week 9 detailed design review
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Week 9 Detailed Design Review
P13211 - Rimless Wheel (Wired)
Customer needsCustomer Needs Importance Detail
CN1 1 Collect data to prove periodic motion
CN2 2 Collect data on current/voltage of battery
CN3 1 Record angular velocity of wheel and frame
CN4 1 Record relative angle between wheel and frame
CN5 2 Collect data on current/voltage of actuators
CN6 1 Attain periodic motion
CN7 1 25 steps ("infinite walking distance")
CN8 2 Resolution of 100 Hz
CN9 1 Minimize energy loss
CN10 1 Portability
CN11 1 Cost of Transport (0.1 or 0.05)
CN12 2 Rigidity/durability
Engineering Specs
Risk ManagementRisk ID
Risk Item Effect Cause Likelihood Severity Importance Mitigation Measure
Owner
1 Lead times and manufacturability
Delay on construction/testing
Late order/lack of knowledge
3 3 9 Plan ahead and gather as much information as possible
Maddy & Dan
2 Discrepancy between simulation and reality
Inaccurate design
3 3 9 Account for as many flaws as possible
Dan
3 Effectiveness of actuation
Unable to sustain motion
Inaccurate design 3 3 9 Be thorough in engineering analysis, and leave room for adjustment of design parameters
Hao
4 Cost vs. quality 2 3 6 Thorough analyses of components
Owen & Becky
5 Technical errors Inaccurate design
Human errors 3 1 3 Double check analysis
All
Risk ManagementRisk ID
Risk Item Effect Cause Likelihood Severity Importance Mitigation Measure
Owner
5 Balancing weights of new components
Unable to maintain periodicity
Inaccurate design
1 3 3 Hao
8 Lag time of controls Ineffective actuation
Delay in signal transmission
3 1 3 Maddy
2 Material flaws Delay on construction/testing
Transportation/human error
2 1 2 Plan ample time for construction and be careful with materials
Owen
6 Accuracy of sensors
Unable to achieve desired time resolution
2 1 2 Double check Data Sheets
Becky
Detailed Block Diagram
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
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
The Problem (cont'd)
• Assuming the following (untrue):o motor has speed up time of 0 secondso at full torque, motor will run at full RPMso the sensors and all electronics use no energyo 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
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 beneficialo Required the change of 2 parts, addition of 1 sleeve,
and addition of 2 bearingso allowed for the removal of 13 parts and simplification
of 2 more parts
Equation of Motion
Single Stance
Equation of MotionDouble Stance
Computational Simulation
Equations of Motion
Actuation: In single stance Angular speed of the wheel Add a constant torque
Reaction forces changedMaintain double stance during actuation
Simulation Results
Control Algorithm
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
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 sidepart number: 34 & 35
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 fromMachine shop orMcMaster Carr
part number: 11 & 38
Brace AssemblyCalculations
• Calculated for bendingand 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
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:
o 20 cap screwso 40 washerso 10 hex nuts part number: 15-17
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 compressionpart number: 5
Mounting Plates(bike wheel side)
• Aluminum - Machine shop• Two purposes:
o Press fit the bearing into the left mounting plateo 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
Axle (for bike wheel)
• Aluminum - self made• Bike wheel rigidly fixed onto axle
o possibly press fittedo 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
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
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
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
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
Axle Sleeve (to motor)
• Aluminum• threaded interior (3/8")• key hole depending on motor axle
configuration• self-machined and threaded
part number: 40
Spring Pulley system
• Same as current design• Self machine housing• Buy bearing from McMaster Carr for $7.45
each
part number: 8 & 9
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
SpringCalculations
• 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
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
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
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
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
Wires
Available in many gauges in the EE senior design lab
part number: 18
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
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
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
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
Encoder
E5 optical kit encoder-Optical encoder-Hole-through design-.3 degree accuracy-Operates at speeds of 17,000 RPM
part number: 23
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
Processing, Control, Storage
TI LaunchPad
Microcontroller Development Kit
• C2000 Piccolo TMS320F28027
part number: 29
Processing, Control, Storage
Motor Controller has not been chosen
It is likely that we will use:
Pololu Jrk 21x3 Controller
part number: 27
Processing, Control, Storage
System Code Testing Benchmarks>inserting test code at different points to ensure
each piece of the system functions properly1. Get a random sensor & see if
a. it can be polled consistentlyb. it generates an interrupt when it is supposed to
2. Sample something simple such as a low frequency sine wavea. will be easily able to see how well the signal is
sampled and reconstructed
Energy Flow Graph
Cost of Transport Analysis
1. No electronics power is included;2. Friction is not accounted for;3. Realitic COT will probably be much higher
Bill of Materials
https://docs.google.com/a/g.rit.edu/spreadsheet/ccc?key=0ApxjvWO1pU8KdHNlaTlsS013WG1aUS1OcTBKdWF5SVE#gid=0
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