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Multi-environment robotic transitions through adaptive morphogenesis


The current proliferation of mobile robots spans ecological monitoring, warehouse management and extreme environment exploration, to an individual consumer’s home1,2,3,4. This expanding frontier of applications requires robots to transit multiple environments, a substantial challenge that traditional robot design strategies have not effectively addressed5,6. For example, biomimetic design—copying an animal’s morphology, propulsion mechanism and gait—constitutes one approach, but it loses the benefits of engineered materials and mechanisms that can be exploited to surpass animal performance7,8. Other approaches add a unique propulsive mechanism for each environment to the same robot body, which can result in energy-inefficient designs9,10,11. Overall, predominant robot design strategies favour immutable structures and behaviours, resulting in systems incapable of specializing across environments12,13. Here, to achieve specialized multi-environment locomotion through terrestrial, aquatic and the in-between transition zones, we implemented ‘adaptive morphogenesis’, a design strategy in which adaptive robot morphology and behaviours are realized through unified structural and actuation systems. Taking inspiration from terrestrial and aquatic turtles, we built a robot that fuses traditional rigid components and soft materials to radically augment the shape of its limbs and shift its gaits for multi-environment locomotion. The interplay of gait, limb shape and the environmental medium revealed vital parameters that govern the robot’s cost of transport. The results attest that adaptive morphogenesis is a powerful method to enhance the efficiency of mobile robots encountering unstructured, changing environments.

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Fig. 1: Turtle-inspired amphibious robot.
Fig. 2: Swimming.
Fig. 3: Walking.
Fig. 4: Crawling on transition substrates.
Fig. 5: Transition policy and COT contextualization.

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Data availability

All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Information.


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We thank V. Wilczynski, Deputy Dean of Yale School of Engineering, for use of his pool. This project was sponsored by the Office of Naval Research under award N00014-21-1-2417. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Office of Naval Research. R.B. was supported by an NSF Graduate Research Fellowship (DGE-1752134).

Author information

Authors and Affiliations



R.B., S.K.P., J.B., T.S. and A.G. designed and built the robot. R.B., S.K.P. and L.R. conducted swimming, terrestrial and transition experiments. R.B., S.K.P., L.R. and F.F. programmed gaits. R.B. conducted CFD simulations and friction tests. R.K.-B. conceived of the project and oversaw the research. All authors contributed to writing the manuscript.

Corresponding author

Correspondence to Rebecca Kramer-Bottiglio.

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The authors declare no competing interests.

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Nature thanks Navinda Kottege and Cecilia Laschi for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 System description.

a, Exploded computer-aided-design view, detailing components of robot. Note that the shoulder joints are typically shrouded in rubber bellows, and thus not visible. For clarity, we only depict the bellows on the back right joint in transparent grey. b, 3-DoF kinematic mechanism used to achieve bio-inspired gaits. Symbols θ, ϕ and α are the rotation axes for the swing forward/backward, up/down, and angle of attack motors, respectively.

Extended Data Fig. 2 Robot workspace.

Workspace visualized in the robot’s kinematic simulation. The explored gaits are superimposed atop the cyan workspace in a darker colour. Top two are swimming gaits; bottom two are terrestrial and transition gaits. Chassis beneath the shell is rendered for context. Links are line segments coloured red, green, and blue. The black arrow points in the forward travel direction.

Extended Data Fig. 3 Fabrication of Morphing Limb.

Fabrication can be broken down into two main tracks: elastomeric actuators (top), and Joule-heating variable-stiffness material (bottom). We fabricate components for each of the limbs’ two halves, A and B. Actuators and variable-stiffness material components for A and B come together in the final step, in which they are hinged together via a sewed joint. The limb cross-section is displayed in the inset. Figure and caption adapted from ref. 22.

Extended Data Fig. 4 Test rig for evaluating force profiles of gaits.

Coordinate system defines positive direction of forces measured via the multi-axis load cell. Adjustable fixtures allowed us to tune the robot’s offset from the pool sides and bottom, as well as its submerged depth.

Extended Data Fig. 5 Representative data for front-right shoulder during paddling and flapping gaits.

Top row gives a robot schematic with superimposed trajectory. Second row gives commanded and actual encoder positions, where the solid line is the actual achieved position. Third row plots the angular velocity. Fourth row is the amperage. Line colour and legend symbols match those of Fig. 1b.

Extended Data Fig. 6 CFD results.

Simulation results of lift and drag forces on the flipper mode of the morphing limb, at 0.3 m/s. Inset depicts definition of Φ with respect to the flow direction.

Extended Data Fig. 7 Representative data from all shoulder joints for creeping gait on the porcelain substrate.

Top row presents snapshots of the robot at key parts of the gait. Graphs underneath give commanded and actual encoder positions, where the solid line is the actual achieved position. Line colour and legend symbols match those of Fig. 1b.

Extended Data Fig. 8 Additional creep data.

a, Left to right: commanded and actual encoder positions, angular velocity, and amperage for front-right shoulder joint. The solid line is the actual achieved position. Line colour and legend symbols match those of Fig. 1b. b, Representative data from motion capture of back-left distal tip of limb during creep gait. Spikes in Z correspond to the limb swinging out, whereas the other portions are the pivot or where the limb serves only to balance the robot. Notice the amplitude and frequency of vibrations occurring at these times, which give an indication of surface normals and roughness. At these sections, we calculated the stability metric to grasp the effect of substrates on COT when creeping. Here, the series are not normalized to all start at 0, for ease of viewing.

Extended Data Fig. 9 Representative data from front-right shoulder joint for crawl gaits across the three substrates.

Top row gives a robot schematic with superimposed trajectory. Second row gives commanded and actual encoder positions, where the solid line is the actual achieved position. Third row plots the angular velocity. Fourth row is the amperage. Line colour and legend symbols match those of Fig. 1b.

Extended Data Fig. 10 Example data from friction tests.

Force versus displacement for elastomer, PLA, or bellows with 500 g weight placed atop them, over the various substrates. Clouds indicate one standard deviation from the mean, over 7 trials, with the solid line as the mean.

Extended Data Table 1 The robot’s modified Denavit–Hartenberg parameters54
Extended Data Table 2 The robot’s velocities and COTs for all gaits
Extended Data Table 3 Experimentally determined friction coefficients between ART’s constituent materials and the various tested substrates

Supplementary information

Peer Review File

Supplementary Video 1

Aquatic testing. We demonstrate how ART can perform multiple types of aquatic gait using the hydrodynamically favourable flipper shape.

Supplementary Video 2

Land locomotion. ART is capable of traversing multiple substrates. Here we show footage from porcelain, concrete and granite substrates, both in the lab and outdoors on Yale campus.

Supplementary Video 3

Transition-substrate tests. An upright creep gait lacks stability on granular and highly fluidized media. ART adapts to a splayed crawling gait, distributing its weight, to traverse such substrates.

Supplementary Video 4

Morphing sequence. We demonstrate how the morphing limb undergoes drastic, reversible shape change.

Supplementary Video 5

Variable-stiffness composite functionality underwater. The morphing limb is waterproof and able to switch between leg and flipper modes underwater.

Supplementary Video 6

Transition field testing. We combined favourable shape-gait policies from terrestrial and aquatic environments to study terrestrial-to-aquatic transitions at an ocean inlet.

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Baines, R., Patiballa, S.K., Booth, J. et al. Multi-environment robotic transitions through adaptive morphogenesis. Nature 610, 283–289 (2022).

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