Introduction: Movable Bridge

We are L^4, coming from JI,which is short for University of Michigan-Shanghai Jiao Tong University Joint Institute. JI aims to cultivate students with innovation, internationalization, interdisciplinarity and quality. As a special institute, JI has many different aspects from other institutes in Shanghai Jiao Tong University, such as unique curriculum system, special arrangement of terms, honor code and plenty of chances to go aboard. JI makes us improve rapidly.

The course VG100's instructors and teaching assistant hold a movable bridge competition. Movable bridge competition requires us to build a bridge using balsa woods, cotton string and wax craft paper. We have to apply our knowledge about structural analysis, programming and mechanics for this project. We have to work as a group to finish our project. In the game day, our bridge will be tested on a few aspects: the function test, vertical weight test and assembly test(optional).


a) Restrictions:

1.Material: Use only balsa woods, cotton string and wax craft paper to build your bridge. You can use the ELMER Wood Glue to stick them. Other materials such as metal and 502 super glue can only use in the movable and rotating parts.

2.Attachment: The bridge can’t attach to other items exclude the abutments.

3.Size: Length--700mm, you can move the abutment to fix your bridge length;

Width-- 200mm to 250mm

b) Functions:

1. Your bridge should able to transform to let the big car(400mm*200mm) pass through and the small car(height=80mm) go through your bridge.

2. You can only use Arduino Uno to move the bridge.

3. Vertical deflection should not exceed 4mm when 1000g load is added.

Result: We get 39.96 out of 100 among 19 groups for the function test and load test

Here is the video of our movable bridge.



Step 1: Material List

Step 2: Concept Diagram

Above is the concept diagram of our bridge.
Our bridge is unique for its structures. Firstly, our bridge is designed to be able to assemble. There are totally eight upper plates and eight floor beams and two side plates. The side plates hold the upper plates, which are stuck onto the side plates. On each part of the bridge, there are four upper plates and four floor beams, which are used to share the pressure and avoid structure failure. What is the most impressive is that all the plates can be taken down and put into a small box. Secondly, we use cables and shorings to support the bridge. The cables conduct forces to the tower while the shorings conduct forces directly to the I beam. There are four strings on each side of the bridge, which serve to connect the bridge and the tower in order to reduce deflection of the bridge.

Step 3: Circuit Diagram

The electric parts of the bridge is mainly composed of an Arduino UNO, two Ultrasonic Sensors, one Servo motor, two Collision Sensors, led lights, one breadboard, two Speed Reduction Geared motors, one L298N Motor driver, and one Li-poly battery.

It is essential for an automated bridge to detect the cars on the bridge and ships under the bridge. Therefore, we put two Collision Sensors on both sides of the bridge to determine whether there are cars on the bridge and we also put two Ultrasonic Sensors under the bridge to detect the ship.When one sensor detects ship, the signal light will turn from green to red and the barrier gate will close. When cars all go off the bridge, the motors will pull the strings connected to the bridge and open the bridge. Once the other sensor detects the ship, which indicates that the ship has passed the bridge, the motors will loose the strings to put the bridge down. Then, the light will return green and the Servo motor will open the barrier gate, ready for cars to go across the bridge.

Step 4: Step by Step 1: Constructing the Bridge (1)

1) Cut down four trapezoids(as shown in the first picture) which length is 350mm, and the width should be 80mm and 10mm, one lengthside of the trapezoid should be parallel.The thickness of the trapezoid should be 3mm.

2)Cut a big triangle hole in the middle of the trapezoid(as shown in the first picture).

3)Make four rectangular (10mm*20mm) on the trapezoid.

4)Cut down eight rectangular(Rectangular A)about 220mm*60mm. The thickness of the rectangular should be 3mm.

5) Cut down a rectangular about 20mm*160mm at the middle of the Rectangular A.

6) Put the eight rectangular on the trapezoids. Make sure the rectangular could fit the trapezoid.

7) Cut smaller rectangular(Rectangular B,as shown in the second picture) and glue it under the Rectangulars A .The length of the Rectangular B should be longer than 20mm. The space you left should be able to fit the rectangular of the trapezoid.

8) Glue a small board on the first rectangular of your trapezoid to create a pilar.

9)Make a hole on the pillar.

Step 5: Step by Step 1: Constructing the Bridge (2)

1) Cut down eight rectangular(Rectangular C) with 220mm*87.5mm. The thickness of the board should be 2mm.

2) Make two holes on each Rectangular C. The hole you make should be able to let you put it on the trapezoids.

3) Cut two hole at two piece of your Rectangular C(shown in the first picture).This Rectangular C should be able to fix the pillar.

4)Cut four piece rectangular about 60mm*40mm (shown in the second picture) and glue it with the Rectangular C and plastic hinge.

5)Make a hole on the rectangular(as shown in the second picture).Your hole should be able to fit into the abutment.

5) Your bridge structure should be similar as the third picture( You can change it yourself if you don't like it).

Step 6: Step by Step 2:Constructing the Tower

1) Cut down 4 pieces of board about 100mm*40mm. The thickness of the board should be bigger than 2.5mm.

2) Make 3 holes on each of the board. The position and diameter of the holes depend on your abudment.

2) Cut 8 pieces of cubic about 20mm*20mm*20mm.

3) Cut 4 trapezoids with 260mm of length, 100mm and 50mm of width.

4) Cut triangle on the trapezoid(as shown in the first picture).

4) Make a hole on two of the trapezoids to put your speed reduction gear motor.

5) Make a hole on the other trapezoids to put your rotating rod. Its diameter should be 5mm.

6) Glue two cubic to each trapezoids at the edge of the widest side.

7) Glue the whole structure you make in step 6 on the board. The cubic should be glue opposite to the hole of the board.

8) Make a long cylinder, length should be 200mm and diameter should be 5mm.

9) Attach the long cylinder to the speed reduction gear motor.You can use 502 super glue to glue it.

Step 7: Step by Step 3: Circuit Assembly

1) Cut 3 pieces 120mm*7mm board.The board should be able to stuck in your tower(as shown in first picture).

2) Glue one collision sensor to middle of the board.The height of the collision sensor should be 80mm to the abutment.

3) Put all your circuit on the boards( shown in second picture).You can rearrange the position of all the component yourself.

4)Glue the servo motor on top of the cubic. Remember to check the direction of the servo motor before you glue it.

5)Put the rotation rod in the top of the tower and glue the speed reduction motor to the tower.

6) Put one of your ultrasonic sensor at the middle of the bridge.

7) Put another ultrasonic sensor beside your bridge and glue it to the abutment.

Step 8: Step by Step 4:Structure Assembly

1)Glue two cotton string at the rotating rod and the pillar at the bridge(as shown in first picture).The cotton string should be tight and parallel. Remember to check your motor direction before you glue it.

2)The cotton string at the middle part is optional. You can attach it at the bridge and the middle of the tower.

3) Make sure your dupont lines are long enough to attach to other side of the bridge.You can use tape to wrap the connection of your dupont lines.

4) Attach your tower on the abutment as shown in the second picture. Remember to fix the hole using the screw.The end of the bridge should be able to contact with the abutment.

Step 9: Step by Step 5: Final System View

So, this is the final view of our movable bridge. The size and the hole of the abutment are conditional. Perhaps you pay more attention on this part. If not, the tower's hole will not fix the abudment.