Extended Data Fig. 7. Sequential-motion control strategy for the microturtle.
(a) Time-sequential images of the microturtle locomotion under a sequential-motion control strategy based on FEA results. Arrow lines illustrate the streamlines of the fluid. Solid and hollow arrows show the magnetic field direction lasting until and starting from the current time points, respectively. (b) Magnetic field sequence in one control cycle with a cycle duration of 3 s. When the magnetic fields cycle among 0°, −15° and 75° to the axial direction of the microturtle, the microturtle gains a net displacement, thanks to the programmed release of the stored energy in the picospring linkages. While the microturtle flippers are responsive to the magnetic field, its large non-magnetic torso is only controlled by the elastic torques from the deformed picosprings, stabilizing the microrobot movement. With the help of the buffering of the picosprings, the left and right pairs of flippers can perform asymmetric movement when the magnetic field direction changes. Hence, by alternating the magnetic actuation field (16 mT) and base field (2 mT) in different directions, the microturtle can gain a net displacement along its axial direction (y-axis) but with a reciprocal motion along its lateral direction (x-axis). (c) Locomotion velocity of the microturtle containing 5% MNPs with respect to the magnetic actuation field (n = 3 microturtles, mean ± s.d.).