Transcript Measuring Work Output Done on a Weightlifting Machine

Measuring Work Output From
Anaerobic Weightlifting
Designed, Built, and Tested by
David Wolney
Prof. Julie Ellis- Advisor
Prof. Chris Scott- Client
Professor Chris Scott of the Department of Exercise,
Health, and Sport Sciences needed a means of measuring
work output done by a weightlifter.
How much
work am I
doing?
 Prof. Scott hopes to find
a correlation between
work output and
calories burned.
Work
Calories
Clarifying the problem: what, exactly is
required for measurement
 Actual work done during a set is zero.
 Only positive displacement is counted.
 Force is the force required to overcome gravity
and lift the weight.
 The average force during the lift is the force
required to hold position, this is equal to the
weight being lifted.
 The only required measurement is distance.
Using a digital rotary encoder to measure
the cable travel
Pulley
The Smith machine, like
many weight machines,
utilizes a cable that is
attached to the moving
weight.
Another pulley
wheel with an
encoder is attached
to the machine to
measure the cable
travel
Counterweight
Weight
Rotary encoder theory of operation
An encoder disk has alternating light
and dark wedges and two
photodetectors. This example disk
has 4 light-dark transitions per
revolution
Radius=0.5 cm
3.14 cm
2r
4
(0.785 cm in this example)
Left-US Digital Encoder, Above-signal from encoder; A and B are in
quadrature. This arrangement allows for determination of direction as
well as improved resolution
The Intel 8051 microcontroller provides the interface.
The 8051’s
serial port
allows for
detailed data
of the lift on
a PC
The encoder wheel attaches
to the Smith machine
Encoder
Wheel
Counterweight
Weight lifted
The 8051
Development
Board from PJRC
works well in this
application
Work Done: Lots of
clicks
The display gives
the distance lifted
in “clicks”
The processor counts transitions
 Signal A is monitored for a high-low transition
 When A goes high, B is checked to determine
direction
 Absolute count is incremented or decremented,
as applicable
 Positive distance count is incremented if
direction is up
 The absolute count is regularly sent to the serial
port and the positive count is sent to the LCD
display
00000003
00000005
00000008
00000009
00000011
00000011
00000014
00000016
00000017
00000020
00000024
00000028
00000032
00000037
00000041
00000047
00000052
00000060
00000067
00000073
00000080
00000085
00000091
00000097
00000106
00000115
00000127
00000144
00000158
00000169
00000179
00000187
00000196
00000203
00000210
00000218
00000224
00000229
00000241
00000256
00000267
00000276
00000287
00000294
00000299
00000300
00000300
00000300
00000300
00000304
00000315
00000336
00000351
00000357
00000367
00000381
00000399
A PC can collect the data from the
serial port so that it can be processed
Raw data is
collected. The
data contains
distances
and, implicitly,
time
A detailed analysis of the lift can be done.
Knowing distance, time, and weight allows
determination of many different statistics of
the lift. Work, power, velocity, acceleration
and others can be calculated
The first prototype has been installed and some
preliminary tests have been performed.
Measuring
Wheel
Smith
Machine
Controller
Client
The wheel installed
Some refinements were necessitated by the preliminary tests.
Reading in
“CLICKS”
A keypad
allows entry
of weights
8-bit counters free
up the processor
Prof. Scott prefers to have
more information on the
display of the device. He
found the detailed
computer analysis less
useful for his purposes,
so efforts were focused
away from the computer
interface
The revised system better fits the client’s
needs.
The encoder wheel
attaches to the Smith
machine
Work Done and
Seconds Clock
The display gives
more information
A keypad
allows
entry of
weights
External 8-bit
counters count
the encoder clicks
and free the
processor for
other tasks
The PC is
treated as an
optional
component