Tec de Monterrey, 2022

How could mechanics at a small airport safely lift and transport heavy aircraft engines, weighing up to 310 kg, from one point to another without risking damage or injury? The answer was to design and validate a mechanical scissor-lift, fully integrating mechanical, electrical, and control elements into a single functional system.

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Building on prior metallographic analysis of aircraft piston pins, the team focused on designing a load-lifting solution that could meet the client’s specific constraints:

• Maximum lifting height of ~1.4 m.

• Platform dimensions of ~1.5 × 1 m.

• Ability to avoid engine contact with the oil pan by using a tailored support surface.

The team chose a scissor-lift mechanism because of its simplicity, structural efficiency, and ease of force distribution. They decided to include electric actuation with a gear transmission, enabling controlled lifting and lowering, and added provisions for safety sensors and emergency stop systems.

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The design process started with a static equilibrium analysis. Using the worst-case load (310 kg), they calculated:

• Reactions at supports (~1.52 kN each).

• Bar angles and force components, including axial and shear reactions.

• The critical force (Ix) required to activate the system (~8.47 kN).

This analysis ensured that each bar, pin, and support could sustain loads without exceeding yield strength. Python scripts were developed to automate reaction calculations and explore different geometric configurations, speeding up iterations and design optimization.

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Initially, direct motor actuation was considered, but calculations showed it would require a 170 hp motor; completely impractical. To solve this, the team designed a multi-stage gear train with a final ratio of 1:10, achieving the required torque with a much smaller motor.

Using gear tooth interference formulas, they defined minimum tooth counts (≥7, chosen as 15 for manufacturability) and designed a four-gear system ending in a rack-and-pinion drive to convert rotation into vertical lift. Python code was used again to calculate transmitted loads, angular velocities, and resulting motor power requirements.

The result: only 22 hp of motor power is needed: achievable with a diesel motor, which also provides field usability where electricity is unavailable.

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To make the system safer and semi-automatic, the team proposed:

• Ultrasonic distance sensors to detect max/min height.

• Load sensors (500 kg capacity) to prevent overloading.

• Manual switches and emergency stops, designed with redundancy.

• LED indicators for system status and fault warnings.

They created a ladder diagram (PLC logic) to define how sensors, switches, and actuators interact, preventing overextension and allowing intuitive operator control. A video simulation demonstrated the control logic in action.

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Once calculations were verified, every component was modeled in SolidWorks, assembled virtually, and tested using finite element analysis (FEA). Stress concentrations were mapped on:

• The scissor arms and pivot holes.

• The platform and base.

• The drive gear (gear 5).

All stress results were far below material limits, with maximum values around 0.147 N·m, confirming that the system could safely operate under maximum loads with a good factor of safety. For holding position under load, two solutions were considered: mechanical brake with pivoted lever lock, or motor holding torque with controlled power delivery (more precise but higher fuel cost). The team recommended a hybrid approach, leaving final selection to cost and maintenance considerations.

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The project culminated in:

• A fully dimensioned CAD model of the scissor-lift.

• Mathematical validation of stresses and power requirements.

• Control logic diagrams and recommended sensor layout.

• Cost estimate between $35,000–$45,000 MXN for materials and fabrication.

• Simulation videos of the assembly and gear transmission in motion.

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The final design is a robust, cost-effective, and safe lifting system tailored to small-aircraft maintenance operations. By combining analytical modeling, Python-assisted computation, CAD design, FEA, and control logic development, the team produced a professional-grade solution that could be prototyped and deployed in a real maintenance environment.

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Please find attached below the relevant documents to this project. (Note: most, if not all documents, are in Spanish)