Passive Battery Transport Using Tendon Soft Grippers in Drones

The study presents the development and evaluation of a tendon-actuated passive soft gripper for transporting external battery modules using a quadrotor platform. The system addresses the power and aerodynamic limitations associated with existing aerial docking and manipulation methods by eliminating the need for continuous actuation during payload retention. The gripper, fabricated using expanding polyurethane foam, features four compliant fingers actuated by a single 35 kg·cm servo motor through tendon routing. Finite Element Analysis validated the finger deformation under applied load using a hyper-elastic material model. The gripper was integrated with a DJI F450 drone for mechanical and functional testing. Experimental trials assessed actuation repeatability, contact area expansion, and retention performance under two loading conditions: 134.64 g and 493.64 g. Fingertip displacement tests showed less than 0.4% variation across ten cycles per finger. The contact area increased from 3.64 cm² at 0% opening to 205.61 cm² at full actuation. Slippage remained below 1 mm under the lighter load and reached up to 13.77 mm at the higher load. Statistical analysis confirmed significant differences in displacement and retention performance between load conditions. Electrical current measurements recorded a drop from 0.476 A during initial actuation to 0.316 A at a steady state, confirming that no continuous power was required to maintain grip. The system offers a lightweight, power-free solution for drone-based battery transport and modular payload handling, removing the need for rigid docking systems or active latching mechanisms. The results demonstrate the feasibility of low-energy aerial operations.