1. Foot Pressure Monitoring System for a Speed Skater
Group 15 MaBeaN
Foot Pressure Monitoring System for a Speed Skater

2. Presentation Outline Project Objectives Performance Specifications
Design Details
Hardware:
Parts list
Construction
Software
Information flow
Post-process flow
Results
Assessment of Design Performance
Evaluation of Results
Possibilities for further improvement
Division of labour
Self Education – Andrew, Ben, Matthew
Schedule / Milestones
Budget
Line
Category analysis
Social, Environmental and Enterprise Context
Conclusions

3. Project Objectives
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

4. Performance Specifications
Requirement
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.

5. Design Details Hardware - Components

6. Design Details Hardware - Parts List
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)

7. Design Details Hardware – Part 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.

8. Design Details Hardware – Construction

9. Design Details Software
Information Flowchart
FSR resistance
Arduino AnalogRead (all 8 sensors)
Serial.println
To Tx baud
XBee packetization and Tx
Base Station Rx XBee
COM Port Serial baud
MATLAB Function WriteCSV
Recorded .csv file

10. Design Details Software
Software Flowchart (Post processing)
Input .csv file & skater footage
Loop
Extract sampling instance, interpolate values
Draw sample and capture frame
Align time index with skater footage
Overlay pressure plot
Capture frame
Produce final .avi file

11. Results Hardware
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

12. 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

13. Results Hardware – FSR Properties

14. Results – Software Simulation pressure profile video
Compiled from fictional .csv file
Uses MATLAB griddata(‘v4’) function to smoothly interpolate between the eight sensor locations

15. Assessment of Design Performance - Hardware
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

16. Assessment of Design Performance - Software
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

17. Evaluation of Results 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

18. Possibilities For Further Improvement
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

19. Division of Labour and Team Effectiveness
Segment
Task
Andrew
Ben
Matthew
Project
FSR research 33 34
Part sourcing 50 25
Scheduling 80 10
Logistics 40 30
Communication
Wikispaces Project website 60 20
Project Calendar 15
Speed Skating Research
Overall 51 24

20. Division of Labour and Team Effectiveness
Segment
Task
Andrew
Ben
Matthew
Hardware
Part Selection 33
Soldering 75 20 5
Wiring Diagramming 60 30 10
Testing
100
Prototyping 45 35
Insole Construction
Overall 65 23 12

21. Division of Labour and Team Effectiveness
Segment
Task
Andrew
Ben
Matthew
Software
Matlab Research 30 50 20
Arduino Subroutine Development
Matlab Data Acquisition
100
Matlab Data Analysis
Video Input 90 10
Data Video Output
Video / Data Marriage 60 40
Overall 7 81 12

22. Division of Labour and Team Effectiveness

23. Self Education – Matthew McKerroll
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

24. Self Education - Ben York
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

25. Self Education – Andrew Yaworski
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

26. Schedule / Milestones Overall Project Timeline

27. Schedule / Milestones Hardware Timeline

28. Schedule / Milestones Software Timeline

29. Budget – Line Item Review
Canakit Supplier Order
Item
Description
Unit Price
Quantity
Extended Price
X-Bee Kit
Xbee Wireless Kit
89.95 1
Arduino Uno
29.95
SX00099
Real Time Clock Module
19.95
SX10088
Arduino Project Enclosure
12.67
SX00844
Dual Axis Accelerometer Breakout Board - ADXL2030
39.95
Subtotal
192.47
Tax
28.29
Freight
20.00
Total
240.76
TekScan Supplier Order (Force Sensitive Resistor)
ZFLEX(A201) 100-8
A Pk
117.00
130.00 US
Conversion
CAD(US*0.9939)
Brokerage
12.5
GST
148.79
The Source Order (Prototyping Silicon Board)
IC PC Board - Multi-purpose 417
6.99
Taxes
0.91
7.90
Project Total
397.45
Slack
2.55

30. Budget – Category Breakdown
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%

31. Social, Environmental and Enterprise Context
The device made already exists but can cost more than $ 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

32. Conclusions
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.