Thomas GutierrezAustin ShoemakerShane Upchurch

Ryan KaysenJoey Miller

Kevin Liekweg

Engineering Analysis

Mobile Laptop Desk

Agenda

• Free Body Diagram• Free Body Analysis• Deflection Analysis• Materials Selection

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Free Body DiagramAy

AxPmax

S

Sy

Sx

SSx

Sy

Fbb

Fbj

Cy

Cx

B

Flw

A

B D E

12”

14.5” 14.5”

P

Ѳ

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Free Body Analysis"These are the given weights in the system"W_b=5 [lbm] "weight of the back pack"W_bj=4 [lbm] "weight of the arms"W_lw=25 [lbm] "weight applied at the laptop center of gravity“

"These are the given dimensions of the apparatus"L_v=15 [in] "vertical distance of back brace"L_1=14.5 [in] "length of first arm"L_2=14.5 [in] "length of second arm"L_lw=0 [in] "center of gravity correction for weight of laptop"L_b=3 [in] "center of gravity correction for weight of book bag"L_t=L_1+L_2

B = Force on waist of userP = Force on shoulders of user

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Free Body Analysis

Summation of moments around top of shoulder straps:(1/3)* Lm_v*P-Lm_b*F_b-Lm_v*B+Lm_1*F_bj+(Lm_t-

Lm_lw)*F_lw-Lm_v*C_x=0

Summation of moments around bottom of should straps:(-2/3)*Lm_v*P+Lm_v*A_x-Lm_b*F_b+Lm_1*F_bj+(Lm_t-

Lm_lw)*F_lw=0

Summation of moments around arm joint D:(-2/3)*Lm_v*P+Lm_v*A_x-(Lm_1+Lm_b)*F_b+(Lm_2-

Lm_lw)*F_lw+Lm_1*C_y+Lm_1*A_y=0

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Free Body AnalysisWorst CaseWith laptop center of gravity (L_lw = 0 [in]) at max distance from user and backpack weight, W_b = 5 lbm.B = 192.3 [N] (roughly 43.1 lbm on waist of user)P = 342.5 [N]No Laptop CaseWith backpack weight, W_b = 5 lbm, and with no laptop placed on apparatus.B = 15.04 [N] (roughly 3.4 lbm on waist of user)P = 71.13 [N]Backpack Weight CaseWith backpack weight increased (W_b = 20 lbm) (i.e. several books in bag) and laptop on apparatus at L_lw = 4 [in].B=59.76 [N] (roughly 13.4 lbm on waist of user)P=277.8 [N] Realistic CaseWith laptop center of gravity 4 inches from end of arms (L_lw = 4 [in]).Also backpack weight increased slightly (W_b=10 lbm) (i.e. about one book).B=118.6 [N] (roughly 26.6 lbm on waist of user)P=291.2 [N]

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Deflection Analysis

EI

PL

3

3

)(64

44io ddI

• E = 10000 ksi• P = Load of laptop (At End of Beam)• L = Length of arms (Joint assumed to be rigid)

• Do = Outer diameter of tubing

• Di = Inner diameter of tubing

(Using Aluminum)

Introduction

Free Body Diagram

Free Body Analysis

Deflection Analysis

Materials Selection

Deflection Analysis

• Aluminum tube with 7/8 inch outer diameter and 1/8 wall thickness.

• Deflects 2.25 inches with 60 pounds at end of beam (29 inches)

• Arms: Aluminum Tube 7/8 inch with 1/8 inch wall thickness

• Joints: Plastic• Table: Lexan• Back Support:

Plastic

Introduction

Free Body Diagram

Free Body Analysis

Materials Selection

Materials Selection

Deflection Analysis

Questions?