Skateboard Wheels - PowerPoint PPT Presentation

Loading...

PPT – Skateboard Wheels PowerPoint presentation | free to view - id: 260d69-ZTBiZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Skateboard Wheels

Description:

From the first push forward on a home driveway to intricate freestyle routines ... On rougher surfaces, such as tarmac or concrete, an important additional factor ... – PowerPoint PPT presentation

Number of Views:166
Avg rating:3.0/5.0
Slides: 25
Provided by: daniel528
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Skateboard Wheels


1
Skateboard Wheels
  • Case Study
  • CHE 620

2
Introduction
  • From the first push forward on a home driveway to
    intricate freestyle routines in a purpose-built
    park, and at all levels in between, skateboarding
    is a very exhilarating and fun-filled activity.
  • In synthesizes the best features of many sports,
    including surfing, skiing, dance, gymnastics, and
    martial arts, combining strength, grace, and
    concentration.

3
Main Parts of a Skateboard
  • Three main parts
  • the deck or flexboard
  • the wheels
  • the truck

4
Main Parts of a Skateboard
  • Common skateboard decks
  • (a) basic flat board
  • (b) kicktail board for rear foot leverage
  • (c) rocker board for lower center of gravity
  • (d) cambered board for slalom and downhill racing

5
Main Parts of a Skateboard
  • Common deck materials
  • wood (ash, teak, oak)
  • polymers (polypropylene, polycarbonate)
  • composites (glass fiber reinforced epoxy resin)
  • wood and fiberglass combinations
  • aluminum and its alloys

6
The Wheels
  • Modern skateboarding probably would not be
    possible without major advances in both the
    design of the wheels and the materials used in
    their manufacture.
  • The wheels generally range in size from 29 mm
    width by 38 mm diameter to 58 mm width by 67 mm
    diameter.

7
The Wheels
  • The wheels contain either loose ball bearings or
    double-sealed precision bearings.
  • The former have the disadvantage of requiring
    regular lubrication and the possibility of the
    wheels being slowed by sand, road grit, and other
    particles.

8
The Wheels
  • Connecting the deck to the wheels is a steering
    and suspension system called a truck.
  • While trucks come in different designs, they all
    feature shock absorbers of elastomeric or
    polymeric bushings or cushions or metallic coiled
    springs.
  • Some trucks are adjustable in length and can be
    tightened or loosened to accommodate the weight
    of the rider.

9
The Wheels
  • Various parts of the truck are made of cast iron,
    forged iron, heat-treated aluminum, or steel.
  • (a) standard wheel with open loose bearings
  • (b) flex wheel with double-sealed precision
    bearings

10
Materials Selection Considerations
  • To perform satisfactorily, the materials for the
    wheel (and bearing assembly) must have the
    following characteristics
  • lowest possible rolling friction resistance, in
    order to maximize the speed of the skateboard
    (the primary requirement)
  • high frictional resistance to lateral movement
    (important for slalom and freestyle motions)
  • good shock absorption qualities to make riding on
    rough surfaces more comfortable
  • high resistance to abrasive wear
  • high resistance to corrosives such as lubricating
    oil

11
Materials Selection Considerations
  • At right is shown the contact stress on a
    perfectly elastic wheel in motion on a rigid
    surface and carrying a static load.
  • Upon rolling, one part of the flat suffers an
    increase in strain while the strain on other
    parts is reduced.

12
Materials Selection Considerations
  • For real materials, however, the stress in the
    section of the flat where the strain is
    constantly decreasing lags behind that in the
    other section of the flat, resulting in a stress
    distribution as shown at right.

13
Materials Selection Considerations
  • The final outcome is that the center of pressure,
    O, moves forward of the center of the wheel O by
    a small amount s, giving rise to a bending
    moment, Ps, that resists rolling.

14
Materials Selection Considerations.
  • The rolling resistance force R is the equivalent
    force acting at the center of the wheel in the
    direction opposite to the bending moment

where Dw is the diameter of the wheel
15
Materials Selection Considerations
  • The coefficient of friction, mrs is thus

16
Materials Selection Considerations
  • Some knowledge of s is needed in order to
    estimate mrs from the above equation.
  • For a perfectly elastic wheel material, s 0.
  • For a worst case material, with the stress
    distribution shown at right, s ac, where c is
    the half-width of the flat and a is a numerical
    constant.

17
Materials Selection Considerations
  • For many real materials, therefore, we can
    assume that, as a first approximation,
  • s a(1-A)c
  • where A is the percentage rebound and is equal to
    the square of the coefficient of restitution e of
    the wheel material.

18
Materials Selection Considerations
  • Now

where b is a numerical constant, usually about
0.8, h is the width of the wheel, and Eef is the
effective modulus of the wheel.
19
Materials Selection Considerations
  • Eef is given by

where Ew and nw are the modulus of elasticity and
Poissons ratio of the wheel material,
respectively, and Ers and nrs are
the corresponding values for the road
surface material.
20
Materials Selection Considerations
  • From the above, we can obtain an expression for
    mrs

21
Materials Selection Considerations
an examination of the above shows that, for a
given wheel with specified values of wheel area
(h x Dw) and wheel load P, the primary design
requirement of low friction may be obtained by
using a material with high values of modulus of
elasticity and coefficient of restitution
22
Materials Selection Considerations
  • On rougher surfaces, such as tarmac or concrete,
    an important additional factor affects friction,
    which leads to a reconsideration of the desirable
    properties for a wheel material.
  • Upon rolling over a rough surface, the wheel load
    will be supported on road asperities where the
    contact pressure is high.
  • The resulting penetration must be countered by
    the elastic deflection of the wheel if energy
    loss and friction are to be minimized.
  • This requires a wheel material with a large
    elastic strain and high elastic modulus, with the
    former becoming more important as road roughness
    increases.
  • For a rough surface, mrs is increased by about
    50 (mrs 1.5mrs)

23
  • From the above, the best material from the
    viewpoint of both mrs and mrs is glass fiber
    reinforced polyimide.
  • However, because of its relatively high cost, low
    shock absorption qualities, and relatively low
    wear resistance, the material currently favored
    for the construction of skateboard wheels are
    hot-cured polyether-based polyurethanes.

24
The End
  • The End
About PowerShow.com