Introduction: Deployable Bridge

Hello! We are Legineers, one of the groups in the course VG100 in UM-SJTU Joint Institute. We designed this deployable bridge as one of the projects in this course, and we are here to teach you how to build this bridge yourself.

Step 1: Concept Diagram

The bridge consists of the following components and functions:

1 3 5: Strings

One end of the string is bound to the axis of the motor while the other end of the string is glued on the surface of the bridge.

2 4 6:Motors

The motors can rotate clockwise and counter-clockwise, changing the length of the string.


The hinges allow the bridge to rotate smoothly.

8:Motor Holder

The motor holder can fix the motor and keep it at a certain height.

Step 2: Materials List


Arduino Uno/¥138($19.71)/1

Balsa Wood Board/¥121.4($17.34)/25

L298N Motor Driving Board (red)/¥20.86($2.98)/2

DC Motor (GA12-N20)/¥48($6.72)/3

Plastic Parts/3D Printing/¥0($0)/2

Bread Board/ id=599542959185/¥5.18($0.59)/1

DuPont Line/¥8.46($1.21)/40



Cotton String/¥15 ($2.14)/3

Nails/Provided in Lab/¥0($0)/22

Battery Pack/¥7($1)/2


Step 3: Bridge Assembly

1. Wood Cutting

a. Cut the balsa wood (3mm in thickness)

a.1. Cut eight sticks of size α1(3mm*10mm*290mm, pic.4 above),

a.2. Cut 8 boards of size α2 (3mm*80mm*290mm),

a.3. Cut 2 triangles of size α3(55mm in width*60mm in length),

a.4. Cut 2 triangles of size α4(80mm in width and length),

a.5. Cut 2 sticks of size α5(3mm*11mm*165mm), one sticks of size α6(3mm*30mm*165mm),

a.6. Cut 2 boards of size α7 (3mm*80mm*200mm), cut them with paper knife.

b. Cut the balsa wood (5mm in thickness) into 12 bricks of size β1(5mm*25mm*32mm, pic.2 above), 4 sticks of size β2(5mm*10mm*160mm) and 4 sticks of size β3(5mm*16mm*180mm).

c. Glue each two of the boards α2 together with wood glue into the big rectangle board and two board α7 together with wood glue.

2. Fabricating the abutment and tower

a. Stick the triangle α3 and 2 sticks α5 to the stick α4 with wood glue as is shown in the pic.6, pic.7 &pic.8.

b. Make a lid for the tower using 3mm balsa wood(30mm*20mm). Stick them to the existing tower.

c. Stick the tower to the middle of the deck of the abutment.

d. Drill 4 holes (30mm between the center of the circle on each side and 160mm between the center of the circle on different sides) at the end of deck to make sure they can be fixed on the abutments with screws.

3. Fabricating the bridge body

a. Stick the four α1 sticks to the big rectangular board evenly in terms of distance. (pic.8)

b. Glue another rectangular of the same size onto the sticks.(pic.9)

c. Repeat step a. on the small rectangular board.

d. Stick two wood bars vertical to the sticks on each side of the recatngular board.

e. Fabricate a small wooden box that a motor can just be put in.

f. Stick the wooden box between the two α1 sticks in the middle.

4. Hinge and Install

a. Drill 4 tiny holes on the end of each components.

b. Use hinges and screws to connect each two parts of the bridge body.

c. Make the motor holder with wood sticks and glue.

d. Fit 3 motors into the 3 small boxes respectively.

Step 4: Control Circuit

Shown in picture above is the diagram of the circuit we used in our bridge.

Several important notes on circuit connection:

1. DC Motors from top to bottom: motor on the short board, motor on the long board, motor on the abutment.

2. The breadboard is used solely to connect the power supply to the Arduino Uno and L298N modules, and you can use one as small as you want.

3. The 9V battery is a placeholder for any kind of power supply. In practice, you can use about 3-5 AA batteries with battery boxes or use a 9V battery.

4. You can choose as you wish whatever pins on the Arduino board to connect to the L298N modules, just remember to change the corresponding pin number in the control program.

5. If the DC Motor is rotating in the opposite direction, swap the pins connected to the L298N module.

6. Make sure to use wires with appropriate length when connecting. If the wires are too short, the bridge may break during deployment.

Step 5: Control Program

Shown above is the main control program for the bridge. After uploading it to the Arduino board, in the serial monitor, input ‘D’ for deployment and ‘R’ for retraction.

Notice the numbers shown in red. Because of speed differentiations in each of the DC Motors, you should test the bridge and change the numbers so that it could work properly.

Step 6: Final View & Troubleshooting

After all assembly and program testing, the bridge should be ready to go!

Here are some notes to common problems:

1. Wait until the wood glue is dry. Otherwise, the wood can’t be tightly sticked together.

2. Curve the end of DuPont Line. This way, the DuPont lines can be tightly connected to the motor. Or the lines might fall off the motor.

3. Add circular disks to the end of motor spiales. This is to prevent the strings from falling off the motor spiales when the spiales rotate.