ECE 791/792 Progress Report
Project Title: Oar Bend to Quantify Rowing
Efficiency
Project Team: Eric Donovan, Jonathan Dwyer, Kenneth Weigel
ECE Faculty Advisor: Wayne Smith PhD
Current Date: December 18, 2011
Project Completion Date: April 2011
Abstract: The intent of this project is to design a system that will allow for coaches and
coxswains to quantitatively evaluate the effectiveness of their rowers. This will be done by
utilizing a strain gauge to measure the bend of the oar, and then feeding this gauge through a
scaling circuit into a control system (microcontroller), which will then be able to save that data to
be analyzed with an on-pc program, transmit to an iPod in serial, and display to an LCD for the
convenient reading of each rower.
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Table of Contents
General Problem Definition……………………………………………………………….3
Specific Project Objectives…………………………………………….………………….4
Proposed Schedule………………………………………………………...………………4
Scaling Circuit…………………………………………………………………………….5
On-PC Program……………………………………………………………………………7
Conclusion…...……………………………………………………………………………9
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General Problem Definition
The general problem that this project hopes to solve is the lack of a quantitative method
for coxswains and coaches to evaluate their rowers’ effect on boat speed. Very strong, but
technically incompetent rowers can often bend their oar while rowing, which indicates
effectiveness. However, weaker but more technically proficient rowers can exert equal bend
simply through form alone. Coaches can subjectively evaluate technique, or objectively view
their fitness scores, but have no way to quantitatively measure their rowers’ effectiveness on the
water. Additionally, lineups are often determined by “seat racing,” which is a complex set of
races where rowers from each boat are interchanged so as to determine who is responsible for
their boat winning. This project would offer a solution to eliminating possible mistakes (which
are easily made) in determining the fastest lineup for a crew.
Phi-2 LCD:
Displays stroke
rating (strokes per
minute), average oar
bend, current oar
bend, and time
elapsed/remaining
Strain Gauge:
differential voltage
due to bend
Analog voltage
scaled to fit Arduino
Mega 2560 A/D
converter
parameters
A/D Converter
Arduino Mega 2560
Microcontroller:
- Save highest value
on chip memory.
Send to...
iPod –
shows graph of boat
average, as well as
one graph per each
rower in boat (so as
to compare
individual oar bend
values versus the
average.
PC:
Java program
provides GUI
through which user
can retrieve
information from
MC. Program will
graph and display
relevant information
such as average oar
bend etc.
Figure 1. Project Execution Diagram
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Specific Project Objectives
1. Accurate bend values derived from bend gauge to be fed into integrated circuit (for
voltage scaling), with clean input (solid SNR and clean sampling) into Arduino
microcontroller.
2. Arduino handles sampling, storage, and transmission to LCD and iPod (serial
connection).
3. iPod correctly inputs data, provides useful graphical interface and display of data.
4. Data stored on external memory is efficiently handled, analyzed, and displayed during
execution of on-board PC program.
Proposed Schedule
December 31st, 2011: On-pc program written, compiled and in testing, scaling circuit design
completed. iPod applet written, entering test phase.
January 31st, 2012: Microcontroller correctly inputs and stores data externally (to USB key).
February 31st, 2012: System correctly outputs to LCD. On-PC program is fully functional.
March 1st, 2012: All phases of execution are operating correctly. Formalized “black box”
testing begins.
March 15th, 2012: Black boxing testing complete. Project is fully functional.
The above schedule has been updated since the project proposal. The on-PC program has
been written and has entered the testing phase, scaling circuit design has been completed, but the
iPod applet has yet to be written, and will require a bit more time than anticipated.
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Scaling Circuit (Kenneth Weigel)
Resistance to
Voltage Converter
Amplifier Circuit
Voltage Limiter
Circuit
(Uncertain)
Low-Pass Filter
(Uncertain)
A/D of
Microcontroller
Figure 3. Block Diagram of Analog Circuit
R6
XSC1
VEE
Ext T rig
+
-4.5V
_
B
A
+
4
_
+
_
R5
2
6
R7
V1
4.5 V
3
7
1
5
V CC
R1
R8
R3
4.5V
V2
Rb1
V1
5k Ω
5k Ω
100%
500Ω
Ke y =A
100%
500Ω
Ke y =A
5k Ω
5k Ω
U1
LM741CN
Rb2
R4
R2
Figure 4. Bend Sensor Bridge Voltage Differential Circuit
Assume
50k Ω
𝑅𝑏 = 𝑅𝑏1 = 𝑅𝑏2 (Bend Sensor Resistance)
500k Ω
500k Ω
𝑅 = 𝑅1 = 𝑅2 = 𝑅3 = 𝑅4 (Other Bridge Circuit Resistors)
𝑅𝑖 = 𝑅5 = 𝑅7
(Differential Amplifier Input Resistance)
𝑅𝑓 = 𝑅6 = 𝑅8 (Differential Amplifier Feedback Resistance)
𝑉𝑟𝑒𝑓 (𝑅𝑏 +𝑅)
2𝑅+𝑅𝑏
𝑉
𝑅
𝑟𝑒𝑓
− 2𝑅+𝑅
≈
𝑏
𝑉𝑟𝑒𝑓 𝑅𝑏
2𝑅
𝑉𝑜𝑙𝑡𝑠
Equation 1. Differential Voltage of Bridge Circuit
𝑉𝑜𝑢𝑡 =
𝑅𝑓
𝑅𝑖
(𝑉2 − 𝑉1 ) 𝑉𝑜𝑙𝑡𝑠
Equation 2. Differential Voltage Amplifier Circuit
𝑉𝑜𝑢𝑡 =
𝑅𝑓 𝑉𝑟𝑒𝑓 𝑅𝑏
𝑅𝑖
2𝑅
= 𝑉𝑜𝑙𝑡𝑠
Equation 3. Overall Circuit Output
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The analog circuit is the first stage needed in the overall project; the voltage readings
found here will be used in all subsequent stages. The first stage of the analog circuit is the bridge
circuit which uses the changing resistance of the bend sensors to create a differential voltage
across the bridge. This voltage is then scaled via a differential operational amplifier
configuration; the particular model is yet to be chosen, but a basic 741 is expected to work in this
application. The bridge circuit is the most common application for strain gauges due to the
expected small variations in bend sensor resistance. Another benefit is that when the oar is in
the straight position the bridge is balanced with a differential voltage of zero. The differential
amplifier is used to upscale the minute changes in the voltage across the bridge to increase
accuracy when sampled by the A/D converter of the microcontroller. Both stages will be
powered using AA batteries of 1.5 volts each, three batteries in series for both the ±4.5 volts
required for the operational amplifier and bridge source voltages, with a total of six AA batteries
needed overall.
The final two stages are still only prospective ideas at this point as the bend sensors are
still in the mail. The low-pass filter will be used depending on the level of noise that is seen after
the differential voltage amplifier, and it will only be utilized if needed. The voltage limiter
circuit is another potential idea that will be used as a final protective measure to make sure that
the voltage sent to the microcontroller will never rise above 5 V, but this stage will most likely
be unnecessary, given that there will only be 4.5 volts applied to the system.
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On-PC Program (uRow) (Eric Donovan, Jonathan Dwyer)
Figure 2. Screenshot Of On-PC Program At Its Current Implementation
The development of the on-pc program has been moving quite quickly. As shown in Figure
2, the program can now display the time elapsed, peak and minimum bend rating, the median
rating, average rating, stroke total, and stroke rating. The minimum and peak bend rating refer to
the smallest and largest bend measurement of the oar. At current implementation, the graph
shown is a graph of the peak bend values i.e. there were nine strokes taken in total, leading to the
graphing of the nine peak values from each of those stroke cycles. Note, the values used for the
oar bend in these calculations are arbitrary and, in the future, these values will be replaced with
the actual angle of bend on the oar. At final implementation there will be an additional graph
below that will display all of the strokes taken with their entire power curves. Additionally, the
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percentage slider shown above will split up the peak ratings into corresponding sized groups to
show the average values across those values i.e. at current value the percentage is 33%, which
means there would be values corresponding to the average bend for the first 33%, second 33%
etc. displayed in the table shown on the right of Figure 2. Finally, with all of the power curves
shown on one graph (bend spectrum for each stroke), we would also have a table value
corresponding to the mode, which would be defined as a range of peak bend values that would
need to be scaled per the range of maximum bend values. This is because the mode, which is
defined as the most common value within a set, cannot really exist in a system where there are
extremely precise double (data type) values (e.g. 59.99 ≠ 60.1). For this reason, there would
need to be a range (e.g. ±5 bend, 59.99 would be within the same level as 60.1) in order to
essentially “round off” each bend value to find a representative number of groupings from which
we can determine this mode value. In simpler terms, this is analogous to quantizing these values
into representative levels.
In terms of execution, the on-pc program is conceptually the final stage of analysis. The
program itself takes a .txt file as an input, using standard read-from-file techniques to load values
into the program’s storage devices (ArrayList). The program will then graph the power curves of
all of the strokes, the peak rating graph (such as that shown in Figure 2), and all of the
aforementioned table values.
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Conclusion
Given the initial schedule, and taking into account the current level of progress, it is clear
that the project has been decisively moving forward. The next step will be the programming and
testing of the Arduino microcontroller and the physical construction of the analog circuit itself.
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