Bridge Design Challenge

3D printing is all about prototyping and experimenting with the design freedom that it allows. This challenge combines the basics of tinkercad design with the basics of 3d printing. The challenge is designed to do in a class, but feel free to challenge each other in the comments!

In this project, you will be the designer of a 3d printed bridge. The aim of the challenge is simple, the strongest bridge wins! However, there is no straightforward best approach, so an original design is encouraged. And creativity will be needed, the constraints for the bridge namely is: only one meter of filament can be used, use it wisely! This tutorial will walk through the various steps of optimization, first in design in tinkercad, then in the 3D printing settings in cura.

The bridge will span 14 cm, so it will be fairly small. In combination with the low filament, costs this allows to quickly print a design for many people at the same printbed, which saves some trouble for a teacher and allows all of the designs to be realized.

Let's get started!

Since this is a 3D printing tutorial, a 3D printer is needed, as a filament I used PLA.

• Testbench
• In order to finally test and compete with the bridges, a test setup is needed. A 3D printable design is made and given in the last steps, although it takes quite a bit of time to print this one. Make sure to do this in time.
• A piece of string
• A small piece of sanding paper (the screws in the testbench often have to be sanded a bit to fit)
• Weights (for example lifting weights, an easier option would be filled up water bottles). It is nice to be able to add small amounts of weights, so make sure to have quite some weights. A few kilo will suffice.

Additionally, the design will make use of:

• Tinkercad (online)
• Cura (free software)

That's it!

(Cura is needed to calculate the amount of filament that is used, which it does automatically after slicing.)

As a starting point a template in Tinkercad is given. This template includes a 14 cm long rod as a reference. Additionally, the hook on which the weight will be hung is shown in the template. Make sure the hook fits in exactly the middle of your design! Remember that you can only use a maximum of 1 meter of filament, so the design should be as light as possible!

Now the constraints are clear, the designing can begin.

(The link to the template)

The simplest bridge would be a square block, but this is certainly not the best approach. A good start would be to google some pictures of bridges for inspiration. What do most of them have in common?

Many bridges use a lot of triangles. Since triangles are a very strong form, it can be a very good idea to use a lot of them in your design. But should you use many small ones, or one very large one? It is up to you!

Some bridges use cables in order to a bridge of ten thousands of kilograms. Maybe this idea would scale quite well to your small bridge when using a lot of small 3D-printed strands?

Yet another approach would be to use a lot of (half) circles, as for example to Romans used in their aqueducts.

An upcoming design approach is "generative design", which creates natural forms based on complicated simulations. Although complex simulations are a bit out of scope, you might be able to find some examples in google and try to recreate it via the "scribble" tool in tinkercad.

A few iterations of the above-mentioned bridges are shown in the pictures, feel free to use them and google as inspiration!

Other aspects to think about:

• Should the bridge be firm or flexible?
• Where will the forces be the strongest?
• Where do you predict your design will break? Why?
• Should the hook with the weights be placed as high or low as possible?

With the first tinkercad model ready, you can click export to .stl in the upper right corner. By dragging the file into cura, your design should pop up. You can rotate and move your design around now.

By clicking slice and preview in cura, you can see what the 3D printer is going to do. More information in the next step!

Cura is a software program that turns your 3D design into instructions for the 3D printer. By clicking the big slice button in the bottom right, and then the preview button, you can see exactly how the model will be built up. You can also see the estimated amount of filaments (and the time) your print will need. By changing the settings you can try to come as close to 1m of filament as possible.

Cura also gives a lot of possibilities for design choices. A number of them are pointed out.

• print quality

print quality determines the line thickness of the 3d printer. Higher quality means the model will be made using thinner layers.

• bottom and top layers

The number of bottom- and top layers can be determined here. Keep in mind that the top and bottom layers often take up a large part of the filament.

• walls

You can also determine the outer layers of the print, just like the bottom and top layers. Which layers need to be the strongest?

• infill density

The inside of the 3D model does not necessarily have to be solid. Often 3D prints are only partly filled. You can choose between values of 0% and 100%. 100% would be very strong, but takes a lot of filament. Often a bigger print with a low infill percentage is stronger! However, close to 0% of the top layers could collapse because there is not enough support. (You don't necessarily need top layers, but if you use them, be sure to keep an infill percentage of about 20%)

• infill pattern

There are many different patterns to fill up the inside of the print. It is best to try some of them out, and see how they affect the inside of the print, with sometimes very complex patterns. Have a look!

• There are quite some extra settings, feel free to explore!

As in a standard design process, the first try will probably not work out too well. Maybe you accidentally created a design that uses 5 meters of filament or has too much overhang to be printed.

Don't be discouraged, this is part of the process. With the new knowledge, go back to step 3 in tinkercad, and tweak some aspects of the design. For example, alter the height or thickness to change the amount of filament you are using.

In most design process, designers will go through multiple of these cycles, each optimizing the design a bit more.

If all is set, you are sure the goal of 1m filament is correct, and the design is as optimal as you can make it, it is time to print!

For teachers: In Cura it is possible to assign different properties to different models and print all of them at one go. This can be done by selecting a model and clicking the "per model settings" option (four small squares). The specific properties can be added and set to the correct value. Make sure everyone clearly shows what cura settings are enabled.

For teachers:

In order to test the bridges a test setup is made. A 3D printable testbench is added as a printable file here. The bridge can be mounted on the testbench with the screws. The hook can be attached to the bridge. A piece of string is added in order to mount the weights on the other side.

Lastly, find two tables and place them approximately 14cm from each other. Place the testbench on top as in the picture in the next step. With the test setup ready, the testing can begin!

The big question: will the design work?

Slowly add more and more weight to the hook. Be careful the moment you release the weight, you don't want the bridge to fail because of a falling weight.

Good luck!

But eventually, all will break...

Keep track of all of the scores, did you correctly guess the bridges that would win? Any surprises? Did the best bridges have a perfect balance of multiple factors or a radical design that worked really well?

I hope you learned to tinker around and how 3D printing can be exciting. Good luck with the next iteration!