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Building Junkbots—Robots from Recycled Materials

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Grade Range
Group Size
2-3 students
Active Time
1 hour
Total Time
1 hour
Area of Science
Key Concepts
Circuits, friction, engineering design
Ben Finio, PhD, Science Buddies
Junkbots Lesson Plan Introduction


Junkbots are easy-to-build robots that you can make using a simple circuit and some recyclable materials. In this lesson, your students will learn about engineering design as they compete to build the fastest robot. No previous robotics experience is required!

Learning Objectives

NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
This lesson focuses on these aspects of NGSS Three Dimensional Learning:

Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Science & Engineering Practices Engaging in Argument from Evidence. Evaluate competing design solutions based on jointly developed and agreed-upon design criteria.
Disciplinary Core Ideas ETS1.B: Developing Possible Solutions. A solution needs to be tested, and then modified on the basis of the test results, in order to improve it.
Crosscutting Concepts Cause and Effect. Cause and effect relationships may be used to predict phenomena in natural or designed systems.

Structure and Function. Structures can be designed to serve particular functions by taking into account properties of different materials, and how materials can be shaped and used.


Household materials used to build a junkbot

To build a junkbot you will need a motor, a battery pack, and two double A batteries. Other household items include a cardboard box, glue, rolls of tape, scissors, plastic cup, plastic bottle, cork, popsicle sticks, paper clips, plastic straws, metal cans, and a cardboard tube.

For each student or small group of students building a robot, you will need these items in the Bristlebot Robotics Kit from our partner Home Science Tools (also available as a Classroom Kit specially priced for teachers):

For the entire class, you will need:

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson.

In this project, your students will build a simple circuit by connecting a motor and a battery. When the motor and battery wires are connected as shown in Figure 1 (top), electrical current can flow in a complete loop, called a closed circuit, and the motor will spin. However, if one pair of wires becomes disconnected, the complete loop is broken and this creates an open circuit (Figure 1, middle), so the motor will stop spinning. Finally, if the exposed metal parts of the wires touch each other, this creates a short circuit, which will stop the motor and cause the battery pack to get hot (Figure 1, bottom). As the robots move and jostle around during class, wires can come loose or bump into each other, creating open or short circuits. This is the number one thing to look out for when students claim their robot is not working.

Wiring diagrams of a battery and motor showing an open circuit, closed circuit and short circuit

A battery must be correctly connected to a motor for both to function properly. In an open circuit, there is no connection between the wires of a battery and motor so the motor receives no power (motor does not spin). In a closed circuit, the positive and negative leads are connected and the motor receives power (motor spins). If the positive and negative leads between a battery and motor are crossed then a short circuit occurs and the motor receives no power (motor does not spin).

Figure 1. Open, closed, and short circuits.

Your students will attach an off-center weight (a cork) to the motor's spinning shaft. This makes the motor vibrate, causing the robot's entire body to wobble. This is the same concept used to make cell phones and video game controllers vibrate—they have tiny motors with off-center weights inside. However, without some careful design choices, junkbots will tend to move randomly or spin in circles. The key to making them move in a (relatively) straight line is directional friction, or making sure the parts of the robot that contact the ground have more friction in one direction than the other. Think about rubbing your finger along sandpaper—it will be rough in any direction. Now think about petting a dog or rubbing your finger along a toothbrush with slanted bristles—it will feel smooth in one direction but rough in the other direction. The same concept can be applied to junkbots by giving them slanted legs (Figure 2). Robots with slanted legs will tend to move more consistently in the direction with less friction.

Diagram shows the angle of legs on a robot will affect the direction of its motion

When vibration based robots have legs that are perpendicular to the ground the motion of the robots will be random as horizontal friction forces are equal. However, robots with legs that are angled to the ground will experience lower friction in the direction the legs are angled and cause the robot to move in that direction.

Figure 2. Slanted legs can be used to give a robot directional friction so it moves forward.

There are many other design factors your students will have to consider when building their robots. They can identify cause and effect relationships between these elements and the robot's movement. For example:

  • Robots that are too tall or skinny might fall over easily.
  • Robots that are too heavy might move very slowly.
  • Robots that are too flexible might move more slowly than stiffer robots.
  • Robots that are not sturdy enough might fall apart due to the vibrations from the motor.

Your students will follow the engineering design process to build their robots and address these problems. The objective is to build a robot that can move forward to cross the finish line of a short race course (as opposed to spinning in circles or moving randomly). It is important for students to understand that there is no single "right answer" to an engineering project. There are many different robot designs that could meet the objective, and it is OK if their designs do not work very well on the first try. The process is iterative, meaning they might repeat the steps of designing, building, and testing multiple times until they get a working robot.

Prep Work (5 minutes)

Engage (5 minutes)

Explore (50 minutes)

Reflect (5 minutes)


Make Career Connections

Lesson Plan Variations

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