# Space Invaders Marble Run School Fete Game (and Maths Fun)

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## Introduction: Space Invaders Marble Run School Fete Game (and Maths Fun)

This is a game we made for the school fete, using a recycled cardboard palette, drinks bottle tops, some party ice cream cups, spare card and lots of hot glue. The idea is like bagatelle (or pinball but without the flippers); you drop a marble at the top and its bounces down the obstacles to land in one of six pots. The pots all have different prizes attached, from 'Lost in Space', 'Recharge Rocket' (play again) to sweeties and small space themed pocket money prizes, based on the odds of landing in a pot.

We had a great learning session with the P4 class taking turns dropping marbles and talking about probability and how sample size affects our confidence in the chance of landing in a particular pot. And we were able to determine which pots to match with which prizes so as not to bankrupt our fete stall!

## Step 1: Materials

1 cardboard pallet with thick card liner, approx. 79cm x 117cm

Several mail order cardboard delivery packages (as they deliver books in)

Approx. 100 mixed bottle tops

7 sheets of thick coloured card (here red, silver and cream)

Glue, tape, fold-back pins

Poster paint; blue, black and white

Marbles to play

Cost: under £5, as mostly recycled

Time: 15 hours, with extra waiting for various stages to dry

The pallet we got from the hospital pharmacy department in Dumfries (big thanks to them!) It is the packaging for bottles of dialysis fluid; they get delivered in big cardboard flats, with a flat card insert for extra stability.

A note on bottle tops: through trial and error we found that the marbles were less likely to catch on tops with finer 'knurling' (finger grip ridges). See photo: lids on the left better than lids on the right. Unfortunately milk bottle tops were easiest to collect but were the worst tops for accidentally stopping the marbles. Best tops were from juice and water bottles.

## Step 2: Stability

It may have been unnecessary but I built up the corners to add stability.

I made right angled struts and attached them both with fold-back pins and lots of glue.

Handy tips: when scoring the cardboard for folding I used a small gauge knitting needle, and also for precision punching holes through several layers of card. Tape the pin heads down to keep them in place until you fold back the tabs.

You now have pointy pin backs right where you might want to the hold the game, so I used red card to cover the corners for both protection and aesthetics.

## Step 3: The Starry Background

This paint effect was produced by squirting blue and black poster paint into a pot and mixing them only slightly.

Using long dragging strokes across the card insert, a nice effect is achieved.

White 'stars' are added last by flicking the paintbrush.

Allow to dry and hope for minimal curling of the card.

Once dry, we used standard pva glue all over the back to secure the card into the pallet base. Weight the card down to maximize flatness: we piled DVD cases 8 deep all over the surface (yes, that's a lot of DVDs...)

The card insert was narrower than the pallet so we filled the two side gaps with strips of cream card the same thickness, again glued down with pva and weighted.

## Step 4: The Hazard Field

Before we glued everything together we trialled our bottle top hazards using a bit of blue tack on the back of each bottle top stuck onto the unpainted surface. You need to ensure that there is enough space between the obstacles for a marble to pass through every gap, and a little extra to allow a bit of ricochet.

Once the bottle tops are glued onto the painted surface they are hard to change, so you need to be confident of your spacing. We did this by eye, but you could easily tie a string round the pallet with knots every 5-6cm to give a guide line that you can move down row by row, staggering the knots back and forth on alternate rows.

For styling, we kept the different colours in bands and had a slightly random 'debris field' with odd sized tops in the middle to make it harder to guess where the marbles would fall.

## Step 5: The Catch Pots

The most difficult part of the build was working out what to use at the bottom to catch the marbles. It needs to be high sided enough to stop the marbles jumping out, but easy to get a hand into to retrieve the marbles at the end of a turn.

We tried using aluminium foil trays (as used for takeaways); the advantaged is that these sit side by side with no gaps, but they proved too flimsy and kept bending, even when doubled up with cardboard sandwiched between the layers.

Instead, these are waxed ice cream tubs from a partyware range. The downside however, is that having a round cross-section leaves a hole between each pot. I tried slicing them down the centre but they became too flimsy and much harder to scoop marbles out of.

Our solution was to create silver wedges that fit into the gaps and acted as ramps into the pots. A 'brilliant' (as in diamond) shape template was used, 4 isosceles triangles 9x9x5cm arranged in a fan that fold into a nice open ended pyramid. With a little careful squeezing, these slid between the pots and filled the curved gaps.

The pots themselves were just held down and liberally hot glued over the ends to caulk the pots to the card base.

## Step 6: Final Touches

At the base where the pots didn't perfectly fill a whole row, I built up a gutter of extra tops to guide any strays into the end pots; this means the end pots have a higher probably of catching a marble.

You need to have bottle tops at the end of some rows that go right up to the edge, otherwise one marble dropped down the side will drop straight to the bottom without ricocheting. But you then have a little pocket where marbles can easily get stuck. We toyed with making little mini card wedges, but instead along the edge bottle tops I built up some extra bumps from 3d stickers used for card decorating, to prevent marbles sticking in the pockets. This is not a perfect solution but managed to discourage most marbles from getting caught.

Finally as an 'in' joke, I wrote a secret message down the edges using the Futurama alien alphabet1, by Darrell Johnson, signing and dating my work, with the school motto.

At the fete the board was propped up on two shoe boxes taped together and lightly secured to the table with blue tack. Smaller children were able to stand on a chair to drop their marbles.

Learning points: by attaching specific prizes to each pot, rather than just 'win a prize, pick what you like from a selection on the table', children were tempted to come back to obtain a 'full set'. Not sure about the moral implications of tempting children into gambling here(!) but from the point of view of maximising profitability, this worked better. Towards the end of the fete as some prizes were running out, I allowed children to swap duplicates for alternatives of their choice and this gave the impression of being less satisfying than winning their desired object.

We tried to have toys that cost 20 pence or less, such as bouncy balls, stretchy men, parachute aliens and charged 20 pence per go. The six pots along the bottom had: 'lost in space', 3 different small prizes, a sweetie and a 'go again'. The stall managed to pay for all the prizes and make the same again in profit.

It was also handy to have a repair kit of 'glue dots' to reattach any stray bottle tops that popped off during use.

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