Baloo: A Large-Scale Hybrid Soft Robotic Torso for Whole-Arm Manipulation

Abstract: Soft robotic actuators can simplify the design of controllers when operating in contact-rich environments. Importantly, their passive compliance fundamentally alters contact mechanics by smoothing impacts and distributing forces over large areas. By integrating soft actuators, we can perform high-impact, dynamic, and contact-rich tasks that are challenging or impossible for traditional rigid robots. In order to explore the benefits of passive structural compliance and learn to utilize it effectively, we present a prototype robotic torso named Baloo. Baloo's hybrid soft-rigid design incorporates both adaptability from soft components and strength from rigid components with two meter-long, pneumatic robot arms mounted on a rigid torso. The hybrid design is capable of lifting end effector payloads of up to 19 kg, far exceeding many hybrid robot designs. Such payloads are competitive with similar-sized rigid robots, but with a much higher strength-to-weight ratio. Through 30 physical whole-body grasping experiments, we also demonstrate how a simple control strategy can generalize for effective lifting across six challenging objects with diverse shapes, sizes, and weights. A 100% success rate across all objects--achieved with the simple control strategy--underscores the potential of our hybrid soft-rigid robot design for contact-rich, whole-body tasks.