MAS.863 How to make (almost) anything.
Assignment October 27, 1999: Materials and Processing
Stefan Marti


Design a bridge and test to failure.


This assignment was actually a contest: Who can make the bridge with the best load-to-weight ratio? The main constraints were: span 8.5 inches, can't weigh more than 60 grams.

My bridge is made out of three pieces of balsa wood, each one looking like that:



The balsa was cut with the laser cutter, probably with a bit too much power. That's why the edges are a bit dark.



Then I glued them together with carbon fiber cloth and epoxy resin:



It looks like burned, but it's not: that's just the black carbon.



And that's how the bridge looked like shortley before it was "tested."



We will have more pictures of the testing process, and even a movie that shows how it crashed.

Anyways, important is: my bridge won! Here are the results:


Bridge testing data

Bridges loaded to failure conditions. Data listed in testing order.

Winning entry was Stefan, with 46.9 N/g and a N/N (strength to weight ratio) of 4785.7

Name

Grams

Newtons

N/g

N/N

Notes

Egon

31.65

269

8.50 N/g

867.3

  

Stefan

30.97

1454

46.90 N/g

4785.7

Winning entry. Carbon fiber and balsa wood.

Adam

17.33

131.6

7.59 N/g

766.7

  

Ben Resner

27.60

612

22.17 N/g

2239.4

  

Dan

10.45

69.9

6.69 N/g

575.8

  

Diana

15.45

144.2

9.33 N/g

942.4

  

Jim

55.76

961

17.23 N/g

1740.4

  

Ben Piper (1)

67

1553

23.18 N/g

2341.4

  

Saul (1)

7.81

137.5

17.60 N/g

1777.8

Lightest bridge.

Saul (2)

10.94

141.2

12.91 N/g

1304.0

  

Ben Piper (2)

105

5000

47.62 N/g

4810.1

Strongest bridge. Loaded with disk. Maxed out load tester.

Rich (1)

8.96

8.3

0.93 N/g

94.5

Folded paper bridge.

Rich (2)

29

104.3

3.60 N/g

363.6

Folded carbon fiber, bad epoxy cure.

Kimiko

16

149

9.31 N/g