Phase 3

Lifting Mechanism

Phase Overview:

In this phase, we are required to make careful calculations in order to create a mechanism that is capable of lifting our claw design and payload from the previous two phases. This requires us to analyze the mechanical advantage that our arm design produces using method of instant centers, as well as an analysis of our h and k values in order to achieve a positive net torque in and out. The MATLab code aids us greatly in determining the torques that our design will achieve.

Design Constraints

Before going forward with our desired mechanical arm design, we had to consider many constraints. Most constraints refer to the calculations we had to make before actually physically assembling our design:

There must be at least one fourbar linkage in the design
The design may not require a counterweight to function
The design must be driven by a second servo motor and activated by a sonar sensor
There must be mechanical advantage in the design, which cannot be achieved using gears
The design must be supported by the standard testing post, which has been provided
The payload must be lifted and returned to the 3" by 3" drop zone, centered 8" from the post
All wires must be secured so they do not get in the way of the mechanism
The payload must be lifted between 1-3" from the ground and successfully suspend the payload for 3 seconds

Sketch Design 1

Pros:

Simple Design

Easy to Analyze

Cons:

Does not yield much of a height difference in the up and down positions

Sketch Design 2

Pros:

Crank is short, yields enough torque

Cons:

Unsure of how well it fits on the post

Sketch Design 3

Pros:

Shows exact orientation on the shoulder

Cons:

May not have enough torque to complete the motion

Sketch Design 4

Pros:

Simplistic design

Cons:

Unsure of how servo would be oriented

Why We Chose Design 1

This design is simplistic and extremely easy for one to analyze, making it optimal for our mechanical arm
The mechanical advantage that is produced is effective and meets the criteria required for it
The torque calculations reflect a positive net torque for the up and down positions (calculations shown below)
Degrees of freedom analysis shows a DOF of 1, as needed

Refinement of Design 1

We ran into some issues while implementing design 1, like;

How to connect the crank to the servo motor in such a confined space
The low mechanical advantage of the four-bar
Initial testing showed that the claw was not centered over the payload

Because of these issues, we were able to make small changes to the design in order to better fit our requirements.

GLS - Lifting Mechanism

In the provided images, you can see the Graphical Linkage System (GLS) in both the up and down position. The image provided to the left has both the Up and Down positions in addition to all the obstructions which are involved in the process. The two images below are the individual positions to better view each. The labeled lengths have their respective dimensions near the bottom of each image.