Emerging worm-like soft robots with various soft materials and different actuation mechanism have been frequently discussed. It is very challenging for soft robots in realizing a fast and untethered crawling. In this article, a biomimetic magnet embedded worm-like robot (shorted as “MagWorm”) in the size of centimeter level is designed and investigated. The actuation of the MagWorm is achieved by housing permanent magnetic patches in its soft body, which interact with an external moving drive-magnet system. A dynamic model is established, coupling the discrete elastic rod model with magnetic actuation. The driving mechanism is then numerically studied. Quantitative comparisons between the numerical solution and experiment results show reasonable agreement. It is shown that the MagWorm can deform part of its body into a “Ω” shape and generate biomimetic crawling locomotion. The crawling speed of the robot is studied experimentally with different sizes. Some potential applications are also proposed and demonstrated. The MagWorm represents compact and low-cost solutions that use permanent magnets for remote actuation of soft robot and can be continuously operated during long procedures.

Periodic orbits over irregularly shaped asteroids and comets are fundamental for understanding vicinal dynamical behaviors and space explorations. In this paper, a new method is proposed to obtain natural periodic orbits, which is based on the optimal control framework with respect to a general form of the irregular gravitational field. Natural elongated asteroids are taken as representatives, whose potentials are approximated by the rotating mass dipole with appropriate parameters. An indirect method is used to transform the optimal control model into a two-point boundary value problem, which can be solved by using a shooting method. Numerical simulations are performed to validate the effectiveness of the proposed method regarding the asteroid 951 Gaspra. Three types of periodic orbits are identified, including the Lyapunov orbit around the collinear equilibrium point, the equatorial retrograde orbit, and the inclined orbit. The connection between the latter two types of orbits is also briefly discussed via numerical continuation.

Recent missions reveal that rubble-pile asteroids usually have a wide distribution of bare rocks in various scales. The dynamical evolution of a lander interacting with such rough surfaces is still an open problem. This article investigates the influence of the explicitly refined rocky terrains on the natural landing motion of a cuboid asteroid lander. The methodology for constructing the local terrains with centimeter-sized to meter-sized rocks is developed based on manipulating the original polyhedron shape model. Local rocky terrains refined with different-sized rocks (20 cm, 40 cm, 80c m, and 1 m) are generated. Moreover, hypothetical local terrains in different numbers of 1-m-sized rocks are presented to assess their influence on the landing motion. Numerical simulations are performed to characterize the dynamical behavior of the lander in rocky terrains. The distributions of the first and second touchdown positions, the transfer time, and the locomotion distance are taken as the three key indicators for examining the motion difference in these rocky terrains. The mechanism for the landing motion is analyzed by considering the collision slope. The results are expected to provide guidelines for the lander deployment and the path planning of a rover on rocky asteroids .