Thomas Gutierrez Austin Shoemaker Shane Upchurch Ryan Kaysen Joey Miller Kevin Liekweg

1. Mobile Laptop Desk Engineering Analysis Thomas Gutierrez Austin Shoemaker Shane Upchurch Ryan Kaysen Joey Miller Kevin Liekweg

2. Agenda Introduction Free Body Diagram • Free Body Diagram • Free Body Analysis • Deflection Analysis • Materials Selection Free Body Analysis Deflection Analysis Materials Selection

3. Free Body Diagram Introduction Ay Ax Free Body Diagram A Pmax S Sx P Free Body Analysis Sy 12” Deflection Analysis Sy Fbb Cy Sx S Materials Selection Ѳ Cx B D E B 14.5” 14.5” Flw Fbj

4. Free Body Analysis Introduction "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 user P = Force on shoulders of user Free Body Diagram Free Body Analysis Deflection Analysis Materials Selection

5. Free Body Analysis Introduction Free Body Diagram 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 Free Body Analysis Deflection Analysis Materials Selection

6. Free Body Analysis Introduction Worst Case With 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 Case With 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 Case With 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 Case With 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] Free Body Diagram Free Body Analysis Deflection Analysis Materials Selection

7. Deflection Analysis Introduction Free Body Diagram • 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 Free Body Analysis (Using Aluminum) Deflection Analysis Materials Selection

8. Deflection Analysis Introduction Free Body Diagram • 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) Free Body Analysis Deflection Analysis Materials Selection

9. Materials Selection Introduction Free Body Diagram • Arms: Aluminum Tube 7/8 inch with 1/8 inch wall thickness • Joints: Plastic • Table: Lexan • Back Support: Plastic Free Body Analysis Deflection Analysis Materials Selection

10. Questions?