Transcript Bicycle Power Meter

Bicycle Power Meter
I love the
bike
blender!!!!
P16214
Team Member Roles
Agenda
-Current Problem
-Bill of Materials
-Systems Architecture
-Power and Information Flow
-Subsystems
-Test Plan
-Pugh of Subsystems
-Risk Assessment
-Feasibility of Subsystems
-Next Steps
-Feasibility for High Level System
-Schedule
Problem to Solve
A bicycle power meter is a device used by professional and amateur cyclists in order to show the cyclist
their power output on the bicycle. The RIT Cycling Team approached this MSD team to provide a power
meter for their ImagineRIT bicycle blender exhibit. Their desire is to have this device take the input force
from the cyclist and display their power output and calories burned. The current devices on the market
which provide these features are not quite instantaneous. There is a lag associated with the time between
the rider exerting force on the bike and when the rider receives feedback from the system.
The goal of this project is to develop a functioning power meter for the bicycle blender exhibit. In order to
achieve this task the MSD team aims to improve upon the communication speed between the power meter
sensors and the display in existing devices. This will assist in achieving a more instantaneous system and
closer to real-time display.
Systems Architecture
Display Out
BLE
iOS and Android App
Subsystems
-Battery
-App
-Strain Gauges
-Microcontroller
-Crankset
-Accelerometer
Pugh for Battery
Capacity
Size (physical)
Battery
Voltage
Cost
-Meets Engineering Req 8 (Battery Life)
Battery Final Decision
WINNER!!
Feasibility for Battery
Question: How much power will the bicycle power meter consume?
1.Need device to last for minimum of 10 hours for ImagineRIT
Analysis:
-Will be based on the accelerometer and strain gauge and how much power they consume
-Efficiency of algorithm will also determine how long battery lasts
Solution:
-Will be narrowed down once algorithm is finalized
-Worst case→ Buy multiple batteries and stack them if the Bicycle Power Meter requires
more power
Pugh for App
-The amount of time it takes to build an app has a direct correlation with cost
-Since Android apps will take 2-3 time longer to build, they will cost more upfront
Cost of publishing
Smartphone App Time from completion to availability
Device Availability
WINNER!!
Selection Criteria
iOS
Android
Cost of publishing
Better
Worse
Time from completion to availability
Better
Worse
N
N
Device Availability
Feasibility for App
-Ability for iOS App to process data from the microcontroller
-iPhone capable of receiving BLE
-Available iPhones to use during ImagineRIT: 3
Pugh for Strain Gauges
Option 1: Measures Tension/Compression with two parallel gauges (350 ohms)
Option 2: Measures Tension/Compression with two parallel gauges (1000 ohms)
Option 3: Measures Tension/Poisson Strain with two perpendicular gauges (350 ohms)
Option 4: Measures Tension/Compression with one gauge (350 ohms)
-Meets Engineering Req 3(Accurate Strain Gauges), 16(Compatible with Bike
Blender), 21(can withstand drop test), and 20(Storage temp range)
Dual Grid Design
● This design will compensate for
an overall temp change, but if
there is a temperature
differential between the top and
bottom of the crank, there will
be incorrect strain readings.
This temp differential is a
concern since the crank will
spin in one direction. Also it
may sit in the sun in a static
state, which would warm the top
of the crank.
● Requires 8 analog I/Os
90 Degree Rosette Design
● This 90 Degree Rosette
uses two strain gauges that
are perpendicular to each
other. One measures the
strain due to bending
tension, the other measures
the strain due to the poisson
effect.
● This design will compensate
for an overall temp change.
Also since the two strain
gauges are very close to
each other, this design will
not have any issues with
temp differential.
● Requires 4 analog I/Os
Feasibility for Strain Gauges
Question: How much strain will be placed on the top
of the crank arm?
Assumptions:
●
Force of 624N applied at end of crank arm
●
Crank arm length (172.5mm)
●
Crank arm thickness (20mm)
●
Assume cantilever beam
●
Elastic modulus of aluminum 69Gpa
M=.1725 * 624 = 107.64 N-M
I= (bh^3)/12 = (.020 * .040^3)/12 = 1.07*10^-7
strain= MC/EI
= (107.64 * .020) / (69*10^9 * 1.07*10^-7) = .00029m/m
0.00029 * 0.1725 = 0.00005m
Question: How much strain will be expected due to the
poisson effect?
Poisson's Ratio Aluminum: 0.32
0.32 = X/0.00029
Strain due to Poisson Effect: X = 0.0000928m/m
Pugh for Microcontroller
Winner: Concept #1 - Bluno Nano
-Meets Engineering Req 5(System latency), 6(throughput transfer rate), 7(range),
9(protocol), 10(storage space), 17(calculation accuracy), 18(Daq uC processing
speed), 20(storage temp range), 21(withstand drop test), 22(has thermometer
Feasibility for Microcontroller
Microcontroller
-Analog Inputs
-Processor
· Sensors require a total of 6 analog inputs
· Must be powerful enough to sample sensor data and package for
wireless transmission through BLE
· Microcontroller has 7 available analog inputs
· Bluno Nano uses an Atmel 20MHz Atmega328 processor with an 8channel 10-bit ADC and a TI CC2540 BLE MCU broadcasting at
2.4GHz
-Input Voltage Required
-Memory
· Microcontroller supply voltage must be low to keep
battery size down
· Very little memory needed; only storing algorithm and small
packages of data for short periods of time
· Bluno Nano has a supply voltage of 5.5V max
· Atmega328 has 32K flash, 1K EEPROM, 2K RAM
Crankset Selection Criteria
Mounting space
Hollow spindle
GXP Bottom Bracket
Aluminum
-Meets Engineering Req 16(compatible with Bike Blender)
Crankset Feasibility/Component Placement
Crankset Dimensions:
Length: 172.5mm
Width: 38mm
Available Mounting Space:
Drive Side ~ 86mm x 38mm
Non-Drive Side ~ 170mm x 38mm
uC Dimensions: 53mm x 19mm
Accelerometer: 21mm x 18mm
Battery: 25mm diameter
Strain Gauges: 7.5mm x 10.8mm
Pugh for Accelerometer
Winner: Concept #1 - FXLN83xxQ
-Meets Engineering Req 5(system latency), 21(withstand drop test),
20(storage temp range)
Feasibility for Accelerometer (Data)
Single Axis of 3-Axis Accelerometer:
Bluno Nano Microcontroller:
Sensing Range = 0-1 G (G = 9.8 m/s2)
Angle Change = 90°
Accelerometer Spec = 230 mV/G
Accelerometer 0G Voltage = 750 mV
Analog to Digital Converter (ADC) = 10 bit (210 = 1024)
Internal Reference Voltage = 1.1V
Feasibility for Accelerometer (Location)
Location of Accelerometer (Worst Case Scenario):
-Based on placing the accelerometer in a
location where it will experience more than
just the acceleration due to gravity
-This location would be anywhere on the
crank arm other than the axis of rotation.
Updated Systems
Architecture
Display Out
BLE
iOS App
Bill of Materials
Predicted
QTY
Unit
Price
Bluno Development Board
1
$35.00
Omega Tee 90 degree Rosette 350 Ohm Strain Gauge
2
$30.00
Bluno Nano Arduino BLE Bluetooth Microcontroller
1
$33.50
Freescale FXLN8361Q Accelerometer Breakout Board
1
$10.00
Renata CR2477N Coin Cell Battery
2
$4.99
iOS App Developer Fee
1
$100.00
TOTAL PRICE FOR PREDICTED QTY=
$288.48
Power and Information Flow
Battery
Microcontroller
Accelerometer
Strain Gauge
Smart Phone
Television
Power
Information
Test Plan
Risk Assessment (FMEA)
Next Steps
Gather Bike Crankset Parts
Continue to Research App Development iOS
Finalize Subsystem Prices
Purchase Subsystem Parts
Finalize Detailed Design
Schedule
Thanks!