Motorized Tri-Wheel Furniture Dolly

Northeastern University – Mechanical Engineering

Team of 5 | Design & Analysis Project

Tools: SolidWorks, FEA, 3D Printing, drivetrain sizing, analytical stress & fatigue analysis, materials selection, design for manufacturability

Problem & Context

Moving heavy furniture across stairs requires significant manual force and poses safety risks. Existing dollies lack autonomous stair-climbing capability, while powered solutions are expensive and inaccessible. This project focused on designing a motorized tri-wheel dolly capable of climbing stairs under load while maintaining durability, user safety, and cost constraints.

Von Mises stress distribution in tri-wheel plate

Solution: System Summary

Core System Features

▪ Tri-wheel climbing geometry enabling continuous contact on stairs

▪ Steel frame and platform designed for 300 lb load capacity

▪ Motorized drivetrain sized to overcome stair torque requirements

▪ Designed for independent operation with minimal user exertion

Structural Validation

▪ Frame and platform evaluated under worst-case stair-climbing load cases

▪ Static stress and deflection analyses performed to ensure adequate stiffness under a 300 lb payload

▪ Fatigue considerations used to verify long-term durability under repeated loading

▪ Design validated to meet safety factors across critical structural components

Tri-Wheel & Axle Analysis

▪ Tri-wheel plates analyzed as cantilevered members during stair engagement

▪ Combined bending and torsional loading evaluated at critical locations

▪ Axle assessed for bending, torsion, and fatigue using free-body diagram-based load cases

Drivetrain Sizing

▪ Required output torque derived from stair-climbing geometry and payload loads

▪ Gear reduction selected to meet torque demand while maintaining controlled climbing speed

▪ Motor selected to meet performance requirements with safety margin

Personal Contributions

▪ Contributed to mechanical design and analysis of the tri-wheel dolly structure

▪ Performed static and fatigue analysis on critical components: frame, axle, platform, and wheel plates

▪ Conducted free-body diagram analysis, bending, shear, torsion, and fatigue calculations to validate safety factors

▪ Supported drivetrain sizing, including torque requirements, gear reduction, and motor selection

▪ Evaluated connections (bolts and welds) under static and cyclic loading to identify design constraints

▪ Participated in design iteration based on analytical results and safety margins

Concept: Motorized tri-wheel dolly designed for autonomous stair climbing under load

Von Mises stress under angled loading

Von Mises stress under horizontal loading

Connections & Manufacturability

▪ Welded joints and fasteners evaluated under static and cyclic loading

▪ Bolt grades and weld sizes selected to satisfy strength and fatigue requirements

▪ Analysis used to inform manufacturable design choices and connection layout

System Feasibility

▪ Designed using commercially available components

▪ Estimated system cost of $560, balancing performance, safety, and accessibility