Junkyard Challenge

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In this event your team must prepare and bring materials to build a device on site to complete a task.

<spoiler text="2009 Season Information">

The Tasks

1. Tipping the scale - teams must build a device that is able to measure the mass of a "challenge object". Teams will not know what the challenge object is until after the impound. It will be no larger then 10.0cm x 10.0cm x 10.0cm for the Regional Tournament,25.0cm x 25.0cm x 25.0cm for the State Tournament, and 25.0cm x 25.0cm x 100.0cm for the National Tournament. Its mass will be between 100.0g and 500.0g for the Regional Tournament, 10.0g and 1000.0g for the State Tournament, and 10.0g and 2000.0g for the National Tournament. You will also have to use a mystery material in your device. Construction time will be between 30-45 minutes. You have 5 minutes to give the judges the weight of the object.

2. Coin Sorter - teams must build a device that is able to sort out five dollars worth of mixed change. The coins must all go into different storage places according to their value. These must be marked and you must be able to get the coins out so they can be scored. You have a minute to sort as many coin as you can using your device. There is a mystery material that must be used. Construction time will be between 30-45 minutes.

Other Info

  • The materials you bring must fit in a box with outside dimensions no greater then 26cmx31cmx46cm. The box can be made of any material but the lid must close completely with all materials inside the box.
  • ALL forms of glue are forbidden at the event site. Pre-glued components are permitted.
  • Tools may be brought in a separate container, they do not have to be impounded. Tools can not become part of the device unless they were impounded in the materials box. Electrical or battery operated power tools may NOT be used.
  • All competitors MUST wear safety spectacles with side shields during construction AND demonstration by ANY competitor.
  • Acids, bases, and flammable liquids may not be brought to the competition.


2010 Event Parameters

For the 2010 event, you must build a device that will use a standard unmodified golf ball to trip 4 mousetraps, within one minute. In a specified order (North, South, West, East) will get you bonus points. All the materials must fit into a box at most 40x40x60cm.

You may not bring glue or power tools to the event. You may preassemble some parts as long as they fit into the 40x40x60cm box, you have 30 minutes to assemble the device on site. You must drop the golf ball into the device at the central point.

You may use up to 6V of electricity to power your device in each circuit to add on to its accuracy.

You may get bonus points if the device operates for at least 5 seconds before you trip the first mousetrap. And 2 bonus points per second the device operates until all the mousetraps are tripped. This means that if you complete the task at 59 seconds or 60.00 seconds, you will have a lot more bonus points.

You may not touch the device after it begins operating unless you want to lose points, you also may not secure the mousetrap directly to the floor. The mousetrap or any part of the device may not become an unshielded projectile at any point.

General Designs

The first thing to do when designing your contraption is to decide how to set off your mousetraps.

Direct Triggering

In this design, each mousetrap directly sets off the next, such as tying a string from the bar of one mousetrap to the trigger of the next. Once one mousetrap goes off, the rest go off in a fairly short amount of time. Sometimes it can be hard to distinguish one trap tripping from another, so they all appear to go off at once.

Direct Triggering
Pros Cons
Very easy timing to achieve maximum time Can be difficult to design a fail-safe
You only need to focus on setting off one mousetrap No bonus points for mousetraps going off in correct order

Indirect Triggering

In this design, each mousetrap starts a series of events to set off the next, such as a mousetrap releasing a ball to roll down a ramp to the next mousetrap. This is a fairly popular design technique, but if one mousetraps fails it can be hard to get your contraption working again mid-competition.

Indirect Triggering
Pros Cons
Easy timing to achieve maximum time Hard to get going mid-competition if mousetrap fails
Easy to earn bonus points for setting mousetraps off in correct order If you aren't careful, you might accidentally set off from a "direct touch"

Independent Triggering

In this design, each mousetrap has nothing to do with the next mousetrap, such as each ball rolling down a separate ramp. If one mousetrap doesn't go off, the next will.

Independent Triggering
Pros Cons
If one mousetrap doesn't go off, the next will More difficult to achieve maximum time
More stable and reliable Harder to separate the mousetraps' setting off

How to get the Most Points

Points Reason
33 Staying within box dimensions
22 Having all supplies and mousetraps labeled
100 Setup within 30 minutes
17 Mousetraps being 90 degrees apart
58 Successful start
60 Successful completion
2 Each whole second
42 Contraption runs at least 5 sec. before first mousetrap tripped
35 Each mousetrap tripped by device
25 North trap tripped first
50 South trap tripped second
75 West trap tripped third
100 East trap tripped fourth
Minus 18 Device Touched
Minus 8 Per Centimeter Device off of the Distance

Lets break down how to get the most points possible:

The first two are gimmies. If you don't get those, drop out right now.

The third is also fairly easy, just pay attention while setting mousetraps.

The fourth, once again, if you don't get it, drop out of Junkyard Challenge.

The next one is more difficult than the others: if all the moustraps don't go off without direct touches then you won't get this one. In the rules it say that any mosetrap that go off "as the result of a direct touch" won' get scored. That penalty also includes not getting those points.

If you get those points, then you will also get 140 pts for all 4 mousetraps going off (35 pts per mousetrap).

As long as you have a system to delay the trigger of each mousetrap, you should get all 225 pts for the mousetraps going off in the right order. This is a lot of points, so its worth it to make a timer to get these points. What confuses most people is that they usually think "North South East West" or "North East South West", so pay attention to the order that you set them to go off. Independant triggering or indirect triggering may get you these points, but direct triggering will not (see above). Take this into account while designing your contraption.

As long as you have some form of delay, you can get the 42 points for lasting 5 secs. The 2 pts per second may not seem like much, but if you do it right, you can get 120 pts out of it, which can make the difference between first and last.

So, in general:

  • Pay attention while setting up mousetrap (this can cause a LOT of penalties!)
  • Make sure you set off the mousetraps in the right order (this can get a LOT of points!)
  • Develope a system to delay the mousetraps (this can get a LOT more points then you may think!)
  • And just use some common sense (bring mousetraps, make sure you drop the golf ball correctly, ect.)

You can find an easy-to-use JYC score sheet here. Just type in Y/N and it'll do the rest!


As mentioned above, you should really design a system to delay the mousetraps going off. Here are a few ideas:


Water behaves in a pretty predicable way. You can use this to your advantage. You can start all of these "water timers" by building a simple sea-saw type item, attatch a bottle of water to one end and drop the golf ball at the other to pour the water into a cup.

Slow Drip

Simple: Cut a small hole into a cup to let the water pour out slowly. You can put another cup, attatched to say, a pulley, underneith that the water can drain into. Experiment with different size holes and drip speed to find the perfect hole size/water volume ratio.

Siphon Drain

This is a pretty nifty trick: by cutting a hole in a cup and placing a bendy straw into your cup, you can create a timer that starts only once the necassary amount of water gets placed into the cup. Look at the following models:

Jyc siphoncup 1.jpgJyc siphoncup 2.jpgJyc siphoncup 3.jpgJyc siphoncup 4.jpg

In this way you can do two things at once:

  1. Fill the cup almost all the way, then add a little water from the way mentioned above, and you can get a lot of water in return. A lot from a little.
  2. Let the water drain slowly, making a timing device.


Small inclines that you can rool marbles, golf balls, ect. down can make a greate timer. Roll a marble down a long ramp with a small incline to a mousetrap. As long as you keep the same incline, this can be a very reliable way to time your contraption.


This is a very reliable method, as long as you keep fresh batteries. Just attatch a motor to say, a piece of string, and the string will slowly get tenser. If you have multiple pieces of string, each a different length, then each string will pull the trigger on a mousetrap when it loses all of its slack. Just watch out to make sure nowhere on the circut does the voltage exceed 6 volts. String, however, is not the only way to do this. Integrated ciruits can do the same thing with much more accuracy.


Both of these pictures show how to wire the NXT and the RCX to use less then 6 volts, the maximum allowed. For the RCX, when standing straight up, you need to put aligator clips in the upper left and the bottom right. For the NXT (bad picture, I know...) you need to put the wires at the bottom right when standing straight up. They both go on the right, one at the very bottom, and one right above the first. The NXT and RCX can be good ways to controll your device, but remember that they are running on less then they are designed to, so you run the risk of them dying in the middle of a competition (NOT GOOD!).

Other Ideas

There are a couple more things you can do to set off mousetraps.

START/TRAP 1: Drop golf ball onto a swith, which starts a motor which starts a propeller spinning. A string is attatched to the propeller and the other end to the trigger of the mousetrap. For each revolution of the propeller, the string is wrapped around the propeller until it loses all slack and sets off the trap. This takes about 15 seconds.

TRAP 2: When mousetrap #2 is set off it has a string attached to its killbar. The string is wrapped around a screwdriver on an axle. When trap 1 snaps it unwraps the string, freeing the screwdriver to fall on trap #2.

TRAP 3: When trap #2 is set off, it triggers a PVC tube to fall on a line of dominos which lead to the mousetrap's trigger.

TRAP 4: The triggering of trap #3 releases a marble to roll down a ramp onto another switch. When the switch is turned on, it repeats the method of setting off trap #1.


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