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Week 9 Detailed Design Review

Week 9 Detailed Design Review. P13211 - Rimless Wheel (Wired). Customer needs. Engineering Specs. Risk Management. Risk Management. Detailed Block Diagram. Old Design (motor to shorten string). motor would rotate to shorten the string, and increase the extension of springs

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Week 9 Detailed Design Review

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  1. Week 9 Detailed Design Review P13211 - Rimless Wheel (Wired)

  2. Customer needs

  3. Engineering Specs

  4. Risk Management

  5. Risk Management

  6. Detailed Block Diagram

  7. Old Design (motor to shorten string) • motor would rotate to shorten the string, and increase the extension of springs • Based on simulation, we would be using K=5 N-m/rad & 1*pi rotation for initial condition • This equates to ~15.7 N-m or ~139 in-lbs • For our design, we would need to apply a torque greater than this at approximately 400 RPMs

  8. The Problem • 400 RPMs at 15.7 N-m of torque is ~657 Watts • With a cost of transport of .1, using our frame design weights and distance traveled, and assuming 1 second step time, we would be able to use 1.59 watts per step

  9. The Problem (cont'd) • Assuming the following (untrue): • motor has speed up time of 0 seconds • at full torque, motor will run at full RPMs • the sensors and all electronics use no energy • the clutch system uses no energy we can only actuate this for 2.4 thousandths of a second • Over this time period, we would only be able to rotate our motor .016 revolutions, much smaller than we were aiming for • We need to change something

  10. The Fix • Decided to go with our initial idea of attaching the motor axle to the bike wheel • At the beginning of MSD1, we could not figure out a way of doing this, because we had to go through the axle to do this • 13212 (Wireless team) provided the solution of rotating the entire axle • This change was extremely beneficial • Required the change of 2 parts, addition of 1 sleeve, and addition of 2 bearings • allowed for the removal of 13 parts and simplification of 2 more parts

  11. Equation of Motion Single Stance

  12. Equation of Motion Double Stance

  13. Computational Simulation Equations of Motion Actuation: In single stance Angular speed of the wheel Add a constant torque Reaction forces changed Maintain double stance during actuation

  14. Simulation Results

  15. Control Algorithm

  16. Frame Plates • Carbon fiber over foam • Order all materials from Noah's Marine Supply • Machine shop will cut out design • We will lay carbon fiber and resin • Very rigid • Holes for plastic inserts so we do not crush foam in compression (from fasteners) part number: 1-4

  17. Plastic Inserts • Self made - Delrin • Lightweight & Rigid • Purpose is to keep fasteners from crushing foam when tightened • 10 of the small ones (on the left), one for each side of the braces • 1 of the large one (on the right), for the mounting plates on the bike wheel side part number: 34 & 35

  18. Brace Assembly • Thin walled steel tubing • Aluminum insert press fitted into tube • Thread screw into aluminum insert to attach to frame plates • Provides rigidity to frame • Tubing from McMaster Carr/inserts from Machine shop or McMaster Carr part number: 11 & 38

  19. Brace Assembly Calculations • Calculated for bending and shear of tubing • Worst case: one frame would see 12.6 N-m or 115.5 in-lbs of torque • Spreading that out over 5 braces, each brace would see (12.6 N-m)/[(.3556 m)*(5 braces)] = 7.09 N or 1.59 lbs • This force would result in a flex of 0.0682 deg (0.032 in) over the length of a tube • This results in 37 Mpa of stress, but failure would not occur until over 250 Mpa part number: 11 & 38

  20. Fasteners • Free from Machine shop • 1/4"-20 x 1" allen wrench cap screws • 1/4"-20 hex nuts • 1/4" washers • usable for almost all applications (if unusable, simply get a large size) • current design calls for: • 20 cap screws • 40 washers • 10 hex nuts part number: 15-17

  21. Mounting plate (motor side) • Aluminum - machine shop • 5, 1/4" holes to mount to frame • Designed to reduce the chance of crushing the plates with our fasteners • Machine shop has said this will be an easy job • can be relatively flimsy as it is not seeing anything other than compression part number: 5

  22. Mounting Plates (bike wheel side) • Aluminum - Machine shop • Two purposes: • Press fit the bearing into the left mounting plate • Prevents the fasteners from crushing the foam plate • Similar dimensions, except for the right plate has a slightly smaller hole, to better house the bearing (lip will cover bearing by .075 inches) • can be relatively flimsy as it is not seeing anything other than compression part number: 5 & 6

  23. Axle (for bike wheel) • Aluminum - self made • Bike wheel rigidly fixed onto axle • possibly press fitted • possible clip depending on bike wheel we use • Threaded end to attach to sleeve (to motor) • Additionally, bearing sleeve will be pin set onto axle part number: 10

  24. Axle (for bike wheel) Calculations • Assume worst case • All torque in wheel is now in frame at time of collision • Max speed of frame and wheel is 1.29 m/s • Assuming .001 meter impact distance, frame would see (1/2)*m*v^2/s = 2.28 kN • Our axle can handle (25.5e9)(pi)(.009525)^2/4 = 1817 kN in shear part number: 10

  25. Axle sleeve (to bearing) • Aluminum - self made or Machine shop • Press fitted into bearing • Set pinned onto axle • Allows for easy disassembly of frame if required part number: 39

  26. Axle (Hollow) • Aluminum - custom made • Houses motor • 1/4" holes for mounting to frame • 7/8" hole for housing bearing • 3" diameter, though may reduce size depending on motor size • Encoder bolted to end (holes not shown in above CAD drawing) part number: 7

  27. Bearings (for axle) • 1 for 3/8" axle (sliding onto axle) • 1 for 5/8" sleeve, sleeve will be press fitted onto axle, sleeve set pinned to axle for easy removal part number: 36 & 37

  28. Axle Sleeve (to motor) • Aluminum • threaded interior (3/8") • key hole depending on motor axle configuration • self-machined and threaded part number: 40

  29. Spring Pulley system • Same as current design • Self machine housing • Buy bearing from McMaster Carr for $7.45 each part number: 8 & 9

  30. Springs • Our design requires at least 7.5 lbs/in and 37 lbs of pull • Going with a 10.88 lbs/in /w max load of 44.6 lbs (1, 6 pack) • Order From McMaster-Carr for $12.70 part number: 12

  31. Spring Calculations • Entering all information into imulation of current design, we need 4 N-m/rad spring with 1*pi rotation initial condition • Converting that to our near linear system, we need 2 springs at ~7.5 lbs/inch and 37 lbs of pull • Focused on the 37 lbs of pull • Wanted a factor of safety of 1.20 • Found a spring on McMaster Carr for relatively cheap that had a safety factor of 1.205 part number: 12

  32. Bike Wheel • Team member has many unused bikes at their house • Will obtain this weekend • Aiming for a weight of 1.25 kg with most of the weight around the outside (batteries) part number: 14

  33. String • Purchase heavy duty fishing line or kevlar string from McMaster Carr or Home Depot • Low Cost/Low lead time component (not concerned with this yet) part number: 13

  34. High Friction Feet • Require something on the ends of the frame to take away the chance for slippage • PC non-slip pads are cheap and redily available • Order 3 packs of 4 each part number: 33

  35. Motor Motor Requirement: Must be able to drive a torque of 1 N*m for .01 seconds (will slightly oversize motor to be conservative) DC motor (ease of wiring, inherent motion) Brushed or Brushless? part number: 26

  36. Wires Available in many gauges in the EE senior design lab part number: 18

  37. Batteries -AA NiMH -NiMH is safer and rechargeable than LiIon -Eneloop 16 pack from Amazon only $38 -retains charge capacity very well over repeated recharging Split into three banks: Motor voltage, 3.6V, and 4.8V for electronics part number: 19

  38. Gyroscope -Adjustable angular velocity setting for better resolution (all give 0.1 deg/sec resolution or better) -Breakout board includes all required components -Quantity 2 part number: 20

  39. Current Sensor Pololu ACS714 -Operates from -30A to +30A -Accuracy of +-1.5% -Hall effect sensor (electrically isolated from current) -Quantity 3 (one for each battery system) part number: 21

  40. Voltage Sensor Can use small surface mount resistor (minimal power loss) measured across each bank of batteries. OR Can use chemistry-specific charger that can measure, report, and control the charge itself and charge information such as current and voltage. part number: 22

  41. Encoder E5 optical kit encoder -Optical encoder -Hole-through design -.3 degree accuracy -Operates at speeds of 17,000 RPM part number: 23

  42. Processing, Control, Storage • TI LaunchPad meets customer need that the coded part of the system be re-configurable by a novice user in the future by having on-board JTAG emulation that can be accessed via USB • Off-board storage is needed but has not been selected

  43. Processing, Control, Storage TI LaunchPad Microcontroller Development Kit • C2000 Piccolo TMS320F28027 part number: 29

  44. Processing, Control, Storage Motor Controller has not been chosen It is likely that we will use: Pololu Jrk 21x3 Controller part number: 27

  45. Processing, Control, Storage System Code Testing Benchmarks >inserting test code at different points to ensure each piece of the system functions properly • Get a random sensor & see if • it can be polled consistently • it generates an interrupt when it is supposed to • Sample something simple such as a low frequency sine wave • will be easily able to see how well the signal is sampled and reconstructed

  46. Energy Flow Graph

  47. Cost of Transport Analysis 1. No electronics power is included; 2. Friction is not accounted for; 3. Realitic COT will probably be much higher

  48. Bill of Materials https://docs.google.com/a/g.rit.edu/spreadsheet/ccc?key=0ApxjvWO1pU8KdHNlaTlsS013WG1aUS1OcTBKdWF5SVE#gid=0

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