How to build a LEGO Mindstorms Competition Robot

001

In this video I would like to show you how to build a competition robot and tell you how we reached the construction used in the videos. Surely it isn’t perfect but it is a good start.

Many times I have heard this question:

Why does the robot end up in different position after each run?

Well there are many reasons for that, like:

the different starting position

the wheel slip

or the bad construction.

Today we will focus on the last one. First, I will begin with giving definition of center of mass. For the purpose of this lesson we will refer to it as the point, where if you put your finger, the robot will stay in balance. As on the picture taken from wikipedia.org. More precise definitions you can find in the links below.

002

One will ask why we begin with this, well there are two reasons. The first one is that to be stable during turns the center of mass of the robot must be as low as possible. The second one is that the center of mass of the robot must be on the same vertical axis as the center of the points of the robot, which touch the ground. By this the weight of the robot is distributed equally.

Next it is very important to choose the right type of back wheels. They must have little friction during turns, so that the robot turns easily.

Then we need a small base construction, because of the many mission models on the field.

Last I would like to point out another common problem. Usually the students begin with solving one of the missions and build construction for solving this mission. After they solve it, they see that the construction is not appropriate for solving the next mission, so they change the construction. By doing that, the program they made for the first mission does not work anymore and they get stuck in a vicious circle. To avoid this you must keep in mind all of the missions during construction of the base and do not change it afterwards. So, we reach the following two conclusions - keep in mind all of the missions and do not change the base.

003

So let’s sum up the conclusions we have made so far. First, we need the center of mass of the robot to be as low as possible and to be on the same vertical axis as the center of the pivot points. We have to choose the right type of back wheels, so that they have a little friction. We need to make a small base construction and keep in mind all of the missions during constructing, so that we do not need to change the base after we finished.

004

Now let’s take a look at the robot. The first point was that the center of mass must be as low as possible, we have accomplished that by choosing the small tires and making a relatively short construction, which is tall only about 15 cm. Next we said that the center of mass must be on the same vertical axis as the center of the pivot points. After you build the robot, you can easily see that the center of mass of the robot is somewhere on this axis, where is exactly the center of the four pivot points. Next, we have chosen these parts from the MINDSTORMS set for back wheels, because they have little friction and the robot turns easily with them. We have made a small base construction and we have optimized the space in it so that there is not any empty space. We have kept in mind several things. The first one was that at some point you will need light sensors, so we have put them in the base construction with this part in front of them for making shadow and also for alignment on the border walls. Next, we have this third motor incorporated in the body of the robot and transmitted the motion using these gears. So that you can put the attachments in here and have the motion for them. By doing this, we actually do not need to change the base construction during the work on the missions. The next thing about the robot is that it is modular and it is easily disassembled into 5 or 6 simple modules. The first part is the back wheels, next we can detach the two motors, like this. Now we detach the third motor with the light sensors and finally it’s the brick with this parts, which are easily disassembled from the brick, as you can see. And we have the six modules of the robot. The instructions for the modules you can find under this video, as well as the instructions for the whole robot.