Introduction to Rhino, Nettfab and Meshmixer

First stage

The first stage was to experiment with low bit files. There were a lot of shapes created, like a sphere, a box and finally an easy-shaped-saddle. All of these shapes were created with Rhinoceros. After this section the 3D reaction models from Avizo were transferred to Rhinoceros. In this section it was important to type WRL in the avizo title so that Rhinoceros automatically convert a WRL file to a STL file and generate a mesh. It was also important to downgrade this files, because this made the experimenting process more fast. Finally, two downgraded Avizo files, one for the hard material and one for the soft material, and one Rhinoceros shaped model were loaded in Rhinoceros. This is done by the function ‘import’.

Schermafbeelding 2016-10-27 om 11.44.06The three meshes in a rendered top view.


 

How to cut out shapes of natural meshes?

This is done with the program Meshmixer from Autodesk. The function Boolean intersection is used in Meshmixer. Meshmixer is used instead of Rhinoceros, because Meshmixer recognizes the patterns as a volume, instead of Rhinoceros. So when two volumes intersect there is created a new closed volume, or a valid mesh/closed double precision polygon mesh. If Rhinoceros does this, there could be a chance that 4 million of triangles need to be flipped by hand and closed again. This would be less secure, and there will be a bigger chance of failure.

Important notice: When the parts were cut out of natural meshes, it was important that the saddle (2 files in this case) was coordinated at the same reference point.

Schermafbeelding 2016-10-31 om 15.30.54The soft part, created with the function Boolean intersection from Meshmixer.


 

Finetuning with Netfabb

After creating two shapes, the soft part and hard part, were the shapes controlled by Netfabb. Why Netfabb? Netfabb has a simple repair mode. This repair mode finds holes and repairs them easily and automatic. After this section, there is created a valid mesh, which is also a closed double precision polygon mesh.

Schermafbeelding 2016-10-31 om 20.14.40The soft part opened in Netfabb, the red sign shows us there is an error.


Creating the product

When the two parts were repaired, they were transferred to Rhinoceros again. And checked if they were both closed and valid meshes. The soft and hard part were seperated and grouped. Now they could be exported both, by export selected, and send as a STL-file to the Connex.

 Schermafbeelding 2016-10-31 om 20.27.06The final product in Rhinoceros, black part is hard, cyan part is soft.

 

Zwick testing our prototypes

Today, Monday the 31st of October, we did a last minute test on our prototype cubes (2 x 2 x 2 cm) with a Zwickmachine: a drawbench that tests materials on their tensile strength. By applying a pressure of 500 N in ~16 seconds on each of the test cubes and measuring the compression, we obtained data of the 5 cubes. Then we compared the data in order to draw a conclusion on which material and pattern will suit the saddle the best. The 5 test cubes:
thumbnail_IMG_20161031_141842

The first test cube was a pink cube made of 100% hard material:
IMG_8460
Grafiek1

This cube compressed with 0,159 mm.

The second test cube was a blue cube made of 50% hard material:

IMG_8463
Grafiek2

This cube compressed with 8,045 mm.

The third test cube was a soft cube with a hard spiral pattern in it:
IMG_8465
Grafiek3

This cube compressed with  0,271 mm.

The fourth test cube was a soft cube with a hard circular pattern in it:
IMG_8466
Grafiek4

This cube compressed with  0,399 mm.

The fifth test cube was a soft cube with a 50% hard circular pattern in it:IMG_8467
Grafiek5

This cube compressed with  9,460 mm.

From least to most compressable:
mm                what
0,159             pink cube 100% hard material
0,271             spiral pattern 100% hard material
0,399             circular pattern 100% hard material
8,045             blue cube 50% hard material
9,460             circular pattern 50% hard material

The results were mostly as we expected and with this information we can conclude that a circular pattern consisting of 50% hard material in a soft cube is best to use for suspension. Sadly, we don’t know how this pattern will work on a big scale (we are afraid it will rip easily).

This experiment was conducted on a short notice and we were unable to use the findings in our final saddle. It did give us an idea about all the variables that have to be taken into account when it comes to pressure distribution. Further research is needed to find the best combination of materials and patterns for optimal suspension. For our final saddle we decided to use a mix of hard and soft material (in a circular pattern) because we know from previous prototypes that this allows suspension to happen and is also strong enough to bear a person.