Crane Strain

Challenge Problem

Design and construct the lightest crane boom that will support a 10 pound load.

Criteria and Constraints

The crane boom must attach to the tower provided.
The pin for crane boom mounting is one-half inch (½") in diameter and 3 inches tall.
All joints must be glued (no mechanical fasteners).
You may not touch the tower or the boom during testing.
The boom must hold a weight fourteen inches (14") from the tower center.
The maximum length of the boom is twenty inches (20").
A mechanism must be provided at the end of the boom for attaching the test hook.

Resources

People: Teams of two students.

Information: Facts and knowledge the individuals possess or obtain and instruction from the teacher. The key terms involved in this challenge are tension and compression, and live load and dead load.

Materials

One piece of ¼" plywood or hardboard (3" x 6")
Forty (40) craft sticks
Glue

Tools and Machines: Students will use appropriate tools and equipment available in the technology laboratory.

Time: 8 Class Periods

Capital: Provided by School

Achievement

Use the engineering design process to solve this problem

Investigate the Problem: Read these rules. Ask the teacher questions. Participate in a one day West Point Bridge Building competition in your class.
Pick a Solution

Open MDSolids on your computer.
Click on Trusses and then New Truss.
Make the horizontal and vertical spacing interval 1 and the grid 20 by 15.
Model the pin for crane boom mounting with a 3 inch vertical member on the left side of the grid with a fixed support at the top and a roller on the bottom.
Draw a truss of your own design that will support a weight 14 inches from the first member. Craft sticks are about 4 inches long.
14 units from the first member add a load of magnitude 10.
Compute the truss.
Make changes to your design to improve it. In general: reduce the maximum load on any member, avoid long compression members, and eliminate members that carry no load (except for the first member that carries the supports).

Make a Prototype (working model)

Note: Everyone in the production area must be wearing safety glasses before any work is done.

Divide the 3" by 6" piece of hardboard into two halves. Find the center of each half (draw diagonals) and then center punch and drill a ½" hole in each half.

Note: Make sure that you clamp the piece down when using the drill press and that you ask the teacher for permission first.

After the holes are drilled, cut the piece of hardboard in half.
Glue the craft sticks to form two of the trusses that you designed. Use binder clips to hold the joints while the glue dries.
Glue the side trusses to the pieces of hardboard so that the hardboard pieces are one above the other not more than 3" apart.
Create a wind truss to hold the two sides together.
Make sure that you provide a place to attach the hook for the weights that is 14" from the two ½" holes.

Test and Improve: Place your crane boom on the tower. Hang the 10 pound weight at least 14" from the pin. If your boom holds the weight, then weigh your boom. If it looks like the boom is easily holding the 10 pounds, add additional weight if available. Your efficiency is the live load (10 pounds, or more) divided by the dead load (weight of the boom). As time permits, modify your boom and test again.
Document Your Efforts: Write down everything you decide and everything you do in your engineer's notebook as it happens. Make sure you write down test results and have a witness sign. Sketch a picture of your truss in the engineer's notebook. Label the sketch.

Evaluation

Performance (20 Points)

The efficiency of each boom will be calculated by dividing the live load (10 or more pounds of weight carried) by the dead load (weight of the crane boom). The boom with the highest efficiency will be declared the winner.

Product — Crane Boom (20 Points)

An innovative, correct, detailed, and well-engineered solution.
All detail requirements met.
Well constructed to close tolerances. Accurately reflects plans and drawings.
Light, efficient, and sound structure.

Product — Informational Report (10 Points)

Provide an informational report in the required format. It will be evaluated for content (2.5 points), organization (2.5 points), style (2.5 points), and presentation (2.5 points) using the standard rubric.

Make sure the report

Contains the required information.
Shows calculations in enough detail to determine if results are correct.
Demonstrates an understanding of the various factors that determine the strength of a boom.
Contains your Gantt chart and approved design(s) from MDSolids. These should be introduced, integrated, and discussed in the text of the report.
Contains a sample calculation for efficiency.
Contains enough information in the Details section to support the conclusions.

In addition to the general requirements, use this guidance.

Summary

Write this section last. The summary (or abstract) should be a clear and concise 3 or 4 sentence version of the report. Be sure and include your best result and most important conclusions. Here is a prompt for the summary:

The goal of Crane Strain was to…. Our boom… and it carried *** times its own weight. The best boom design is one that…

Introduction

Summarize the tesk for a student who was absent. Be sure and include all rules and limits.

Then explain the terms tension and compression and the terms live and dead load. Explain how efficiency is calculated.

Details

Tell the whole story from the beginning in several well-organized paragraphs. Tell what you expected your boom to do and how this compares to the results that you got.

Make sure that you include enough information to support each of your conclusions.

Conclusions

What was your best result? Live load, dead load efficiency?

What did you learn by taking part in this challenge? About structures? About working in teams?

If you could start over tomorrow with a new boon design, what would it look like?

Make sure you are being specific. Go back to the Details section and make sure that all of your conclusions are supported.