Phase 3: Lifting Mechanism Design

Overview of Phase 3

In this phase, our group needed to design a mechanism that could lift our grasping mechanism and payload. For this phase, our group needed to create a design that utilizes mechanical advantage to lift the grasping mechanism. By maximizing the k and h values of the instant center between the ground and the coupler (I24), we could maximize the mechanical advantage of the linkage. Our group used a MATLAB script to calculate whether our mechanism could lift based upon our dimensions and center of mass.

Design Constraints

Implicit Constraints

Must connect to the 1''x 2'' test rig
Mechanism pieces would be created of 1/4" plywood using laser cutter.
Must connect to previous phase's 0.2 inch diameter hole
Wires must be secured to not interfere with mechanism
The servomotor cannot exceed 180 degrees of rotation

Explicit Constraints

The lifting mechanism must include one four bar linkage to create mechanical advantage to lift the grasping mechanism and the payload.
The mechanism cannot rely on a counter weight in order to lift the payload. The mechanism use cannot use gears to create mechanical advantage either.
Must use 180° servo motor and activated by a sonar sensor
Must be lifted 1-3 inches off the ground
The lifting mechanism must be able to lift payload from the middle of the 3"x3" drop zone. The mechanism must return to payload to any position the drop zone.

Emma's Design

Pros:

-Can lift the minimum height

-Is not a parallelogram

Moshier's Design

Pros:

-Consists of fourbar linkage

-Can lift 3 inches off the ground

Brenden's Design

Pros:

-Consists of simple fourbar linkage.

-k/h ratio of 21 resulting in high mechanical advantage at maximum extension.

Lifting Mechanism

We chose Brenden's design for our final lifting mechanism. The mechanism has a ground length of 6.00in, crank length of 3.02in, coupler 4.75in, and rocker length of 7.47in. The rocker has an elbow where it bends downward at a 125.91 degree angle and connects to the grasping mechanism. This design is a four-bar linkage that consists of a k/h ratio of 24 in its fully extended position, which makes it the highest mechanical advantage of the 3 designs we made. This means that this design produces the largest output force at the maximum extension of the lifting rig. This will allow the robotic arm to lift more weight. This design utilizes the servomotor to lift the grasping mechanism and payload three inches high. In terms of Degrees of Freedom, the equation would result in there being 3 Degrees of Freedom, meaning it is a mechanism that can be controlled by a motor.