Investigation: K'nex Bridges




About: Inactive user (currently) :p ============================================== 100th Comment - ~KGB~ 200th Comment - nerfrocketeer 300th Comment - DarkOwlKnex 400th Comment - The Red Book of Westmarch 500...

Hey All!!

Today, I present to you my latest Instructable: An investigation! In this Instructable, you will be guided on designing, developing and making your own bridges using K'nex. Stumbling across the Scientific Method Contest, I wondered if there was a way to link the world of K'nexing in with Science. This is the final product that I came up with, which I am very pleased with. :-)

The objective of this investigation is to find the best design for a bridge, that is able to hold the most weight possible. So the question for this Investigation is:

What is the best design for a bridge made from K'nex, able to hold the largest amount of weight?

I hope you enjoy this Instructable as I had making it!

Also, this is (correct me if I am wrong), the first K'nex investigation on Instructables! :D

This is for the Science Method Contest, and so I would really appreciate a vote - it would make my day!

Anyways, lets proceed with the investigation, beginning with the hypothesis on step 2, and designing on the next step! :-)

Step 1: The Variables, Regulations and Beginning Design Ideas

Firstly, lets begin the investigation by starting designing, what could be bridge designs for your K'nex bridges for the test. However, lets start by stating the different variable as well as the regulations for this test.

There are three different types of variables for tests in general. These are Control, Independent and Dependant. Below are are the different variables, categorised between the three. If you think of any more variables, feel free to comment.

Control Variables

The Control Variables (the variables we keep the same) of this investigation are:

  • The blocks are kept the same
  • The blocks are identical to each other
  • The blocks are kept the same distance away for each test (25cm)
  • The weights are put in the middle of the bridge
  • The same types of weights are used

Independent Variable

The Independent Variable (the variable we change) of this investigation is:

  • The bridges
Dependant Variable

The final variable, the Dependant Variable (the variable we measure) of this investigation is:
  •  The maximum weight the bridge can hold before it collapses.
Now with all the variables stated, here are the regulations (rules) for this investigation


The bridge should be....
  1. Made from K'nex
  2. At least 30cm in length
  3. Able to support its own weight without collapsing
Here are some questions that you should think about before beginning your design:
  • How can you make your bridge really strong? Jot as many ideas as you can down on paper
  • How can you prevent your bridge from sagging in the centre?
  • How can you prevent the bridge breaking under its own weight?
Once thinking about these ideas, it is finally time to begin designing your bridges! Above are 2 designs of 2 that I made. This is how you should try to present your ideas as they will be easy to develop. These designs are rough and so a ruler is not required. Be sure to use a pencil in case you wish to erase anything :-) 

For a new design, you should start fresh on a blank piece of paper and make sure that you have a sharp pencil when sketching.

You done that already!?! Wow, in that case, proceed to the next step, where you will be thinking of a Hypothesis and developing your designs further! :D

Step 2: Developing Ideas and Hypothesis

In this step, you will be developing your ideas that you sketched in step 1 into scale drawings and designs with colour. This will help you in the building process of your bridges. Below one example of a scale I used for one of my bridges. In order to do a scale for your bridge, you will need to have a set number of squares for each rod. For my one I used 4 squares for a blue rod, 1 square for a purple connector and the hypotenuse was the yellow rod.

For this part, you will need to use a pencil (like in step 1) a ruler (for straight lines) and ideally some graph paper for neatness and precision (this is all shown in picture 2). This will make it much easier when making your bridges!

At this stage of the investigation, you should also come up with an hypothesis (what you think is going to happen). You must also give a reason why you think this.

My hypothesis is that I think bridge D will be the strongest to hold the most weight since it is supported from all four sides, although it is the longest (meaning it may sag more in the middle).

After you have finished with this part, and have your scales and developed drawings of your bridges, it is finally time to build! :D Yay!!!

Step 3: Begin Building: Part 1

Finally!!!!! It is time to take out your K'nex, and begin tinkering away at your ideas. In total, I made eight bridges for my investigation, but it is entirly up to you how many bridges you wish to test! :D

While building, you should use your designs for reference to help you build (picture 3). This will make it far easier to make. You should test particular aspects of your bridge in this step, to ensure it is strong! :-) 

When you have got the basic structure for your bridge, move on to the next step (part 2).

Step 4: Building: Part 2, Finalising Bridges

In this step, you will be finishing off the bridges and seeing how well they match there designs you did previously. As shown below, you should finish off all your bridges and line them up as shown in picture 2.

You should do steps 1-4 for each of your bridges. After this, you should see if they have similarities with your plans that you did. :D

After you have finished your bridges, onto step 5! :-)

Step 5: Drawing a Table of Results

Next, you will be doing a Table of Results. This will be what you will use to record your results. You should have 3 tests for each bridge (in order to increase reliability). You should then have an average column, which you will work out after the test. For each bridge, you should use a letter to represent them.

After you done this, yes, we will be preparing the test. :D

Step 6: Preparing for Testing

In this step, preparations for the test will need to be made. These are making sure that the blocks that the bridge will rest on are the same length away each time (25cm). They must also be parallel with each other.

To make this a fair test, this should be done before testing each bridge in the next step. You will also need to make sure that each bridge is at least 30cm in length (as mentioned in step 1). If not, try to extend your bridge so it reaches this requirement.

And finally, the moment you have been waiting for has arrived....testing!!! :D :D :D

Step 7: Testing and Recording Results!

Congratulations if you have made it this far, as now we are testing! Follow the pictures on how to test correctly. Since I did not have any level blocks, I used 2 of my identical K'nex boxes (except the colour of them).

Prepare a range of weights to use to test your bridges as shown in picture 2. You should record your results in your table after each bridge that you test so that you don't forget at later stages of the investigation! :-)

You should apply weights one by one until the bridge collapses and record the results. It is ideal to do this on a hard surface as material like carpet, it is likely that the bridge will/may leave marks and go down.

After testing, you will be calculating the averages in the next step.

Step 8: Calculating the Averages

In this step, as you may have guessed from the title :) we are calculating the averages. To do this, you add up all the values for one bridge and divide by 3. I used a calculator for this for the most accurate results.

After this, you should have a complete table of results.

Step 9: Graphing the Results

Lastly, you will be inputting your results into a graph. Since I did the table by hand, to do the graph, I used Microsoft Excel. Here you should reflect on your results and think of improvements. If you do think of improvements, feel free to test your bridges again as I have. You can see my improved results compared in my second graph.

Remember that the independent variable always goes on the X-axis and the dependant variable goes on the Y-axis. You should use the averages of the tests for each bridge. :D

After this, go to the next step. :-)

Step 10: Conclusion

Finally in this step you will be writing a conclusion to draw an end to your investigation. Here is mine:

In conclusion to which bridge is the best design to hold the largest amount of weight, I found out from my results, that bridge D was the strongest. This proves that my hypothesis was correct. This might be because it was the only bridge supported from all sides and areas as well as being the most compact. In the investigation,one thing that went well was all the bridges had unique designs and therefore the results were varied. In the future, if this investigation was ever to be repeated, I would have more bridges to show a wider range of results. I would also test the bridges more than three times in order to increase reliability of the test. I could increase the accuracy of this test by checking my averages and results more than once. Thus, this answers the question:
What is the best design for a bridge made from K'nex, able to hold the largest amount of weight?
The best design for a bridge is one that uses the idea and structure of triangles. This is because triangles are the only polygon that cannot be 'squished' without changing the length of one or more sides. An example is that the angles are held constant. This is also the same for real life bridges.

Some real life famous bridges that use this structure are
Since triangles have been proven to be the strongest structure for a bridge, a famous worldwide attraction, the Eiffel Tower in Paris, France, is also a structure that consists of triangles.

Step 11: Ending Statement

Thank you for reading through this Instructable! :D I hope you enjoyed it as much as I had making this instructable.

If you did enjoy it, please vote for it! I appreciate it deeply :-)

Thank you again!!! :D

Also, be sure to leave a comment. I would love to know your designs, what you think, and how well your investigation went.

Full Spectrum Laser Contest

Participated in the
Full Spectrum Laser Contest

Scientific Method Contest

Participated in the
Scientific Method Contest



    • Frozen Treats Challenge

      Frozen Treats Challenge
    • Growing Beyond Earth Maker Contest

      Growing Beyond Earth Maker Contest
    • Colors of the Rainbow Contest

      Colors of the Rainbow Contest

    86 Discussions


    4 years ago

    Wow!! This is really cool and interesting!


    5 years ago

    Tried to build a 3 meter long bridge from not very much K'nex, to allow trains to drive from one set of shelves to another. It collapsed on the second test run, resulting in more K'nex being bought to add more structure at the ends, and have two sets of rods running the length of the bottom of the bridge, which unlike the connected purple connectors, will not pull apart under pressure. Also eventually added a support in the middle (made from cardboard boxes - the K'nex bill was getting expensive >.<) and an 'emergency rope system' - string going along the bridge and back that would keep it together in event of another collapse which thankfully never happened.

    knex bridge.jpg

    Reply 5 years ago on Introduction

    Thank you so much Linda for your positive, kind words! I am appreciate it more than word can express! :D

    A vote would make my day - thanks Linda!! :-)


    Reply 5 years ago on Introduction

    Thanks so much! :D I can't wait for more 'Ibles from you. Also, good luck in the Pet Contest!! :-)


    Reply 5 years ago on Introduction

    You too Linda! Seems like the entries for the Jewellery contest are building up, I'm sure you will pull it off though. :-) I'm not sure if you know, but do you know how long Emily has gone to Paris for? (*PM's)


    Reply 5 years ago on Introduction

    I didn't even know that she went to Paris! Now I must admit that I am veeeery envious :D

    It's ok about the jewelry contest, I'm not much into jewelry, I have never done that much...there are people here who are so much better than me at that and really deserve to win! :)

    Yaaay! So I'm still in time to hide into Emily's suitcase haha :D (kidding!)
    Have a great time in Paris, it's beautiful!

    ps: I'm not sure if you are following the Eurovision Song Contest, but I love The Netherlands song! I couldn't watch the second semifinals tonight but that song was definitely my favorite one in the first semifinals...fingers crossed for you! :)

    I really hope the weather will be a bit better than here :D

    I'm not really following it, but I did see the performance, loved it!

    I went to Paris in May 2010 and I remember it was already warm here so we thought it was the same there...well, we were totally wrong :D It was sunny but still cold in Paris. We should have thought about it since it's more on the north compared to where I live, but I think that your country is colder so Paris will probably be warmer for you :)

    I have been to Paris before, in May 2010 (yes, I know!!). Let me just say I saw a lot of rain ; )

    But still, I love Paris : )

    Oh my god, really?? :O I was lucky enough to be there when it was sunny enough, cloudy sometimes, but no rain luckily!

    I love Paris too and I hope to go back someday and visit more of it. I was staying at Disneyland (lol) so I couldn't see the whole city as well as I wanted to!


    Reply 5 years ago on Introduction

    Me and you both! When I went to Disney land in June 2010, I went for the rides and coasters - did not really spend much time in looking at the whole city. Though I did see the Sacré-Cœur, Notre Dame, Arc de Triomphe, Champs Elysees (I jogged the whole way :-)), Place de la Concorde, the Louvre and not to forget the Eiffel Tower.....the list goes on and on :D I actually visited all those in the space of 2 days.

    Did you go on any coasters at DisneyLand? (I actually got all the signatures of every Disney character) Aerosmith was by far my favourite, though the Hollywood Tower of Terror was a close second!!


    Reply 5 years ago on Introduction

    Wow, you were able to visit more than I did! Did you stay there 3 days too? I was with a friend and we ended up spending way too much time in a shopping center close to the park haha. 3 days are definitely not enough to visit so many things at once. I desperately need to go now you are reminding me of all that and I really miss it. What a great time I had!

    The coaster I remember the most is the Space Mountain: Mission (I've just researched the name because I couldn't remember it). All I can tell you is that it was all dark, I had no idea what the hell was happening to me, but I could feel my head going all over the place. When the ride ended one of my ears hurt for days (?!), I had a stomach ache and hated my friend who pushed me to do it :D As you can see, I'm not a fan of that kind of coasters lol. But I loved the park and I remember I really liked the Panthom Manor and all the other ones I visited.

    I really want to go back NOW! :D


    Reply 5 years ago on Introduction

    Sorry for not responding - I only actually saw the message now!

    Did I really visit more?! Haha, I went with friends too. When I went, I stayed for 7 days! I know, I was really lucky :D I totally agree with you!! 3 days just flies by and it's just not enough time to visit all the major attractions. :-) There was so, so much to do in Disneyland. I love the parades that went on, along with the fireworks every night :D It was just....paradise. Did you go to any of the restaurants there? Most of the nights at Disney Land, we went to the Plaza Gardens (restaurant) and the Lucky Nugget (that's were I met Mickey!! :D :D :D). I hope you got some good things in the shopping mall. :-) The only time we went shopping was for a bit in the morning and maybe at night if we had time!! It was so amazing. The atmosphere and all.......I soooooooo want to go back and relive those moments!! :D

    Yeah!! I remember Space Mountain, I loved it. I'm so sorry to hear that your ears hurt and you had a stomach ache. I personally wasn't too keen on going on it, though all my other friends went and so, like you, I went along. It did make me dizzy though after, which wasn't too pleasant! :-) Haha, did you go on the Buzz Lightyears Astro Blasters? I really enjoyed that. Too bad, a year later (in 2011), the new RC racer coaster was released (I saw it being built). I loved the Fantaillusion every night!! I liked Phantom Manor too! :D Also, I loved Big Thunder Mountain. Did you go on it? :-)

    Same here, I really want to go back. I even was lucky to talk to Jack Sparrow! :D :D :D