EV3 Phi. Teacher's Note about the motors with which to impress the students Pro Preview

Sometimes a good teacher needs a few tricks in his sleeve, so that he can surprise and entertain his students.


  • #375
  • 04 Feb 2017
  • 5:44

Motor and Generator are reversible

Connect two motors together with a cable. Turn motor one. Motor two will start turning. The reason behind this is that you hand rotating the motor generates electricity that travels to the other motor and makes it turn.

Using the generator effect

If you need to test a motor with an attachment and you don't have a program yet, you may connect two motors together and activate the attachment.

Servo motor with an encoder

EV3 LEGO motors are actually servo motors. That means that there is encoder inside that can measure the turning of the motor.

Synchronization between two motors

A move block controls both motors at once. If one of the motors is blocked or disconnected, the other will not move as well. This situation is detected with the help of the encoder in the servo motor.
The controller (the Brick) tells both motors to turn a little bit and measures the result of the turn, returned from the encoders. If there is difference, the faster motor must wait for the slower motor.
So when the cable is disconnected, there is no turning detected and both motors stop. When there is obstacle for one of the motors, the second one also stops.


In this video I'd like to stop at a few very important points for the teacher, for the instructor with which you can actually impress most of the students.

First, I'll remove the cables and now I'll connect both motors, I'll connect this motor like this to the other motor. So, we have no connection to the brick, we can actually remove the brick. I am not going to remove it because I need a constructed robot. But I have the two motors connected to each other. And now if I rotate one of the wheels, I am going to rotate this one, the other motor will also rotate.

See. And you can even do it in reverse. I'll rotate this one and the other motor will rotate. Now if I rotate this one very slowly

the other does not rotate. The basic idea is that this motor consumes electricity. It needs electricity so that it can rotate. This could come from the battery of the brick. But it could also come from another motor that generates electricity. With the work that you do with your hand you rotate the internal parts of the motor and they generate electricity. And when you generate electricity we have the conductor the cable between the two motors and we can generate electricity from one of the motors and this electricity will be consumed by the other motor. These are simple electromotors.

It is very useful if you have a robot with an attachment. You can imagine a third attachment. And you'd like to experiment but you haven't implemented the program. Then it's very useful to just connect another motor to the attachment if you have the attachment somewhere on the robot. Like this.

This here is the attachment. And now I don't have a program but I'd like to experiment. And I just rotate it and this will rotate

the axle of this motor. So, this is very useful and you can sometimes probably most of the times impress the students with this because this is something very tricky. Next thing about the motors is the synchronization between the two motors. When you start a program you've probably seen in the previous videos but when you start a program and you disconnect one of the cables. And now I'll start the program. They don't move. The moment you connect they start moving.

So, if one of the motors is disconnected the other also does not move. The other interesting thing is that if you have both motors connected, if I just hold one of the motors with my hand like this, so that it does not rotate and I start the program

they both don't move. And the moment when I release the motor they will start rotating. If I catch them again they stop. Now these motors are servo motors. These servo motors return some feedback to the controller. So, when the controller directs the motor move forward for a couple of rotations the motor has an encoder the so called encoder inside. And this encoder helps the motor return some feedback to the controller. Okay, I've rotated one degree then I've rotated a second, I've rotated 0.10 rotations and in this way there's a constant communication between the brick and the motor. Now, when you use this steering block, this steering block tries to keep the motors synchronized in the configuration that the steering motor is set. And as it tries to keep the motors synchronized when you stop one of the motors the other will also not move. If you just hold them. Because the motor returns some feedback to the brick that it cannot move. The one the time holding and the brick tries to keep the motors synchronized so it stops also the second motor. And this happens mostly because these motors are servo. With other type of motors with other set this probably wouldn't behave in the same way. But with servo motors this is the way they work and especially with the settings configurations of the steering block.

Courses and lessons with this Tutorial

This Tutorial is used in the following courses and lessons

Image for EV3 Phi. Introduction to robotics with LEGO Mindstorms
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