By: Noemi Y. Rodriguez

Antonio GallozaLevi L VargasJulio Alvarez

Objectives In this project we were told to design the

shaft that joints the two pedals of a mini-stepper that could support a maximum weight of 250 lb. by analyzing combined loads and stress concentrators. We should take in consideration the type of material to be selected, deflections and deformations in the material. We will be also considering finite life, the critical section and safety factors of the components.

Mini-Stepper

Design Details

Why do we design this device, what is its application?

We design this device because it’s something that we have in our daily use.

A mini-stepper helps people maintain a healthy life exercising themselves.

What are the most important engineering considerations in our design?

MaterialSafetyCosts

Design

Stress Analysis (Static Load)

Bendings:σx=Mc/Iσy=Mc/I

Shears:τx=4V/3Aτy=4V/3A

Torsions:Due to the sleeve the:

Torsion→0Sleeve

Stress Analysis (Static Load)

Bending Stresses

X Mc

I

X 340lb. in 1.0in.

2

4

1.0in.

2

4

0.90in

2

4

X 10070.4029Psi.

Y Mc

I

Y 588.92lb. in 1.0in.

2

4

1.0in.

2

4

0.90in

2

4

Y 17442.449Psi.

Stress Analysis (Static Load)

Shear Stresses

X 4V3A

X 4 85lb.

3 0.14922565in.2

X 759.47622Psi.

YZ 4V3A

YZ 4 147.53lb.

3 0.14922565in.2

YZ 1315.4514Psi.

Stress Analysis (Static Load) Von Misses Stress

VM X Y 2 Y Z 2 Z X 2 6 XY

2 YZ2 ZX

2 2

VM 24253.3751Psi.

Stress Analysis (Static Load) Safety Factor

n Y

VM

n 60,200Psi.

24253.3751Psi.

n 2.48

Deflection Analysis

EIV=F EIM=EI∫Vdx EIθ=EI∫Mdx Eiv=EI∫θdx

Deflection Analysis Force component Fy Force component Fx

0.006414in2

22.1476

22.147

00,02

22.1476

22.147

22.1472

22.147

00,0

22.1472

22.147

22.147*22.147

22.1470,

*22.147

22.147

max

23

3

3

23

2

2

2

2

1

1

v

xL

xEIv

Cvx

Cx

Lx

EIv

Lxx

EIangulo

Cangulox

CLxx

EIangulo

LxEIM

LCMLx

CxEIM

lbEIV

0.003703in2

856

85

00,02

856

85

852

85

00,0

852

85

85*85

850,

*85

85

max

23

3

3

23

2

2

2

2

1

1

v

xL

xEIv

Cvx

Cx

Lx

EIv

Lxx

EIangulo

Cangulox

CLxx

EIangulo

LxEIM

LCMLx

CxEIM

lbEIV

Deflection Analysis

Overall

0.007407in2

1706

170

00,02

1706

170

1702

170

00,0

1702

170

170*170

1700,

*170

170

17080250

max

23

3

3

23

2

2

2

2

1

1

v

xL

xEIv

Cvx

Cx

Lx

EIv

Lxx

EIangulo

Cangulox

CLxx

EIangulo

LxEIM

LCMLx

CxEIM

lbEIV

lbFy

Material Selection

Material IndexesM=Cvr/E^(1/2)M=Cvr/σf^(2/3)

Has to be minimized

Material Selection

Material Selection

Material SelectionMaterial Modulus E GPa Fracture Strength MPa Relative cost Cvr

Al Alloys 70 190 .9

Steel 1040 200 450 .75

Cast Iron 150 690 .65

For Al Alloy For Steel 1040 For Cast Iron

Dynamic Load Analysis

For the Stress concentration

Endurance LimitSe=ksize*ksurface*kload*ktemperature*

kreliability*Se’

Dynamic Load Analysis

Endurance LimitSe=(0.957092)*(0.819629)*(0.7532)*(44.95)

=26.5519ksi

Component live: 10^6 Cycles

Dynamic Loads Analysis Stress concentration factor

Kt,bend=1.62

Kt,shear=1.35

Kf,bend=1.52

Kf,shear=1.29

Dynamic Load Analysis

Fmax,Fmin

Dynamic Loads

Fa,Fm

Dynamic Load Analysis

Dynamic Load AnalysisPoint A

Point B

Dynamic Load Analysis

Safety Factor (Modified Goodman)

What is the unique part of our project?

In our project we analyzed a shaft for a mini-stepper, the unique part comes when four minds merge to achieve the goal of a design of a safety shaft.

What is the most challenging part in our project?

Determine the outer and inner diameters of our shaft to obtain an appropriate safety factor without overdesign

What is the weakness of our project?

The weakness of our project is that in a long period of time, the corrosion will affect our shaft due to the selection of an inexpensive material.

What we learn from this project?

Team workDesign is not just stetic, but is a more

complex analysis on which men life depends

QUESTIONS?