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A Playful Robot

Creative Fields

Engineering

 

Course or Client

ENGS 76 Machine Engineering

 

Completion Date

Fall 2014

 

Skills

Mechanical Design                    Milling, Lathing 

SolidWorks Certification             Power transmission                             

Machining

Analysis & synthesis of mechanical components & sysems

                        

Challenge: To design and built a playful robot to navigate a four part challenge course.

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The Great Blue Heron in Competition
ENGS 76 Team

Overview

 

   To design and manufacture a remote controlled robot using limited materials to navigate a four part obstacle course. We developed requirement specifications based on the obstacles to drive our ideation and design process.  The overarching goal was to develop our understanding of the machine design process, and to develop competency in mechanical CAD design and machining to specification.   

 

My Contribution

 

  • Created over 25 iterative design with sketches, foam core, SolidWorks, and machining

  • Led chassis and gearbox design, manufacturing and full assembly

  • Calculated optimal gear ratio, and fits necessary for bearings and bushings

  • Created chassis and gearbox engineering drawings, compiled final report

 

Design Process

 

   Initially, our team brainstormed and prototyped competing designs. Image 1 is my initial design, which my team chose to pursue for the final competition. It was chosen over the other designs specifically because the low-to-the-ground chassis, parallel motor configuration, and gear box design optimized space in a small footprint for the maze, and maintained low center of mass for the slope and teeter-totter.

   To optimize the gearbox ratio for our desired torque and speed specifications, I developed a flexible excel model which suggested the gears necessary to achieve desired velocity and Newton-meter inputs.

   Furthermore, I used a flexible CAD assembly of the motor and selected gears (3) to fit the gearbox between the wheels (2), keeping the vehicle narrow. Knowing from previous competitions that access to the gearbox is important for refinement and repair I placed it accessibly on the outside of the chassis wall, and secured the chain on sprockets outside the wheels to make the chain easy to remove. 

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Strategy

 

  Our team decided to tackle three hard challenges, the maze, teeter-totter, and slope. We rapidly iterated our prototype to meet the key design constraints based on this strategy.

 

Design Constraints

 

  • Two Mabuchi motor drive system & high gear reduction provides both necessary speed and torque, mitigates need for a differential

  • Maneuverable steering through tank drive system

  • Small 10”x 7” footprint enables vehicle to fit through the hard maze

  • Low center of mass maintains stability over the teeter-totter and slope challenges.

  • Rigid chassis enables precise meshing of the gearbox for efficient power transmission and smooth driving

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Prototyping
Rough. Iterative. Fail early, fail often.
First Foam Mockup
Laser cut prototype
Precision Axle Placement
Alternate Design
SolidWorks Gear Box
Wheel friction and force stackup
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Manufacturing

 

  One of our key specifications was ease of manufacturing. In designing the chassis I thought carefully about the aluminum plate thickness, 1/8” versus ¼”.  Eighth inch minimizes weight, but quarter inch is thick enough to tap a 3/16th screw hole.  I also knew that a rigid chassis was important for precise gear meshing.  This forethought enabled our team to easily assemble and disassemble our design for quick changes and refinement. 

 

Analysis 

 

  Even though our team scored third place out of ten, we had set higher expectations.  Based on practice laps, and our first lap time in under 50 seconds, our design was competitive for first place.  In the middle of our third lap our wheel axle sheared off and we lost a wheel, rendering our vehicle inoperable. Ultimately this offered me an excellent opportunity to assess the failure and to understand how to produce a more reliable design in the future.

 

Competion Day | Team featured at 0:09 and 0:37 sec

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© 2017 by Hilary Johnson

Laser cut prototype