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Redesign for Sustainability:

Detailed Design and Design Verification of Personal Mobility Device

D4S-1

Sebastian Mukuria, Jerry Tsu

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TABLE OF CONTENTS

Design Requirements

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Sustainability

Problem Statement

Approach to Solution

Detailed Design & Design Verification

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Detailed requirements that we decided upon for our design

Define sustainability and our project’s approach to sustainability

Here we describe the problem statement used to develop our design

Steps and methods used to reach our desired design

Final design and methods used to verify our design

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“Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. “

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—UN World Commission on Environment and Development

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Sustainability

Our sustainability approach is threefold:

  • Reduce Cost
  • Increase Lifespan
  • Use less material in product

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Problem Statement

Last-mile Problem

Our Design Goals

Our Design Plans

Our goal is to design a product that is portable, affordable, able to be used by most people, safe, and uses minimal materials in the design.

Current last-mile solutions like micro mobility devices and rideshare services present issues in carbon emissions and safety

Our design plans to address these issues by making a product that is widely accessible to users who currently use other last mile solutions

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Design Requirements

  • The price will be set at under $600
  • Carbon emissions under 110g CO2 / mi ridden
  • Capable of traveling at speeds of 10 mph
  • Capable of accelerating to 10 mph within 10 seconds
  • Capable of traveling up 10% grade hills at 5 mph
  • Capable of traveling 10 miles on a single battery charge
  • Weigh 10 lbs or less
  • Less than 4 inches in height

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Approach to Solution

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Concept Generation

Morphological chart created 6 potential solutions

Functional decomposition was used to identify design restrictions and requirements

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6-3-5 method was used to generate concepts

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Decision Matrices

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Concept Design 1

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Concept Design 2

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Concept Design 3

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Detailed Design & Virtual Prototyping

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Chassis

  • Dimensions: 13.5” x 14” x 1”
  • Machined from 1060 Alloy
  • Internal component casing printed out of ABS

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Controls

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Controls

The Arduino sends power into the Velostat sensor, which sends a signal back to the arduino and subsequently to the electronic speed controller (ESC) as a pulse width modulation signal. The power supply goes through the electronic speed controller, and then to the motors. The ESC then sends an appropriate voltage to the motors which turns the wheel.

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Turning left or right on the device comes down to the differential between the left and right pressure pads; depending on the magnitude of the difference, the inner turning wheel slows down and the outer turning wheel accelerates to achieve a turn.

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Controls

  • Velostat Pressure Sensors
    • Velostat is a piezoresistive material, meaning its electrical resistance decreases when pressured.
    • You can make a sensor with it by sandwiching the material between two wires or metal surfaces.
    • When you run a current through it, you can change the voltage by applying pressure. This voltage output is sent to the arduino.
    • Cheap and effective

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Battery

  • LiPo Battery Pack
  • 10s4p (10 in series, 4 in parallel)
  • Estimated energy output (185Wh)
  • 37V(nominal) - 42V (max)
  • According to calculations, allows for nearly a 10 mile range.

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Motor

  • Device will be powered by 2 motors that are incorporated directly into the hub of the two front wheels
  • 90mm - 3.54inches
  • Max Torque = 14.32 Nm

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Design Verification Methods

  • Static stress analysis modeling of critical components
    • Can our device appropriately handle the weight of a 150 lb rider?
  • Dynamics verification and testing
    • Can our device achieve our speed and acceleration requirements based on the components we selected?
      • 10S4P LiPo Battery
      • (2) 90mm 100Kv Dual Hub Motors
      • 150 lb, 5’8 Rider

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Stress Analysis: Chassis

  • A simple static stress analysis was done to verify if the chassis and other critical components could withstand our design requirement of a 150 lb rider
  • The chassis had a maximum stress value of approximately 400 Psi, which is under the yield strength of 1060 aluminum (70000 Psi) by a factor of 10
  • The motor component saw a maximum stress value of 33 Psi, which is under the yield strength of ABS (7000 Psi)

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Dynamic Modeling

Assuming 5’7, 150 lb rider

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Te - torque = IaKT

Ia - Pack Constant Discharge Current

KT - Torque Constant of Motors

FT = Fi + Fs + Fr + FD

FT - tractive force = Te / rwd

Fi - inertial force = ma

Fs - slope force = mgsin(θ)

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Fr - road load force = mgcrcos(θ)

FD - Drag force = ½ ⍴cdAv2

a = 1/m [FT - (Fs + Fr + FD)]

v = 1/m ∫ [FT - (Fs + Fr + FD)]dt

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Dynamic Modeling

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Dynamic Modeling

Velocity vs Time (varying slopes)

Acceleration vs Time (varying slopes)

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THANKS

Does anyone have any questions?