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Zonker's LEGO(*) Marble Machine

http://BayLUG.org/zonker/ZMarble.html

Navigation MenuI've always been interested in the various Kinetic Motion Machines I've seen. Over the years I've seen machines that told the time, or played a variety of musical notes on pseudo-instruments, such as wire xylophones, or wooden drums. Most involved some type of sphere, transported to the top of the machine, and left to work their way to the bottom again, cascading and racing through a maze of pathways, gates, bridges, and obstructions, to finally reach the bottom and start again.

I finally decided to try to create one from LEGO bricks. Without chain links or tread links, this becomes very difficult. I tried using strings to lift boxes and platforms (and motors to move the strings) with limited success. Sadly, my attempts to create something that would be able to lift a 1" glass marble quickly and reliably to the top of a structure failed. It seemed that 'quickly' and 'reliably' don't work well together. :-(

I took a break from the problem of lifting the marble to the top, and proceeded to work on the problem of guiding the marble through the maze. This covered a variety of things to think about. Things like Friction, and Momentum. I finally got that working, after remembering a lot of basic science facts. you can read about my Marble Machine at the end of this page

Friction

Take the normal bricks. There is a standard grid position for stacking one brick on another. I refer to it as 'one stud' separation, referring to the stud, or post on the top of a 1x1 brick. There is also the placement of the studs on top of bricks. The studs limit the size of the marble you can use!

For example, take (2) 1x8 bricks, and place them on a plate with a 1-stud gap in the middle.

You now have a minimum marble size. If the marble is smaller than one-stud diameter, the marble will fall between the bricks, and not be supported. But, the marble cannot be much larger than this, or the marble will start touching the studs as it rolls, which would create friction that would slow the marble down, and perhaps cause it to fly off course. So, there is a minimum size, and a maximum size.

Place a few different size marbles on the bricks (one at a time), and try to roll them back and forth.

  • Do you feel the bumping against the studs?
    • If so, that marble is "too big".
  • Try pushing the marble side to side.
    • Is it easy to bump off the bricks, or hard?
    • How does the size affect how easy it is to bump it off?

For another example, try putting the two bricks on a plate, but this time with 2-stud separation.

How small can the marble be, and still sit on the bricks?

How big can it be before it touches the studs?

How easy is it to knock the marble off the side?

Try it again, with 3-stud separation...

How small can the marble be, and still sit on the bricks?

How big can it be before it touches the studs?

How easy is it to knock the marble off the side?

Finally, try placing a 1x8 flat plate on top of each brick. No more studs! How does this change the examples you tried? You can now use larger marbles, right? Is there a maximum size? Could you use a baseball? Or a softball? How about a volleyball or soccer ball? (Is there a size that is "too big" for any of the three different stud-separation examples above, if you have plates on top of the bricks? How easy is it to knock the ball/marble off the side?)

Momentum

We know that an object at rest will remain at rest, until acted upon by a force.We also understand the an object, once placed in motion, will continue in motion, unless acted upon by external forces. (When you hit a tetherball, the tether pulls the ball around the pole. If the tether broke, the ball would fly off in a straight line, until gravity pulled it to the ground.)

In the marble machine, these rules mean;

  • The marble won't start rolling by itself. It will need help.
  • Once the marble starts rolling in one direction, it will want to continue to roll in that direction, unless we do something to change that. (Think about turning the corner...)
  • Friction and gravity will try to slow the marble down, so we need to do something to keep the marble going, to get it all the way through the maze.

I figured that I could use my hands, in the beginning, to put the marble at the top of the maze. I could use a finger to push the marble, to give it some initial energy.

Using the LEGO bricks, you are pretty much stuck with making 90-degree turns. There are a few things you can do for 45-degree turns, but it gets complicated really fast if you do that. If you are trying to make a fast 90-degree turn, this is where you will run into trouble with that marble trying to jump off the course. This presents the first problem to solve. How do you affect the course of the marble, without stopping it?

You could build a wall, to keep it from leaving the course, but bouncing off the wall take a lot of energy from the marble!

I chose to try a gradual approach, using plates instead of bricks for the maze. This lets me add a small vertical drop occasionally, which can replace some of the energy lost changing course.

By lowering one side of the path at the start of a corner, the course of the marble tends to want to fall into the corner. In some cases, I needed to add a plate sticking out of a wall at the outside-edge of a corner to provide support and keep the marble from getting stuck. By lowering both the edges after the corner, I was able to add lost momentum in the direction I wanted. I use colors in this diagram to illustrate the different layers in the example

Another idea that deserves investigation is the height of the marble, and trying to make one path run over another. There is where two-stud-wide plates and bricks come into play. (Of course, this method depends on the size of the marble you will use.) The 2-stud-wide parts form the foundation of the maze. The marble rests on one edge of the brick, and the other edge will be the base of the walls that will support the next level.

You will need to test this method with your own marble, and make sure that it will roll through, but that it won't touch the wall on the way through. I built some windows in the walls of my maze, so I could poke a finger in if the marble got stuck.

About my Marble Machine

I started with a 5" x 5" base plate, and built from the bottom up. I learned my lessons above by trial and error, learning as I went. By the time I was building a path along all four sides, I stumbled through the exercise of adding a second level. When I finally had a maze that worked, completing two complete rotations, I added a launch platform to give the marble a good start. You can click on the buttons below to view any of the 5 photos that I took from different angles. Someday in the future you will be able to FTP back a small MPEG animation of the marble running through the maze.

view 1

view 2

view 3

view 4

view 5

view 6

view MPEG movie (someday)

I'd like to hear from students who try to solve this problem by email to frenezulo at baylug.org.


Disclaimer:
These pages are NOT sponsored or endorsed by the LEGO companies.
They are the creation of an enthusiast of LEGO bricks.
The official LEGO home page is www.lego.com.
(The LEGO companies have their own pages. This page is mine. :-)


Copyright 1996-99, David K. Z. Harris, N6UOW
Questions? Comments? Additions? Email
frenezulo at baylug.org

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