4-bar linkage system [Fall 2021]

Course: Engineering Design I

Task: To create a 4-bar linkage system that will fully close a button for a maximum duration in a 2 minute cycle of a DC motor.

Challenge/constraints:

  • Minimize mass

  • No motor stall

  • Entire system must remain within rig boundary

  • All components must move during one cycle

  • Linkage system can only be pinned at mounting plate in one location

Material: 1/8” acrylic

 

Process

1)

Initial sketches (accounting for pin constraint)

2)

Hand calculations:

  • Performed simple stress analysis to assess most likely failure modes (compression/buckling, axial stress, bending, etc.)

  • Used a Factor of Safety (FoS) of 2.5 to solve for which material to use in fabrication (accounting for differnt tensile strengths and thicknesses).

3)

Created CAD model to dimension in SolidWorks

4)

Performed motion analysis to ensure that rocker link would clear button distance during cycle of motor

5)

Performed complex stress analysis using FEA to find the points and values of highest stress, maximum displacement, and FoS to compare with hand calculations.

6)

Prototyped using laser cutter (Rabbit Laser, RDWorks) with total link mass = 13.3 g

7)

Intermittent testing on rig to finalize link dimensions and configuration of spacers and clevis pins

8)

Final testing on rig: full button push condition fulfilled for ~ 40 s, one third of total 2 minute cycle.