McWilliams, Jessica

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  • Publication
    Drag Coefficient Characterization of the Origami Magic Ball (Inproceedings)
    (2023-08-29) Chen, Guanyu; Chen, Dongsheng; Weakly, Jessica; Sung, Cynthia
    The drag coefficient plays a vital role in the design and optimization of robots that move through fluids. From aircraft to underwater vehicles, their geometries are specially engineered so that the drag coefficients are as low as possible to achieve energy-efficient performances. Origami magic balls are 3-dimensional reconfigurable geometries composed of repeated simple waterbomb units. Their volumes can change as their geometries vary and we have used this concept in a recent underwater robot design. This paper characterizes the drag coefficient of an origami magic ball in a wind tunnel. Through dimensional analysis, the scenario where the robot swims underwater is equivalently transferred to the situation when it is in the wind tunnel. With experiments, we have collected and analyzed the drag force data. It is concluded that the drag coefficient of the magic ball increases from around 0.64 to 1.26 as it transforms from a slim ellipsoidal shape to an oblate spherical shape. Additionally, three different magic balls produce increases in the drag coefficient of between 57% and 86% on average compared to the smooth geometries of the same size and aspect ratio. The results will be useful in future designs of robots using waterbomb origami in fluidic environments.
  • Publication
    Push-On Push-Off: A Compliant Bistable Gripper with Mechanical Sensing and Actuation
    (2021-03-13) McWilliams, Jessica; Yuan, Yifan; Sung, Cynthia; Friedman, Jason
    Grasping is an essential task in robotic applications and is an open challenge due to the complexity and uncertainty of contact interactions. In order to achieve robust grasping, systems typically rely on precise actuators and reliable sensing in order to control the contact state. We propose an alternative design paradigm that leverages contact and a compliant bistable mechanism in order to achieve "sensing" and "actuation" purely mechanically. To grasp an object, the manipulator holding our end effector presses the bistable mechanism into the object until snap-through causes the gripper to enclose it. To release the object, the tips of the gripper are pushed against the ground, until rotation of the linkages causes snap-through in the other direction. This push-on push-off scheme reduces the complexity of the grasping task by allowing the manipulator to automatically achieve the correct grasping behavior as long as it can get the end effector to the correct location and apply sufficient force. We present our dynamic model for the bistable gripping mechanism, propose an optimized result, and demonstrate the functionality of the concept on a fabricated prototype. We discuss our stiffness tuning strategy for the 3D printed springs, and verify the snap-through behavior of the system using compression tests on an MTS machine. Acknowledgements Support for this project has been provided in part by NSF Grant No. 1138847 and DGE-1845298. We also thank Terry Kientz, Jeremy Wang, Peter Szczesniak, and Joe Valdez for their assistance with the fabrication, and Neal Tinaikar for assistance with initial prototypes. We are grateful.