Hello! We are Alligators, a team of VG100 from UM-Shanghai Jiao Tong University Joint Institute. University of Michigan-Shanghai Jiao Tong University Joint Institute is located in 800 Dong Chuan Road, Minhang District, Shanghai, 200240, China. Joint Institute is an excellent institute where international views, rigorous scholarships and spirits of engineers are advocated, and students are educated to possess innovation abilities and leader spirits.

Racing Rules & Regulations
The bridge we built is ranked according to 5 tests.

The first part of the race is called “weight test”, where the whole bridge, together with electronic products is put on an electronic scale to get its weight. Note that batteries are excluded.

Then, we will fix the bridge on one abutment within 3 minutes to prepare for the size test. In the size test, the bridge should fit in a box with the size 350mm*350mm*250mm.

After that comes the function test. The function test includes two elements, the deployment test and the retraction test, which require the bridge to be deployed and retracted automatically within 1 minute for each test.

The third part is the load test. In the load test, a weighted plate is placed at 0.25 and 0.75 length of the span. As long as the deflection is less than 2mm, and the loads doesn’t achieve 3000g, more loads will be added. The score is the smaller load of the two positions. The final score of the weight test and the load test is to rank the ratio of loads and weight.

The link below is the video of our performance on the gameday:

function test

Step 1: Concept Diagram

Shown above is the concept diagram of our design.

The wood we use in this bridge is all balsa wood.

We use bolts at the connection part to enable the bridge to rotate so that it can achieve the function required.

We use Arduino Uno board, stepper motors and lines to lift up the bridge.

Also, some springs are used to help deploy the bridge above the connection part.

Step 2: Materials List

Item Price Hyperlink

Balsa wood 194 RMB(27.2 USD） https://m.tb.cn/h.eo8hcrM?sm=578522

Wood glue 43 RMB(6.03 USD） https://m.tb.cn/h.eo85hvK?sm=a639d2

Bolt 88.1 RMB(12.4 USD） https://m.tb.cn/h.eMCLLLY?sm=a64198

String 10 RMB(1.4 USD) https://c.tb.cn/h.eMCPU9k?sm=ada4b4

Arduino Uno Board 138 RMB(19.5 USD) https://m.tb.cn/h.eLPwQa7?sm=84b1bf

5V Stepper Motor & ULN2003 Driver Board 9.82 RMB(1.4 USD) https://c.tb.cn/h.eLPE3xJ?sm=661ce7

Touch Switch 5.4 RMB(0.76 USD) https://c.tb.cn/h.eoKeksA?sm=6d39f9

DuPont Line 8.7 RMB(1.2 USD) https://c.tb.cn/h.eLXvDhp?sm=82c6e9

Spring 4.5 RMB(0.64 USD) https://c.tb.cn/h.eLCbWvb

Step 3: Circuit Diagram

Shown above is our circuit diagram.

All we use is an Arduino Uno Board, a 5V Stepper Motor & ULN2003 Driver Board and a touch switch.

The stepper motor is used to control the angle of the string precisely to achieve the best outcome. And the touch switch is used to control on&off of the circuits.

Step 4: Construction Process

a. i) Attach component No.1 and No.2 together.

The operation of both sides is the same.

ii) Attach 5V Stepper Motor to component No.6

iii) Attach the product of step ii) to component No.3

iv) Attach the product of step i) to the plane of the product of step iii)

v) Attach component No.5 together to form a product which will be used in the following steps.

Notice that the quantity is two.

vi) Attach the product of step 5 to the product of step iv)

Notice that the picture is the effect picture with bridge deck B.

vii) Attach the springs to the slope of the product of iv). Since that we want to increase the length of springs, we add a piece of wooden brick to the bottom of one spring. Like the picture.Another side is similar.

viii) At last we form our bridge deck A.

b. i) Attach component No. 7 and No.8 together. And the same for another side.

ii) Attach the springs to the slope of the product of i). Since that we want to increase the length of springs, we add a piece of wooden brick to the bottom of the springs.

iii) Attach the product of step ii) to component No.9.

Notice that in order to make the wooden brick right on the middle pillar, we attach component No. 9 to make the bridge bottom flat.

iv) Attach the product of step iii) to component No. 15

Notice the effect of it is similar to step a.

v) Since that we want the bridge to support more weight, we use a wooden brick instead of two wooden strips.

vi) At last we form our bridge deck B.

c. i) Attach component No.10 together and then attach them to component No. 11

ii) Attach the “L” shape components tightly to the surface of the sides. Like the picture shows.

Notice that the springs on deck B can successfully reach the “L” shape components and get compressed.

iii) Attach the product of step ii) to component No. 13 and then we can form our bridge deck C.

d. Now we are going to connect deck A B C together to form the whole bridge.

i) We use bolts to connect each deck A and B, B and C.

ii) Then we attach one side of the string to deck C and another side rolled to component No. 14 which is capped onto the 5V Stepper Motor.

iii) Finally, we roll up the bridge. Then we have made our final product.

Step 5: Final View

Step 6: Reflection

On the gameday, our bridge performed perfectly in function test. However, due to some carelessness on not reading the manual well, we get a deduction on the size test about width.

The main problem of the bridge is that it almost fails the load test. This is partly because that though each part of the bridge is symmetrical, the whole bridge isn’t symmetrical, which means the first part weighs more than the third part so that it causes unbalance. So, to avoid such cases, the tip is to make the bridge balanced, which means symmetrical here.