Introduction: UniEng Deployable Bridge
We are team UniEng from University of Michigan – Shanghai Jiao Tong Joint Institute, consisting of five members from all geographical regions of China, ranging from the very north to the very south.
Our group name is made up of two prefixes: “Uni” and “Eng.” “Uni” is derived from “universal” and “unity” while “Eng” symbolizes “English” and “engineering” – and our team strives to become a collection and hybrid of these diverse essence.
Throughout the campus, the large grassland would come first on our preference list. Being a space of nature and openness, it could bring us a sense of carefree pleasure out of our daily packed schedules.
About Joint Institute
University of Michigan – Shanghai Jiao Tong University Joint Institute, formally abbreviated as Joint Institute or JI, is located in Minhang District, Shanghai, China. It combines the educational concepts and resources from both China and the US, thus forming a unique learning atmosphere which sheds new light on engineer cultivation and modern innovation.
About the course
VG100 Introduction to Engineering is a preliminary course in JI for freshmen aiming to help them fulfill future engineering qualifications. Besides in-class lectures and homework, the course also involves active engagement where students need to complete two group projects throughout the term.
Students enrolled in the course are randomly divided into twenty five-member groups. In the six weeks from September 11th to October 16th, all groups are required to build a fully automated deployable bridge as their Project One. Eventually, on the Game Day that marks the end of bridge development, the prototypes will be graded and ranked on the basis of a wide range of criterion and tests.
Step 1: Game Day Specifications
In the process of fabrication, rules are set upon the materials allowed to build the bridge.
> Only balsa wood and wood glue manufactured by Elmer’s may be used to construct the skeleton of the bridge.
> Metal components are not allowed to appear anywhere else than the digital circuits.
> Cables and ropes are allowed for aiding the deployment process but must not carry weight during the Game Day load test.
> Special structural connections may be employed in the bridge structure, but prior permission from the instructors is required.
The fabricated bridge prototype presented on the Game Day should stand the following tests.
> The bridge span should fall between 70cm and 75cm and width between 16cm and 20cm. An imaginary vehicle of 9cm in width should also be able to completely stand on the bridge.
> The bridge should be capable of deploying and retracting automatically when controlled with pre-installed circuits within 1 minute respectively.
> The bridge, before the deployment and after the retraction, should both fit into a cubic space measuring 35cm×25cm×35cm.
> The load that the bridge can hold at 25% and 75% length of its span with deformation below 2mm would be recorded, with “maximum load” being defined as the minimum of the two values. The “maximum load” should exceed both 1kg and 3.33 times of the bridge weight (from which power source is excluded) and only 3kg will be counted if it should surpass 3kg.
Additionally, bonuses are open for application to groups whose prototype is outstanding in terms of unique appearance, stable structure, exceptional load, etc.
Step 2: Material Preparation
A list of needed materials:
> Arduino Uno board (1×, ¥138 / $19.5, link)
> Dupont line (2×, ¥6 / $0.8 each, link)
> L298N motor driving board (2×, ¥10 / $1.4 each, link)
> Button (3×, ¥9.9 / $1.4 each, link)
> Bread board (1×, ¥6 / $0.8, link)
> USB cable (1×, ¥3.9 / $0.6, link)
> 11.4V Battery (1×, ¥48 / $6.8, link)
> 130 type DC motor (2×, ¥2 / $0.3 each, link)
> Tape (2×, ¥3.4 / $0.5 each, link)
> Balsa wood plank [6×100×330(mm)] (8×, ¥9.56 / $1.4 each, link)
> Balsa wood stick [6×6×500(mm)] (6×, ¥1.47 / $0.2 each, link)
> Balsa wood stick [10×10×500(mm)] (6×, ¥2.94 / $0.4 each, link)
> Plastic hinge (4×, ¥0.65 / $0.1 each, link)
A list of essential tools:
> Electric drill
> Utility knife
> Wood glue
Step 3: Concept Design
The whole bridge takes the form of three-fold. A short plank is sandwiched between two long planks, symmetrical on each side. When the motor is powered, the third plate is pulled up under the traction of the line, and the second plate is gradually lifted upright. Eventually, under the action of gravity, the third plate buckled onto the first, forming a symmetrical U shape.
The trapezoidal fence erected on the bridge slab not only supports the third plate in the contracting state, but also improves the load bearing capacity of the bridge.
To pull up bridge plate 2 and 3, we use the lever principle. As it is a hard lever, to guarantee the whole weight of bridge plate 2 and 3 can be held on, we make sure the two motors fixed on the supports have enough driving force to withstand the moment of 280g (the weight of the bridge plate 2 and 3) ×9.8N/kg×26cm (half the length of bridge plate 2 and 3) =0.7134N·m. From the result of this equation and some experiments we employ the ideal motors.
On the basis of analyses above, the concept diagram, exploded view and dimensioned views of the deployable bridge are generated with SolidWorks.
Step 4: Prototype Construction [Phase 1]
Phase 1: Processing wooden components
Out of the purchased wooden planks and sticks, create the following components with saw and utility knife:
> Cut one plank into a 16.5×5(cm) piece.
> Cut one plank into a 16.5×2(cm) piece.
> Cut one plank into a 6×18.8(cm) piece.
> Cut two planks into two 28×10(cm) pieces.
> Cut three planks into five 16.5×10(cm) pieces.
> Cut four planks into four trapezoids with 10cm in height, 20cm at top and 30cm at bottom. From each trapezoid, carve off five same triangles whose edges are 1cm away from the edges parallel to them. (As shown in image)
> Cut two 6×6×500(mm) sticks into two 32.4cm-long sticks.
> Cut two 6×6×500(mm) sticks into two 31.4cm-long sticks.
> Cut two 6×6×500(mm) sticks into four 16.5cm-long sticks.
> Cut one 10×10×500(mm) stick into two 15cm-long sticks.
> Cut one 10×10×500(mm) stick into four cubes measuring 1cm in edge length.
> Cut four 10×10×500(mm) sticks into four 33cm-long sticks.
Step 5: Prototype Construction [Phase 2]
Phase 2: Building bridge plate 1
1. Stick two (28cm×10cm) boards on the (6mm×16.5cm) sides with wood glue together.
2. Stick the (16.5cm×6mm) side of the (5cm×16.5cm) board onto the middle of (20cm×6mm) side of the board that has been processed in step 1.
3. Stick a (16.5cm×6mm×6mm) stick on the (16.5cm×5cm) side of the board that has been processed in step 2 and fix it on the 16.5cm-long edge.
4. Stick two 32.4cm-long sticks onto the bottom (the side that has had sticks on it) of the board that has been processed in step 2 and locate each of them one-third length from the 28cm-long edge.
5. Stick two carved boards of trapezoid onto the board that has been processed in step 4 and locate both of them symmetrically 2.25cm from the 28cm-long edge and 2cm from the 16.5cm-long edge. (As shown in image 1)
6. Drill three holes symmetrically 2cm from the 28cm-long edge in both sides of the board that has been processed in step 3 and locate the three holes in the same side 3cm between each other. (As shown in image 2)
Step 6: Prototype Construction [Phase 3]
Phase 3: Building bridge plate 2
1. Stick two (16.5cm×10cm) boards on the (16.5cm×6mm) side together with wood glue.
2. Stick two (16.5cm×6mm×6mm) sticks on the (16.5cm×20cm) side of the board that has been processed in phase 2 and fix both of them on each 16.5cm-long edge.
3. Stick two 15cm-long sticks on both (20cm×6mm) sides of the board that has been processed in phase 2 and their extruding part form the edge of board measures 5cm.
Step 7: Prototype Construction [Phase 4]
Phase 4: Building bridge plate 3
1. Stick two (16.5cm×10cm) boards together on (16.5cm×6mm) sides with wood glue.
2. Stick the (16.5cm×6mm) side of the (2cm×16.5cm) board onto the (16.5cm×6mm) side of the board that has been processed in step 1.
3. Stick the (16.5cm×6mm) side of another (16.5cm×10cm) board onto the (16.5cm×6mm) side of the board that has been processed in the phase 2.
4. Stick a (16.5cm×6mm×6mm) stick on the (16.5cm×32cm) side of the board that has been processed in phase 2 and fix it on the 16.5cm-long edge.
5. Stick two 31.4cm-long sticks onto the bottom (the side that has already had sticks on it) of the board that has been processed in step 2.5 and locate each of them one-third length from the 32cm-long edge.
6. Stick two carved boards of trapezoid onto the board that has been processed in step 1 and locate each of them symmetrically 2.25cm from the 32cm-long edge and 2cm from the 16.5cm-long edge. (As shown in image)
Step 8: Prototype Construction [Phase 5]
Phase 5: Building motor supports
1. Stick two 33cm-long sticks together with a cube in the middle using wood glue, which forms an H-shape.
2. Stick another cube between the two 33cm-long sticks and 1cm from the top.
3. Repeat step 1 and step 2 for the other motor.
Step 9: Prototype Construction [Phase 6]
Phase 6: Assembling the bridge
1. Stick two supports made in phase 5 on the board processed in step phase 2 and locate them 2cm from the 20cm-long edge and let them both match the 28cm-long edge.
2. Fix two hinges to the gap between bridge plate 1 and 2, with their outer sides aligning with the edge of bridge plates.
3. Repeat step 2 with another two hinges for bridge plate 2 and 3.
Step 10: Prototype Construction [Phase 7]
Phase 7: Installing motors and string
1. Fix two motors on each upper cubes of the two supports using tapes. (As shown in image)
2. Fix a motor on the middle of the bridge plate 1 and locate it 2cm from the 20cm-long edge.
3. Glue the end of three strings onto three spindles of three motors.
4. Glue another end of the string that is connected to the motor on the board on the 16.5cm-long edge (between bridge plate 1 and bridge plate 2) of the bridge plate 1.
5. Glue another ends of the strings that is connected to the motors on the supports on the edge between bridge plate 2 and bridge plate 3.
Step 11: Prototype Construction [Phase 8]
Phase 8: Implementing Arduino
The circuit diagram is first planned and generated with Fritzing. (As shown in image 1)
1. Attach Arduino output and input pins to the bread board by Dupont lines. (As shown in image 2)
2. Attach Arduino GND pin to the bread board by Dupont lines. (As shown in image 3)
3. Connect Dupont lines with the motor drive boards in order to use later. (As shown in image 4)
4. Connect motor drive boards with the Dupont lines that link to the output pins. (As shown in image 5)
5. Connect the motor driving boards with the positive and negative poles of the power supply. (As shown in image 6)
6. Arrange buttons that connect with the input pins. (As shown in image 7)
7. Link the other side of the button with the GND pin of Arduino. (As shown in image 8)
8. This is a overview of the finished motor and controller. The last step is to attach motors to the motor driving boards. (As shown in image 9)
Please refer to ar07FINALMo.ino for the Arduino code.
Step 12: Prototype Evaluation
The bridge, both in its deployed (as shown in images 1 and 2) and retracted states (as shown in images 3 and 4), is observed and inspected from different angles.
The final views of the prototype are recorded in the form of photos accordingly.
Step 13: Troubleshooting
"It is so hard to stick two boards precisely parallel on the 16.5cm×6mm sides due to their small contact area!"
Put the boards you have stuck together on a horizontal desk to stabilize. Also avoid touching it during the glue’s drying process.
"Polishing the boards actually causes error in the size of the planks / sticks!"
Cut bigger planks / sticks in size to make more room for polishing. (e.g. if you need a 15cm-long stick, cut a 15.2cm-long stick before polishing.)
"There is too much friction in the hinge, which makes deploying the bridge extremely difficult!"
Buy more hinges than your actual need and select the ones with the smaller friction. You may also consider adding grease to the hinges, or adding transparent tapes to the paths of strings to decrease external friction.
"I have encountered some complex problems with the bridge that are beyond explanation!"
Feel free to contact via email at email@example.com for more information and clarifications!