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Physics in LEGO Mindstorms: Energy Accumulation and Conservation. Part 1

How can you accumulate some energy in an LEGO Mindstorms EV3 construction an use this energy at a later moment? How does a Flywheel work, why is it important and what is the purpose? What is energy, inertial moment and angular velocity. These are just some of the questions we would answer in this series on Physics and LEGO Mindstorms.

  • #114
  • 24 Oct 2015
  • 11:38

While recording the attachment with a Flywheel and a rubber band we felt we should try to get deeper into the physics of the Flywheel. It is pretty interesting to see the formulas in action and to understand the purpose of the mathematics behind the flywheels. We would try to keep it very simple, and introduce every concept clearly and at the end of the series you would have a good understanding of Energy of rotating objects, Flywheel, Inertia Moment, angular velocity.

Previous video tutorials from which the idea came:

  1. Rubber band attachment with a flywheel - solving FLL 2014 Search Engine

Flywheels constructions for experimenting for physics moment and energy

User this flywheels construction for experiments in physics. Start rotating the wheel and they would accumulate energy. You can try to calculate this energy and to measure how fast it would be consumed.

The construction is built with LEGO Mindstorms EV3


In the previous video that you can find in the links below we did a very interesting attachment that was using a flywheel to solve a competition model. Now there's much physics involved in the flywheel and we got a number of questions from you, so we decided to dig deeper into the subject. For the last couple of years we stayed away from the physics, but actually the LEGO Mindstorms robots are very interesting tool with which we can explore different laws of physics and we can talk about motion, energy and in this series, we'll try to explore flywheels, accumulation of energy, inertia momentum and we'll get into more physics and I think it would be quite fun, quite interesting and you'll learn a lot.

Now my plan for the series is to use model that we built especially for this purpose and we'll do a number of videos first, we'll try to build a block that will accelerate this whole module and accumulate some energy. Then we'll calculate what exactly energy is and then we'll think about how can we use this energy to do other things, for example, if we have the attachment, it's not actually attachment it's whole module. When we rotate the tire with my right hand we can see that the 3 tires inside start rotating, we accumulate some energy in them and we can do something with this energy at a later stage. For example, we can rotate.

You can see this same laws in many cars, for example, in F1, you can see them in flywheels and we'll try to do a number of calculations about the inertia momentum, what momentum is, what energy is, how it is accumulated and how can we use it. First, I'll start with something very simple as you can see if we now rotate the wheel here we'll rotate the 3 wheels on the inside. There's a gear system here inside you can find the instructions for building this construction below the video. If I rotate the gear, we rotate the 3 wheels here, some of the energy is accumulated. If I rotate it very slowly, like this I'll have enough energy for something like 50-60 degrees of turning, but if I rotate it very fast, like this,

I'll have more energy accumulated and we can turn for a longer distance, so it's like 200 degrees. Now the question is if we have a motor, EV3 motor from the set, how fast can we actually rotate the 3 wheels on the inside, that's the question. So we must first find what the speed of rotation of this motor on it's maximum power and what's the speed of rotation that we can actually use to rotate the 3 wheels.

This here is the EV3 software, it's a teachers edition so it is possible for me to add program and experiment, this is important distinction because with an experiment I could actually find the speed of rotation of the motor. I assume that some you will have the retail version not the teacher edition so I'll have to implement a program without the experiment option here. A program that will give us the speed of rotation of the EV3 motor. The maximum speed of rotation. The question is the following. If we have a large motor and we set this large motor to rotate for let's say 10 rotation and a 100% power. Then what will be the speed of rotation of this motor and by speed I mean what's the number of rotations that this motor does for 1 second.

I have now connected motor D to our robot and I'll configure it to rotate for seconds, let's say 10 seconds. We are rotating motor D for 10 seconds and we're searching for the speed of the motor. How many rotations is the motor making for 1 second? I'll now start the program. We can hear that the motor is running for about ten seconds, exactly 10 seconds. Then when we finish, we can see the result in the lower right corner.

We see that we've done 8400 degrees. That's the number of degrees that we've rotated for 10 seconds. We can also switch this to rotations.

It's 23,5 rotations for 10 seconds, which means that for each second we are doing 2.35 rotations. That's the speed of the motor. Let's now try to show this speed on the brick display. I would like to show the speed of the motor on the brick screen because it would be much easier to show the experiment. How do we display the speed of the motor? First, the speed is actually the number of rotations that we're doing for 1 second so we must measure the number of rotations. We'll take one sensor from here, the motor rotation sensor for port D and we'll reset this. Then we rotate the motor with the power of a 100 and we rotate this motor constantly we wait for 1 second and after this second has passed we measure how much is the motor rotated. We measure the number of degrees. We measure the number of degrees this motor has rotated for 1 second. We reset, we start rotating, we wait for a second, we measure how much has the motor rotated. After we do this we must show this on the screen. Let's show this on the screen we have a display and for this display we can show some text and this text would be a wired text.

We start rotating, we wait for a second, we show the number of degrees that we've rotated for 1 second. That's not what we want to show on the display, we want to show the speed.

For the speed, that's actually degrees per second or rotations per second, so it's something per second. Let's do it the following way. We need a loop and we put this whole functionality in a loop.

I'll just zoom out a little.

We have the program now let's try and run it and see the number of degrees that we are rotating for 1 second.

This here is the brick, this here is the motor I'll now start the program and we'll see the values on the display.


As you can see the motor is currently rotating with about 870 degrees per second. That's the speed of rotation of our motor. And this will continue forever because that's how we set up this loop. Now let's connect this motor to our construction. Add the motor right here, so that it will rotate the wheel on the inside.

Now the question is what would be the speed of rotation of this motor when we attach it to this whole construction. I'll now start the program.

I'll hold the whole construction together.

As you can see the speed of rotation does not actually reach the maximum speed of rotation.

The question is and what we're going to explore in the next video because this is now getting pretty long. How much energy in terms of energy in joules have we accumulated in this mechanism and how can we use this energy.