Bike Lab #3
Lab Procedure
The goal in this lab is to find a correlation between the weight of the bicycle rider and the stress/strain due to bending in the front fork.
Conditioning Circuit: The Wheatstone Bridge
The change in the output voltage from the Wheatstone Bridge is related to the strain of the strain gage by: where:

V out

V in

A

S g
 
in


2 .
500
5
(


out
g

2 .
085 (
)
Note that ΔV out
is the voltage_read minus the
‘voltage_with_no_load_on_the_bike’.
The equation can be solved to give the strain as a function of the output voltage.
The stress ( σ ) in the fork can be calculated from the strain ( ε ), by using Hooke’s law:
 
E

Where E is the Modulus of Elasticity
For the bike fork (steel) E = 29.0 x 10 6 psi (pounds force per square inch).
Lab Procedure
1. Set up the data logger as described in the instruction sheet.
2. Toggle the BATT switch to ON.
3. Toggle the DATA switch to ON when members are ready.
4. Collect voltage data with the data logger for each member of your team. Use the following sequence for tests (all times are approximate):
 5 seconds for an unloaded bike.
 5-10 seconds for rider 1 in riding position (no pedaling).

15 seconds for rider 1 pedaling
 5 seconds for unloaded bike.
 5-10 seconds for rider 2 in riding position (no pedaling).

15 seconds for rider 2 pedaling.
 Repeat above sequence for remaining riders
Bike Lab 3 Procedure
WHHS Updated 07/17/02 mjh 1

* In the riding position the feet are on the pedals and the hands are on the handle bar.
3. Toggle the DATA switch to OFF.
4. Toggle the BATT switch to OFF.
5. Upload the data from the data logger to the PC and save it to a disk.
6. Import the data into Excel and save it as a spreadsheet.
After Lab
1. Open the .csv file in Excel by selecting ‘File’, ‘Open’,’3 ½ Floppy’,’All files’,’Open’. In the spreadsheet, create a column of time data as described in the data logger instructions.
2.
Select Excel charting, ‘XY Scatter Plot’ and plot the raw voltage data vs. time and identify each event on the graph, i.e. unloaded bike, rider 1 gets on, rider
1 sits on bike, rider 1 pedals bike, etc…..
3. Calculate the strain at each data point.
4. Calculate the stress at each data point.
5. Create a graph of stress vs. time. Label your graph.
6. Using average value of stress for each rider in the riding position while pedaling, create a plot of stress vs. weight of each rider. Create a linear trend line for the data and show the equation of the line on the graph.
Prepare a team Lab Report using the standard format given and include the following:
 Plot of raw voltage data with activities labeled

Plot of stress vs. time
 Plot of stress vs. rider weight with trend line equation
 First page of s preadsheet (don’t include all pages of data)

Sample calculations (calculating strain from voltage, calculating stress from strain)
Bike Lab 3 Procedure
WHHS Updated 07/17/02 mjh 2