Phase III

Objective

In this phase of the project, the team created the lifting mechanism to lift the grasping mechanism and payload designed in phase 1 and phase 2, respectively.

Design Constraints

Must have at least one fourbar linkage
Cannot require addition of a counterweight to move
Must be driven by a second 180 degree servo motor & be activated by sonar sensor
Must have mechanical advantage & must not be created using gears
Must be supported by a 1" x 2" post on the test rig
Must be lifted from and returned to a 3" x 3" square area centered 8" away from the post
Must be made of 1/4" plywood
Wires must not interfere with mechanism

Design Considerations

Sketch 1

Pros:

Fourbar Parallelogram Linkage

Cons:

No Mechanical Advantage

Sketch 2

Pros:

Squares save time

Cons:

Squares are unpredictable in rotation

Sketch 3

Pros:

The Slightest Mechanical Advantage

Cons:

A trapezoidal design is still basic

Final Mechanism

The final design is a Non-Grashof fourbar linkage. The linkage has the crank on the top, the coupler on the left, the rocker on the bottom, and ground on right (test rig). The linkage is capable of producing the desired motion using mechanical advantage. An input force is applied to the crank pin and an output force is produced by the rocker to produce an up and down motion.

Degrees of Freedom Analysis

Graphical Linkage Synthesis

The crank rotates and produces an input force at the crank pin. The coupler is responsible for the trade off between the input and output force. The rocker produces the output force and the linkage moves downward. When the crank rotates back, the reverse occurs and the linkage moves back to its starting position.