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Course

Computer-Aided Mechanical Engineering Design

Timeline

mitt rOMNI

A human-powered omnidirectional vehicle

Mar-June 2019

Team of

4

My Role

Mechanical Engineer

Challenge

To design and build a human-powered vehicle that can move in any direction while facing any direction and achieve a zero-turn radius. Vehicles were also required to fit within a 3'x3'x3' box and weigh less than 75 pounds.

Final Design

My team's final vehicle, named mitt rOMNI, features a drive system inspired by a handcar mechanism. It uses pedals to power a 3-bar linkage system that turns a set of sprockets to drive one of the front wheels while the other rotates passively. The pedals were offset by 90 degrees to prevent stalling at the top and bottom of each stroke. The front driver can move both forward and backwards, and this combined with two rear caster wheels allows our vehicle to achieve omnidirectionality.

The chassis is made of wood-foam composite and features several rows of slots so the chair can be inserted at different distances from the pedals to accommodate riders of different heights. 

Achievements

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Lightest Vehicle

Weighed only 57 pounds, with a 30 pound difference in the next ranked vehicle

Lowest material cost

Out of 5 teams, our vehicle had the lowest material cost

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Most Unique Drive System

While all other teams utilized bevel gearboxes, we achieved omnidirectionality with a unique linkage system

Ideation & Prototyping

Analysis

We started the brainstorming process by ideating various mechanisms to drive the vehicle​. One of our most promising ideas was a handcar-inspired design, so we created small scale laser cut and foam core prototypes to test its feasibility. These prototypes verified that this linkage system would work.

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After verifying that this mechanism would work, we used Sketch Blocks in Solidworks to determine the proper linkage ratios that would fit within the size constraint of the vehicle and not come in contact with the floor when driven. We also performed FEA on the chassis and other subassemblies of our vehicle. Based on these, we made adjustments to avoid failure and increase safety for riders. For example, through our FEA, we found that the front neck of our chassis experienced the greatest stress concentration under the load of a rider, so we reinforced that area by replacing the foam with a pine block.

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Fabrication

After finalizing our design, we machined our parts in the Thayer Machine Shop and assembled it with enough time to practice driving before race day. All of the wooden and foam parts were made using a Shopbot. The metal and plastic parts were machined on the mill and lathe.

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Thanks to my incredible teammates (left to right), Sharon, Rebecca, and Ellie!

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