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12.1- Project Proposal

12.1- Project Proposal

Introduction

  • Automation plays an important role in many manufacturing and packaging processes where objects must be repeatedly moved from one location to another. Robotic arms are commonly used for these tasks because they can perform precise and repeatable motions. The goal of this project is to design a robotic arm that can pick up an object and place it at a different location using a controlled mechanical system.

Problem Statement

  • The objective of this project is to create a robotic arm capable of performing a simple pick-and-place task. The system must move the end effector to the object, grasp it securely, lift it, and transport it to a second location where it will be released. This requires coordinated motion of multiple joints and sufficient gripping force to hold the object during movement.

Mechanism

  • The mechanism will have a grounded base with two links that pivot about the servo and a claw like hand which represents the output. The whole mechanism serves as a 4 bar mechanism. We plan on using servo motors for each joint and an arduino to control movement.
    Key challenges: claw mechanism (servo motor? rack and pinion? etc.), weight and stability 

Screenshot 2026-03-12 203953.png

 

Proposed Scope

  • We want to get our arduino coding system complete first so that we can confirm the movement of the servo motors with a joystick. We also need to get an understanding of the structure of the build and how exactly we want the claw mechanism to work. Certain analysis for complex motion we will need to do consists of angular displacement analysis for the joints and movement profiles. 

Preliminary Design

1. Overview of Proposed Mechanism

The proposed robot arm consists of two coordinated subsystems:

  1. A four-bar crank-rocker linkage that generates the up-and-down lifting motion of the claw assembly.

  2. A gear-driven claw mechanism that opens and closes the gripper.

The full system is powered by two motors. One motor drives the crank-rocker linkage, and the second motor drives the claw gear train. This separates the lifting and gripping functions into two independently controlled motions.

2. Four-Bar Lifting Mechanism

Kinematic Description

The lifting mechanism is modeled as a planar four-bar linkage with four revolute joints:

  • Link 1: ground

  • Link 2: input crank

  • Link 3: coupler

  • Link 4: output rocker

The input crank is driven by Motor 1, and the rocker supports the claw assembly. As the crank rotates, the rocker oscillates and raises or lowers the claw.

Mobility Using Gruebler Equation

For a planar four-bar linkage:

M=3(L−1)−2JM

where:

  • L=4

  • J=4

M=3(4−1)−2(4)=9−8=1

So the lifting subsystem has 1 degree of freedom.

Grashof Condition

The four-bar is intended to operate as a crank-rocker mechanism. The motion type depends on the Grashof condition:

S+L≤P+QS

where:

  • S is the shortest link

  • L is the longest link

  • P and Q are the other two links

S+L=3+10=13

P+Q=6+7=13

Since the linkage satisfies the equality condition, it is a change-point mechanism, meaning it will pass through a collinear configuration where motion may become indeterminate. In practice, the operating range will be limited to avoid this configuration.

Design Intent

The four-bar mechanism was selected because it:

  • converts rotary input into controlled lifting motion

  • provides a compact and analyzable arm motion

  • uses only one actuator for the lifting function

  • is simpler to fabricate than a multi-joint robotic arm

3. Gear-Driven Claw Mechanism

Kinematic Description

The claw mechanism consists of:

  • two outer gears connected to the claw arms

  • two middle gears that transmit motion from the second motor

  • Motor 2, which actuates the claw gear train

The middle gears are powered by the second motor and rotate the outer gears. Since the outer gears are attached to the claw arms, this causes the two jaws to rotate and open or close.

The purpose of this arrangement is to create symmetric jaw motion, so both claw arms move in a coordinated way about the centerline of the object.

Mobility

The claw subsystem has one independent input, which is the rotation of Motor 2. All other gear and jaw motions are constrained by the gear contacts and gear ratios. Therefore, the claw subsystem has:

M=1

So the claw mechanism also has 1 degree of freedom.

Gear Relationships

For meshing gears, the angular displacement relationship is:

θout=−Nin/Nout(θin)​

where:

  • Nin​ is the number of teeth on the driving gear

  • Nout​ is the number of teeth on the driven gear

This same ratio applies to angular velocity and angular acceleration. Because the gears reverse direction at each mesh, the output gears rotate in directions determined by the arrangement of the middle gears. Since the outer gears are connected to the claw arms, their rotation directly controls jaw opening and closing.

Design Intent

The gear-driven claw was selected because it:

  • produces synchronized motion of both jaws

  • keeps the object centered while grasping

  • is mechanically simpler than controlling each claw arm independently

  • provides a clear kinematic relationship between motor input and jaw motion

4. Combined System Mobility

The complete mechanism consists of two separate one-degree-of-freedom subsystems:

  • four-bar lifting mechanism: M=1

  • gear-driven claw mechanism: M=1

So the full system has:

Mtotal=2

This means the robot arm has two independently controlled degrees of freedom:

  1. vertical lifting motion

  2. claw opening and closing motion

5. Preliminary Design Intent

The design is intended to satisfy the project requirements while remaining simple enough to build and analyze. The mechanism uses:

  • one motor for lifting

  • one motor for gripping

  • a planar four-bar for arm motion

  • a gear train for synchronized claw motion

This allows the overall system to perform basic pick-and-place style tasks without requiring a complex multi-axis industrial arm.