Rubber Band Cars STEM Project

About the project

This is a project I worked on with a group of students at both the schools I work at. The original goal was to have the students at both schools build the cars then meet up and talk about their cars and have races to see whose car can go the furthest. Sadly COVID-19 resulted in us being unable to meet up, but we still built them and had in school races anyway!
The basic principle is the Rubber Band cars are planned on paper, designed in TinkerCAD on the computer and then 3D Printed and assembled by the students.
A little bit of background on me:  I’m the Technology Officer in two primary schools and I’ve been doing this job for 11 years now. My background is in IT and I’m a tech enthusiast – I’ve done a bit of everything! I’m not actually a qualified teacher, so I do my planning alongside the teacher who I’m working with to make sure that it ticks all the boxes.

High Potential Learners – Goals, selection criteria, Failures

One thing I’d like to note, the students I was working with were regarded as “High Potential” students, usually either hand picked or selected by their test scores in Science and Math. One of the goals of the High Potential Program was to challenge the students and to build resilience. One of the common faults I’ve seen with these types of students is if they’re not good at something right away, they’ll just give up. With this in mind, I only explained the basics of how the cars work and left it entirely up to them to build it.  I essentially wanted the students to fail, so that they could then build on what they’ve learned and redesign their car to work better (or to work at all!) I do make sure that by the end of the project they’ve got something that works.  I’m not flawless either, I make plenty of little mistakes along the way (so I lead by example!)
I’ll go through some of the problems we faced below.

Lesson Plans – Week by Week

Week 1 – 3D Printers

The first week I gave the students a run down on what we’re doing, 3D Printing, TinkerCAD, Name Badges and very briefly mentioned Rubber Band Cars.
Here’s the Slides I used for the intro to 3D Printing and getting started with TinkerCAD, they’re not super detailed and are designed as a series of images to go with me talking about 3D Printing etc.
I had a 3D Printer set up and printing (I usually start it going well before the lessons so they can see it printing). The first lesson I did, the print I was working on failed and came off the print bed – a perfect example of something not going to plan!

This is called Spaghetti and is generally undesirable.

To get the students familiar with TinkerCAD, I got them to design a Bag Tag/Name Badge. First on paper then in TinkerCAD.
Some things I noted:
  • Sizing is important! TinkerCAD works in millimeters and I found a lot of students have trouble with sizes of things. Doing a drawing to scale on paper with measurements written down helps a lot here!
  • Using the Group option in TinkerCAD is brilliant. It lets you make up a weird shape by just adding/subtracting shapes until you’ve got the shape you want.
  • Be aware of the limitations of the 3D Printer you’re using. Small details sometimes come out looking really bad, or they might design a model that takes many hours to print. If the design is too big, I’ll usually scale it down to fit.  Sometimes a design is just too good, so I’ll print it out overnight. This print took over 10 hours to print!

The printer didn’t like the fine detail here

What it was supposed to look like

  •  3D Printing does cost money, but it’s not a lot thankfully. The other important factor is time. I had 4 printers at my disposal (2 were my personal printers and 2 were school owned see below for more info). Here’s some examples and costs.

Print Time: 6 hours 19minutes. 48grams of filament ($1.06AUD)

Week 2 – Rubber Band Car Design

This week I showed them the basic design of the rubber band car. I didn’t really have a good slideshow for this one. I tried to emphasise the following points:
  • Measure the skewer to use for the axles first, then allow ~0.5-1mm extra for the axle holes so they can rotate freely.
  • Make sure there’s something to attach the rubber band to
  • Think about the size/shape of the wheels – are they big enough to keep the body of the car off the ground, and small enough that they don’t hit the other wheels?
I had them quickly draw up a few designs on paper for what they were trying to make. This kind of fell apart a bit as they were way too keen to get into TinkerCAD straight away! Most of them ended up looking completely different from the sketches anyway.
I gave them no basis of a model to design off as I was curious to see what they would design. While they were doing this, I built one myself (The King Duck Transport of Kings). I’m still not sure if building this was a good idea or not. It gave the students a lot of awesome design ideas, but then a lot the designs kind of looked similar.

My glorious creation

I think in hindsight, I would show them a bunch of different designs to begin with, just to give them some more ideas instead of them all trying to copy my design.
There was a lot of little problems with the designs, some I didn’t tell them about (prepare to fail!), others would have made it not work at all so I helped them correct this before printing and some problems I didn’t forsee until they were printed and put together!  Here’s a list of them – depending on if you want to let the students make big mistakes, you might want to carefully look through the designs and make sure they’re going to be okay
Size
    One design was about 5cm long and 1cm wide. It was tiny, but I printed it anyway! (Note: their second design was way bigger and better!)
    Some designs were massive – too big to print!  If I scaled the whole thing down, then the holes for the axles would be too small.
Wheels
    Some weren’t round, they were more of an oval shape.
    Some wheels had axle holes not in the center of the wheel.
    Some wheels were too small and couldn’t touch the ground.
    Some wheels were too big and would hit the other wheels.
Axle Holes
    Many of the axle holes were too small, so the skewer wouldn’t fit (also: we had 2 sizes of skewers and they vary a lot in thickness, so plan accordingly!)
    Some axle holes weren’t round and were more oval shaped, this causes them to get stuck sometimes.
    Some axle holes didn’t have anywhere to attach the rubber band
    Some axle holes were so close to the body there was no clearance to attach the rubber band
Other design issues
    Some designs had pieces floating and not touching the other pieces – 3D Printers don’t like this!
    Some had very small details that were a bit too small for the printer to handle
    Some had difficult overhangs – most printers will generate support material to make it work and it’s okay most of the time!
    Some forgot to include somewhere to attach the rubber band to.
Some of these mistakes we managed to engineer a solution to, eg. borrowing someone elses wheels to test with, cutting away pieces of plastic to make space to fit things etc.  In every case, the students knew what went wrong and were able to go back into TinkerCAD and fix their designs for the next round of testing!

Week 3 – Test runs!

This week we put the parts together using hot glue and let them loose!
One super interesting thing to note here – 3D Printed wheels don’t have much traction. We wrapped a rubber band around the wheels to give them something to hold on to.  I let them make this mistake and had the students try to work out what went wrong.
I had about 7 cars 3D Printed ready to go. Out of these, I had one that worked really well (travelling about 4 meters), 2 that worked okay with some modification and the rest hit some serious problems that had to be corrected before they would work.
After the test runs, many had to go back to their designs and revise ready to be printed for the next week.

Week 4 – More Test runs

Same as Week 3 – This time all the cars worked (in varying degrees). They were given one more chance to refine and revise their cars ready for the finale next week.

Week 5 – The race!

We got the students to line up their cars in the hall and measure how far they travelled as well as how straight they went, then compile the results.
The winning car was this glorious pig shaped car with a distance of 6.8 meters created by two year 5 students.

Equipment used

The most expensive part here is getting a 3D Printer. I may do a post later on what I’m using (and all the modifications).  In short though, my main printer is an Ender 3 Pro, it cost me about $300AUD, along with a whole bunch of tweaks to get even better print quality out of it, but it is pretty easy to use and can get some good results without any tweaking at all, straight out of the box.

As for other parts, skewers, hot glue guns and rubber bands. All super easy to obtain!

 

All up, the students loved this project and learnt a lot about 3D Modelling, measurement (and visualising how big their cars will be).  It’s definitely a project I’ll run again!

If you’ve got any questions/comments or like my work, please leave a comment below!

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