# A Low-Cost IoT-Based Bidirectional Torque Measurement System with Strain Gauge Technology
## 6 Conclusions  
This study establishes a transparent methodology for bidirectional torque measurement using open-source hardware. The shaft-mounted node, comprising strain gauges, HX711 conditioning, a Wemos D1 Mini ESP8266, and an onboard battery, was calibrated with a certified dynamometric wrench and validated over \(\pm\)5-50 N\(\cdot\)m. Testing confirmed a mean absolute error of 0.559 N\(\cdot\)m and precision within \(\pm\)2.5 N\(\cdot\)m (95% confidence) while keeping material cost under EUR 30. Although these results substantiate the feasibility of an accurate, low-cost, and IoT-enabled sensor, the study remains at the proof-of-concept stage, and the novelty of the study resides in integrating wireless transmission, straightforward assembly, and rigorous calibration within a compact platform. The system thereby lowers the barrier to advanced torque monitoring in automotive, industrial, and research applications. Future work will address battery endurance, environmental sealing, and multi-axis capability, enabling extended field trials that will verify long-term reliability, broaden deployment scenarios, and support predictive maintenance architectures aligned with Industry 4.0.  
Conceptualization, V.S. and M.I.; methodology, V.S., M.I. and C.C.S.; software, V.S.; validation, C.C.S., V.S. and R.I.; formal analysis, C.C.S., V.S. and M.I.; investigation, C.C.S. and V.S.; resources, C.C.S. and I.I.; data curation, C.C.S.; writing--original draft preparation, C.C.S., V.S., I.I. and M.I.; writing--review and editing, C.C.S., V.S., I.I., M.I. and R.I.; visualization, C.C.S., V.S. and I.I.; supervision, V.S. and I.I.; project administration, V.S. and I.I. All authors have read and agreed to the published version of the manuscript.  
There was no financial support for the research.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Aspect** & **Advantages** & **Disadvantages/Limitations** \\ \hline Cost & Significantly lower than commercial systems; & May lack some features of high-end \\ Modularity & \begin{tabular}{c} affordable components \\ Easily adapted to various shaft sizes and applications \\ Bidirectional, high-order polynomial fit \\ enables accurate reversible/oscillatory load \\ measurement \\ Open-Source Design \\ Maintenance \\ \end{tabular} & \
\begin{tabular}{c} Low MAE and SD; comparable to \\ commercial systems \\ commercial systems \\ Easily replicated for multi-point or \\ distributed sensing \\ Simple, low-cost replacement of components \\ \end{tabular} &
\begin{tabular}{c} Performance may degrade if \\ installation quality is poor \\ Network congestion possible with \\ many devices \\ Long-term stability and drift require \\ periodic recalibration \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 7: Critical analysis of the proposed IoT-based torque measurement system.  
Data Availability Statement: All data underlying the results are available as part of the article; no additional source data are required. Further details or raw data can be provided by the corresponding author upon reasonable request.  
The authors gratefully acknowledge that this research formed a core component of the first author's PhD studies at Politehnica University of Timisoara. The constructive feedback and support provided by the reviewers have been instrumental in enhancing the quality and completion of this work.  
The authors declare no conflicts of interest.