Penguin inspired torso motion improves biped walking on slippery surfaces
When to Waddle: A Comparative Study of Bipedal Torso-Stabilization on Low-Friction Surfaces
Robotics
Summary
Walking on slippery floors is tricky because feet can slip. This paper looks at how waddling like a penguin — moving the torso sideways over the leg that’s on the ground — helps keep balance and walk faster. The authors tested a robot in simulations and real hardware, finding that this torso motion and how high the robot’s center of mass is placed really affect walking speed and energy use. On very slippery surfaces, high torso placement with waddling helped most, while on less slippery surfaces, lower placements worked better.
What this means in practice
- •For roboticists: Build bipedal robots that walk more efficiently on slippery surfaces using lateral torso motion inspired by penguins.
- •For prosthetics designers: Design prosthetic limbs or exoskeletons that adjust torso movement and center of mass placement to improve stability on low-friction ground.
Authors
Naomi Oke, Ben Gu, George Ortiz, Stacy Ashlyn, Cordelia Pride, Sarah Bergbreiter, Aaron M. Johnson
Abstract
Low-friction surfaces challenge bipedal locomotion by limiting the contact forces available during stepping. Inspired by penguin waddling, we investigate how lateral torso motion and center of mass (COM) placement affect locomotion as surface friction changes. Using a five-actuator biped, we compare an upright-gait strategy with a penguin-inspired torso-over-stance-leg strategy across multiple COM placements in simulation and hardware. In the 3-D simulator MuJoCo, we sweep through sinusoidal leg and hip actuation parameters across four friction coefficients mu = 0.1, 0.3, 0.5, 0.7. In simulation, torso-over-stance-leg motion produces more successful controllers and higher forward speeds at low friction, with the highest speed occurring for the high-COM configuration. Hardware experiments show the same low-friction speed trend: at mu=0.12, torso-over-stance-leg motion increases forward speed and reduces cost of transport at both tested COM ratios, and the higher COM also improves both measures. The high-COM penguin configuration is the fastest and most energy efficient while maintaining low sideways foot motion. At mu=0.45, the COM trend reverses: the lower-COM configurations are faster and more energy efficient, while gait strategy has little effect on forward speed but still changes sideways foot motion. These results show that the effects of lateral torso motion and COM placement depend on the available friction, and that forward speed, energy use, and slip-related foot motion can be modulated with a penguin-inspired torso motion on hardware.