Introduction: Movable Bridge

About: We are META_XIII, coming from UM-Shanghai Jiao Tong University Joint Institute (JI).

We are META_XIII, coming from University of Michigan-Shanghai Jiao Tong University Joint Institute (JI). This demonstrative manual is made for our VG100 course design, a movable bridge controlled by Arduino.

JI was jointly established in 2006 by two premier universities, UM and SJTU. JI leads international education cooperation in China, featuring both American and Chinese educational styles. It is located in the Minhang campus of SJTU, southwest in Shanghai, where technology companies cluster.

There are two course projects in VG100, both of which require analyzing, scheduling and cooperating. This course prepares students for being engineers with 4 qualifications that JI appreciates, Internationalization, Interdisciplinary, Innovation, and Quality. In the Project1 competition, each group should build "a movable bridge" with specified materials, and the performance of bridge on game day makes a great difference to the course grade.

On the game day, all 19 groups should come to the lab in JI building and complete several parts of tests. The first part is the function test, where bridges should be able to stop the cars and then open to let a ship pass. We completed the whole process successfully and got the full mark. The second part of tests is the size and load tests. More scores will be attained if the bridge is lighter and better at load-bearing. We could bear 1kg within shape variables of 2.83mm. We ranked 9th in terms of the Aesthetics and ranked 8th in the weight test.

Finally our bridge got the grade of 76.7, ranking 4th .

There's a short version of rules shown below:

A. Function test process

a. A car A can pass the bridge.

b. When A is still on the bridge, a big ship C approaches the bridge from underneath.

c. The bridge can detect C, and lift itself after the car A leave the bridge to let C pass underneath.

d. After C passes, the bridge can return to normal in 15s.

B. Load test

Some small weights will be put on the bridge 100g more each time. Weights are added up to 1kg or until the deflection reaches 4 mm and then record the data.

C. Size test

The total mass of the bridge (including the circuit part except batteries) will be recorded and compared with other groups.

Video links:Click here to enjoy our gameday bridge video!

We hope the introduction can leave a general impression on you about our bridge.

Step 1: Concept Diagram

Step 2: Analysis

Here are some explanations for our calculation about the shape variables of the bridge so that we could design an extremely light structure that can bear more weight in theory.

This part involves the knowledge of force analysis and integral. We hope this can help you understand the principle and apply it to similar situations when you build your bridge.

Step 3: Materials List:

**The price of the wood glue, cotton wires, wax craft paper and other tools is not included.

Here are some hyperlink for the items you can buy at Taobao.

Arduino Uno(21.90)


Connection wires(27.61)

Motor Driving Board L298N(10.43)

Infrared Sensors 2-30cm 3.3V-5V(31.00)

Micro Servo(8.81)

Gear Motor(30.00)

Balsa wood board(402.5)

Balsa wood batten(232.06)



Step 4: Circuit Diagram

Shown above is a brief circuit diagram. Wires with different colours should be connected to corresponding logic mouths. All of the red wires mean 9V power supply. All of the black wires mean the ground. The green wire means the green LED as the pink wire means the red LED.

Two Gear Motors, which have 100 revolutions per second, offer the main force to lift the bridge. They are driven by a cheap motor driver, L298N coreless motor driver.

The Micro Servo is designed to turn a stick that will prevent a car from passing the bridge when the bridge has been lifted. It could rotate 90 degrees and return to the original place.

Four Infrared sensors are essential when detecting the car and the ship. They can be helpful to decide when the bridge should be lifted and put down.

The whole process that meets the requirements of the function tests should be conducted as following:

·Sensor 1 detects the approach of a Car A. Sensor 2 detects the approach of a Ship C. They send the signals to Arduino so that the red LED gives out light and the Micro Servo turns the stick to stop a Car B.

·Sensor 3 detects the departure of Car A. Then the Gear Motors start to run and lift the bridge to a proper height for the Ship C’s passing.

·Sensor 4 detects the departure of Ship C. They send the signals to Arduino. After an interval of 15s, the Gear Motors start to reverse and put down the bridge.

·The Micro Servo returns to its original condition and the green LED gives out light to show the permission of a Car B’s passing.

**Pay attention that Infrared sensors we use to build our bridge are not quite the same with the diagram shown above. We choose a kind of cheaper one that can be equally useful. The picture of this kind is shown in the material list.

Step 5: Fabricate Deck

a. Cut four 1m*120mm*3mm boards into 50cm long.

b. Draw several closely spaced right triangles with the size of 4cm-long and 3cm-wide. Reserve a space of 2cm wide each side and 0.5cm wide between triangles. Cut these triangles out with knives. **Be careful not to break the side.

c. Stick every two boards together with wood glue. Lay and stick a piece of wax craft paper on both sides of the decks.

Step 6: Fabricate Frames

a. Cut 3mm wood battens into 15cm、35cm and 38cm long . Slightly adjust their ends to proper shapes to fit into the frame without interstice. Glue them together. Then make 3 more identical triangles.

b. Cut several 3mm wood battens of proper size. Stick them with the (a) wood triangles to form several isosceles right triangle of different sizes. (This step is to increase its vertical stability and beauty.)

c. Cut and glue several 2mm wood chips to the connecting parts to reinforce them.

d. Cut several 5mm wood battens into 23cm. Set two (c) wood triangles apart with the distance of 23cm. Stick six battens between triangles. Make sure they are equidistant. Then make another identical one.

e. Go on to use 5mm wood battens of proper size to fill the space between (d) six battens with similar trigonal shapes. Stick them together. (d,e step is to increase its lateral stability, which is supposed to be tested but cancelled due to some reasons. So this structure is unnecessary for the requirements.)

Step 7: Assembly

a. Stick the deck with the frame. One frame’s cusp should exceed the edge of the board while the other one retracts.

b. Cut one of the (a) board into 35cm long

Step 8: Perfection

a. Drill four tiny holes on one end of the 35cm-long board . Drill two corresponding holes on a 24cm long board. Connect them with a hinge and screws.

b. Cut four 8mm wood battens into 15cm long. Drill a hole on each batten at the height of 12cm. Stick two battens to each board parallelly with a distance of 18cm. Then cut four 6cm sticks to reinforce the “towers”.

c. Stick a beam across the two battens.

d. Drill two holes on one end of the two boards. Thread the cotton wires through the holes on the bridge boards and vertical battens.

e. Drill six holes at the end of both decks to make sure they can be fixed on the abutments with screws.

Step 9: Circuit Assembly

a. Cut two 2cm wood cubes and glue them to the edge of the hinged deck in the last step . Then glue a Gear motor to each of the cube respectively. Glue the end of the thread to the spindle with 502.

b. Glue two infrared sensors downwards to the two cross beams (a). Glue another two infrared sensors to both sides of the frame, adjust them to be appropriate for detecting the ship.

c. Glue a micro servo to one of the batten on the movable part of bridge. Then glue a wood stick to it as a barrier gate.

d. Cut a small part of breadboard and attach it to the other batten on the movable part of bridge. Put a red LED and a green LED on the small breadboard.

e. Connect all of the wires and test repeatedly to ensure the feasibility of Arduino code.

Step 10: Final System View

Thank you for referring to our manual!

We hope it can give you some inspirations when you design your movable bridge.