvements leading to the final resulting performance. Conceptual contributions include a growing understanding of the Ground Reaction Complex as an effective abstraction for classifying and generating transitional contact behaviors in robotics
The Penn Jerboa: A Platform for Exploring Parallel Composition of Templates
We have built a 12DOF, passive-compliant legged, tailed biped actuated by
four brushless DC motors. We anticipate that this machine will achieve varied
modes of quasistatic and dynamic balance, enabling a broad range of locomotion
tasks including sitting, standing, walking, hopping, running, turning, leaping,
and more. Achieving this diversity of behavior with a single under-actuated
body, requires a correspondingly diverse array of controllers, motivating our
interest in compositional techniques that promote mixing and reuse of a
relatively few base constituents to achieve a combinatorially growing array of
available choices. Here we report on the development of one important example
of such a behavioral programming method, the construction of a novel monopedal
sagittal plane hopping gait through parallel composition of four decoupled 1DOF
base controllers.
For this example behavior, the legs are locked in phase and the body is
fastened to a boom to restrict motion to the sagittal plane. The platform's
locomotion is powered by the hip motor that adjusts leg touchdown angle in
flight and balance in stance, along with a tail motor that adjusts body shape
in flight and drives energy into the passive leg shank spring during stance.
The motor control signals arise from the application in parallel of four
simple, completely decoupled 1DOF feedback laws that provably stabilize in
isolation four corresponding 1DOF abstract reference plants. Each of these
abstract 1DOF closed loop dynamics represents some simple but crucial specific
component of the locomotion task at hand. We present a partial proof of
correctness for this parallel composition of template reference systems along
with data from the physical platform suggesting these templates are anchored as
evidenced by the correspondence of their characteristic motions with a suitably
transformed image of traces from the physical platform.Comment: Technical Report to Accompany: A. De and D. Koditschek, "Parallel
composition of templates for tail-energized planar hopping," in 2015 IEEE
International Conference on Robotics and Automation (ICRA), May 2015. v2:
Used plain latex article, correct gap radius and specific force/torque
number
Towards a Comparative Measure for Legged Agility
We introduce an agility measure enabling the comparison of two very different leaping-from-rest transitions by two comparably powered but morphologically different legged robots. We use the measure to show that a flexible spine outperforms a rigid back in the leaping- from-rest task. The agility measure also sheds light on the source of this benefit: core actuation through a sufficiently powerful parallel elastic actuated spine outperforms a similar power budget applied either only to preload the spine or only to actuate the spine during the leap, as well as a rigid backed configuration of the identical machine
The Effect of Tail Stiffness on a Sprawling Quadruped Locomotion
A distinctive feature of quadrupeds that is integral to their locomotion is
the tail. Tails serve many purposes in biological systems including propulsion,
counterbalance, and stabilization while walking, running, climbing, or jumping.
Similarly, tails in legged robots may augment the stability and maneuverability
of legged robots by providing an additional point of contact with the ground.
However, in the field of terrestrial bio-inspired legged robotics, the tail is
often ignored because of the difficulties in design and control. This study
will test the hypothesis that a variable stiffness robotic tail can improve the
performance of a sprawling quadruped robot by enhancing its stability and
maneuverability in various environments. To test our hypothesis, we add a
multi-segment, cable-driven, flexible tail, whose stiffness is controlled by a
single servo motor in conjunction with a reel and cable system, to the
underactuated sprawling quadruped robot. By controlling the stiffness of the
tail, we have shown that the stability of locomotion on rough terrain and the
climbing ability of the robot are improved compared to the movement with a
rigid tail and no tail. The flexible tail design also provides passively
controlled tail undulation capabilities through the robot's lateral movement,
which contributes to stability
Analytically-Guided Design of a Tailed Bipedal Hopping Robot
We present the first fully spatial hopping gait of a 12 DoF tailed biped driven by only 4 actuators. The control of this physical machine is built up from parallel compositions of controllers for progressively higher DoF extensions of a simple 2 DoF, 1 actuator template. These template dynamics are still not themselves integrable, but a new hybrid averaging analysis yields a conjectured closed form representation of the approximate hopping limit cycle as a function of its physical and control parameters. The resulting insight into the role of the machine\u27s kinematic and dynamical design choices affords a redesign leading to the newly achieved behavior
Empirical validation of a spined sagittal-plane quadrupedal model
We document empirically stable bounding using an actively powered spine on the Inu quadrupedal robot, and propose a reduced-order model to capture the dynamics associated with this additional, actuated spine degree of freedom. This model is sufficiently accurate as to roughly describe the robots mass center trajectory during a bounding limit cycle, thus making it a potential option for low dimensional representations of spine actuation in steady-state legged locomotion
Towards Agility: Definition, Benchmark and Design Considerations for Small, Quadrupedal Robots
Agile quadrupedal locomotion in animals and robots is yet to be fully understood, quantified
or achieved. An intuitive notion of agility exists, but neither a concise definition nor a common
benchmark can be found. Further, it is unclear, what minimal level of mechatronic complexity
is needed for this particular aspect of locomotion.
In this thesis we address and partially answer two primary questions: (Q1) What is agile
legged locomotion (agility) and how can wemeasure it? (Q2) How can wemake agile legged
locomotion with a robot a reality?
To answer our first question, we define agility for robot and animal alike, building a common
ground for this particular component of locomotion and introduce quantitative measures
to enhance robot evaluation and comparison. The definition is based on and inspired by
features of agility observed in nature, sports, and suggested in robotics related publications.
Using the results of this observational and literature review, we build a novel and extendable
benchmark of thirteen different tasks that implement our vision of quantitatively classifying
agility. All scores are calculated from simple measures, such as time, distance, angles and
characteristic geometric values for robot scaling. We normalize all unit-less scores to reach
comparability between different systems. An initial implementation with available robots and
real agility-dogs as baseline finalize our effort of answering the first question.
Bio-inspired designs introducing and benefiting from morphological aspects present in nature
allowed the generation of fast, robust and energy efficient locomotion. We use engineering
tools and interdisciplinary knowledge transferred from biology to build low-cost robots able
to achieve a certain level of agility and as a result of this addressing our second question. This
iterative process led to a series of robots from Lynx over Cheetah-Cub-S, Cheetah-Cub-AL,
and Oncilla to Serval, a compliant robot with actuated spine, high range of motion in all joints.
Serval presents a high level of mobility at medium speeds. With many successfully implemented
skills, using a basic kinematics-duplication from dogs (copying the foot-trajectories
of real animals and replaying themotion on the robot using a mathematical interpretation),
we found strengths to emphasize, weaknesses to correct and made Serval ready for future
attempts to achieve even more agile locomotion. We calculated Servalâs agility scores with the
result of it performing better than any of its predecessors. Our small, safe and low-cost robot
is able to execute up to 6 agility tasks out of 13 with the potential to reachmore after extended
development. Concluding, we like to mention that Serval is able to cope with step-downs,
smooth, bumpy terrain and falling orthogonally to the ground
Towards dynamic Narrow path walking on NU's Husky
This research focuses on enabling Northeastern University's Husky, a
multi-modal quadrupedal robot, to navigate narrow paths akin to various animals
in nature. The Husky is equipped with thrusters to stabilize its body during
dynamic maneuvers, addressing challenges inherent in aerial-legged systems. The
approach involves modeling the robot as HROM (Husky Reduced Model) and creating
an optimal control framework using linearized dynamics for narrow path walking.
The thesis introduces a gait scheduling method to generate an open-loop walking
gait and validates these gaits through a high-fidelity Simscape simulation.
Experimental results of the open-loop walking are presented, accompanied by
potential directions for advancing this robotic system.Comment: 60 pages, 27 figure
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