Angular Velocity: Sweet Wheels
A LEGO MINDSTORMS EV3 robot and its different wheel sizes.Copyright 2014 AMPS, NYU-Poly
Students analyze the relationship between wheel radius, linear velocity and angular velocity by using LEGO® MINDSTORMS® EV3 robots. Given various robots with different wheel sizes and fixed motor speeds, they predict which has the fastest linear velocity. Then student teams collect and graph data to analyze the relationships between wheel size and linear velocity and find the angular velocity of the robot given its motor speed. Students explore other ways to increase linear velocity by changing motor speeds, and discuss and evaluate the optimal wheel size and desired linear velocities on vehicles.
Being able to isolate one target variable and observe how it changes while holding all other possible variables constant helps engineers of all disciplines better understand how the target variable works within the constraints of the system. Engineering examples of isolating variables to observe how they respond in a constrained system include the stress testing of materials, integration of wireless transceivers, and culturing of proteins for specific tasks. As another example, when a company tests a new fertilizer, it uses standard soil conditions and a constant test plant with a known growth pattern in order to isolate the fertilizer as the variable. To test, the fertilizer is fed to a group of plants and their growth patterns are compared to the patterns of the constant ("control") plants that did not receive the fertilizer. Data analysis indicates whether or not the company should market the compound (due to positive results) or do more testing. In this activity, to determine what wheel configurations result in the robot traveling a 200-cm distance in the fastest time, students isolate and observe the wheel size variable, while constraining the problem to have the same power level and frame.
After this activity, students should be able to:
- Describe the relationship between wheel radius, diameter, angular velocity and linear velocity.
- Change a robot's motor speed and wheel radius/diameter to produce various linear velocities.
- Evaluate the design choice of different wheel sizes on various types of vehicles.