Cited by 1,156Robotic Locomotion and ControlReinforcement Learning in RoboticsProsthetics and Rehabilitation Robotics

Learning quadrupedal locomotion over challenging terrain

Open access
Lee, Joonho, Hwangbo, Jemin, Wellhausen, Lorenz, Koltun, Vladlen, Hutter, Marco·2020·Science Robotics

Abstract

A learning-based locomotion controller enables a quadrupedal ANYmal robot to traverse challenging natural environments.

AI snapshot

Written from the paper’s full text.

TL;DR

The paper presents a reinforcement-learning controller for blind quadrupedal locomotion that uses only proprioceptive history and transfers zero-shot from simulation to challenging natural terrain. It was deployed on two generations of ANYmal robots across mud, snow, vegetation, water, rubble, and the DARPA Subterranean Challenge Urban Circuit without environment-specific tuning.

Key findings

  • In moss, mud, and vegetation, the presented controller achieved higher average speeds than a state-of-the-art baseline: 0.452, 0.338, and 0.248 m/s versus 0.199, 0.197, and not reported for vegetation; mechanical cost of transport was lower: 0.423, 0.692, and 1.23 versus 0.625, 0.931, and not reported.
  • The controller showed zero-shot generalization to conditions never encountered in training, including deformable terrain, dynamic footholds, and overground impediments; it drove two ANYmal-B robots in four 60-minute DARPA Subterranean Challenge Urban Circuit missions with a zero failure rate.
  • It developed an emergent foot-trapping reflex: it overcame a 16.8 cm step, with maximum foot clearance on flat terrain of 12.9 cm and 13.6 cm for LF/RF legs increasing to 22.5 cm and 18.5 cm during foot-trapping; with a 10 kg payload (22.7% of total weight) it traversed steps up to 13.4 cm, while the baseline could not traverse any steps with the payload.
  • Ablations showed longer proprioceptive memory improved robustness: under a 50 N lateral force for 5 s, TCN-100 deviation was 35.5% lower than TCN-1; privileged training and adaptive terrain curriculum were both important for learning and performance.

Methods

  • Two-stage privileged learning: a teacher MLP was trained via TRPO in simulation with privileged terrain and contact information, then distilled via DAgger into a proprioceptive student temporal convolutional network (TCN) using a history of proprioceptive observations; the controller used PMTG motion primitives, analytic inverse kinematics, and joint PD control, with no exteroceptive input.
  • Training used RaiSim with learned actuator models, domain randomization, and an adaptive terrain curriculum that used particle filtering over parameterized hills, steps, and stairs; the student policy was deployed directly on physical ANYmal-B and ANYmal-C robots at 400 Hz onboard.
  • Evaluation included natural-environment deployments, DARPA Subterranean Challenge missions, indoor debris and step tests, payload tests, foot-slippage tests, and ablation studies with 5 random seeds and 100 trials per diagnostic test.

Limitations

  • The paper states that the controller only exhibits the trot gait, narrower than gaits seen in nature, and relies solely on proprioception, so blind locomotion is inherently limited—for example, it will walk off a cliff if commanded, and its gait is conservative because it must feel out the environment.
  • The paper states that training uses only rigid terrains and a small set of procedurally generated profiles, with no compliance or overground obstructions such as vegetation.
  • The text makes evident that the quantitative baseline comparison understates the difference between controllers because baseline failures were reset by a human operator and catastrophic failures were not factored into the speed and efficiency measurements.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1126/scirobotics.abc5986

Cites

37 of 37 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 62 cited sources checked · 0 supported · 0 flagged

  • Findingown data
    § 1. INTRODUCTION · p. 3

    The controller reliably trots through mud, sand, rubble, thick vegetation, snow, running water, and a variety of other off-road terrain.

    “The controller reliably trots through mud, sand, rubble, thick vegetation, snow, running water, and a variety of other off-road terrain.”
    Quote in the paperSubstantial claim
  • Findingown data
    § 1. INTRODUCTION · p. 3

    Realistic modeling and parameter randomization were not sufficient to achieve robust locomotion on rough terrain.

    “We use these ideas as well, but have found that they were not sufficient to achieve robust locomotion on rough terrain.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Natural environments · p. 5

    The presented controller achieves higher locomotion speed than the baseline in all conditions: moss, mud, and vegetation.

    “The presented controller achieves higher locomotion speed in all conditions.”
    Quote in the paperSubstantial claim
  • Findingcitation
    § 1. INTRODUCTION · p. 3

    The controller was used to drive two generations of ANYmal quadrupeds in a variety of conditions that are beyond the reach of prior published work in legged robotics.

    “The controller was used to drive two generations of ANYmal quadrupeds [20] in a variety of conditions that are beyond the reach of prior published work in legged robotics.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [20] 20. M. Hutter, C. Gehring, D. Jud, A. Lauber, C. D. Bellicoso, V. Tsounis, J. Hwangbo, K. Bodie, P . Fankhauser, M. Bloesch, R. Diethelm, S. Bachmann, A. Melzer, M. A. Höpflinger, ANYmal - a highly mobile and dynamic quadrupedal robot, IEEE/RSJ International Conference on Intelligent Robots and Systems , 38-44 (IEEE, 2016). source

      Not checked in the free run.

  • Findingown data
    § Natural environments · p. 3

    The presented controller has been deployed in diverse natural environments including steep mountain trails, creeks with running water, mud, thick vegetation, loose rubble, snow-covered hills, and a damp forest.

    “The presented controller has been deployed in diverse natural environments, as shown in Fig. 1 and Movies 1 and S1. These include steep mountain trails, creeks with running water, mud, thick vegetation, loose rubble, snow-covered hills, and a damp forest.”
    Quote in the paperSubstantial claim
  • May combine two claims. 38
  • The quote only partly states this claim. 2
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    Findingown data
    § Natural environments · p. 5

    The baseline could traverse flat and unobstructed patches but failed frequently upon encountering loose branches, thick vegetation, and mud; our controller never failed in these experiments.

    “The baseline could traverse flat and unobstructed patches, but failed frequently upon encountering loose branches, thick vegetation, and mud, as shown in Movie S1. Our controller never failed in these experiments.”
    Quote in the paperSubstantial claim
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    Findingown data
    § Indoor experiments · p. 5

    The presented controller can stably locomote over shifting support surfaces in an indoor environment populated by loose debris.

    “The presented controller can stably locomote over shifting support surfaces.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data
    § Natural environments · p. 5

    The presented controller is more energy-efficient, with a lower cost of transport than the baseline.

    “As shown in Table 1, the presented controller is more energy-efficient, with a lower COT than the baseline.”
    Quote in the paperSubstantial claim
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    Findingown data
    § 1. INTRODUCTION · p. 3

    The controller is consistently effective in zero-shot generalization settings; it remains robust when tested in conditions that have never been encountered during training.

    “Remarkably, the controller is consistently effective in zero-shot generalization settings. That is, it remains robust when tested in conditions that have never been encountered during training.”
    Quote in the paperSubstantial claim
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    Findingown data
    § 1. INTRODUCTION · p. 3

    When deployed on physical quadrupeds, the controller successfully handles deformable terrain such as mud, moss, and snow, dynamic footholds such as a rolling board or debris, and overground impediments such as thick vegetation, rubble, and gushing water.

    “Yet when deployed on physical quadrupeds, the controller successfully handles deformable terrain (mud, moss, snow), dynamic footholds (stepping on a rolling board in a cluttered indoor environment, or debris in the field), and overground impediments such as thick vegetation, rubble, and gushing water.”
    Quote in the paperSubstantial claim
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    Findingown data
    § 1. INTRODUCTION · p. 3

    Training a rough-terrain locomotion policy directly via reinforcement learning was not successful: the supervisory signal was sparse and the network failed to learn locomotion within reasonable time budgets.

    “We have found that training a rough-terrain locomotion policy directly via reinforcement learning was not successful: the supervisory signal was sparse and the presented network failed to learn locomotion within reasonable time budgets.”
    Quote in the paperSubstantial claim
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    Findingown data
    § DARPA Subterranean Challenge · p. 5

    The presented controller drove two ANYmal-B robots in four missions of 60 minutes and exhibited a zero failure rate throughout the DARPA Subterranean Challenge Urban Circuit.

    “The presented controller drove two ANYmal-B robots in four missions of 60 minutes. The controller exhibited a zero failure rate throughout the competition.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning
    § 1. INTRODUCTION · p. 3

    The privileged learning protocol is enabled by simulation, but the resulting proprioceptive policy is deployed on physical machines.

    “This privileged learning protocol is enabled by simulation, but the resulting proprioceptive policy is not confined to simulation and is deployed on physical machines.”
    Quote in the paperSubstantial claim
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    Findingown data
    § Indoor experiments · p. 6

    The presented controller adapts to slippery terrain and successfully locomotes in the commanded direction, whereas the baseline quickly loses balance, aggressively swings the legs, and falls.

    “The baseline quickly loses balance, aggressively swings the legs, and falls. In contrast, the presented controller adapts to the slippery terrain and successfully locomotes in the commanded direction.”
    Quote in the paperSubstantial claim
  • May combine two claims. The quote only partly states this claim.

    Findingown data
    § Indoor experiments · p. 6

    With a 10 kg payload, which is 22.7% of the total weight of the robot and was never simulated during training, the presented controller can still traverse steps up to 13.4 cm despite the model mismatch.

    “As shown in Fig. 3E, the presented controller can still traverse steps up to 13.4 cm despite the model mismatch.”
    Quote in the paperSubstantial claim
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    Findingown data
    § Privileged training · p. 12

    The baseline fails to learn to balance and locomote, as indicated by mean episode length during training.

    “Fig. 5G shows the mean episode length during training, which indicates that the baseline fails to learn to balance and locomote.”
    Quote in the paperSubstantial claim
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    Findingnone given
    § 3. DISCUSSION · p. 6

    Our training environment features only rigid terrain, with no compliance or overground obstructions such as vegetation; nevertheless, controllers trained in this environment successfully meet the diversity of field conditions encountered at deployment.

    “Our training environment features only rigid terrain, with no compliance or overground obstructions such as vegetation. Nevertheless, controllers trained in this environment successfully meet the diversity of field conditions encountered at deployment.”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim.

    Findingown data
    § Motion synthesis · p. 8

    The controller input does not contain any handcrafted features such as foot contact states or estimated terrain geometry.

    “The input also does not contain any handcrafted features such as foot contact states or estimated terrain geometry.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingnone given
    § Adaptive terrain curriculum · p. 9

    The threshold 0.2 m/s is about one third of the maximum speed of our robot.

    “The threshold is a hyperparameter; 0.2 m/s is about one third of the maximum speed of our robot.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingnone given
    § Indoor experiments · p. 5

    Such reflexes were not specified in any way during training; they developed adaptively.

    “Such reflexes were not specified in any way during training: they developed adaptively.”
    Quote in the paperSubstantial claim
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    Findingown data
    § Further analysis of emergent behavior · p. 12

    The decoder network can detect foot contacts with horizontal and vertical surfaces while successfully identifying frontal collision as such.

    “Additionally, the decoder network can detect foot contacts with horizontal and vertical surfaces while successfully identifying frontal collision as such, as indicated by the estimated terrain normal vector (i + iii).”
    Quote in the paperNot a substantial claim
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    Findingcitation
    § 3. DISCUSSION · p. 6

    The presented controller only exhibits the trot gait, which is narrower than the range of gait patterns discovered by quadrupeds in nature.

    “First, the presented controller only exhibits the trot gait. This is narrower than the range of gate patterns discovered by quadrupeds in nature [33].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [33] 33. R. M. Alexander, Principles of Animal Locomotion (Princeton University Press, 2003).

      Not checked in the free run.

  • May combine two claims.

    Findingown data
    § Further analysis of emergent behavior · p. 12

    When the LF foot collides with the step, the estimated elevation in front of the front legs increases and its uncertainty grows.

    “When the LF foot collides with the step, the estimated elevation in front of the front legs increases and its uncertainty grows (i+ii).”
    Quote in the paperNot a substantial claim
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    Findingown data
    § Indoor experiments · p. 5

    The presented controller outperforms the baseline in both stepping up and down.

    “The presented controller outperforms the baseline in both stepping up and down.”
    Quote in the paperSubstantial claim
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    Findingown data
    § S7. Reconstruction of the privileged information in different situations · p. 16

    External disturbance and terrain information can be reconstructed from the TCN embedding.

    “The external disturbance and terrain information can also be reconstructed from the TCN embedding.”
    Quote in the paperNot a substantial claim
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    Findingown data
    § S7. Reconstruction of the privileged information in different situations · p. 16

    The estimated friction coefficient between the feet and the terrain decreases as soon as the first foot starts slipping, remains low throughout the traversal, and increases about 2 s after the robot returns to normal ground.

    “The estimate decreases as soon as the first foot starts slipping (i), remains low throughout the traversal (ii) and increases about 2 s after the robot returns to normal ground (iii).”
    Quote in the paperNot a substantial claim
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    Findingown data
    § S6. Qualitative evaluation of the adaptive terrain curriculum · p. 16

    The particle filter fits the latent distribution of desirable terrains, which has a bow shape in the frequency-amplitude marginal.

    “Fig. S1B-C shows that the particle filter fits the latent distribution of desirable terrains, which has a bow shape in the frequency-amplitude marginal (middle).”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: Within Nevaluate iterations, the performance of the policy is similar.
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    Findingown data
    § S9. Ablation of the latent representation loss for student training · p. 17

    The performance is comparable in the uniform slope setting and under external disturbances.

    “The performance is comparable in the uniform slope setting and under external disturbances.”
    Quote in the paperNot a substantial claim
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    Findingown data
    § S6. Qualitative evaluation of the adaptive terrain curriculum · p. 16

    The curriculum initially focuses on wide and shallow steps, and then broadens the distribution to include narrower steps.

    “The curriculum initially focuses on wide and shallow steps (middle panels, particularly Iter. 50-60), and then broadens the distribution to include narrower steps (rightmost panels).”
    Quote in the paperNot a substantial claim
    • The authors state this as an assumption: Within Nevaluate iterations, the performance of the policy is similar.
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    Premisecitation
    § 1. INTRODUCTION · p. 1

    Under challenging natural environments, existing published controllers manifest frequent foot slippage, loss of balance, and ultimately catastrophic failure.

    “Under such conditions, existing published controllers manifest frequent foot slippage, loss of balance, and ultimately catastrophic failure.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [1] 1. F. Jenelten, J. Hwangbo, F . Tresoldi, C. D. Bellicoso, M. Hutter, Dynamic locomotion on slippery ground, IEEE Robotics and Automation Letters 4170-4176 (2019).

      Not checked in the free run.

    • cites [2] 2. G. Bledt, P . M. Wensing, S. Ingersoll, S. Kim, Contact model fusion for

      Not checked in the free run.

    • cites [3]

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    • cites [4] 4. J. Reher, W. Ma, A. D. Ames, Dynamic walking with compliance on a Cassie bipedal robot, European Control Conference , 2589-2595 (IEEE, 2019).

      Not checked in the free run.

    • cites [5] 5. Y. Gong, R. Hartley, X. Da, A. Hereid, O. Harib, J. Huang, J. W. Grizzle, Feedback control of a Cassie bipedal robot: Walking, standing, and riding a Segway, American Control Conference , 4559-4566 (IEEE, 2019).

      Not checked in the free run.

  • May combine two claims.

    Study design and conductnone given
    § 1. INTRODUCTION · p. 3

    In all deployments, robots of the same generation were driven by exactly the same controller under all conditions, and no tuning was required to adapt to different environments.

    “In all deployments, robots of the same generation were driven by exactly the same controller under all conditions. No tuning was required to adapt to different environments.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § 1. INTRODUCTION · p. 3

    Realistic modeling of the physical system, including the actuators, is a practice for successful transfer of legged locomotion controllers from simulation to physical machines.

    “One is realistic modeling of the physical system, including the actuators [12].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [12] 12. J. Hwangbo, J. Lee, A. Dosovitskiy, D. Bellicoso, V. Tsounis, V. Koltun, M. Hutter, Learning agile and dynamic motor skills for legged robots, Science Robotics p. eaau5872 (2019).

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § 1. INTRODUCTION · p. 3

    Randomization of physical parameters that vary between simulation and reality is a practice for successful transfer, making the controller robust to a range of conditions without precise a priori modeling.

    “Another is randomization of physical parameters that vary between simulation and reality, such that the controller becomes robust to a range of conditions that cover those that arise in physical deployment, without the necessity to precisely model these conditions a priori [21].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [21] 21. X. B. Peng, M. Andrychowicz, W. Zaremba, P . Abbeel, Sim-to-real transfer of robotic control with dynamics randomization, IEEE International Conference on Robotics and Automation (ICRA) (IEEE, 2018). source

      Not checked in the free run.

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    Interpretationcitation
    § Indoor experiments · p. 5

    This level of robustness is beyond the reach of prior controllers for ANYmal robots and is comparable to the state of the art.

    “This level of robustness is beyond the reach of prior controllers for ANYmal robots [1, 26] and is comparable to the state of the art [2, 29].”
    Quote in the paperSubstantial claim0 of 4 sources checked
    • cites [1] 1. F. Jenelten, J. Hwangbo, F . Tresoldi, C. D. Bellicoso, M. Hutter, Dynamic locomotion on slippery ground, IEEE Robotics and Automation Letters 4170-4176 (2019).

      Not checked in the free run.

    • cites [26]

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    • cites [2] 2. G. Bledt, P . M. Wensing, S. Ingersoll, S. Kim, Contact model fusion for

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    • cites [29] 29. Ghost Robotics, Vision 60: Latest blind-mode stress testing of V60 legged robot, www.youtube.com/watch?v=tQsLauQWp8M (2019).

      Not checked in the free run.

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    Interpretationreasoning
    § 1. INTRODUCTION · p. 3

    The training conditions grow increasingly more challenging, yielding an omnidirectional controller that combines agility with unprecedented resilience.

    “The training conditions grow increasingly more challenging, yielding an omnidirectional controller that combines agility with unprecedented resilience.”
    Quote in the paperSubstantial claim
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    Premisereasoning
    § 1. INTRODUCTION · p. 1

    Conventional systems for legged locomotion on rough terrain escalate in complexity as more scenarios are taken into account, are laborious to develop and maintain, and remain vulnerable to corner cases.

    “Overall, conventional systems for legged locomotion on rough terrain escalate in complexity as more scenarios are taken into account, have become extremely laborious to develop and maintain, and remain vulnerable to corner cases.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [1] 1. F. Jenelten, J. Hwangbo, F . Tresoldi, C. D. Bellicoso, M. Hutter, Dynamic locomotion on slippery ground, IEEE Robotics and Automation Letters 4170-4176 (2019).

      Not checked in the free run.

    • cites [2] 2. G. Bledt, P . M. Wensing, S. Ingersoll, S. Kim, Contact model fusion for

      Not checked in the free run.

    • cites [3]

      Not checked in the free run.

    • cites [4] 4. J. Reher, W. Ma, A. D. Ames, Dynamic walking with compliance on a Cassie bipedal robot, European Control Conference , 2589-2595 (IEEE, 2019).

      Not checked in the free run.

    • cites [5] 5. Y. Gong, R. Hartley, X. Da, A. Hereid, O. Harib, J. Huang, J. W. Grizzle, Feedback control of a Cassie bipedal robot: Walking, standing, and riding a Segway, American Control Conference , 4559-4566 (IEEE, 2019).

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning
    § Natural environments · p. 5

    The quantitative evaluation in Table 1 understates the difference between the two controllers because it only measures speed and energetic efficiency of the baseline when it successfully locomotes, and baseline catastrophic failures are not factored into these measurements.

    “The quantitative evaluation reported in Table 1 understates the difference between the two controllers because it only measures speed and energetic efficiency of the baseline when it successfully locomotes. The baseline's catastrophic failures are not factored into these measurements: when the baseline fails, it is reset by a human operator in a more stable configuration.”
    Quote in the paperNot a substantial claim
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    Premisecitation
    § 1. INTRODUCTION · p. 1

    Exteroceptive sensors such as cameras and LiDAR cannot reliably measure physical characteristics such as friction and compliance, are impeded by obstructions such as vegetation, snow, and water, and may not have the coverage and temporal resolution to capture changes induced by the robot itself.

    “Exteroceptive sensors such as cameras and LiDAR cannot reliably measure physical characteristics such as friction and compliance, are impeded by obstructions such as vegetation, snow, and water, and may not have the coverage and temporal resolution to capture changes induced by the robot itself, such as the crumbling of loose ground under the robot's feet.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [27] 27. P. Fankhauser, M. Bloesch, C. Gehring, M. Hutter, R. Siegwart. Robotcentric elevation mapping with uncertainty estimates. Mobile Service Robotics (World Scientific, 2014), 433-440.

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    Interpretationreasoning
    § Natural environments · p. 3

    Our controller does not rely on exteroception and is immune to failure of exteroceptive terrain estimation in snow, water, or dense vegetation.

    “Our controller does not rely on exteroception and is immune to such failure.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Premisecitation
    § 1. INTRODUCTION · p. 1

    Model-free reinforcement learning has recently emerged as an alternative approach in the development of legged locomotion skills.

    “Model-free reinforcement learning (RL) has recently emerged as an alternative approach in the development of legged locomotion skills [12-14].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [12] 12. J. Hwangbo, J. Lee, A. Dosovitskiy, D. Bellicoso, V. Tsounis, V. Koltun, M. Hutter, Learning agile and dynamic motor skills for legged robots, Science Robotics p. eaau5872 (2019).

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    • cites [13] 13. T. Haarnoja, S. Ha, A. Zhou, J. Tan, G. Tucker, S. Levine, Learning to walk via deep reinforcement learning, Robotics: Science and Systems (2019).

      Not checked in the free run.

    • cites [14] 14. Z. Xie, P . Clary, J. Dao, P . Morais, J. Hurst, M. van de Panne, Learning locomotion skills for Cassie: Iterative design and sim-to-real, Conference on Robot Learning (2019).

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based). May combine two claims.

    Interpretationreasoning
    § 3. DISCUSSION · p. 6

    The presented results expedite the deployment of legged machines in environments that are beyond the reach of wheeled and tracked robots and are dangerous or inaccessible to humans, while the presented methodology opens new frontiers for training complex robotic systems in simulation and deploying them in the full richness and complexity of the physical world.

    “More broadly, the presented results expedite the deployment of legged machines in environments that are beyond the reach of wheeled and tracked robots and are dangerous or inaccessible to humans, while the presented methodology opens new frontiers for training complex robotic systems in simulation and deploying them in the full richness and complexity of the physical world.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Interpretationreasoning
    § 3. DISCUSSION · p. 6

    The presented controller relies solely on proprioception, which is a significant advantage because it makes few assumptions on the sensor suite and is not susceptible to failure when exteroception breaks down.

    “Second, the presented controller relies solely on proprioception. This is a significant advantage in that the controller makes few assumptions on the sensor suite and is not susceptible to failure when exteroception breaks down.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data
    § Further analysis of emergent behavior · p. 12

    The policy has direct access to the measurements at the moment of foot-trapping, and leverages this in the following swing phase.

    “The policy has direct access to the measurements at the moment of foot-trapping, and leverages this in the following swing phase.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Adaptive terrain curriculum · p. 9

    Florensa et al. similarly choose achievable yet difficult goals for RL agents.

    “Florensa et al. [39] similarly choose achievable yet difficult goals for RL agents.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [39] 39. C. Florensa, D. Held, X. Geng, P . Abbeel, Automatic goal generation for reinforcement learning agents, International Conference on Machine Learning , 1514-1523 (2018).

      Not checked in the free run.

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    Interpretationreasoning
    § 3. DISCUSSION · p. 6

    Blind locomotion is inherently limited: if the machine is commanded to walk off a cliff, it will; even in less extreme conditions, the robot's gait is fairly conservative because it must feel out the environment with its body as it locomotes.

    “Nevertheless, blind locomotion is inherently limited. If the machine is commanded to walk off a cliff, it will. Even in less extreme conditions, the robot's gait is fairly conservative since it must by necessity feel out the environment with its body as it locomotes.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Motion synthesis · p. 8

    Previous works commonly leveraged predefined foot contact schedules.

    “Previous works commonly leveraged predefined foot contact schedules [2, 26, 35].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [2] 2. G. Bledt, P . M. Wensing, S. Ingersoll, S. Kim, Contact model fusion for

      Not checked in the free run.

    • cites [26]

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    • cites [35] 35. V. Barasuol, J. Buchli, C. Semini, M. Frigerio, E. R. De Pieri, D. G. Caldwell, A reactive controller framework for quadrupedal locomotion on challenging terrain, 2013 IEEE International Conference on Robotics and Automation , 2554-2561 (IEEE, 2013).

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning
    § A. Overview · p. 6

    In our formulation, only the direction of the target velocity is given to the controller, unlike many existing works that focus on tracking the target velocity of the base, because the feasible range of target speeds is often unclear on challenging terrain.

    “In our formulation, unlike many existing works [12, 14, 16] that focus on tracking the target velocity of the base ( B IB vT ), only the direction ( B IB ˆ vT ) is given to the controller. The reason is that the feasible range of target speeds is often unclear on challenging terrain.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [12] 12. J. Hwangbo, J. Lee, A. Dosovitskiy, D. Bellicoso, V. Tsounis, V. Koltun, M. Hutter, Learning agile and dynamic motor skills for legged robots, Science Robotics p. eaau5872 (2019).

      Not checked in the free run.

    • cites [14] 14. Z. Xie, P . Clary, J. Dao, P . Morais, J. Hurst, M. van de Panne, Learning locomotion skills for Cassie: Iterative design and sim-to-real, Conference on Robot Learning (2019).

      Not checked in the free run.

    • cites [16] 16. J. Tan, T. Zhang, E. Coumans, A. Iscen, Y. Bai, D. Hafner, S. Bohez, V. Vanhoucke, Sim-to-real: Learning agile locomotion for quadruped robots, Robotics: Science and Systems (2018).

      Not checked in the free run.

  • May combine two claims.

    Premisecitation
    § Motion synthesis · p. 8

    Defining the target foot positions in the horizontal frames of the feet reduces the effect of base attitude on the foot motions and consequently stabilizes training.

    “This kinematic trick reduces the effect of base attitude on the foot motions [35] and consequently stabilizes training.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [35] 35. V. Barasuol, J. Buchli, C. Semini, M. Frigerio, E. R. De Pieri, D. G. Caldwell, A reactive controller framework for quadrupedal locomotion on challenging terrain, 2013 IEEE International Conference on Robotics and Automation , 2554-2561 (IEEE, 2013).

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation
    § S2. Implementation details · p. 15

    Randomization of dynamic properties improves the robustness of the policy.

    “As several studies have shown that randomization of dynamic properties improves the robustness of the policy [12, 16]”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [12] 12. J. Hwangbo, J. Lee, A. Dosovitskiy, D. Bellicoso, V. Tsounis, V. Koltun, M. Hutter, Learning agile and dynamic motor skills for legged robots, Science Robotics p. eaau5872 (2019).

      Not checked in the free run.

    • cites [16] 16. J. Tan, T. Zhang, E. Coumans, A. Iscen, Y. Bai, D. Hafner, S. Bohez, V. Vanhoucke, Sim-to-real: Learning agile locomotion for quadruped robots, Robotics: Science and Systems (2018).

      Not checked in the free run.

  • May combine two claims.

    Premisecitation
    § Motion synthesis · p. 8

    Using analytic inverse kinematics maximizes computational efficiency and allows reuse of existing position control actuator models for the sim-to-real transfer.

    “The main reason for using analytic IK is to maximize computational efficiency and to reuse existing position control actuator models [6, 15] for the sim-to-real transfer.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [6] 6. J. Hwangbo, C. D. Bellicoso, P . Fankhauser, M. Huttery, Probabilistic foot contact estimation by fusing information from dynamics and differential/forward kinematics, 2016 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) , 3872-3878 (IEEE, 2016).

      Not checked in the free run.

    • cites [15] 15. J. Lee, J. Hwangbo, M. Hutter, Robust recovery controller for a quadrupedal robot using deep reinforcement learning, arXiv:1901.07517 (2019).

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable).

    Interpretationreasoning
    § 3. DISCUSSION · p. 6

    The presented results substantially advance the published state of the art in legged robotics.

    “The presented results substantially advance the published state of the art in legged robotics.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § S4. Reward function for teacher policy training · p. 16

    The maximum speed reachable on flat terrain with the existing controller is 0.6 m/s.

    “The velocity threshold is defined as 0.6 m/s which is the maximum speed reachable on the flat terrain with the existing controller [26].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [26]

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation
    § Adaptive terrain curriculum · p. 9

    The POET method employs minimal criteria and aims to choose environmental parameters that are neither too challenging nor trivial for the agents, realized by selecting task parameters that yield mid-range rewards.

    “The method employs minimal criteria (MC) [24, 40] and aims to choose environmental parameters that are neither too challenging nor trivial for the agents: this is realized by selecting task parameters that yield mid-range rewards.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [24] 24. J. C. Brant, K. O. Stanley, Minimal criterion coevolution: a new approach to open-ended search, Genetic and Evolutionary Computation Conference , 67-74 (2017).

      Not checked in the free run.

    • cites [40] 40. J. Lehman, K. O. Stanley, Revising the evolutionary computation abstraction: minimal criteria novelty search, Genetic and Evolutionary Computation Conference , 103-110 (2010).

      Not checked in the free run.

  • May combine two claims.

    Premisecitation
    § Student policy · p. 9

    The TCN architecture affords transparent control over the input history length, can accommodate long histories, and is known to be robust to hyperparameter settings.

    “We use the TCN architecture because it affords transparent control over the input history length, can accommodate long histories, and is known to be robust to hyperparameter settings [22].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [22] 22. S. Bai, J. Z. Kolter, V. Koltun, An empirical evaluation of generic convolutional and recurrent networks for sequence modeling, arXiv:1803.01271 (2018).

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given
    § Teacher policy · p. 8

    Using <cos(f), sin(f)> instead of f to encode the leg phase is a smooth and unique representation for the angle.

    “To encode the leg phase, we use 〈 cos ( f ) , sin ( f ) 〉 instead of f , which is a smooth and unique representation for the angle.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Adaptive terrain curriculum · p. 9

    The POET approach generates diverse parameterized terrains for a 2D bipedal agent.

    “The paired open-ended trailblazer (POET) approach [25] generates diverse parameterized terrains for a 2D bipedal agent.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [25] 25. R. Wang, J. Lehman, J. Clune, K. O. Stanley, Paired open-ended trailblazer (poet): Endlessly generating increasingly complex and diverse learning environments and their solutions, arXiv:1901.01753 (2019).

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § S3. Foot trajectory generator · p. 15

    With a set of reasonably tuned f0, h and fi,0, a quadruped can stably step in place.

    “With a set of reasonably tuned f 0 , h and f i ,0 , a quadruped can stably step in place.”
    Quote in the paperNot a substantial claim
52 of 52
  • The paper relies on this without support.

    Legged robots have the potential to traverse any terrain that their animal counterparts can.

    “Legged robots have the potential to traverse any terrain that their animal counterparts can.”
  • The paper relies on this without support.

    Joint encoders and an inertial measurement unit are the most durable and reliable sensors on legged machines.

    “The controller uses only proprioceptive measurements from joint encoders and an inertial measurement unit (IMU), which are the most durable and reliable sensors on legged machines.”
  • The authors state this as an assumption.

    The environment is fully observable to the teacher.

    “Assuming the environment is fully observable to the teacher, we formulate locomotion control as an MDP and use an off-the-shelf RL method [36] to solve it.”
  • The authors state this as an assumption.

    Terrain parameters with similar traversability are close in Euclidean distance in parameter space.

    “1. Terrain parameters with similar Tr ( · , p ) are close in Euclidean distance in parameter space.”
  • The authors state this as an assumption.

    A policy trained over the terrains generated by cTs in some area of C will learn to interpolate to nearby terrain parameters.

    “2. A policy trained over the terrains generated by c T s in some area of C will learn to interpolate to nearby terrain parameters.”
  • The authors state this as an assumption.

    The evolution of each terrain parameter is a Markov process (only relies on the current value and randomly sampled noise).

    “It satisfies the third assumption (Markov process) because the evolution of each parameter only relies on the current value and randomly sampled noise.”
  • The authors state this as an assumption.

    Within Nevaluate iterations, the performance of the policy is similar.

    “We assume that within Nevaluate iterations, the performance of the policy is similar.”
7 of 7

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • This opens interesting research opportunities for the adaptation of lab-generated simulation to real-world conditions, similar to what has been observed in image synthesis for self driving and robotics.

    “This opens interesting research opportunities for the adaptation of lab-generated simulation to real-world conditions, similar to what has been observed in the field of image synthesis for self driving143 and robotics144 in the last decade.”

    From Perspectives in machine learning for wildlife conservation (2022) · cites this paper as [144]

Cites

Flagged first, then by citations

Research works printed but not linked: 8

  1. Z. Xie P. Clary J. Dao P. Morais J. Hurst M. van de Panne Learning locomotion skills for Cassie: Iterative design and sim-to-real in Conference on Robot Learning (PMLR 2019).
  2. Y. Yang K. Caluwaerts A. Iscen T. Zhang J. Tan V. Sindhwani Data efficient reinforcement learning for legged robots in Conference on Robot Learning (PMLR 2019).
  3. D. Chen B. Zhou V. Koltun P. Krähenbühl Learning by cheating in Conference on Robot Learning (2019).
  4. A. Iscen K. Caluwaerts J. Tan T. Zhang E. Coumans V. Sindhwani V. Vanhoucke Policies modulating trajectory generators in Conference on Robot Learning (PMLR 2018) pp. 916–926.
  5. J. Schulman S. Levine P. Abbeel M. Jordan P. Moritz Trust region policy optimization in International Conference on Machine Learning (PMLR 2015) pp. 1889–1897.
  6. S. Ross G. Gordon D. Bagnell A reduction of imitation learning and structured prediction to no-regret online learning in International Conference on Artificial Intelligence and Statistics (AISTATS 2011) pp. 627–635.
  7. C. Florensa D. Held X. Geng P. Abbeel Automatic goal generation for reinforcement learning agents in International Conference on Machine Learning (PMLR 2018) pp. 1514–1523.
  8. A. Kendall Y. Gal What uncertainties do we need in bayesian deep learning for computer vision? in Advances in Neural Information Processing Systems 30 (Neural Information Processing Systems Foundation 2017) pp. 5574–5584.

Cited by

Sorted by citations

Authors
Lee, J., Hwangbo, J., Wellhausen, L., Koltun, V., & Hutter, M.
Affiliations
  • ETH Zurich (CH)
  • Korea Advanced Institute of Science and Technology (KR)
  • Intel (United States) (US)
Corresponding author
Lee, Joonho
Venue
Science Robotics
Published
2020-10-21
Volume
5
Issue
47
ISSN
2470-9476 (ISSN-L)
OpenAlex
W3093922502
Cited by
1,156
References
29
Citations by year
2026: 184 · 2025: 298 · 2024: 244 · 2023: 209 · 2022: 140 · 2021: 79 · 2020: 2
FWCI
33.76
Type
journal article
Language
en
Open access
Locations
  • Science Robotics (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • H2020 European Research Council (852044)
  • Horizon 2020 (780883)
  • National Centre of Competence in Research Robotics
  • Intel Network on Intelligent Systems
Topics
  • Physical Sciences › Engineering › Biomedical Engineering › Robotic Locomotion and Control
  • Physical Sciences › Computer Science › Artificial Intelligence › Reinforcement Learning in Robotics
  • Physical Sciences › Engineering › Biomedical Engineering › Prosthetics and Rehabilitation Robotics
Keywords
quadrupedal locomotion, legged robots, proprioceptive feedback, reinforcement learning, sim-to-real transfer, zero-shot generalization, deformable terrain, neural network policy

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

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