Mobile robots have revolutionized the public and private sectors for transportation, exploration, and search and rescue. Efficient energy consumption and robust environmental interaction needed for complex tasks can be achieved in aerial–terrestrial robots by combining advantages of each locomotion mode. This review surveys over two decades of development in multimodal robots that move on the ground and in air. Multimodality can be achieved by leveraging three main design approaches: adding morphological features, adapting forms for locomotion transitions, and integrating multiple vehicle platforms. Each classification is thoroughly examined and synthesized, encompassing both qualitative and quantitative aspects. The authors delved into the intricacies of these approaches and explored the challenges and opportunities that lie ahead in pursuit of the next generation of mobile robots. This review aims to advance future deployment of multimodal robots in the real world for challenging operations in dangerous, unstructured, contact-prone, cluttered and subterranean environments.

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Traditional landing gear consists of rigid linkages with dampers. They require a flat surface to function. In unstructured environments such as lunar craters or the martian polar region, these conditions are not always met. In this work, we equip a conventional quadrotor with four continuously deformable passive landing limbs with a logarithmic spiral geometry. By choosing the right geometric design as well as tension on the tendon running through the length of the limbs, we ensure that the limbs support the overall weight while passively complying to the environment. Hence, no active control during the landing process is needed in order to adapt to irregular ground. In a set of experiments, these compliant limbs showcase their ability to adjust to uneven landing terrain while maintaining the horizontal attitude of the base vehicle. Overall, this work highlights the future potential to access more challenging environments, leveraging physical compliance for robust landings.@en