Mechanical Arm Project

Project Summary: Worked on a team of 5 to design and test a functioning mechanical arm across 4 phases, using the skills and techniques that were learned in my Mechanical Design class to achieve the goals. The end goal of the mechanism is to pick up a designed payload in one given position and rotate in order to drop off the payload in another given position.

Phase 1: Payload Design

In this phase, the team collaborated on drawing and considering various designs. From these, one would be selected to be printed and used for the remainder of the project. The design that was selected was a bottle cap design based on a YETI Tumbler. Below are the detailed modeling constraints and mass properties.

Modeling Constraints

Bounding Box including Dimensions

All dimensions are under 1.5 in.

Estimated Mass in Cura

Estimated mass is 8.5 g.

Mass Properties of Payload

Estimated value is 1.06 cubic inches

Link to Files

Link to SLDPRT file: https://drive.google.com/file/d/1JojN3HcNy3xnkfNHBNVgES-PimOWl6UU/view?usp=sharing

Link to STL file: https://drive.google.com/file/d/1FkzRfjY9wJwSK0cIBe16TfTYL6VHts1c/view?usp=sharing

Phase 2: Grasping Mechanism

In this project phase, we designed and tested a Grasping Mechanism for a mechanical arm, considering design constraints and movement simulation. We created detailed renderings for pre-assembly visualization and followed specific instructions for electronic assembly and soldering. The mechanism was then tested through a predefined lifting sequence to ensure its functionality and effectiveness.

Design Constraints

Explicitly stated constraints: Must have at least one four-bar linkage. Must be able to mount to the test rig, and will be actuated by one 180 degree servo motor. Pieces should be made of 1/4" plywood cut using the laser cutter. Must be able to perform the steps described in the testing portion of the assignment.

Implicit constraints: Needs to at least be able to pick up the payload that was designed in Phase 1. Best case scenario would be able to pick up the payload of every group.

Team imposed constraints: Should be a type of grasping mechanism that performs a sweeping action to pick up the payload rather than a grabbing action, this way would give the team a better chance of being able to pick up other teams payloads as well as their own.

Alex's Sketch

After considering the pros and cons of each design, the group chose to use Alex's sketch as the design for the grasping mechanism. His design would have the most ease with picking up payloads, and it should not be too difficult to replicate in SolidWorks and then assemble in the class.

Degrees of Freedom Analysis

Graphical Linkage Synthesis (GLS) for Grasping Mechanism

Design Renderings

Open Position

Closed Position

Open Position

Closed Position

Grasping Mechanism Summary

The design chosen uses a sweeping motion to grasp the payload, which the team decided would be best for testing, since it should be able to pick up various payloads. The mechanism has one side which will be in motion, and one side which stays stationary, which should reduce the chance of error in grasping.

Phase 3: Lifting Mechanism

The goal of this phase is to create a lifting mechanism to lift our grasping mechanism and payload designed earlier in this project. The group will design and compare the various designs to choose which one to continue with. We will then have to make a graphical linkage analysis of the winning design to prove that the motion works. Afterwards, the mechanical advantage will have to be calculated to determine if the motor can lift the entire arm and grasping mechanism. After a design is made and proven to work, we will model and create the design to test the arm mechanism.

Design Constraints

Explicitly stated constraints: The lifting mechanism must have at least one four-bar linkage in its design. It should not require any additional counterweight to move the arm. The arm is going to use a servo motor like in Phase 2 that turns 180 degrees. The lifting mechanism must be supported by the 1” x 2” post on the testing rig. The pieces should be made out of 1/4" plywood similar to the Phase 2. Wire must be secure to prevent them from tangling during testing.

Implicit constraints: The arm should be able to lift up the grasping mechanism while the grasping mechanism holds the payload. The hope is to make a design that allows the team to not make any changes to the previous design for the grasping mechanism.

Team imposed constraints: The team wants to design an arm that has the servo motor located on the opposite end of the stand.

Kevin's Sketch

Degrees of Freedom Analysis

Graphical Linkage Synthesis (GLS) for Arm

Up Position

Down Position

The design employs a servo and crank that are positioned on the opposite side of the mast from the claw from phase 2 and payload from phase 1 in order to maximize the torque able to be applied about the rocker pin. This design has only 3 physical links, which helps to keep everything simple when designing and assembling the parts.

Mechanical Advantage Calculations

Image of GLS in up and down positions with instant centers and dimensions used in calculations.

Sample Calculations for Mechanical Advantage

MATLAB script used to calculate mechanical advantage and torque values for up and down positions

MATLAB Output for Up Position

MATLAB Output for Down Position

Design Renderings

Photo of Lifting Mechanism

Phase 4: Rotation Mechanism

The goal of this phase is for the team to design a shoulder mechanism that rotates the lifting mechanism, grasping mechanism, and the designed payload from the previous 3 phases. The payload will be picked up at one position, and dropped off at another given position after the mechanism is rotated.

Design Constraints

Explicitly stated constraints: A rotary table driven by gears and being powered by a servo should be used to rotate the mechanism. This should be able to rotate at least 150 degrees, and be able to rotate through the 108 degree pick-up and drop-off sequence. An MDF circle is given to mount the base to, and pick-up and drop-off zones are also given.

Implicit constraints: The rotation mechanism designed should be able to move the arm and claw from previous phases and stop moving when instructed to do so. Plywood was used to create the gears. Acrylic is to be used for the spacers and the external design. The new tower and servo table are to be 3D printed using PLA filament. Any other parts are to be cut from plywood.

Team imposed constraints: The mechanism should also rotate at such an angle that a payload can be passed in a circle by all of the class team's mechanisms.

Gear Train Calculations

As shown in these calculations, the claw can rotate up to 172 degrees and the lifter assembly can easily move between the pick up and drop off angles, which are 108 degrees apart.

2D Plan of Gear Train