Week 9 Detailed Design Review

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


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


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


TI LaunchPad

Microcontroller Development Kit

• C2000 Piccolo TMS320F28027

part number: 29


Motor Controller has not been chosen

It is likely that we will use:

Pololu Jrk 21x3 Controller

part number: 27


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




Documents

Week 9 Detailed Design Review