A Minimally Actuated Hopping Rover for Exploration of Celestial Bodies Most exploratory mobility systems (wheels or legs) use many actuators and/or complex linkages. Sojourner: 10 motors; Rocky 8: 12 motors E. Hale, N. Schara, J. Burdick P. Fiorini Engineering & Applied Science Jet Propulsion Laboratory California Institute of Technology NASA/California Institute of Technology Disadvantages: cost, complexity, weight, robustness Goal: user fewer actuators smaller, lighter, systems simpler, cheaper designs lower risk of failure suited to future colony scenarios

A Minimally Actuated Hopping Rover for Exploration of Celestial Bodies Most exploratory mobility systems are wheeled. many actuators (Sojourner: 10; Rocky 8: 12) can’t overcome obstacles > 1.5 wheel dia. may not scale well to small sizes Legged systems: many motors AND complex linkages E. Hale, N. Schara, J. Burdick P. Fiorini Engineering & Applied Science Jet Propulsion Laboratory California Institute of Technology NASA/California Institute of Technology Goal: reduce the number of actuators smaller, lighter, simpler, cheaper systems lower risk of failure suited to future colony scenarios

Prior Work Lunar Hopping Proposals: Obert (1959), Seifert (1967), Kaplan & Seifert (1969) Motion discontinuity Raibert Hoppers: require many motors and complex control to stablize not energy efficient Advantages of Hopping (for planetary exploration) Can be efficient in low gravity Hopping Mobility

Goals & Constraints Philosophical: how much mobility with one actuator? Mechanically durable Energy efficient Contributions innovative and efficient leg thrusting mechanism unique mobility system that hops, steers, self-rights via a single actuator strategies (beginning of formal design methodology) for minimalist locomotion systems.

First Generation Design (Fiorini et. al., IEEE Aerospace Conf. 1999) Internal Structure Operation Sequence

First Generation Design (Fiorini et. al., IEEE Aerospace Conf. 1999) Operation Sequence Thrust by decompression of linear spring Off-axis camera mass orients body Self-righting via low center of mass

First Generation Post-Mortem LOW hopping performance 80 cm height (2.4 m on Mars) 60 cmdistance (1.8 m on Mars) LOW thrust efficiency (~20%) Energy vs. Time Linear springs inherently poor premature lift-off/lift-off chatter high peak motor design torque

Second Generation Design Goal: Solve 1 st generation shortcomings Inefficient hopping Unrobust steering & self-righting Result: A single actuator system that can: efficiently hop actively steer & self-right itself control on-board camera/sensors

Leg Thrusting Mechanism Geared 6-bar linkage makes a linear spring nonlinear! 70 % efficient Lower peak motor torque Force vs. Displacement Lock/release mechanism

Steering and Self-Righting Mechanisms Steering (about vertical) engages when leg compressed

Hopping Cycle Jumping On-side landingRolling on to Back On its backStanding upAlmost up!