1. The HOPPER: Engineering Analysis Update Team Meathead March 9, 2005

2. The Past Frequently asked questions –Updated the FAQ page to contain actual questions Layout drawings

3. The Present Engineering analysis: –Motor Selection –Bearing Analyses –Lid Design and Spring Selection –Materials Selection –Tolerance of critical components –Mass determination

4. Motor Selection Motor (N2738-083-G-3) –3.6V –3850rpm –4.55 mNm –0.97A –1.84W –52.6% efficiency

5. Bearings 2 bearings needed: –Rotor –Gear Rotor bearing must withstand: –Axial (thrust) force of balls (from forcing plate/spring) –Radial force: non-tangential component from torsion spring twisted by motor

6. Axial Force Force on rotor comes from spring attached to forcing plate Calculated to be 15.5 N (worst case) 15.5 * 2 (SF) = 31 N

7. Radial Force From torsion gear spring there is a component that will act radially: –Assume 90% efficiency in delivering torque tangentially –Consider max. torque of motor

8. Radial Force, cont’d Motor Max. torque = 4.4 x 10 -3 N-m With minimum radius of 0.75 inch, find tangential force of 0.231 N 0.231*0.1 = 0.0231 N 0.0231 * 2 (SF) = 0.0462 N

9. Bearing Calc. For plain bearings (per McMaster-Carr) –Pmax = (Max. load) / [brg length * shaft diam] –Vmax = (Max. shaft RPM) * 0.262 * (shaft diam) –Actual PV= (Actual load/[brg length * shaft diam]) * (Actual RPM) * 0.262 * (shaft diam)

10. Bearing Calc., cont’d Pmax = 74.3 psi Vmax = 24.6 fpm PVmax = 1826 SAE 841 Bronze brg with oil-impregnation –All three criteria met by factor of 20 or more –Cost: $0.43 each (cheapest avail.) –Suffices for both gear and rotor –Ball bearings can be investigated if needed

11. Ball Removal Mechanism Radius at which balls hit removal piece: –3.75/2 -.68/2 = 1.535 in. = 0.039 m T = r x F : –4.4 x 10 -3 N-m = (0.039 m) x F –F = 0.113 N –Material to be chosen and part to be designed using this as a max. force

12. Lid Design and Spring Selection Lid Design Dimensions Torsion spring design Inner and Outer Lids

13. Lid Design and Spring Selection

15. Lid Clasp

16. Gear Tolerances Gear and pinion clearances: –c g = c p = 0.0129 in. Gear and pinion pitch radii –r pg = 1.875 in. –r pp =.2968 in. Addenda –a g =.063 in. –a p =.0623 in. Center distance –C = 2.172 in. (+ 0.003 in, -0.0065 in.)

17. Materials Selection Body –Polypropylene ρ = 0.9 Mg/m 3 Price = $1.00/kg Young’s Modulus = 1.2 GPa Wear Resistance, Average Lid (both parts) and Rotor –Phenolic ρ = 1.3 Mg/m3 Price = $1.50/kg Young’s Modulus = 7.8 GPa Wear Resistance, Average

18. Mass Determination Volumes from CAD * material selection densities Mass of batteries found on web ~600g empty (with lid)

19. Mass properties of Hopper Body: Output coordinate System: -- default -- Density = 0.9 grams per cubic centimeter (Polyproplene) Mass = 93.32 grams Volume = 103689.36 cubic millimeters Surface area = 79983.97 square millimeters Mass properties of Rotor: Output coordinate System: -- default -- Density = 1.3 grams per cubic centimeter (Phenolic) Mass = 132.26 grams Volume = 101741.33 cubic millimeters Surface area = 34221.39 square millimeters DC motor Mass = 60-70 grams Batteries Mass properties from Panasonic Industrial Alkaline Battery Technical Specifications AAA = 12 grams AA = 24 grams C = 70 grams D = 141 grams Preferred setup with 6 AA batteries = 144 grams Mass properties of Rotor Gear Output coordinate System: -- default -- Density = 2.7 grams per cubic centimeter (Al 6061-T6) Mass = 122.17 grams Volume = 45247.39 cubic millimeters Surface area = 16151.30 square millimeters Total Assembly Mass = 562 grams

20. The Future Full CAD model Yet another research outing Further design refinement