Sir Wilfrid Laurier S.S.
Technology Department

LEVEL 4 REPORT
CANTILEVER ARM
Problem Statement: To research, design, construct and report on the testing of a cantilever arm that can hold the most amount of weight in relation to the distance from the abutment.

Design Criteria
The specifications must be followed.
- A maximum of 6 pieces of wooden stick may be used.
- The structures minimum length 7 inches, width 2 inches wide and maximum height 3 inches at the roadbed. (tolerance +/- 1/8”)
- The wood cannot be treated in any way to change its strength or appearance.
- Wood pieces may be bonded together with cement ONLY at joints, and may not be laminated together in parallel fashion. If two or more strips of weed are placed parallel to each other, they must be at least the thickness of this paper apart from each other. Splitting or laminating is not allowed.
- You must design your bridge leaving at least a 1 inch opening at the end of the Cantilever Arm roadbed.
- The cantilever arm must be designed and constructed within the time limit.


20 FAST FACTS

1. A Torsion stress is when forces seek to coil and twist material.
2. Four sided cantilever arms are more stable than three sided cantilever arms for the torsion is distributed evenly.
3. Putting the dowel on top provides more stability because it tests the strength of where you place the sticks as opposed to the glue.
4. For less force to be put onto each stick, create smaller triangles on your bridge.
5. Put the sticks that create the width of the bridge on top of the sticks that create the length to increase overall strength.
6. Triangles distribute the weight onto supplementary sticks as it also secures the formation of your bridge.
7. For the arm to hold a mass, the foundation must be heavier then the free end.
8. Forces that attempt to cause materials to split and slide next to each other are labelled “Shear” stresses.
9. There are different types of truss deigns. They are as follows; King post truss, James Warren truss, Latice truss, Squire whipple truss, Pratt truss, Albert fink truss, William Howe truss, K-truss.
10. The strongest shapes to have on your bridge are triangles and arcs.
11. To aid the cantilever arm from bending while the mass is applied, add some support in the center.
12. Forces with the intention of stretching material and pulling it to one side are identified as “Tensile” stresses.
13. Sloping the beam assists to hold up the arm.
14. The shorter the length of the arm is, the more strength it will have.
15. A Compression stress is forces that strive to shove or press material together.
16. There should be enough support under the bridge to hold up more weight.
17. Descending energy is circulated among sections in triangular form.
18. Adding miter cut sticks diagonally to your squares give extra strength.
19. Cutting a section of wood in two doubles its potency.
20. Examples of cantilever arms would be: diving boards, balconies and large cranes.

SOLUTION CHART:
Criteria
#1
#2
#3
#4
#5
Strength
4
2
5
3
1
Potential to build in time given
4
4
0
3
5
Follows design-criteria
5
5
5
5
5
Able to build with only 6 sticks of wood
4
3
2
2
3
Ability to attach hook
4
3
4
3
3
TOTAL
21
17
16
16
17
Scale used:
Rank
Value
Awesome
5
Very Good
4
OK
3
Average
2
Poor
1
No chance
0

RATIONAL: From the criteria above, I found that going with thumbnail number 1 would be the best sketch to construct. There are a few things to consider when deciding on what cantilever bridge to build for this assignment. They are as follows: it must be strong, it must have the potential to be built in the short amount of time given, it must abide by the design-criteria set, you must be able to build it with only six pieces of 1/8” x 1/8” x 24” wood and there should be a space available on your project to attach the hook on which the bucket that will be full of weight is to connect to. As you can clearly see, design number 1’s total value is superior to the rest. Judging from the sketch, it should have enough strength to hold a good amount of weight, it can be built in the short amount of weeks given, it abides by the design criteria set, it should be able to be built of six pieces of 1/8” x 1/8” x 24” wood and it would be built in a way that could easily have a hook attached onto it.

BILL OF MATERIALS

PART
LENGHT
QUANTITY NEEDED
A
10”
2
B
8 1/8”
2
C
2”
8
D
2 11/16”
8
E
2 ½”
2
F
2”
2
G
1 5/8”
2
H
1 3/16”
2
I
¾”
2
J
2 1/8”
4
K
2 1/16”
4
L
2”
4
M
1 13/16”
4
N*
3”
1
O*
2 7/8”
1
P*
2 ¼”
1
Q*
2 3/16”
1
*= Not shown in technical drawing, internal webbing
TOTAL WOOD USED: 132.1875”
TOTAL WOOD WASTED: 11.8125”


TESTING

Name
Size (“) (lwh)
Weight held (lbs)
Magic number
(Length x Weight)

Observations
1
Cory
8 1/6 x
2 ¼ x
2 5/8

DQ
(27 pounds however)


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• Potential to kick out by abutment
2
Jordan
6 7/8 x
2 x
3

8
55
• Not enough support at the front end of the dowel
• Too much emphasis at the abutment
• Symmetrical design

3
Mitchell
7 1/8 x
2 1/8 x
2 5/8

16
114
• Hock didn’t fit; caused the sticks to shift and break
4
Robyn
7 x
2 5/16 x
3

DQ
(23 pounds however)


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• Side broke off; glue let go
• Too any sticks in the way

5
Amanda
7 5/8 x
2 ¼ x
2 ¾

DQ
(30 pounds however)

---

• Side let go; poor gluing
• Not proper support at the abutment

6
Layal
7 7/16 x
1 5/8 x
3 5/16

DQ
(4 pounds however)

---

• Not enough structure to prevent torsion
• Too narrow, too tall
• Hock was hitting a piece across bottom

7
Christina
7 1/8 x
2 1/16 x
2 3/8

23
163.875
• Glue let go at the bottom
• Wasn’t well connected to abutment; needed more glue

8
Charlene (ME)
8 1/8 x
2 1/3 x
3

32
260
• Front broke off; need more support in the front
9
Kyle N.
7 x
2 1/16 x
3

ND

---


---
10
Birinder
6 15/16 x
2 x
3 1/8

52
360.75
• Bad gluing at sides
11
Wahid
7 15/16 x
2 3/16 x
3 1/16

DQ
(7 pounds however)

---

• Poor construction
12
Ian
7 1/8 x
2 x
3 1/16

10
71.25
• Poor gluing at the abutment
• Glue gave away at the top


CONCLUSION: As seen from the ‘testing chart’ above, my cantilever bridge placed in second with 32 pounds giving me the magic number of 260 (length x weight)! It broke at the very front right where the dowel was placed. Obviously my bridge lacked enough support near the front because only two pieces of wood on one side at the front snapped off causing the dowel and bucket bull of weights to break as well. Before it broke however, my bridge must have required one more vertical 2” piece of wood to support one of the diagonal pieces at the bottom. The reason I did not add it before was because I had thought that the hock on which the bucket full of weights would need to be hung to, required that space to be placed on. However once I saw the hocked placed on my cantilever bridge for the first time, I noticed that adding that additional piece of wood would not have been in the way after all. If I were to redo this project, I would make sure to add that extra piece at the bottom. I’d also be more precise when cutting the bits of wood because on the side that broke, they were a little off the technical design causing them not to fit all too properly where they were supposed to. If I were to give any advice to someone who was to do this assignment in the future, it would be to add internal webbing to the bridge because as seen from my bridge’s performance, it was definitely beneficiary. Because I had added internal webbing to my project, my bridge was stronger and lasted a lot longer than it would have without it. This assignment has certainly taught me a lot about how to build a strong bridge. I’ve learnt that every single piece of wood needs to collaborate with one another because even one weak link can make the strongest bridge fall.