Introduction: Rolling Ball Contraption

About: Hello! My name is Murilo, I am a Brazilian technologist (or a full stack developer if you prefer). I am profoundly interested in education and technology. More specifically when technology is used to build a …

Imagine you have a truck with 892152 ping pong balls and you want to sort them and put into small cardboard boxes. What would be the best way to do it?

Sometimes the best way to solve situations like that is to break big problems in smaller ones. Let's say we have the problem of putting all those ping pong balls inside cardboard boxes. First we need something to take the balls from the truck, bring them to a queue where they get one by one inside the cardboard boxes that are also in a queue that comes from the cardboard boxes and there we go. All this small steps can be broken in smaller and smaller tasks that are often solved by a simple movement.

In a way, very complex machines and factories are the sum of very simple movements in some sort of choreography assisted or not by human hands. We are going to show now how to build some simple and adjustable contraptions that guide a ping pong ball (or something alike) from one place to another.

Step 1: Material List

A bunch of Strawbees

One Quirkbot

A bunch of drinking straws (Any drinking straw that you can fit a Strawbee inside. Around 6mm diameter)

Servo motor (comes with Quirkbot but you can find in any electronic shop like Adafruit, Sparkfun, Seed Studio, etc)

Step 2: Rails

The first step when you want to create a rolling ball contraption (aka marble run) is the rail. After all, your rolling ball must roll on something, right? Here is one of the best and simplest rail for guiding a ping pong ball through many adventures!

Step 3: Support

Once you get your rail you will probably ask yourself: How am I going to make a ramp out of this? While the answer for this is easy, just put one side higher then the other, the next question is a bit more elaborated: What can I use to make one side higher then the other? My overall answer would be you can use anything your eyes can see, your hands can touch and it won’t hurt anyone. In this case we will use two tetrahedrons (pyramids).

Step 4: Transitions

You can make the ball roll from one rail to the other by creating controlled falls like this one. There is a lot of room for exploring what are the best angles, speed and distance between the rails. You should try yourself and try to understand what are the consequences of moving the rail a tiny bit to the left or adding a book under the support!

Step 5: Changing Direction

Once you have your rails, support and know how that you can make the ball fall from one rail to the other, you can start thinking about more complex transitions like this one that changes the ball’s direction. And keep in mind that is all about trial, error and patience!

Step 6: Falling Through

This will look pretty much like a failure but sometimes what looks like a problem might be a feature! On the previous transitions we made the ball fall on the other rail and you probably noticed that the ball is kind of launched in to the other rail more or less like a parabola. This is cool but sometimes you just want the ball to fall slower and more in a straight line. You can achieve this by increasing the space between the straws in one side of the rail (go wild on how to do this, everything goes) and let the ball fall through it. You see? It’s not a problem, it’s a feature!

Step 7: Curves

You can change the direction of your track not only with falls but also making a curve with the rails. While this is an elegant solution for making small curves, it gets really tricky when direction changes too much and the ball is either too fast or too slow. The best way to understand it is trying, you will get what I mean!

Step 8: Ramp Lift

So if you are as lazy as I am you will look to those rails, curves, falls and think: No way I will be fetching this ball all the time to put it back on the track! At least that is what I thought after 2 hours doing it. This is why I developed this simple lift to put the ball back on top of my track after it rolled all the way down. It’s beautiful, right? But don’t think it will be so easy, it takes time and fine adjustment to make the perfect lift. Sometimes you need to add extra weight to the rail support because we are still talking about lightweight stuff like ping pong balls and straws. They tend to shake a lot and move.

Step 9: Weird Questions Worthy to Answer

Why would you want to put 892152 ping pong balls inside cardboard boxes?

What else could you use the ramp for? What else could you use as a ramp?

What is the fastest and the slowest time record of your path?

Can you make a path that cross the place you are in from one side to the other?

Can you make the ping pong ball return to the beginning of the path when it finishes the track?

Can you make a loop? What about a jump?