This paper presents the process of designing, fabricating, assembling, programming and optimizing a prototype nonlinear mechatronic Ball-Plate System (BPS) as a laboratory platform for engineering education STEM. Due to the nonlinearity and complexity of BPS, the task presents challenges such as: (1) difficulty in controlling the stabilization of a particular position point, known as steady-state error, (2) position resolution, known as specific distance error, and (3) adverse environmental effects—light-shadow error, which is also discussed in this paper. The laboratory prototype BPS for education was designed, manufactured and installed at Karlovac University of Applied Sciences in the Department of Mechanical Engineering, Mechatronics program. The low-cost two-degree BPS uses a USB HD camera for computer vision as a feedback sensor and two DC servo motors as actuators. Due to control problems, an advanced block diagram of the control system is proposed and discussed. An open-source control system based on Python scripts, which allows the use of ready-made functions from the library, allows the color of the ball and the parameters of the PID controller to be changed, indirectly simplifying the control system and performing mathematical calculations directly. The authors will continue their research on this BPS mechatronic platform and control algorithms.

This paper presents an approach to a go-kart chassis design, vehicle dynamics calculation, Li-ion battery capacity analysis, and electric motor choice for optimized vehicle performance. The chassis analysis shown in this paper was performed using a CAD/FEA software package, SolidWorks Student Edition. Three highlights can be found in this paper: (1) An original design was implemented; the basic analysis was composed of chassis optimization using beam elements and modeling such an optimized chassis “locally” with solid elements for sub-modeling purposes. (2) The most stressed tube joint was sub-modeled to calculate the risk of tube wall stability. (3) Vehicle dynamics were calculated for the case of braking on a curved path and the case of a collision with the front tire due to road imperfection. The authors intend to install a data acquisition system in the future to analyze the stress of local chassis tubes. The results of the SolidWorks analysis indicate a safety design for the chassis concept. The results for the sub-model stability (buckling) analysis show that the chosen tube wall thickness-to-diameter ratio gives safety factor values ranging from 1.6 to 5. Based on the stress distribution, some improvement in the middle part of the chassis can be made by using a half-a-millimeter-thicker wall tube or a larger tube diameter of a few millimeters to lower the stress. The latter will be described in this paper.

This paper presents the process of designing, fabrication, assembling, programming and optimizing a prototype of a nonlinear mechatronic Ball-Plate System (BPS) as a laboratory platform for STEM engineer education. Due to the nonlinearity and complexity of BPS, task presents challenging issues, such as: 1) difficulties in controlling the stabilization of a given position point known as steady state error, 2) position resolution known as specific distance error and 3) adverse environmental effects - light shadow error, also discussed in this paper. The laboratory BPS prototype for education was designed, manufactured and installed at the Karlovac University of Applied Sciences at the Department of Mechanical Engineering, Study of mechatronics. The low-cost two degrees BPS system uses a USB HD camera for computer vision as feedback and two DC servomotors as actuators. Due to controlling problems, an advanced block diagram of control system is proposed and discussed. An open-source control system based on Python scripts that allows the use of ready-made functions from the library allows changing the color of the ball and the parameters of the PID controller, thus indirectly simplifying control system and directly the mathematical calculation. The authors will continue their research on this BPS mechatronic platform and control algorithms.

Flexible thermoplastic polyurethane (TPU) materials fabricated using fused deposition modeling (FDM) are increasingly used in engineering and biomedical applications where exposure to moisture is unavoidable. However, the relationship between material hardness, water absorption, diffusion behaviour, and dimensional stability remains insufficiently understood and investigated. In this study, the hygroscopic behaviour of eight commercially available TPU filaments (60A–98A Shore hardness) was systematically investigated. Specimens were produced using an FDM 3D printer under controlled processing conditions and immersed in physiological solution (0.9% NaCl) for up to 96 h. Water absorption, dimensional changes, and diffusion characteristics were analyzed. Diffusion coefficients were determined using the Fickian diffusion model based on the initial stage of water uptake. The results suggest a transition in behaviour between lower- and higher-hardness materials. Softer TPU materials (60A–85A) exhibited higher water absorption (up to ~1.80%) and an apparent linear trend between hardness and absorption within the investigated material group (R² = 0.999). In contrast, higher-hardness materials (89A–98A) showed lower absorption (~1.18–1.42%) and a weaker apparent relationship with hardness (R² = 0.4214). Diffusion coefficients ranged from 1.40 × 10⁻¹³ to 3.40 × 10⁻¹² m² s⁻¹, with no monotonic dependence on hardness. Additionally, no clear correlation between diffusion kinetics and equilibrium absorption or volumetric expansion was observed. These findings indicate that hygroscopic behaviour of FDM-printed TPU materials cannot be reliably predicted based solely on hardness, and that diffusion, absorption, and swelling may be influenced by different mechanisms. The identified transition from hardness-dependent to behaviour potentially influenced by material structure provides new insight for the design and selection of flexible polymer components in moisture-exposed environments, particularly in biomedical applications.

The paper presents the development of a correlation model for initial tensile elastic modulus for flexible polymers as a function of Shore hardness in OO and A scale based on measurement. Measured polymers are in groups of silicone rubber, nitrile butadiene rubber (NBR), thermoplastic polyurethane (TPU) and silicone. The model is composed of piecewise exponential functions with fixed coefficients chosen to minimize the S₂ error norm and absolute value of relative error at the measured data points. Every chosen section of the hardness scale has one exponential function correlating the hardness to tensile elastic modulus with the argument in the form of a polynomial up to the fourth degree. The coefficients for the polynomial arguments were determined by enforcing interpolation conditions in a chosen set of points in the logarithmic scale for the elastic modulus. The correlation model possesses C0 continuity. For each material, five specimens were used for hardness measurements and five for the elastic modulus testing. The correlation model gives a positive value for elastic modulus of 0 for hardness, and a “finite”, “reasonable” value of 100 for hardness and is monotonic. Tensile properties were evaluated using true stress and logarithmic (Hencky) strain, with iterative correction of the changing cross-sectional area to account for large strain. The maximum relative error achieved in the correlation model for the OO scale is 13.4%, while for the A scale it is 7%. The developed model provides a practical and rapid method for estimating the initial tensile elastic modulus from non-destructive hardness measurements and is particularly useful in industrial applications and in the development of material models for dental surgery simulations.

Numerous studies show that the use of dental guides that rest on the patient's teeth improves the precision of implant placement, but the currently developed procedures and selected materials are still not perfect and could result in deviations from the planned implant position. The impact of the surgeon's hand force on the deformation of dental guides during implant placement has not yet been investigated or documented. In this study the behavior of the 3D guide model is evaluated by FEA analysis to validate the influence of the force of the surgical hand on dental guides due to their application. FEM simulation of deformation and stress was designed for four different types of dental guides that are supported on teeth for different ways of supporting the guide due to the action of the surgeon's manual force (chosen arbitrarily 30 N). The finite element simulation method performed on 5 sets of commonly used biocompatible polymer materials, Stratasys MED610 and VeroGlaze MED620, EOS PA2200, Formlabs FLSGAM01 and Stratasys ULTEM 1010, successfully numerically quantified the deformation of the dental guide caused by the surgeon's arbitrarily manual forces during manipulation. Based on the conducted analyses, guidelines were proposed for improving the design of guides, with an emphasis on optimal selection of supports, stability on the patient's anatomy, and reduction of deformations, thereby increasing the accuracy of implant placement. It was found for all four designs of dental guides that the deflection depends on the size of the arm, i.e. the distance of the support from the point of application of the force. As a result of the study, diagrams were created that serve as guidelines for the design of beam (A and A1) and cantilever (B and B1) versions of dental guides that rely on teeth. Guidelines for enhancing guide design were put out based on the analyses that were carried out, with a focus on the best choice of supports, stability on the patient's anatomy, and minimization of deformations in order to improve implant placement accuracy.