Bicycle Power Meter P16214 I love the bike blender!!!! Team Member Roles Agenda -Current Problem -Systems Architecture -Subsystems -Pugh of Subsystems -Feasibility of Subsystems -Feasibility for High Level System -Bill of Materials -Power and Information Flow -Test Plan -Risk Assessment -Next Steps -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 iOS and Android App Display Out BLE Subsystems -Battery -App -Strain Gauges -Microcontroller -Crankset -Accelerometer Pugh for Battery Battery Capacity Size (physical) 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 Selection CriteriaiOSAndroid Cost of publishing BetterWorse Time from completion to availability BetterWorse Device Availability NN Smartphone App Cost of publishing Time from completion to availability Device Availability WINNER!! 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 = N-M I= (bh^3)/12 = (.020 *.040^3)/12 = 1.07*10^-7 strain= MC/EI = ( *.020) / (69*10^9 * 1.07*10^-7) =.00029m/m * = m Question: How much strain will be expected due to the poisson effect? Poisson's Ratio Aluminum: = X/ Strain due to Poisson Effect: X = m/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 Sensors require a total of 6 analog inputs Microcontroller has 7 available analog inputs -Input Voltage Required Microcontroller supply voltage must be low to keep battery size down Bluno Nano has a supply voltage of 5.5V max -Processor Must be powerful enough to sample sensor data and package for wireless transmission through BLE Bluno Nano uses an Atmel 20MHz Atmega328 processor with an 8- channel 10-bit ADC and a TI CC2540 BLE MCU broadcasting at 2.4GHz -Memory Very little memory needed; only storing algorithm and small packages of data for short periods of time 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: Sensing Range = 0-1 G (G = 9.8 m/s 2 ) Angle Change = 90 Accelerometer Spec = 230 mV/G Accelerometer 0G Voltage = 750 mV Bluno Nano Microcontroller: Analog to Digital Converter (ADC) = 10 bit (2 10 = 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 iOS App Display Out BLE Bill of Materials Bluno Development Board1$35.00 Omega Tee 90 degree Rosette 350 Ohm Strain Gauge2$30.00 Bluno Nano Arduino BLE Bluetooth Microcontroller1$33.50 Freescale FXLN8361Q Accelerometer Breakout Board1$10.00 Renata CR2477N Coin Cell Battery2$4.99 iOS AppDeveloper Fee1$ TOTAL PRICE FOR PREDICTED QTY= $ QTY Price Predicted Unit Power and Information Flow Power Information BatteryMicrocontroller Strain Gauge Accelerometer Smart Phone Television 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!