Scaling down an insect-size microrobot, HAMR-VI into HAMR-Jr

Here we present HAMR-Jr, a \SI{22.5}{\milli\meter}, \SI{320}{\milli\gram} quadrupedal microrobot. With eight independently actuated degrees of freedom, HAMR-Jr is, to our knowledge, the most mechanically dexterous legged robot at its scale and is capable of high-speed locomotion (\SI{13.91}{bodylengths~\second^{-1}}) at a variety of stride frequencies (\SI{1}{}-\SI{200}{\hertz}) using multiple gaits. We achieved this using a design and fabrication process that is flexible, allowing scaling with minimum changes to our workflow. We further characterized HAMR-Jr's open-loop locomotion and compared it with the larger scale HAMR-VI microrobot to demonstrate the effectiveness of scaling laws in predicting running performance.Comment: IEEE International Conference on Robotics and Automation 2020 (accepted

Femtosecond laser fabricated nitinol living hinges for millimeter-sized robots

Nitinol is a smart material that can be used as an actuator, a sensor, or a structural element, and has the potential to significantly enhance the capabilities of microrobots. Femtosecond laser technology can be used to process nitinol while avoiding heat-affected zones (HAZ), thus retaining superelastic properties. In this work, we manufacture living hinges of arbitrary cross-sections from nitinol using a femtosecond laser micromachining process. We first determined the laser cutting parameters, 4.1 Jcm^-2 fluence with 5 passes for 5 um ablation, by varying laser power level and number of passes. Next, we modeled the hinges using an analytical model as well as creating an Abaqus finite element method, and showed the accuracy of the models by comparing them to the torque produced by eight different hinges, four with a rectangular cross-section and four with an arc cross-section. Finally, we manufactured three prototype miniature devices to illustrate the usefulness of these nitinol hinges: a sample spherical 5-bar mechanism, a sarrus linkage, and a piezoelectric actuated robotic wing mechanism.Comment: 6 pages, 6 figures, submitted to IEEE RA-

Geometric Mechanics of Contact-Switching Systems

Discrete and periodic contact switching is a key characteristic of steady state legged locomotion. This paper introduces a framework for modeling and analyzing this contact-switching behavior through the framework of geometric mechanics on a toy robot model that can make continuous limb swings and discrete contact switches. The kinematics of this model forms a hybrid shape space and by extending the generalized Stokes' theorem to compute discrete curvature functions called stratified panels, we determine average locomotion generated by gaits spanning multiple contact modes. Using this tool, we also demonstrate the ability to optimize gaits based on system's locomotion constraints and perform gait reduction on a complex gait spanning multiple contact modes to highlight the scalability to multilegged systems.Comment: 6 pages, 7 figures, and link to associated video: https://drive.google.com/file/d/12Sgl0R1oDLDWRrqlwwAt3JR2Gc3rEB4T/view?usp=sharin