# Useful Technical Tips to Build a Rube Goldberg Machine : Deconstructing Photosynthesis

33,010

35

3

This week-end we took part in The Deconstruction, as « The Carrots of Patagonia ». Our project was to deconstruct photosynthesis into a Rube Goldberg machine. Our machine starts with a light bulb and ends with a sugar cube. It was a way to show how incredibly complex this process is and how energy conversion is a huge part of it, rather than to « teach » something. To make a long story short, we failed to represent photosynthesis accurately (too complicated...) but we had fun!
Here is an overview of what we built during this 48h event.

But because every Rube Goldberg Machine is what you want it to be, we are not going to do a step-by-step guide for the exact machine we've built. Rather, we choose to present you with a toolbox with all the technical tricks we discovered by trial and error to build the things we envisioned.

Here are some solutions for these technical puzzles:

1. How to trigger a domino cascade with a light bulb
2. How to build a seesaw
3. How to reception a projectile propelled by a seesaw and channel its energy into moving a ball
4. How to build a straight railway
5. How to use a ball going down a railway to drop an item
6. How to build a catapult
7. How to trigger a catapult with a rat trap

### Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

## Step 1: How to Trigger a Domino Cascade With a Light Bulb

You might say triggering a domino cascade is a pretty easy thing. And you'd be right: just push the first domino down and here you are!

But we wanted to trigger our domino cascade with "light", because the starting point of photosynthesis is light.

So we used a pendulum design where a light bulb knocked the first domino down.

As you can see on the picture, the light bulb is swinging on the side of a cardboard. It is hold by a metal piece that was coming with it, so except if you have the exact same old recycled lamp home, you will have to find your own way to attach the electric cord to the cardboard.

The electric cord is optimized so the light bulb is just half a centimeter above the platform after it's fallen.

We used forks stuck into the cardboard to both hold the light bulb in waiting position and stop it when it's down.

The first domino is put just before the second fork. You will have to calibrate it so the light bulb knock it down with the exact strength you want, but here are a few general tips:
Leave enough space between the domino and the fork for the domino to be able to fall.
Don't put the domino to close to the cardboard else it might be knocked against it by the light bulb.
Don't put the domino to far from the cardboard either, or the light bulb might swing between the domino and the cardboard.

If you can, put something on the fork to take up the shock, like foam. We didn't do it and after about a hundred tries (to calibrate the rest of the machine), when the machine was finally ready to run, our light bulb died.

## Step 2: How to Build a Seesaw

We wanted to propel a Lego football supporter in the air to make him crash into a transparent Christmas ball (pushing it down the rails) so we built a seesaw. The layout is pretty basic: a long flat rectangular platform fastened to allow seesaw movements to a vertical support.

For this, we used some cardboard, metallic wire, some plastic foam*, a figurine and a little bit modeling clay.

So first, the support. To make it sturdy and stable, we used the plastic foam and the base was attached to a cardboard. The platform is just a cardboard rectangle but beware of the orientation of the cardboard, the faint lines that make bending the cardboard easier in a direction or in another should be aligned with the direction of the figurine fly.

To attach the platform to the support, fasten metallic wire to a top side of the support then insert the free end of the wire into the platform between the folds of the cardboard, parallel to the platform plan and going through the width of it to exit on the other side. No holes are pierced in the platform to attach it. Then fasten the exiting wire to the other top side of the support.

To trigger the seesaw, we used the last domino as it falls over the edge of the cardboard box but there has to be a very precise tuning so that the figurine does fly but not too far.

We made a slight modeling clay outer ring to stop the figurine from falling when the platform is in a rest position.

## Step 3: How to Reception a Projectile Propelled by a Seesaw and Channel Its Energy Into Moving a Ball

Activating the seesaw with the fall of a (heavy Lego) domino does propel the figurine in the air but the landing spot is.. highly variable. So we made a big funnel to reception the figurine and channel its landing on the transparent Christmas ball (video in the Introduction).
For that, you will need an empty plastic bottle, paper sheets and paint (to decorate ^^).  The sawed off bottle provides the tip of the funnel and rolled sheets of paper the width of it.

Then, the difficult part is to hang it in the air. Providing you put the funnel next to a 'cardboard wall', here is how you can make the funnel 'float' in the air. You'll need cardboard, two old fen-tip pens (or just pens), small rubber bands, expansed plastic or polystyrene, a screwdriver or something sharp and pointy.

The idea is to make a platform (with a hole in it to support the cone) float horizontally next to a vertical cardboard. This platform rests on the two horizontal pens inserted into the vertical cardboard. The pens are maintained horizontally because their ends (on the cardboard side) are immobilized in a big block of foam plastic (or maybe polystyrene) behind the vertical cardboard.

The holes in the vertical cardboard and the plastic foam can easily be made with a screwdriver (making straight holes). To fasten the horizontal platform on the horizontal pens, the easiest way is to make two holes on the cardboard on either side of the pen and then use a cut rubber band to tie the pen to the cardboard.

Now you can orient the giant ice cream cone.. hum funnel in the direction of the coming figurine. If the funnel moves, set his position with sticky tape.

## Step 4: How to Build a Straight Railway

I've always wanted to make railways: dominoes are cool and artsy but a pain to reload, a flying figurine is awesome but the launch (via a Lego domino fall) is unreliable so you spend hours fine-tuning it. But railways, they never fail once they're set and you can accidentally move them, it still works!

So let's make them! But first we have to make the ball going down the rails then we have to set the straight rails. We used a transparent plastic Christmas ball to roll down the rails and we put two steel marbles inside to weigh it down (see pictures). Once we know the diameter of the ball, we can set the rails.

You'll need two metallic bars: they should be rigid but with a small diameter (we used a one meter-long and 4 mm wide bar),  some cardboard, rubber bands and metallic wire.
The trick is to set the rails so that they won't move while the ball goes down. For this, make two cardboard platforms and attach a piece of metallic wire to the platform at one end and to the metallic bar at the other end. Then use a cut rubber band as a thread to maintain the position of the metallic wire on the bar.

## Step 5: How to Use a Ball Going Down a Railway to Drop an Item

That's the truly cool part of building a railway: you can use the passage of the ball on the rails to trigger another action via a reel mechanism, for example a marble falling down.

So you already have built and set up the ball and railways. You also need more metallic wire and rubber bands, a small piece of large thread (raffia works), a thin and long thread, a cotton bud and a small hollow pvc tube (sawed out-of-order fen-tip pen works).

Then you need to:
- build the axis around which your reel will turn and attach it to the rails
- attach to the reel a strand holding the dropping item
- set a strip activated by the passage of the ball on the reel
- block the strip in an off position (so that it could be activated by the rolling ball).

The axis is the stick of the cotton bud (after the cotton is removed) because it is sturdy, small and hollow. To stick it close to the rails, put metallic wire through the stick.
Next, cut the ends of an old fen-tip pen (or a smooth ballpoint pen) to obtain a smooth plastic cylinder; ideally, the length of it should be inferior to the gap between the rails. Slip this reel on the axis.

Take a thin thread and attach one extremity to the reel, a good way to stabilize this is to make knots with a cut rubber band. Attach the other extremity to a (metallic cage containing the) marble marble. Turn the reel to make the marble go up, if you let go, it goes down. Bend a metallic wire to make a strap (see the pictures) and fix it: make a knot with a cut rubber band to freeze the strap on the reel.

When this is ready, you can take the wide strand of thread and attach it on one of the rail at the reel level. On the opposite spot, knot two small cut rubber bands on the rail and insert one end of the small piece of large rubber band into each small rubber circle. The large rubber band pressures the rail.

To arm the mechanism, turn the reel to make the marble go up, use the free extremity of the large thread to block the metallic strap and stabilize that position by putting this extremity under the big rubber band. When the big ball goes down the railway, the large rubber won't hold the strap, so the strap will get free and the reel with turn, bringing the marble down.

## Step 6: How to Build a Catapult

Hey, who's never dreamed to build a catapult?!

I was adamant that we should have a catapult in our project. I wanted it to be a marshmallow-teddy-bear catapult, but we choose photosynthesis as a theme, so a sugar catapult it was.

Now, here are a few tips if you want to build a simple catapult too. And please, if you build a marshmallow-teddy-bear catapult, send me the photos !

To build the catapult you will need a strong spring, a wooden spoon, wire and elastic bands. You can use something that looks like a spoon if you don't have one, but it has to be strong enough not to break. You also need wire, glue and cardboard if you want to fix the catapult to a platform. We used an armchair spring and it was perfect.

It's actually pretty simple: you just have to tie the spoon on the inside of the spring with wire. Then hold the wire in place with elastic bands. There it is!!
The catapult can be loaded with a string or a latch (see next step).

To fix the catapult to cardboard, position your catapult where you want it to be then make holes to attach the spring to the cardboard with wire. Before you tie the wire, glue the catapult in place with extra-strong glue and wait for it to dry. Then tie the catapult to the cardboard with wire, using the holes you have just done in the cardboard.

Now you can play with your splendid catapult

## Step 7: How to Trigger a Catapult With a Rat Trap

To implement that, we went for the rat trap solution, so you will need your catapult (fixed on a support), some cardboard (again...), wire, strong glue, some large thread (raffia works well) and a mouse trap.

To maintain the catapult winded on, we used a cardboard rectangle as a latch. The tension of the big spoon made it go up and we held it down with two threads of wire sewed on the cardboard platform. But how can we release the latch?

We used the large thread: it is fastened to the latch at one end and to the moving part of the mouse trap at the other end. When the mouse trap is winded on, the latch block the catapult. When the mouse trap is triggered, the thread is brutally brought back, pulling on the latch which also pulls back and release the catapult. You can see it on the pictures.

The mouse trap is highly sensitive: a small pressure activates it, so when we made the marble fall on it, it naturally triggered the catapult.

THE END!

Flora&Emma for the team "The Carrots of Patagonia"

## Recommendations

• ### Internet of Things Class

22,882 Enrolled

## 3 Discussions

Hmm, maybe I should make one like this- it's triggered by opening my bedroom door, which. . . . . . . . . . . .The intruder is left soaking wet :D

2 replies