Importance of the caster ball on the LEGO Mindstorms robot movement Pro Preview

You could use the LEGO Steel Balls as a third wheel on the robot. It is a caster wheel. But this is steel and as we know from basic existence on this planet, where there is steel there is also rust. The steel ball could get quite rusty and this could have an influence on the behaviour of the robot

  • #650
  • 09 Jan 2018
  • 2:02

Rust on the steel ball

Check your steel ball. If it is very rust try to replace it or to remove the rust. If it is rusty there is more traction between the ball and the plastic "container" of the ball.

Five Minute Bot

Building instructions for a LEGO Mindstorms EV3 Robot that we call the Five Minute Bot because it could be built in Five Minutes.

Note: If the robot is making inconsistent turns due to the floor, modify the castor wheel so it is placed further back in the construction. Thus the center of mass falls more over the tires and the turns are more consistent.


In this video I would like to discuss a question and to give an answer to a question that we receive very often and this is about the importance of these steel balls - the castor wheels of your robot and how they influence the movement of the robot. It is quite challenging for me to capture this difference between the two steel balls on a camera and that's why I'm going to discuss this with you. When you buy these steel balls they come brand new and they are very smooth. And this one here is an example. When you move with this there is almost no sound

while if you use an older one, it gets more rusty and if you move this ball, you hear a sound.

Let me try to move it closer to the mine and to see if there is a difference. First, I'll move the smoother one

and now the rusty one.

It's difficult to capture this but if this steel ball is very rusty, what happens is that it will have some influence of the movement of the robot. So, you should always check them and make sure that these are not very rusty.

Courses and lessons with this Tutorial

This Tutorial is used in the following courses and lessons

Image for Moving Straight with LEGO Mindstorms EV3 robots
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Image for Understanding the issues with moving straight
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  • 3d_rotation 2