Introduction: 【S.A.】Movable Bridge

About: We are S.A. from JI in SJTU! S.A. -----stay aware, stay awake, stay alive!

1 Background Information

We are team S.A. from University of Michigan-Shanghai Jiao Tong University Joint Institute, which is usually called JI. JI is located on the campus of Shanghai Jiao Tong University Minhang District. The education in JI is guided by the principle “Internationalization, Interdisciplinary, Innovation, and Quality”. JI develops a unique educational system featured Chinese and American educational philosophies and fosters future innovators and leaders with a global perspective.

2 Course Information

The full name of VG100 is Introduction to Engineering. The purpose of the course is to introduce students to technical communication and technologies. It features two main projects, focusing on shaping a real-world overall perspective on engineering.

3 Project Information

Project1 is to build a deployable bridge which can be deployed to let cars pass over and retracted to let boats pass under. The evaluation of the bridge is based on weight, load, size, deployment and retraction. Our team got the grade of 109.15,ranking 2nd among 20 groups. We passed all the function tests smoothly, but didn’t do a great job in the infinity test because of the overall design. Here’s the video of the Game Day! View our video here

4 Rules & Regulations

a. Retraction and deployment

1. The procedure of deployment and retraction should be automated within 1 minute.

b. Size

1. The bridge should be able to be fixed in a cubic box (350mm * 350mm * 250 mm) before and after the Retraction and deployment Test.

2. The length of the bridge ranges from 700mm to 750mm.

3.The width of the bridge ranges from 160mm to 200mm.

c. Load

1. Load will be loaded on 1/4 and 3/4 the length of the bridge.

2. Maximum load is recorded when the vertical deflection reaches 2mm.

3. Ratio =Weight of Maximum Load/Weight of the Bridge will be used to rank. (The maximum load of a bridge is limited to 3000g.)


1. Structural components: balsa wood

2. Wood Glue: Elmer’s

3. Cable: any materials

4. Construction of Electrical Devices: any materials, especially metal.

5. Structural Connections: any materials permitted by the instructor.

5. Function

1. It can deploy from one abutment to another and retract automatically.

2. It can afford about 8kg loads.

3. It is designed to let the cars pass by when deployed, and let the ships go through when retracted.

Step 1: Material List

Step 2: Concept Diagram

The concept diagram and dimension are shown in the pictures.

Step 3: A. Build the Deck

1. Cut 3mm wood sticks into 16cm long.

2. Glue every 3sticks together.

3. Construct them into cross structure.

Build 2 decks.

Step 4: B. Build Slope Faces and Top Faces

1. Cut boards of 3mm thickness into battens of 1cm width.

2. Construct frames (16*12cm and 16*10cm) for four slope surfaces and one top surface.

3. Attach small wood particles to the joints to stabilize the structure.

Build 4 slope faces and 2 top faces.

Step 5: C. Build Side Faces

1. Use the balsa wood with 2mm thickness to construct a trapezoid (10cm in upper side width, 35cm in lower side width and 10cm in height)

2. Attach wood sticks between the upper and lower sides in order to transmit the pressure on the deck to the upper structure.

Build 4 side faces.

Step 6: D. Build Stands

1. Use 6mm balsa wood board and cut it into 8 small pieces(35*25mm).

2. Stick every 4 pieces together to construct 2 cuboids.

Build 2 stands.

Step 7: E. Assembly

1. Stick 2 slope faces, 1 top face,2 side faces and 1 deck together, to construct 1 part. Make two parts in total.

2. Stick two stands to the bottom of one of the deck.

3. Add hubs to the connection part to enhance the structure.

Step 8: F. Assembling Servos

1. Construct holders for servos according to a servo’s size.

2. Drill holes on side faces for fixation (Be careful not to get hurt)

3. Fix servos to the holders.

Assemble two servos.

Step 9: G. Fixation

1. Locate the holes on the foundation according to the holes on the abutment.

2. Drill holes with radius of 5mm on the foundation.

Step 10: H. Connecting

Connect the circuit as shown in the pictures.

Step 11: I. Trouble Shooting - Angle Adjustment

Problem: In order to fit in the box for size test, our bridge must get folded completely.

Measure: 1. Cut the outer and upper corners of the stands

2. Set the angles of two servos both 180°

Step 12: I. Trouble Shooting - File the Stands

Problem: The stands should be perfectly fit to the abutment so that the vertical deformation can be controlled to minimum.

Measure: File the stands to keep the bridge horizontal.

Step 13: Final System View

This is the final system view of the bridge!

Thank you for reading our instruction! Hope you can do this project successfully!