Introduction: Movable Bridge


◇Our Team
We are team Insight with five outstanding future engineers (see figure 1). Our team name is Insight because we are working hard be engineers who have an insight in human needs and then meet them, who have an insight in human future and then improve it. These above are reflected in our team logo (see figure 2), which consists of five keys and a key hole in the center. We five teammates hope to open the door to the future like five keys and make the world a better place.

◇Where Do We From
We are from University of Michigan-Shanghai Jiao Tong University Joint Institute (UM-SJTU JI) (see figure 3), located atMinhang district of Shanghai. Our institute focuses on engineering, especially mechanical and electronic and computer engineering, and is committing to cultivating world-class engineers. Compared to some traditional ones,our institute is relatively new but it is thriving and will have a lot to offer.

◇Course& Project Information
VG100 (Introduction to engineering) is a unique course dedicated to laying a solid foundation for our future excellence as an engineer who will benefit the world. This course requires creativity, engineering basic theories, hands-on ability and above all, teamwork. The Movable Bridge is our first project in this course for fall semester 2019. We made a bridge which can deploy and retract automatically. The rules and restrictions are as follows.

1. The material for the bridge must be balsa wood and wood glue. Other materials (especially metal) can only be used in the construction electrical devices.
2. The bridge should be 700mm-750mm long and 160mm-200mm wide.

3. The bridge can be fixed in a box before deployment and after retraction.

4. The bridge can be deployed automatically within 1 minute and retracted automatically within 1 minute.

5. The bridge can hold 1000g-3000g load or more than 3.33 times of its own weight.

6. A 90 mm wide car can be placed on any part of the bridge.

Step 1: Concept Diagram

Step 2: Material List

NO. Items Descriptions Quantity Price (RMB) Hyperlink

1 Balsa wood a.500×100×5mm b.500×100×3mm a.8 b.4 84

2 Sandpapers CW1000,A4 3 2.55

3 Bread boards Small type 2 8

4 Batteries& Battery case Load 2 batteries (7.4V in total) 1 28

5 Arduino R3 1 19.5

6 Servo motor a.SG90(90~180º) b.S3003 a.2 b.1 a.20.62 b.30

7 Switches 6×6×4.3mm 2 0.1

8 Bolts M5×20mm M4×20mm a.2 b.2 0.3

9 Gromments d4mm×d6mm Thickness:0.3mm 100 5.9

Step 3: Step-by Step Process

Step 1: Scratch on paper and then by AutoCAD (see concept diagram).

Step 2: Prepare materials (see material list).

Step 3: Cut balsa woods into expected shapes by laser cutting.

Step 4: Use wood glue to connect different components. (Construct three main parts----two halves of bridge floors and one side of pier)

Step 5: Screw the screws through the holes at the connecting points of the three main parts mentioned above. Step 6: Write codes by Arduino and store them into two servo motors. Step 7: Bound the SG90 servo motors onto the center of the bridge and a S3003 servo motor at the connecting point of the floor and the pier.

Step 4: Final Views

Step 5: Arduino Codes


Servo servo1;

Servo servo2;

Servo servo3;

Servo servo4;

int pos; int i;

void setup() {










void loop() {

if (digitalRead(6)==LOW){

for (pos = 180; pos >= 0; pos --) {





for (pos = 90; pos<= 140; pos ++) {






if (digitalRead(7)==LOW){

for (pos = 140; pos >= 90; pos --) {





for (pos = 0; pos <= 180; pos ++) {







Step 6: Circuit

Step 7: Game Day Results

Weight: 293g

Deployment: Pass

Retraction: Pass

Size test: Pass

Load test: 1.5kg

Bonus Infinite load: 10kg

Total Score: 108.25 out of 100

(High: 126.5 Mean: 51.1 Low: 5)

Step 8: Video Hyperlinks