SMARTI: A 60-mg Steerable Robot Driven by High-Frequency Shape-Memory Alloy Actuation

We present the shape-memory alloy (SMA) robotic traveling insect (SMARTI), a 60-mg crawling microrobot that is driven by two 6-mg high-frequency SMA bending actuators and whose two-module configuration enables controlled differential steering and path following. During operation, the two modules are coordinately excited to generate locomotion patterns based on anisotropic friction. This functionality is enabled by the high compliance of the robotic structure, which comprises very few parts, is easily fabricated, achieves both high precision and performance, and is sufficiently predictable to be controlled in open and closed loop. To demonstrate the locomotive and steering capabilities of the SMARTI, we present a series of experimental tests, including open-loop crawling, closed-loop path following, and high-speed controlled turning. These experiments were performed using a motion capture system for sensing and an off-board digital signal processor for control. In closed loop, the SMARTI reaches a maximum sustained speed of 46 mm/s, equivalent to 3.54 body-lengths per second (BL/s), and a turning rate of 107 degrees per second (D/s) with root-mean-square (RMS) tracking errors as low as 1.7 mm. This combination of speed and maneuverability is currently unparalleled, making the SMARTI the lightest, smallest, and fastest (in BL/s) steerable and controllable crawling robot developed to date.