Here’s a neat LEGO® project that will allow kids to explore the concepts of gravity, mass, force, and momentum, all while playing with LEGO® bricks!  

One day, Gresham build a little tiny LEGO® TIE Fighter (from Star Wars) out of little tiny pieces, and he discovered that when he would set it down on the table, it would keep itself rolling.  One side was heavier than the other, and so the heavy side would cause it to roll until the heavy side was on top again, and then it would tip past the center point and roll again! I thought it was a brilliant discovery!

We got to work figuring out if we could build other LEGO rolling contraptions that would keep themselves going.

LEGO Gravity Rollers: A Contraption that Rolls Itself!

Unfortunately, we can’t find Gresham’s original TIE Fighter rolling contraption.  We’ve have looked and looked, but there is a strong possibility that Janie stuck it somewhere that she can’t remember.  We did build several more!

We made an interesting discovery while building these rolling contraptions… there is not a single level surface in our entire house!  Some of our gravity rollers seemed to be a little temperamental.  They would roll well, and then turn around and not work at all.  Finally I got out a level and discovered that every table in our house is sloped slightly, and it’s enough to affect these little gravity rollers.  You’ll need to make sure that your gravity roller is heading “downhill,” even on what seems like a flat table.  We were not able to build any that would roll uphill at all – even the tiniest bit uphill!  No need to have a level, though. Just test your gravity roller in more than one direction on the table before concluding that it doesn’t work!

Want to see our LEGO® Gravity Rollers in action?

Here are the pieces you’ll need to build one.

LEGO Gravity Rollers: A Contraption that Rolls Itself!

The 1 x 2 brick with the x – shaped hole is essential for attaching the weight.  Slide it on to the middle of your axle.  Then add two little gray pieces – the name for these (on Brick Link, http://bricklink.com) is Technic bush.

LEGO Gravity Rollers

You want the wheels to *not* turn on the axle.  The axle and wheels should roll together as one unit for this to work.  If the wheels spin freely, then your contraption will just roll along with the weight always at the bottom, and you will have to push it to get it to roll.

The Technic bush pieces hold the wheels still.

LEGO Gravity Rollers

You’ll probably need to experiment with exactly how much weight to add.  This worked for us, but if the surface you are rolling it on has more or less friction (or any amount of slope) you may need to change the amount of weight.

LEGO Gravity Rollers: A Contraption that Rolls Itself!

To roll it, hold it with the weight slightly off center at the top, and then let go.  The weight will propel it forward!  Hopefully it will have enough momentum for the weight to make it back up to the top and repeat the cycle.  If not, try changing the design. Add more weight, or take some off.

Here’s another roller we created:

LEGO Gravity Rollers

And these little tiny ones were fun:

LEGO Gravity Rollers

Here are the pieces used to make this one.

LEGO Gravity Rollers

Science Discussion Starters:

  • Which has more mass, a 2 x 3 brick or three 2 x 3 plates stack on top of each other?  They take up the same amount of space, but which is heavier?
  • Does it matter if the weight is centered along the axle?  Can it be closer to one wheel or the other?
  • How can you tell if you have added too much weight? How does your LEGO® gravity roller behave? (rocks back and forth rather than rolling)
  • Does it matter if the gravity roller has wheels that are widely spaced or close together?

Have fun exploring!

LEGO® is a trademark of the LEGO® group of companies which does not sponsor, authorize, or endorse this site.

LEGO Gravity Rollers: A Contraption that Rolls Itself!

6 Comments

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  1. megan Mar 6, 2017

    Thanks!, my son loves his legos we can never have enough instructions of things for him to build.

    Reply
    1. Cathy Mar 14, 2017

      Looking forward to try it with my boys tomorrow

      Reply
      1. Marcelaine Mar 27, 2017

        I was trying to do this today and my physicist husband pointed out that it's physically impossible to make one roll from at rest on a flat surface because of conservation of energy. There's a small amount of friction as it rolls and that takes energy out of the system. It's the same reason that a pendulum can't go up as high as where it started.

        Reply
        1. Marcelaine Mar 27, 2017

          Here is a YouTube video that shows how to make something similar out of records or CDs, and these ones do roll uphill because they're powered by potential energy stored in rubber bands. If your kids enjoyed the lego contraptions I bet they would enjoy making these.

          https://youtu.be/oKmEcsNqsWU

          Reply
          1. Jennifer Parker Mar 11, 2019

            I would like to have the kids in my LEGO club at the Library build these during the Summer. Do you know what LEGO Technic axle you used for the larger roller? Was it Technic, Axle 9? https://www.toypro.com/us/product/1830/technic-axle-9/light-bluish-gray

            Reply
            1. Marie Nov 28, 2019

              This is a cool idea.

              Reply

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