Introduction: Deplorable Bridge

Background information

We are team Tech Union, from University of Michigan-Shanghai Jiao Tong University Joint Institute (UM-SJTU JI), which is a world-class educational and research institute situated on the campus of Shanghai Jiao Tong University (SJTU) in Shanghai, China. Our team consists of four JI freshmen as well as one exchange student from the United States. We are all fond of engineering principles and hope to create meaningful projects for the common good.

Rules & Regulations

1. The whole structure of the bridge must be constructed by balsa wood (the connection part can use other material).

2. Only Elmers wood glue can be used to connect different parts.

3. Cables are allowed in the deployment and restriction test, but they must be loosen in the Load Test.

4. The distance between abutments on the two sides is 700mm long. If the bridge is quite long, the actual distance between two abutments can be adjusted to fit the bridge, but the part exceeding 750 mm will be deducted each 10mm.

5. The completed bridge needs to pass size test(twice), deployment test, retraction test, and load test (at the one quarter and three quarters respectively). Every part of the test has the corresponding grades, and the lower one will be used as final grade.

6. A team could get some bonus points if their bridge is exceptional in some way.


Balsa wood (10*10*500) (mm)

Balsa wood (12*12*300) (mm)

Balsa wood board (3*100*1000) (mm)

Arduino Uno R3

L298N RC DC Motor Driver Module

Nylon rope (2mm)

Battery (12V 1500mA*h)

Eimers glue (236ml)

GW12N20 DC motor (12V 10r/min)


Dupont line

Screws (M5)

Step 1: Concept Diagram

Build concept diagrams above using SolidWorks

Step 2: Preparation of Material

1. Sticks of different length (3 sticks of 365*10*10mm, 3 sticks of 350*10*10, 2 sticks of 150*10*10mm, 6 sticks of 170*10*10mm, 1 stick of 120*10*10mm, 1 stick of 320*10*10mm, 24 sticks of 50*10*10mm, 20 sticks of 70.5*10*10mm, 1 stick of 130*10*10mm,2 round sticks whose diameter is 5mm and length is 180mm).

2. Planks of different size (6 planks of 170*100mm, 1 plank of 170*50mm, 1 plank of 170*65mm, 6 planks of 5*5mm).

Step 3: ​Process of the Material

1. Burrow holes on one side of the three 365mm sticks, both sides of the three 350mm sticks, one side of the 150mm stick. The centers of holes are 7.5mm away from the margin and make sure that they are in a line.

2. Burrow holes on.

3. Polish edges of the long sticks to arch.

4. Select the 130mm stick and cut off both of its edges after which forms a vertical flat and a horizontal flat.

5. Burrow 3 holes on the two 150mm sticks respectively and make sure their distance are 30mm.

Step 4: ​Construction of Different Parts of the Bridge

a) Main loading parts

1. Take out 3 long sticks (365*10*10mm), 12 short sticks (50*10*10mm) and 3 planks (170*100mm), a plank (170*65mm).

2. Apply glue to the long stick and stick six short sticks vertically to the long stick whose length between each other is 50mm.

3. Repeat 1&2 and complete the 2 kinds of frame parts.

4. Place the two 365mm sticks paralleled whose width is 170mm (including their width).

5. Stick 3 170mm sticks to the long sticks perpendicularly in average.

6. Apply glue to the planks and stick the planks to the prepared long sticks.

7. Cover the bottom of frame with planks.

8. Build another one with 350mm sticks in the same way.

b) Basis and controlling part

1. Prepare sticks of different length (2 of 150mm, 1 of 160mm, 1 of 320mm, the polished stick).

2. Stick the shorter sticks to the two sides of the long stick.

3. Select the stick of 320mm and stick it to the middle of the long stick vertically.

4. Stick the polished stick to the vertical stick and make sure that the bottom of this can reach the ground.

c) Process of splice

1. Place two loading part and the basis in right places to make sure that their holes are in lines (the one with 350mm sticks is in the middle).

2. Select three sticks more than 16mm and insert them into the holes.

Step 5: Installment of Electric Controlling Devices

1. Enwind strings to the wheels of the motors and apply glue to the side on wheels to fix them.

2. Glue two motors on the vertical stick of the basis, one of which is on the bottom while the other one is on the top.

3. Fix the Arduino board and L298N DC motor driver module and connect wires.

4. Twine the string from the bottom motor to the connection stick between two loading part.

5. Twine the string from the top motor to the opposite side of the bridge.

Step 6: Circuit Coding and Testing

1. Download necessary software: Arduino IDE, fritzing(for circuit design).

2. Design Circuit Diagram using fritzing.

3. Code the bridge

<p>int input1 = 4;<br> int input2 = 7;
 int input3 = 2;
 int input4 = 8;</p><p> void setup ()
  pinMode( input1 ,OUTPUT);
  pinMode( input2 ,OUTPUT);
  pinMode( input3 ,OUTPUT);
  pinMode( input4 ,OUTPUT);
  Serial.begin(9600);             //set pin modes
}</p><p>void loop ()
  char x;;
  if (x=='d'){                            //For deployment
 digitalWrite ( input3 ,HIGH);
 digitalWrite ( input4 ,LOW);
 digitalWrite(input2, HIGH);
 Serial.println("deployment complete!");
  } else
  if (x=='r'){                           //For retraction
    digitalWrite ( input1 ,HIGH);
    digitalWrite ( input2 ,LOW);
    Serial.println("retraction complete!");
  if (x=='c'){                            //Canellation for unexpected conditon

Step 7: Final System Views

The pictures above are taken during the race.