Correction and finalizing the construction

Correcting common problems in LEGO Mindstorms robot constructions

We will demonstrate the common mistakes students make when building a robot.

Un/intentional mistakes

The robot will not move exactly as programmed because there are some intentional errors in the construction. Fix these errors and avoid them in future constructions. 

Frictionless or frictional

Blue axle pins have intentional friction and are used for stable building. Thеse must be replaced with beige frictionless axle pins.

Caster wheels

The rear wheels a.k.a caster wheels must not have tires, as tires create friction with the ground during turns which is not desired. We will go into detail about caster wheels later in the course.

Tires distance and bushes

Bushes must be placed between the tire and the motor so that the tire does not move toward the motor and jam it. Also, a bush on the outer side of the rim will prevent the tire from moving out or even falling.

Stability of construction

Stabilize the motors, which are unstable now and need to be stabilized, with a beam connecting them together, or at a second point on the brick.

Task for fixing the EasyBot robot construction

Do it yourself, fix the errors in the construction of the EasyBot

Correct the rear wheels

Change the friction axle-pins for the rear wheels with frictionless pins.
Remove the tires from the rear wheels, if you have added any.


Corrections on the motors

Add bushes around the wheel rims. One between the wheel and the motor, and one on the outside of the wheel so that it does not accidentally fall off.
And finally, connect the motors to the brick at a second contact point so that the motors are more stable.


Introduction to EV3 Controller - the LEGO Mindstorms EV3 brick

Let's review the LEGO Mindstorms EV3 Intelligent Brick

The EV3 brick is the main computer of your LEGO robot and it has a display, a few buttons and various ports.

The openings are called Ports. There are a few types of ports - USB ports, SD port, cable ports.

Mindstorms cable ports

Cable ports are two types.

On top with letters A, B, C and D are the *output* ports - with these the brick sends commands to the motors.
Below are the input ports with numbers 1, 2, 3 and 4. With these, the brick receives information about the world around it. Usually, sensors provide that information.


USB ports

There are two USB ports on the brick.
Next to the output ports, there is а micro USB port that is used for establishing a connection with a computer. You are going to download programs from your computer to the Brick via that port.
The other standard-size USB port is used for the so-called "Daisy-chain" mode, where you connect two EV3 Bricks. This mode will be covered later in an advanced EV3 course.


SD card

If you happen to need extra memory, you can add an SD card to your EV3 brick. Usually, that is not needed as the robot has 16MB internal memory.

The rechargeable battery

This is the battery and you should leave it alone most of the time. If you happen to open it, here is how you close it back. Keep the spring on position.
The brick is running a simplified linux OS and that is why it starts for about 30 seconds.

Starting the Brick

Press the central dark gray button to turn on the brick. It boots а Linux OS and starting and stopping the brick will take some 30 seconds after which you will hear a sound signal.

Using cables to connect the motors to the brick

We will learn how to connect and disconnect LEGO cables and on which ports exactly to connect the motors.

A cable is used to connect the Brick with the motors. In the future you will connect your sensors with cables, too.
The cables transport electrical power and electrical command signals from the Brick to the motors and the sensors.

How to connect and disconnect them properly

Make sure to hear the click sound when pushing the cable in the port. This way the cable is fixed in the port and will not fall off on its own.
In order to disconnect it, just press lightly on the transparent plastic part of the jack that comes out of the port.

Cable length

There are three types of cables by length - use the optimal length for each situation. Use а short cable when the motor/sensor is close and а medium or long cable otherwise.

Default motor ports

Always respect the default ports for each motor and sensor.
Large motors must be connected to ports B and C.

Task: Connect motors to the brick with cables

We will demonstrate how to connect the brick and the motors by using cables correctly and reliably.

Cable lengths

Any pair of cables will do. For your convenience use two cables of the same length.
There are three types of cables by length - use the optimal length for each situation. Use a short cable when the motor/sensor is close and a medium/long cable otherwise.

Output ports

The brick ports A, B, C and D are output ports. These ports send commands from the brick to the motors. This is called output.

Managing cables

Long cables must be taken special care of. Make sure they are not near tires or moving parts, as they might get tangled.
In order to force the cable to position, a simple loop is enough. Twist the cable and let the twist forces keep the cable at the desired position.

How to connect and disconnect them properly

Make sure you hear the click sound.
Always respect the default ports for each motor and sensor.