Shakebot: a low-cost, open-source shake table for structural seismology research

Zhiang Chen, Devin Keating, Yash Shethwala, Aravind Adhith Pandian Saravanakumaran, Jnaneshwar Das, Ramon Arrowsmith, Christopher Madugo, & Albert Kottke

Published September 11, 2022, SCEC Contribution #12310, 2022 SCEC Annual Meeting Poster #272

Our previous study built a virtual shake robot to simulate dynamics of precariously balanced rocks (PBR); however, simulation results need to be validated through physical experiments. We have developed a low-cost, open-source shake table, also known as Shakebot, for the simulation validation and other related structural seismology research. The Shakebot integrates a one-dimensional prismatic robotic system with customized software developed using the Robot Operating System (ROS). Inspired by recent low-cost, high-accuracy 3D printer technology, the Shakebot adopts a straightforward hardware design with a closed-loop stepper motor for actuation and a toothed belt for transmission. The powerful motor enables the bed to reach a maximum horizontal acceleration of 1.2 g and velocity of 1.2 m/s under a 2 kg payload. For usage safety, we implement two emergency stop mechanisms. The Shakebot also has an accurate perception system. Besides an accelerometer, we additionally equip the Shakebot with a high frame-rate camera to measure bed displacement. By fusing the acceleration and displacement measurements, the Shakebot has a more accurate bed velocity estimation than conventional shake tables that only use accelerometers. We develop control and perception software based on ROS. One advantage of using ROS is to simplify the transition from our previous virtual shake robot to the physical Shakebot. Because both are developed based on ROS, we reuse the code of the control system from the virtual shake robot to Shakebot. This also ensures that the ground motions are consistent for both the simulation and physical experiments, which is critical to validate simulation experiments. Despite the small payload capacity (2 kg maximum), the Shakebot offers a low-cost platform (under $2,000) for simulation validation as well as low-payload seismic experiments. We also open source the Shakebot hardware and software for education outreach. The Shakebot provides a reverse method for simulation validation. Using the Shakebot, we first test the overturning dynamics of small-scale, free-standing blocks including 3D print PBRs and wooden blocks. We build models of the same free-standing blocks in simulation and validate the overturning dynamics using the virtual shake robot. We have qualitatively demonstrated the anisotropy of a PBR from the Double Rock site in California, which agrees with previous simulation results. We are working on quantitative validation experiments.

Key Words
PBR, shake table, robot

Citation
Chen, Z., Keating, D., Shethwala, Y., Pandian Saravanakumaran, A., Das, J., Arrowsmith, R., Madugo, C., & Kottke, A. (2022, 09). Shakebot: a low-cost, open-source shake table for structural seismology research. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Engineering Implementation Interface (EEII)