Minimally Actuated Dynamic Climbing in the Sagittal Plane
- Author(s): Birkmeyer, Paul Michael
- Advisor(s): Fearing, Ronald S
- et al.
This thesis explores the design of systems that can climb vertical surfaces with non-negligible dynamics in the sagittal plane. The development of a low-dimensional model addresses a lack of understanding of sagittal plane dynamics during climbing in the space of reduced-order dynamic models of legged systems. Using a construction derived from the well-known and well-studied Spring-Loaded Inverted Pendulum (SLIP), we propose a two-legged system with both torsional and linear compliance driven by a position-controlled rotational actuator. Two simple foot models are considered to explore their effect on the dynamics and stability of the system. Results of the model indicate the existence of passively stable gaits during climbing as well as during inverted running and also suggest mechanical tuning parameters for physical climbing systems. A robotic platform capable of producing dynamic climbing behaviors is introduced. A reduced profile, sprawled posture, and improved internal mechanics allow the CLASH platform to be adapted to different climbing substrates. A passive claw engagement mechanism is proposed and tested with simulated steps to verify the design. With these mechanisms, CLASH becomes the first robotic platform capable of climbing loose cloth and climbs vertically at 15cm/s or 1.5 body-lengths per second. When climbing ferromagnetic surfaces, the system is capable of climbing at 1.8 body-lengths per second. To climb smooth, hard surfaces, a foot with a passively aligning ankle with a tendon-loaded gecko-inspired adhesive is designed and tested using simulated steps. With these engagement mechanisms, the system is able to climb at 1 body-length per second on acrylic with a 70-degree incline. A simple foot-impact model is created to explain the robot's inability to climb faster or up steeper inclines due to the sagittal plane reaction forces created during rapid running.