Your Challenge: Tug-of-War
Your team will design a vehicle that can pull with the greatest force possible.
Your vehicle can include only two VEX V5 Smart Motors. You will use the
Vernier® Go Direct® Force and Acceleration sensor to measure how much
force your robot pulls with. You will also measure your robot’s success by
competing in tug-of-war battles with classmates.
1. Construct an initial prototype. For help constructing your tug-of-war
machine, use the VEX V5 Build Support Guides.
INSERT PHOTO OF VEX ROBOT
2. Create a Tug-of-War code onto your VEX V5 Brain. This code makes
your robot drive forward until the code ends.
3. Consult the python reference (attached Schoology resource) to create
your code. You can also use the help section of VEXCodeV5 software to
help create your code.
INSERT SNIP OF YOUR WORKING CODE AND MOTOR SETUP
FROM THE VEX V5 SOFTWARE
Note: Your code should be designed to run two motors plugged into Ports 1
and 2. Make sure your motors are plugged into these ports; otherwise, the
code will not work. If you want to change the direction your robot drives,
switch the port each motor is plugged into and the drive direction will
switch.
a. Use the Vernier Go Direct Force and Acceleration Sensor to
measure how many Newtons of force your tug-of-war machine
pulls with.
Additional Information: If you need further guidance or support, review
the Graphical Analysis and Sensors and Probes resources.
b. Hook the sensor to the back of your robot. To get the best
readings, select a square hole toward the center of a C-Channel
or similar metal assembly piece as shown in Figure 1. Once
attached, hold the sensor firmly in place.
Figure 1. Example Force Measurement Setup
c. Have one partner start collecting data in the Graphical Analysis
software while the other partner runs the Tug-of-War code on the
VEX V5 Robot Brain.
i. View the graph of your data and determine the force
exerted by your tug-of-war machine.
d. Perform steps 3a–c several times to eliminate any errors in
measuring.
SNIP THE VERNIER GRAPH AND RECORD THE MAXIMUM
FORCE YOUR ROBOT EXERTS
4. Engage in an initial competition.
a. Connect your robot to another group’s robot using a 1x25 Steel
Bar (Figure 2) so that your robot pulls in the opposite direction of
the other robot when you run the code.
b. Position the midpoint of the steel bar perpendicular to the
midpoint of the tug-of-war centerline (shown in Figure 3).
c. When both teams are ready, simultaneously run the Tug-of-War
code on each robot and see what happens. Whichever robot pulls
the other one across the centerline,
wins!
Figure 2. 1x25 Steel Bar for Tug-of-War
Figure 3. Example Tug-of-War Competition Setup
5. Be sure to record your results. Did your vehicle pull the competing
vehicle over the line? Was your vehicle pulled over the line? Was it a
tie?
ANSWER
6. Reflect on your design. Why do you think it performed the way it did?
What factors affected your vehicle’s ability to maximize its pulling or
pull force? In particular, consider the following questions:
a. How could you use gears to maximize the pull force of your
robot?
b. How does your robot’s mass impact how much weight it can
pull?
c. How might friction impact your robot’s tugging ability?
ANSWER THE ABOVE QUESTIONS IN A FEW SENTENCES
7. Iterate on your initial prototype and make sure to incorporate the
concepts of mass, gearing, and friction.
VEX V5 Build Support Guides: For help incorporating gears into your
design, reference the VEX V5 Build Support Guides.
8. For each iteration, use the Vernier Go Direct Force and Acceleration
sensor to measure the pull force exerted by your tug-of-war machine,
and complete at least one tug-of-war battle with another group. Record
your results and note how your iterative changes impacted your
robot’s pulling performance.
DISCUSS CHANGES YOU MADE TO YOUR BOT TO IMPROVE YOUR
COMPETITION PERFORMANCE
INSERT A PHOTO OF YOUR REDESIGNED ROBOT
Conclusion
1. How did you apply your understanding of energy, work, and power to
your design?
ANSWER
2. Did your robot reach maximum motor power? How do you know?
ANSWER
3. If you repeated this challenge, what would you do differently? Why?
ANSWER
4. Outside of farming and tug-of-war, list examples of other situations
where devices or machines are optimized to pull with a lot of force.
ANSWER
