14.1 Project Proposal
Introduction:
Our team is proposing to design a hand mechanism based on the “Thing” or walking hand from the show The Addams Family. Our hand design will simulate walking movement with three moving fingers propelling it forward while the thumb and the pinky will remain static to provide stabilization. We decided to pursue this project as it has complexity in the design mechanism as well as is an interesting project in terms of understanding a form of animatronic design. This project idea is particularly useful for understanding animatronic design and future applications in engineering projects in the themed entertainment industry.
Problem Statement:
The main mechanism problem focus on the movement of the fingers. The idea is to translate the rotational motion of a motor into an specific pattern that the tip of the fingers will have to follow to archive linear translation of the entire hand. This implies the following challenges and constrains:
It needs to simulate the movement of a real articulated finger
It is required an specific trajectory path that will determine the dimensions of the moving linkages.
The velocity output o the tip of the finger will have to be as constant as possible to generate a continuous natural movement.
The three fingers will have to be actuated only using 1 DOF (The action of one motor)
The tip of the fingers will need enough fiction to archive movent in a normal flat surface
Weight distribution and space management of the mechanical and electrical component will be key factor to consider.
Mechanism:
As a primary draft of the finger, its presented a five bar mechanism with one degree of freedom where the two rotary actuators have the same diameter and move in opposite direction representing a gear union.
To have an idea of the entire assembly, the next image present the 3 moving fingers precisely orientated to generate movement while the thumb and the pinky are fixed linkages to add stability.
To align the movement of the tree fingers having only one actuator, its planned to have a crank shaft which will be storage in the palm of the hand along with other electrical components as showed bellow.
Proposed Scope:
To address the mechanical challenge of our project, we will break it down into key components: fingers, the palm, and a thumb that serves as a fixed support point. The primary complexity arises from coordinating different timing motions for each finger using a single motor input to generate forward motion.
Our analysis will begin with positional analysis, which will be conducted using MotionGen, Python or MATLAB to optimize the motion of the fingers. In SolidWorks, we will determine the appropriate link lengths to ensure sufficient range of motion while maintaining proper weight distribution. This analytical phase is crucial to achieving both functionality and mechanical efficiency.
For the manufacturing process, we will:
Laser cut the linkages for the fingers.
3D print complex geometries, such as fingertips and the palm structure, to optimize design.
Incorporate bearings and shafts with a cam follower system to control the timing of finger movements.
Use a DC motor (voltage to be determined based on weight considerations).
Employ screws and fasteners for assembly.
The electronic system will include:
A basic control mechanism with an I/O button to operate the motor.
A power system consisting of a battery, coupler, and wiring.
Potential additional features: If time permits, we aim to explore integrating ultrasonic or haptic sensors to refine speed and direction control.
By the end of the semester, we aim to have a fully functional mechanical prototype with basic motorized actuation. The core analyses, including kinematics, weight distribution, and material selection, will be completed before fabrication to ensure a well-optimized design.
While our primary goal is to develop a mechanically sound and operational prototype, future iterations could explore. It would be interesting to control the motion speed and direction using ultrasonic or haptic sensors; if the times allow, we will be working on that as an extra feature. Additionally, our background in mechanical engineering and fabrication techniques provides an opportunity to refine this project beyond the scope of this semester.
Preliminary Design Ideas:
After modeling the assembly and path in MotionGen, we then designed our first physical prototype in SolidWorks with both the finger and knuckle gear mechanisms.
After designing and assembling our first design idea, there were some noticeable differences between how the prototype worked in the real world model as compared to the simulation model. We initially connected the links using screws and bolts but this caused gaps and out of plane motion to occur. Additionally, the finger tip link was not acting as first simulated. This led to the realization that if we simplified our model, using less linkages, and extended the triangle linkage (in the image above) to be the finger link, we achieved the desired path.