Design and Validation of a Secure LoRa-Based Wireless Control System for DC Motor-Driven Laboratory Equipment: A Case Study from an Academic Robotics Laboratory

Academic laboratories increasingly deploy DC motor-driven equipment, but wireless control faces two challenges: congestion in the 2.4 GHz band and the absence of application-layer confidentiality. This paper presents a 433 MHz LoRa-based wireless joystick control system with AES-128 confidentiality protection, validated using an ABU Robocon robot as a representative testbed. Performance was characterized outdoors across six Spreading Factors (SF7–SF12) under line-of-sight (LoS) and non-line-of-sight (NLoS) propagation (n = 6 per condition), and across three indoor campaigns (n ≈ 100 packets per condition) to quantify the gap between outdoor boundary estimates and indoor deployment. One-way ANOVA confirmed significant SF effects on latency, RSSI, and SNR (F = 10.4–5812, p < 0.001); normality and homogeneity-of-variance assumptions were formally tested, frequently violated for RSSI/SNR, and corroborated by Kruskal–Wallis tests, with large effect sizes (η2 = 0.27–0.99). A preliminary low-antenna indoor test showed severe PDR degradation (as low as 14%), plausibly from ground-reflection multipath; elevating both antennas (≈70/60 cm) produced mixed, not uniformly improved, results. Indoor-NLoS testing showed low Spreading Factors failing almost completely beyond 5 m (SF7/SF8 near 0% PDR at 10–15 m) while SF10–SF12 remained robust (89–100%), a more consequential finding than outdoor boundary conditions (100% PDR at 5–15 m) suggest alone. Interference experiments characterized position-dependent and cross-Spreading-Factor resilience, with an explicit literature-grounded caveat rather than an unconditional quasi-orthogonality claim. SF10/SF11 with a 5 dBi antenna remains the best outdoor compromise (147–176 m range, 206–357 ms latency); indoor deployments require SF-specific de-rating and antenna-height practice. AES-128 added no measurable latency overhead. Contributions include a validated retrofit blueprint, a statistically grounded SF selection matrix spanning outdoor and indoor conditions, a practical antenna-height recommendation, and a controlled characterization of indoor interference resilience. The AES-128 ECB implementation provides confidentiality only, not authentication or replay resistance; limitations and a migration roadmap are discussed.