Transcript Wheel Size vs Distance

Wheel Size Matters: Programmed Rotations
Introduction:
An Investigation into the effect that changing
wheel size has on the distance traveled.
Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc.
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The Investigation
• Hypothesis: If the
number of rotations of the
motor axes is held
constant, then a larger
diameter wheel will move
the vehicle a
proportionately greater
distance.
• Variables:
– Independent: Wheel
size (3 diameters)
– Dependent: Distance
traveled.
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Practical Applications
• Prepares the
student to
understand
gears and ratios
• Helps in design
of robots,
especially where
speed is an
important factor.
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Prepare Test Bed
•
Prepare the
test bed
(including a
starting line
taped to the
board).
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Modify the Squarebot
•
Modify the
Squarebot as
shown in the
Helper Section
at the end of
Teacher’s
Notes
document.
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Prepare the Program
•
•
•
•
1. Open ROBOTC. Go to
File/Open Sample
Program.
2. Open Encoder.
3. Open
vex_line_track_rotations.
c
Download the program to
the Squarebot
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Step 1 Position the Squarebot
•
Place the rear
frame of the
modified
Squarebot
against the test
bed boundary,
with the small
front wheels on
the starting
line.
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Step 2 Run the Robot
•
Run the
vehicle by
turning the
controller
off, then on.
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Step 3 Mark Stopping Point
•
•
When the MOTOR
STOPS RUNNING
mark the location of the
front end of Squarebot
as closely as possible.
This may be
accomplished by
dropping a ruler at the
estimated spot (Fig. 1),
then marking the board
as shown in Figure 2.
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Step 4 Measure Distances
•
Measure the
distance from
the starting line
to the spot
where the front
of the Squarebot
stopped.
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Step 5 Record Data
•
Record this distance on a data table of Wheel
Size vs. Distance Traveled
CONDITION
(Wheel Size)
TRIALS
(inches)
1
2
3
4
5
Average
1 (Small)
44 ½
42 ¼
43 ½
42 ¾
41 ½
2 (Medium)
1
1
1
1
1
1
3 (Large)
1
1
1
1
1
1
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Step 6 Gather More Data
•
Repeat the
procedure at
least two more
times to insure
that your
measurements
are accurate
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Step 7 Average Values
•
Find the average of
the trials for the
condition and record
it on the table.
Example:
(44.50in  42.25in  43.50in  42.75in  41.50in)
 42.88in
5
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Step 8 Medium Wheels
•
Switch to
medium sized
wheels and
repeat the
steps #1-7
with the new
wheels.
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Step 9 Largest Wheels
•
Switch to the
large wheels
and repeat in
the same
manner as the
other sized
wheels.
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Step 10 Plot Diameter vs. Distance
Wheel Size vs.
Distance Traveled
(5 Rotations)
Distance
Traveled
(inches)
• The plot is a powerful
visual demonstration
leading to a clear
conclusion
• As wheel size
increases, distance
traveled increases
proportionally.
100.0
80.0
60.0
40.0
20.0
0.0
0.00
2.00
4.00
6.00
Wheel Size (inches)
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