2. Lesson 2 - Third Wheels and Square


Today we will test different support wheels and determine which one is most suitable for a robot that we will send to the moon.

The robot on the moon will be powered by a solar battery, but that means it has very little electricity and must not waste much of it to turn and navigate. You will need to find which support wheel resists the least when turning.

Another terrible problem would be if the robot got stuck. It will be too expensive to send a mechanic to the moon to help him. We will have to determine which wheels would get stuck easily in a small hole and which wheel can the robot pull out.

All teams should build different third wheels after which students can swap them.

At the end of the lesson, the most successful teams will be awarded a bonus task!

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Construction and Theory

Today we will build and compare several different third wheel constructions which support the robot.

The teacher will distribute the four constructions shown in the lesson among the class teams so that each team builds a different third wheel.

Young Earl Bot - Simplified LEGO Mindstorms Robot

The goal of these building instructions is to build a simple LEGO Mindstorms EV3 robot without wheels. You should then think of yourself how exactly to add the wheel. Which wheels would you use on the front? How are you going to build the third wheel? Here are for example a few recommendations on building the third wheel - 1, 2, 3, 4 

Later on you can expland this construction with a grabber as demosntrated here

How to choose your third wheel for a LEGO Mindstorms EV3 robot

Take a look at the constructions. Some of the wheels move left and right freely and this is necessary to increase the rates of maneuverability of the robot. Choose wisely. Because if you don't..well you can choose again. No pressure here. 

Castor wheels and non-turning wheels

What is special about the wheels which do not turn left and right and when do we use such third wheels? Wheels with low rates of maneuverability are used in robots which have to execute forward-backward movement. Robots with such wheels turn very hard. Still, if our robot has such a wheel and we what it to turn without changing the construction, we can just remove the tire from the rim. This will reduce friction and the robot will turn easier.

Horizontal and vertical attachment

It is important to notice that in some of the constructions the pins attach to the robot vertically while in others – horizontally.

You can use the various constructions for building robots in the future.

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Now, after the robot is built, close the box so that it's out of your way and the desk is clear.

  1. Collect all parts from the desk and put them back in their places in the box.
  2. Close the box and move it to the side so it's not in your way.

Programming and theory

Today we won’t cover any new material but will make some revision of what we already know. We will review how to turn 90 degrees and how to work with the loop block. Use Loop.

90-degree turn with LEGO Mindstorms robot

The 90-degree turn of the robot is different from 90-degree turn of the motor!

90-degree turn of the motor

Ninety degrees are a quarter of a rotation of the wheel. During a pivot turn, only one motor is turning. A quarter of a rotation is a very short distance and the result is that the robot moves only a little.

90-degrees turn of the robot

The expected result of a 90-degree turn of a robot is that the robot spatially turns 90 degrees to the side. That turn is very different from the quarter-turn of the motor.

Test different castor wheels and comment on the differences

You already have your square with the robot.

Now, let's compare different castor wheel constructions. Build them all or borrow them from other students in the classroom. Take turns so that everyone can use every caster wheel construction and note the results in the challenge below.

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A reward after completing the challenges for Third Wheels

Additional tasks. Yes. That's the reward. And it is awesome

Depending on how well you solved the challenges, your teacher can give you one of the two extra challenges:

 - Change the wheels of your robot and test. Adjust the program if needed.


 - Add a grabber to your robot. Program the medium motor to close and open the grabber. Grab an object.

Earl Bot - Grabbing and Clearing LEGO Mindstorms Robot without wheels

The goal of these building instructions is to build a LEGO Mindstorms EV3 robot without wheels. You should then decide on your own how exactly to add the wheel. Which wheels would you use at the front? How are you going to build the third wheel? Here are some recommendations on building the third wheel - 1,2,3,4 

Tasks to finish a class

  1. Take pictures and make videos of your robots
  2. Disassemble and arrange the robot
  3. Arrange your workplace
    • It is important to arrange the electronics of the robots on the cover of the box.
    • Wind up the programming cable so that it is assembled.
    • Put the robot cables next to the electronics.
    • Wind up the mouse cable around the mouse.
    • Wind up the cable of the laptop charger in a way that your teacher will show you.
    • When you turn off the computer, leave it next to the robot box.
  4. Turn off all programs on your computer
  5. Exit FLLCasts  
  6. Shut down your computer
  7. Put your chair under the desk.