Integrated Drum Motor — Compact Drivetrain Concept

Problem

This project presents the development of a compact drum motor concept combining an integrated motor and a multi-stage gearbox. The objective was to package the transmission, motor, and supporting mechanical structure within a very limited diameter while maintaining functional robustness and serviceability.

Context

The concept was developed from defined requirements for power, drum diameter, speed range, and expected production volume. The focus was therefore not only on functional layout, but also on compact integration, component selection, and cost-aware engineering decisions.

Constraints

• Motor power: 0.75 kW
• Drum diameter: 160 mm
• Speed range: 0.5–0.8 m/s
• Annual production target: 400–600 units
• Transmission and bearings had to fit within a constrained internal geometry

Mechanical architecture

The complete system was built around the central axis of the drum. An interactive sketch in SolidWorks was used early in the process to position shafts and gears compactly while keeping the layout adaptable to ratio and geometry changes. The architecture combined gearbox housing, stator housing, and end piece into a concentric assembly designed with attention to assembly, lubrication, and manufacturing efficiency.

Drivetrain concept

The total transmission ratio was defined at approximately 1/17 and distributed over three gear stages in order to make the gearbox physically fit inside the drum. A 1000 rpm motor was selected because a 1500 rpm alternative led to larger dimensions. The drivetrain concept therefore became a balance between compactness, loading, gear geometry, and internal packaging.

Design approach

One important decision was to integrate the pinions on shafts 1 and 2 directly into the shafts in order to increase compactness. Bearing selection was driven by both loading and packaging limits, and a thin needle bearing was chosen for the most highly loaded position. The design also addressed assembly, oil access, cable routing through the output shaft, and cost-efficient use of identical outer wheels.

Validation

The concept was validated through calculations of gear forces, output shaft loading, bearing reactions, angular deflection, bending moment development, interference fit behavior, and lubrication requirements. This ensured that the work went beyond CAD layout and into a technically assessed drivetrain concept.

Result

Projektet resulterede i et sammenhængende koncept for en kompakt tromlemotor, hvor mekanisk arkitektur, transmission og centrale belastninger blev bearbejdet som én samlet løsning. Samtidig blev de mest kritiske områder identificeret tidligt, hvilket gav et klart grundlag for videre optimering.