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Speed-Reduction Gearbox
Level: Mechanical Design B
Grade: First Class Honours
Team Size: 3
My Responsibilities: Gear Design, Shaft Design Calculations, Bearing Ratings, Seal and Lubrication, CAD (Fusion 360 and SolidWorks), DFM, DFA, Technical Drawings, DFX (Manufacturing Cost Analysis, Functional Analysis, Feeding and Fitting Analysis), and Bill of Material Generation.
3rd Year Mechanical Engineering
2023
This project focuses on designing a speed-reduction gearbox for an ultralight aircraft with a high-speed Wankel engine. The gearbox will reduce engine speed from 6500 rpm to 2000 rpm, increasing torque for the propeller to support high-G maneuvers. It must handle specific power inputs, fit within defined shaft distances, and ensure reliability with a lifespan of 2000 hours. The design includes standardized gears, lightweight materials, proper lubrication, and a shaft safety factor above 4. Production is targeted at 200 units annually, with a focus on safety, weight efficiency, and minimizing manufacturing and assembly costs.
There are 3 parts to this project:
Scroll for Overview of Each Section
BRIEF OVERVIEW
Design Validation
Gear Design
The maximum power generated by the Wankel engine is 50 hp at 7000 rpm; therefore, the maximum
power transmitted through the gearbox is 36774.9 kW. The gear ratio is set to be 3.25 to meet the
product design specification of maximum cruising speed. All the dimensions used in the calculations are
in metric units. The data were inputted into the GP100 software to calculate the specific gearing
parameters shown below:
Gear Forces
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Withstanding higher speed than spur gears
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Hbility to generate axial thrust loads used to counter the thrust produced by the propellor
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Higher power capacity for the same volume occupied
- Its more gradual and smoother power transmissions, with less noise and wear induced.
Materials chosen for the gears wth AISI equivalents are:
- Pinion: EN39 Surface Hardened (AISI 1340, oil quenched & tempered at 315oC)
- Wheel: EN24 Surface Hardened (AISI)
Shaft Design Justifications
Shear Force Diagram
Using the Von Mises Theory and Tresca Theory, the diameter of the output shaft was determined to be 30 mm, and 20 mm for the input shaft. While with calculations for Critical Speed, Linear Deflection, Torsional Angular Deflection, and Fatigue, the materials for the input and output shafts were decided to be Carbon Steel AISI 1040 and Carbon Steel AISI 1340 respectively.
Bearing Ratings
Detail calculations for this section including shaft design (critical speed, torsional angular deflection, fatigue), bearing ratings, torque transmission couplings (keyway and spline sleeve), and seal and lubrication can be found in the:
Design
Final Design
DFA Design Optimizations
Improved Design
Sketched Ideation of Optimizations from Old Design
The design optimizations for DFA resulted in the reduction of parts by 37.9%, resulting in a lower assembly difficulty shown in the decrease of feeding and fitting ratios. Its design efficiency climbed by 39.4% assessed with the Lucas Method in my functional analysis that focuses on movement, isolation, and replacement to reduce parts was used, to determine whether all components are essential to its performance. In addition, the manufacturing cost index has been reduced by 2.1% which constitutes to a huge impact in the production of 2000 parts.
The detailed s oections of BOM Generation, Assembly Sequencing, Design for Excellence (Functional Analysis, Feeding and Fitting Analysis, Manufacturing Cost Analysis), and Design Improvements can be found here: