### Meeting Abstract

**P2.187** Thursday, Jan. 5 **Lift-off in a hopping robot** *AGUILAR, J.J.*; LESOV, Alex; WIESENFELD, Kurt; GOLDMAN, D.I.; Georgia Tech, Atlanta GA; Georgia Tech, Atlanta GA; Georgia Tech, Atlanta GA; Georgia Tech, Atlanta GA* gth657s@mail.gatech.edu

Jumping from rest has been studied for different initial movement strategies. For example, Bobbert et. al, 1996 found that among the countermovement jump and three different variations of the squat jump, the countermovement achieved maximum jump height. To systematically determine how actuation strategy affects movement amplitude needed to achieve lift-off, we studied an actuated robotic instantiation of the 1-D spring-loaded inverted pendulum (SLIP) model, commonly used to study hopping and running in humans and animals. The 1 kg robot consisted of a prismatic actuator (a tubular linear motor) connected in series to a linear spring (2.8 to 12.2 kN/m) which can make contact with the ground. A continuity sensor recording at 1000Hz on the bottom of the spring determines if the robot is in contact with the ground. The motor is forced to move starting from rest in a sinusoidal trajectory at a specific frequency and amplitude, and phase, and the number of oscillations required before lift-off is recorded. We measured number of cycles to lift-off, N, as a function of forcing amplitude, frequency, and initial phase. Since resonance in a linear spring-mass system occurs at the natural frequency, we expected that the optimal forcing frequency required for lift-off, defined as the frequency f0 at which forcing amplitude is a minimum, would be the natural frequency. We found that this is true when N>~2, but not necessarily the case for N<~2. For N<1, f0 is sensitive to the initial phase of the driving. A theoretical model of the robot captured these observed phenomena.