Building an inertia dynamometer with vocational students: a low-budget apparatus for teaching rotational dynamics

TL;DR

This paper details the design and classroom implementation of a low-cost inertia dynamometer using simple materials and digital signal processing, enhancing physics education for vocational students.

Contribution

It introduces a novel, affordable inertia dynamometer built with student-welded parts and open-source software, integrating practical fabrication and sensor physics lessons.

Findings

The apparatus accurately measures torque and power curves.

The dynamometer effectively demonstrates the physics of rotational dynamics.

Students engaged with the project showed improved understanding of abstract concepts.

Abstract

We report the design, construction, and classroom use of a low-cost inertia dynamometer, built as a year-long project-based learning (PBL) activity with adult students at a Greek Evening Vocational High School (EPAL). The apparatus consists of a machined steel drum of calculated moment of inertia $I = 0.6507~\mathrm{kg\,m^2}$, mounted on a student-welded frame and instrumented with a green-laser / light-dependent resistor (LDR) optical interrupter. The analogue output is sampled at 44.1\,kHz by the microphone input of a laptop computer, which is used as an opportunistic analogue-to-digital converter; torque and power curves are then reconstructed in software from the inter-pulse intervals via $\tau = I\alpha$ and $P = \tau\omega$. The drum's moment of inertia is cross-checked by an inclined-plane rolling experiment. A wide-open-throttle test with a 50\,cc scooter reproduces the expected flat-power / falling-torque signature of a continuously variable transmission in the low-to-moderate RPM range; the LDR's millisecond-scale recovery time imposes an upper bandwidth limit that provides an unplanned but pedagogically rich lesson in sensor physics. The project integrated industrial-lathe fabrication, arc welding, analogue electronics, and numerical differentiation into a single coherent workflow. We describe the apparatus, the physics, the signal-processing pipeline (for which MATLAB and Python/Octave code are provided as supplementary material), and reflect on the pedagogical outcomes for a student population traditionally disengaged from abstract physics.