Mass-Optimized Lever-Lifting Transmission

Role

Mechanical Engineer, responsible for transmission design, structural analysis, and prototyping

Team Members

Caitlin Ramos, Isabella Correa

Responsibilities

Transmission analysis, CAD modeling, gear selection, structural design, FEA, prototyping, testing

Skills

  • CAD
  • FEA
  • Laser Cutting
  • 3D Printing

Challenge

  • Design a lightweight, efficient transmission to lift a 10kg weight on a lever by 10 cm using a maximum vertical mass drop of 2m.
  • Minimize system mass and mass drop while maintaining structural integrity and mechanical efficiency

Action

  • Transmission Design: Developed a two-stage gear system with two capstans to optimize force output and lever-lifting distance
    • Performed inverse analysis and free body diagram calculations to determine gear ratios, torque requirements, and capstan radii
    • Selected acetal gears for first stage and PLA 3D-printed gears for the second stage due to strength, mass efficiency, and manufacturability
    • Implemented MATLAB script to iterate face width, pitch, and gear teeth for optimized gear strength and torque output

Gear Transmission and Capstan Layout
Gear layout showing two-stage transmission and capstan arrangement

  • Capstan Design: Two PLA capstans with optimized radii (0.258’’ input, 0.163’’ output) to maintain 19:1 total transmission ratio
    • Tapered geometry guides string toward the middle to reduce slipping and tension loss
    • Validated using FEA, ensuring sufficient factor of safety under lever-lifting loads (up to 200 N)

Capstan FEA
FEA of output capstan under lever-lifting load

  • Acrylic Support Structure: Mass-optimized 30 cm high laser-cut acrylic frame
    • Designed extended bottom leg and horizontal support beams to prevent tipping and bending
    • Central vertical beam in compression, right vertical beam in tension; fillets increased to reduce stress concentration
    • FEA confirmed stress distribution and stability under applied loads

Acrylic Support Structure
Laser-cut acrylic support structure with horizontal and vertical stabilizing beams

  • Component Selection:
    • Shafts: 12L14 carbon steel, 3/16’’ and 5/16’’ diameters for strength and cost efficiency
    • Bearings: Stainless steel flanged ball bearings, selected for dynamic load capacity and smooth rotation
    • Kevlar Strings: Matched breaking strength to input/output loads, achieving safety factors of 2.9 (output) and 18 (input)
    • Shaft collars to prevent axial movement and account for non-orthogonal loads

Result

  • Built a functional lever-lifting transmission system with a 19:1 total gear ratio, achieving 10 cm lift with 2 kg mass drop

Acrylic Support Structure
10 cm lever lift through the transmission system

  • Validated structural integrity and mechanical efficiency through FEA, component analysis, and experimental testing
  • Optimized mass, cost, and complexity by using two-stage transmission and lightweight materials
  • One of four out of fifteen teams to achieve the required lift height