Using LEGO building blocks to build robot and bridge

Categories: BuildingRobot

The goal of this project is to use LEGO building blocks to build a robot, using chopsticks, glue and rope to construct a bridge. Besides the robot has to go over the bridge and then go through the bridge opening. The comprehensive results are calculated with the quality of the bridge from each team and the total time consumed by the process of going over the bridges and going across the bridge. Through the joint efforts of all members in the Robot Downey team, this project was accomplished with high quality and the robot passed the final test successfully.

The robot in Robot Downey team has the characteristics of low center of gravity, speciality of going uphill and rear wheel drive. In addition, a bridge with reasonable structure, strong bearing capacity, wide bridge opening and light weight was built according to the weight and the structure of the robot,

In the whole process, a series of problems such as unstable follower, high center of gravity, deviation of robot from the preset trajectory, low accuracy of turning angle, long driving time, excessive weight of bridge, improper handling of bridge deck and incline joints had hinder the course of Robot Downey team.

After extensive inquiry of relevant information, reading the corresponding literature, discussing together, doing experiments on each prototype of the models repeatedly, the above problems were solved one by one. And Robot Downey team finally perfectly met the requirements of the electrical design project.

In the robot test on 13th week, the bridge weight of Robot Downey team was 11 ounces according to the field measurement data and the total time for the robot to complete the whole process was 10.

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9 seconds, with a total score of 294. After analyzing the final results and considering the internal factors of robots and bridges, Robot Downey team evaluated the design, pointed out the shortcomings appeared the design, production and experiment. Then some corresponding suggestions were put forward for improvement.


  • Motivation for the work

According to Dr. Peter’s introduce video, all of the students were required to build a robot and create a chopstick bridge. The second requirement was to let the robot go over the bridge deck and then go through the bridge opening. As is known to all, the contemporary college students are rich in theoretical knowledge but their actual hands-on ability is relatively deficient. By taking electrical design course, students can develop their innovative inspiration and improve their hands-on ability by designing and manufacturing. As the project being conducted, students’ communication skills and cooperation ability can also be improved. In conclusion, the motivations are not only finish the objectives of building the robot and bridge then testing them until they can meet the requirement, but also improving students’ practical ability and experiencing the importance of teamwork in a project.

  • Goal establishment
  • Build a robot with compact structure (to minimize height), proper width and weight.
  • The center of gravity of the robot should be lower enough to ensure that it won’t turn over during the uphill.
  • Construct a well-designed bridge with stable structure and proper weight to avoid sliding when robot is going uphill.
  • Bridge design should be as relevant as possible to the characteristics of robot so as to reduce the total test time.
  • The programs should be accurate and suitable, it’s also required to enable the robot to finish all the processes with the shortest time.
  • Every member in the team are asked to take part in the project to make sure that the design can be completed perfectly before the due date.
  • Description of expected returns
  • It’s beneficial for students to work on a real engineering project and do the teamwork.
  • Everyone will be aware of the significance of teamwork further.
  • Everyone will improve the ability of teamwork and technological innovation.
  • Everyone will make great progress on the practical application.
  • Specifications and constraints

1. The bridge:

  • The length of the bridge is 108.5cm.
  • The width of slopes is 19.5cm.
  • The length of the deck is 39cm.
  • The width of the deck is 14cm.
  • The height of the bridge is 15cm.
  • At the junction of the bridge deck and the slopes, two chopsticks were used to connect the deck and the slopes. The width of the interface is 1.2cm.
  • The deck is made up of the ten basic unit structures that were glued by three chopsticks. The width of the structure is 5.5cm.
  • The slopes are made up of the eight basic unit structures that were glued by three chopsticks. The width of the structure is 4.5cm.

2. The robot:

  • The length of the robot is 23cm.
  • The width of the robot is 15cm.
  • The height of the robot is 13cm.
  • The weight of the robot is 0.55kg.
  • The height of the underpan is 2.5cm.

Literature review

  • Brainstorming and Research Process Records

1. Bridge Part

After collecting information on the Internet and studying Conceptual design of bridge [1] , we found inspiration and finally determined the structure of arch bridge. In the book Bridge structure mechanics [2] , we learned the analysis method of geometric composition and learned that the superstructure of arch bridge includes arch ring and arch building, the substructure includes pier, foundation and arch hinge. Therefore, we designed the supporting part of the bridge into a triangular structure. After discussion with team members, the initial draft model was designed (see Figure 1, Figure 2, Figure 3) and a detailed design of the supporting part and the connecting part was made. In order to reducing the weight of the bridge, the bridge deck was designed with hollow design and laid according to the width of each tire. Considering the difficulty of the robot passing through the bridge deck and turning, the slope was lengthened and the angel was also minimized.

Figure 1. Three views draft of the bridge,

Figure 2. Perspective view of the bridge,

Figure 3. Bottom connection part,

2. Robot Part

By searching for information on the Internet, some knowledge about robots is known?According to Mei Hong, Li Yunxia and Li Wenge:” Robots with wheels have the advantages of light weight, large load, convenient to drive and control, fast speed, flexibility and high efficiency.” [5] After coming up with some thoughts, the design team checked some photos about the robots with wheels (see figure 4)

Figure 4. Photo of robot model with wheels on the Internet,

In order to increasing the stability of the robot during the course of running, we decided to design a four-wheels robot. After the discussion of the design team, rubber tyres will be used in the driving device in order to increasing the friction between the wheel and the surface to prevent skidding. The first prototype of the robot model was designed. Here is the sketch. (see figure 5)

Figure 5. The Initial model of robot,

  • Related information

1. Bridge Part

(1)According to Xiang Haifan (2011) ” Most Bridges are arched. The most important reason is the need for structural mechanics. The main force on the bridge is the load weight of the bridge deck and its own weight, these forces are vertical downward. Arches are used to transfer vertical forces to transverse piers or to the shore floor, which can widen the width of the passage under the bridge or reduce the number of piers. This is both scientific and elegant. It is a kill two birds with one stone design.” [1]

(2)On the relative webpage , it is said: “Arch bridge consists of arch ring, arch structure, pier and foundation. Arch ring is the main bearing part of bridge span structure. The bridge span structure above the arch ring becomes the superarch structure to support the bridge deck. The arch with reasonable design mainly bears the pressure but bears little bending moment and shearing force”. [3]

(3)On the relative webpage , it is said: “Consider the architectural roof of the Shanghai expo as a reference and crossbar material should be placed alternately. Crossbar material at both ends of the direct force is easy to break, try to shorten the distance between the stress point.” [4]

2. Robot Part

(1)Mei Hong, Li Yunxia and Li Wenge (2013) said: “Wheeled or caterpillar mobile robots have the advantages of high efficiency, but their adaptability to the ground is poor. Generally, they can only run on relative flat ground. The motion stability of wheeled robot is closely related to the road condition.” [5]

(2) According to Zhao Tiejun and Sun Jian (2009) “Stability analysis can be divided into static stability and dynamic stability. Static stability is only related to the kinematic model of the robot. It means that when the robot is in a static or low speed state, the vertical line of its center falls in the support plane determined by the landing position and makes it in a balanced state. Dynamic stability refers to the system balance of the robot in the course of walking or operation. It is related to kinematics model and dynamics model at the same time.” [7]

(3) According to Ge Jun (2012) “When a car is running, the rubber will produce large elastic deformation repeatedly under the action of larger micro-convex body and tread pattern. Because the internal friction of rubber will lose part of mechanical energy, the resilience of elastic deformation of rubber is always less than that of the elastic deformation of rubber. These two resultant forces compose the friction force. A part of that is the post-elastic phenomenon. Therefore, the supporting force of the road to the rolling tire is no longer directly below the axle, but leans forward, resulting in a moment that prevents the wheel from turning. ” [8]

Project objectives

1. The aim of this project is to build a bridge with chopsticks.

2. A further aim is to get the robot across the deck and through the hole in a relatively short period of time.


  • Brainstorming

From the beginning, we searched some structural drawings of the foundation of the bridge on the Internet and preliminarily determined two types of bridge forms, including the arch bridge and the cable-stayed bridge. After discussion, considering the design difficulty and material problems, we decided to build the arch bridge and drew the design drawing in detail. In order to reduce the weight of the bridge, we designed the deck to be hollow out and laid according to the width of the tire. For crane span structure, we wanted to use the triangular stable structure to support the entire bridge surface. Considering the difficulty of getting on the bridge and turning, we lengthened the slope length and reduced the slope.

According to the robot introduction diagram, we knew the general structure of the robot. In the power part, we planed to design two active wheels and two driving wheels. Considering the difficulty of turning, the rear wheel drive is adopted. For the car body part, in order to prevent the upper bridge from turning over, we lengthened the car body, lowered the center of gravity, and made the body part close to the center of the whole robot. The connection part, we intended to connect the main engine with the front wheel, and the main engine with the chassis for overall stability.

  • The process of building the robot

After the brain storming, the construction of the robot was separated into several parts: the actuating device construction; connection part; and reinforce part. From the ideas which were produced from the brain storming, the production team created the first prototype of the robot.

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Using LEGO building blocks to build robot and bridge. (2019, Dec 18). Retrieved from

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