Design and Feasibility Analysis of a Foldable Robot Arm for Drones Using a Twisted String Actuator: FRAD-TSA

This paper presents a feasible analysis of a foldable robot arm for drones (FRAD) for payload lifting without drone landing. The arm design is aimed to be light, foldable and energy-efficient. FRAD is designed with a scissor mechanism in a parallel arrangement actuated by a twisted string actuator (TSA) with a guide. The robot arm can fold, unfold, and easily deploy on drones by having benefit from inherent TSA advantages. We propose a linkage design approach to provide a solution to mechanical singularity and to improve a space-saving capability. The nonlinear pulling force of twisted strings' transmission ratio (decreasing with twisting) closely matched the typical force profile requirement for folding the arm. This fact was used in the foldable robot arm for its optimal actuation design. The required string torque and twist angle were calculated to generate a pulling force to fold the arm with a 0.3kg payload from the unfolded to the fully folded situation. Preliminary experimental trials demonstrated that the proposed FRAD could generate the required lifting force and fold the arm without a high torque motor.