This National Science Foundation National Robotics Initiative project investigates the ability to leverage Fluid-Structure Interaction in the design of gait assistive systems and is conducted in collaboration with Prof. Yahya Modarres-Sadeghi, director of the FSI lab at UMass Amherst. We are attempting to use the vortices generated in the wake of an oscillating rod placed in a fluid flow to impart forces on a hydrofoil placed within the wake. When a hydrofoil is attached to a subject, this system can be used in conjunction with an underwater treadmill to interact with the subject's gait in the same way a rigid exoskeleton would. Through this project, we aim to understand the magnitude of the forces such a system can generate, the appropriateness of these forces for modifying gait trajectory, and the ability of the operator to adjust these forces to align with the desired gait performance.

I was tasked with designing the actuation mechanism (vortex generator) for this system. Our first iterations explored multi-stage actuation methods using belt-drives; however we eventually moved on to a direct-drive transmission approach using waterproof dynamixel servo motors. We 3D printed the entire assembly except for the cylinders which were made from PVC pipes. The transmission uses a torque reduction/speed multiplier gearbox that was also part of the design process.We explored position and velocity control modes to obtain the desired oscillations on the cylinders to induce gait-like trajectories in the downstream hydrofoil placed in the wake of the vrotices generated by the rotating/oscillating cylinders. The design illustrates 2 independent drives for each cylinder to actuate each leg seperately to realize the out-of-phase motion for generating the gait trajectory. Further testing and evaluation work of this system is still in progress to characterize the assitive forces generated on the persons limbs as part of the rehabilitation process.