Group 15MaBeaN

Foot Pressure Monitoring System for a Speed Skater

1. Project Objectives2. Performance Specifications3. Design Details• Hardware:• Parts list• Construction

• Software• Information flow• Post-process flow

4. Results5. Assessment of Design

Performance6. Evaluation of Results

Presentation Outline7. Possibilities for further

improvement8. Division of labour9. Self Education – Andrew,

Ben, Matthew10. Schedule / Milestones11. Budget • Line • Category analysis

12. Social, Environmental and Enterprise Context

13. Conclusions

Improving a system to monitor foot pressure on the soles of speed skaters

Display pressure results alongside skater footage for use as a training tool to club level skaters

Ensure a minimum hindrance to the safety and performance of the speed skater

Skater stats (typical Kingston Striders skater) Max velocity = 34km/h Average stride duration = 720ms

Project Objectives

Performance SpecificationsRequirement Target Reasoning

Sensor placement

8 FSRs per foot Allows reasonable spread of inputs to identify mass distribution over sole

Sampling frequency

40Hz sampling Gives average of 29 discrete steps per stride – sufficient to identify mass transitions within stride

Wireless fidelity Max range 60m;<3% Tx error

Operation inside short track speed skating rink; Tx error limit corresponding to one sample packet lost per stride

Compact transmission unit

Minimize injury potential

Consider Tx unit placement and size such that the skater is at no additional risk in a fall situation

Minimally intrusive insole

~1mm thickness

Low profile to maximize skater comfort, but must be robust to withstand mechanical strain inside skate

Data visualization

Max time drift 25ms

Display data in contour map and bar graph alongside time matched skater footage.

Design Details Hardware - Components

Arduino Uno – Micro-controller chosen for project, has 6 analog and 16 digital inputs

Xbee Chip – employed for wireless communication

WiFi Shield: Shield designed to extend the Arduino Uno providing wireless capabilities

Dual Axis accelerometer: to determine the initial start of a speed skater

RTC: real time clock to provide a clock time stamp

4051 Analog multiplexer: accepts the analog inputs of the force sensitive resistors

Resistors and holders: specific to each individual FSR; scaled to provide a scaled force output

(components not to scale)

Design Details Hardware - Parts List

Tekscan Force Sensitive Resistor (FSR) – used to evaluate the pressure exerted at a given point on the foot

Xbee base station chip: used to enable wireless capabilities of Arduino Uno

Base Station Shield: enables wireless Xbee chip to establish communication between a laptop and the Data Acquisition Pack.

Design Details Hardware – Part List

Design Details Hardware – Construction

Information Flowchart

Design Details Software

Serial.printlnTo Tx Xbee @ 38400 baud

MATLAB Function WriteCSV

COM Port Serial Buffer

@ 38400 baud

Arduino AnalogRead

(all 8 sensors)

FSR resistance

Recorded .csv file

Base Station Rx XBee

XBee packetization

and Tx

Software Flowchart (Post processing)

Design Details Software

Draw sample and capture

frame

Extract sampling instance,

interpolate values

Input .csv file & skater

footage

Overlay pressure plot

Produce final .avi file

Align time index with

skater footage

Capture frame

Loop

Reaction times of parts vary, the slowest of which contributes to delay

Maximum allowed sampling rate per sensor is 500Hz because of MCU limit

Maximum allowable full sample reading is 42Hz due to added multiplexer delay

Currently sampling at 40hz

Results Hardware

Xbee is able to send wirelessly at many different baud rates.

Currently it sends at 38400 This was chosen because of reliability and

for speed, and provides enough overhead bandwidth when sampling at 40Hz

Results Hardware

Results Hardware – FSR Properties

Simulation pressure profile video◦ Compiled from

fictional .csv file◦ Uses MATLAB

griddata(‘v4’) function to smoothly interpolate between the eight sensor locations

Results – Software

Sampling rate of 40Hz Allows accurate readings for all speeds up

to 55km/hr Data collection is very fast, and occurs in

real time All hardware components react almost

instantaneously The major speed bottleneck is the wireless

transfer of information through the Xbee

Assessment of Design Performance - Hardware

Post processing is very slow and cannot happen in real time

MATLAB must redraw the plots for every iteration

And another program must save a screenshot of the plot which will later be a frame of the resultant video

Assessment of Design Performance - Software

Pressure data (errors in uniform calibration)◦ Useful for identifying relative pressures rather than

absolute pressures◦ Meets expectations as interest is in distribution of

pressure over quantifiable values

Wireless reliability (possible loss of data)◦ Tests returned ice-side data which met our specs

Hardware integrity (mechanical failure)◦ Construction methods are developed to withstand

mechanical stress and minimize intrusiveness

Evaluation of Results

Employ the accelerometer for further data acquisition beyond the current application of a trigger to start sending data when a speed skater starts moving

Inclusion of a triple axis accelerometer to measure acceleration in 3 degrees of movement for turn analysis

Separation of scaled resistors to outside the DAQPAC for ease of exchange and to ensure the DAQPAC seals tightly

Use of a rechargeable lithium battery pack system for greater battery life while minimizing the environmental footprint of the unit

Further refinements to the placement and number of sensors in the foot sensor system for greater resolution

Possibilities For Further Improvement

Division of Labour and Team EffectivenessSegment Task Andrew Ben Matthew

Project FSR research 33 34 33

Project Part sourcing 50 25 25

Project Scheduling 80 10 10

Project Logistics 40 30 30

Project Communication 50 25 25

ProjectWikispaces Project

website 60 20 20

Project Project Calendar 60 25 15

ProjectSpeed Skating

Research 33 33 34

Project Overall 51 25 24

Division of Labour and Team Effectiveness

Segment Task Andrew Ben Matthew

Hardware Part Selection 33 33 33

Hardware Soldering 75 20 5

HardwareWiring

Diagramming 60 30 10

Hardware Testing 100 0 0

Hardware Prototyping 45 35 20

Hardware Insole Construction 75 20 5

Hardware Overall 65 23 12

Division of Labour and Team EffectivenessSegment Task Andrew Ben Matthew

Software Matlab Research 30 50 20

SoftwareArduino Subroutine

Development 20 50 30

SoftwareMatlab Data Acquisition 0 100 0

SoftwareMatlab Data

Analysis 0 100 0

Software Video Input 0 90 10

Software Data Video Output 0 100 0

SoftwareVideo / Data

Marriage 0 60 40

Software Overall 7 81 12

Division of Labour and Team Effectiveness

Projec

t Cat

egor

y

Hardw

are

Categ

ory

Softw

are

Categ

ory

Projec

t Con

tribu

tion

0%

20%

40%

60%

80%

100%

Work Division Breakdown

Andrew Ben Matthew

Project Category

Work

Perf

orm

ed

Digital and analog inputs work very differently, and both can be used for very different things

How IC’s actually perform and the speed they can react at

How the design process works, trying different things to see if they work within a time limit.

Everything can change in a design once it is starting to be built

Self Education – Matthew McKerroll

Choosing the best visualization method Colour blindness Ease of interpretation for youth audience

Fail fast design Build a prototype early, learn from it, then move on

Considering transient behaviour of ICs When trying to maximize the sampling rate,

components (i.e. MUX) do not behave instantaneously

Weekly meeting with supervisors A source of unrivalled brainstorming and suggestions

for improvement

Self Education - Ben York

Micro-electronics are very approachable; the Arduino platform is a versatile platform to make use with an invaluable open source community

Soldering is an art that is a necessity when working with micro-electronics

The good news: Crazy glue is not conductive; the bad news: Crazy glue is not conductive.

Planning a design project requires more time than the actual project process itself; it is completely true that an engineer spends ½ of the time working, ¼ of the time writing reports and ¼ of the time presenting those reports to keep those involved updated with the current status

Project planning is a necessity. The amount of time spent planning at the beginning of the project is directly proportional to the success of the project and inversely proportional to the work required to complete the project.

Fail fast prototypes are integral to bypassing project bottlenecks

Self Education – Andrew Yaworski

Schedule / MilestonesOverall Project Timeline

Schedule / MilestonesHardware Timeline

Schedule / MilestonesSoftware Timeline

Budget – Line Item ReviewCanakit Supplier Order

Item Description Unit Price Quantity Extended Price X-Bee Kit Xbee Wireless Kit 89.95 1 89.95

Arduino Uno Arduino Uno 29.95 1 29.95 SX00099 Real Time Clock Module 19.95 1 19.95

SX10088 Arduino Project Enclosure 12.67 1 12.67

SX00844Dual Axis Accelerometer Breakout Board -

ADXL2030 39.95 1 39.95 Subtotal 192.47 Tax 28.29 Freight 20.00 Total 240.76

TekScan Supplier Order (Force Sensitive Resistor)

ZFLEX(A201) 100-8 A201 Sensor @ 100 - 8 Pk 117.00 1 130.00 US Conversion 129.207 CAD(US*0.9939) Brokerage 12.5 GST 7.08535 148.79

The Source Order (Prototyping Silicon Board)

2760150 IC PC Board - Multi-purpose 417 6.99 1 6.99 Taxes 0.91 Total 7.90

Project Total 397.45Slack 2.55

Budget – Category Breakdown

Wireless Components Micro-controller Peripheral ComponentsSensors Taxes ShippingSlack

Analysis of the budget provides insight into the limitations due to component cost

FSR Sensors: 33%

Wireless Components: 22%

Peripheral Components: 20 %

Taxes / Shipping: 17%

Microcontroller: 7%

The device made already exists but can cost more than $10 000 dollars. The one made for this project is meant for the club level of skating – many uses, cost effective

Other applications of this project include heath-care and rehabilitation

This project has little to no environmental impact, but changes could be made so that it is more environmentally friendly

Social, Environmental and Enterprise Context

Cost limitations of the design project stem from the high initial cost of sensor equipment

The least expensive component cost was the Arduino MCU

The ease of use and reliability of Xbee unit was worth the 22% budget allocation.

Pressure sensor insole additional applications◦ Ergonomics analysis of repetitive and stressful working conditions◦ Sport-specific analysis of the movements◦ Gait analysis for diagnosing issues relating to back problems◦ Data collection unit that can be interfaced with any type of data acquisition

system beyond just the foot

Highly versatile Arduino platform allows extension to other applications while being highly approachable in those disparate implementations.

Conclusions