Autonomous stairs climbing carrier cart for enhanced accessibility

Department of Mechatronics, Nelson Mandela University, Gquberha, 6013, South Africa

^* Corresponding authors: s219149658@mandela.ac.za, farouk.smith@mandela.ac.za

Abstract

This paper presents the design, analysis, and experimental validation of an autonomous stair-climbing carrier cart equipped with a rocker–bogie suspension system to improve accessibility in multi-level indoor environments. The vehicle is capable of traversing staircases in both manual and autonomous modes while maintaining stability. The mechanical design uses a six-wheel rocker–bogie chassis inspired by planetary rover suspensions. A web-server interface enables remote manual control, while on-board sensors and PID feedback loops enable line-following and obstacle/stair detection. Mathematical modelling quantified the required torque, power, and stability margins. On flat ground, rolling resistance (with coefficient c≈0.015 for rubber on concrete) yields a negligible torque demand (~0.0013 N·m per wheel), whereas climbing a 30° stair imposes a torque on each wheel on the order of 0.04 N·m, which is well below the motor’s stall torque (≈0.679 N·m). Simulation and analysis were performed using multibody dynamics and finite element software. FEA under static loads shows a maximum von Mises stress of only ~0.33 MPa and a peak displacement of ~0.11 mm in the chassis, yielding an extremely high safety factor (yield stress on the order of 200–300 MPa). The robot successfully climbed standard office stairs without tipping, and sensor feedback enabled reliable stair detection and line-tracking. The results demonstrate strong agreement between theoretical calculations, simulation, and experiment.