Fab Academy 2017 - Joern Kiwitt

Week 02 - Computer-Aided Design (CAD)

Computer-Aided Design Tools

CAD are very powerful if it comes to actually designing 2D or 3D parts. I have worked with a lot of different tools in the past, but barely scratched the surface of their capabilities. These range from design to rendering, simulation and computer-aided manufacturing (CAM), with we'll deal in the future as well. I gained my experience with SolidEdge, CATIA, Blender and Autodesk Inventor.

Professional CAD allows so-called parametric design, whereas rather design focussed tools often don't, e. g. Rhino and Blender. For simple 2D designs, I used to use Inkscape which is also relatively easy to and for simple tasks absolutely sufficient (e. g. boxes for a laser cut design).

3D Design with Blender

Blender is also a really cool (and free) design tool, but it takes while to get used to it and it is not parametric. Especially, the rendering and compositing part is really interesting as it allows to make Hollywood-like special effects. To create of the actual video however pushes my computer to its limits and took several hours. Just to give you an idea of what is possible, here are some videos I made some time ago on simulating physics as well as compositing and animation plus a rendered image. Compositing bascially means to add computer-generated effects to a regular footage like most of the movies these days.

Compositing with Blender (animated ball)

Explosion with physics and lighting

Animation of characters

Rendering with Cycles-Engine in Blender

Modelling with Fusion 360

Autodesk Fusion 360 is rather new for me, but it seems to similar Autodesk Inventor which I have used more often. With the extension into simulation, rendering and CAM it also seems extremely powerful. I highly recommend doing some tutorials before starting your project. A bunch of these can be found on Youtube, in the Fusion 360 channel.

For the time being, I will work with the "MODEL" module only. This allows 2D and 3D design of single parts as well as assemblies of interacting parts. By aligning these parts and constraining the their relationship, simulations will later on be possible as well. This helps in discovering physical collision before they occur (and cost you a lot of time fixing!).

2D design - first part

In this case, I will use Fusion 360 and Inkscape for 2D sketching. Here are some basic functionalities. Let me credit Jonathan Yen for an excellent live tutorial on this which helped understanding some basic concepts, I summarized below.

Sketching

This involves basic shapes, e. g. lines, rectangles, circles and splines which can be called by a shortcut within Fusion. Typing s brings in the search function which helps finding certain things faster than via the menu. Right clicking will offer you to add dimensions to a form.

Basic shapes

Pattern

In order to reduce repetitive tasks, patterns are a very versatile tool. In this case the a circle is copied six times in circular pattern, e. g. to create a hole for a bolt. This diameter could be given parameter in order to have a flexible design. If you were to change your design later on, only the parameter would have to be updated, the rest happens automatically.

Patterns

Mirroring

As most constructed product a usually a high degree of symmetry, it makes no sense to design both sides in parallel. The mirroring tool needs an object and an axis as input. The axis is represented as a line here. Press x to turn a regular line into a construction line. The so-called symmetry contraints will depict the two objects as mirrored. Contraints are in fact a very important concept in order to fix the underlying relationship between objects.

Mirror

Contraints

There are a bunch of constraints to take into consideration, when designing a model. Most are pretty straight forward.

Coincident: Constrains a Point to occupy the same one-dimensional plane of a Line or another Point
Collinear: Constrains a Line to occupy the same one-dimensional plane of another Line
Concentric: Constrains a Center Point of a circle, ellipse, or arc to another
Parallel: Constrains two straight line segments to be parallel to each other
Perpendicular: Constrains two straight line segments to be perpendicular to each other
Horizontal/Vertical: Forces straight line segments to be either completely horizontal or vertical
Tangent: Constrains a line segment to be tangent to a circular or arced line
Smooth: Important to smooth spline curves (inclination)
Equal: Sets two line segments to be equal in length to each other
Symmetry: Sets two lines to be equidistant from a third center line

Contraints

Hello-World part

I designed a small hexagon which is slotted. I applied mirroring, as well as circular patterns, added constraints and the trim tool. It is available in the download section.

HelloWorld file

Inkscape

I also used Inkscape to design a press fit kit. It is not as comfortable to design complex 2D parts accurately. You can however use a bunch of boolean operation to design a simple press fits.

Simple press fit design

Within Inkscape, there are some import feature you should know about.

First, layers: layers will help you in aligning your geometric forms in order get things in the pattern you would like to design.

Second, align: once you have created your tongues and grooves, you have to align them in x and y. Furthermore, you want them equidistant. The "align" feature are very helpful in accomplishing that.

Third, stroke and fill: These feature control the fill color as well as the line color of an object. Set the line width to 0.01 mm and select no fill to define a cut.

Fourth, pattern: in order to repeat a given pattern, the "create tiles clone" feature turned out to be very helpful. I used it to create a bendable piece of wood.

Standard settings

The standard settings for the lasercutter have to be adapted according the material and its thickness. For 5 mm MDF material, I set the speed to 4 %, the power to 100 % and the frequency to 20 %. The outside edges were set to red line color. Inner edges will be set to green and will be cut at first.

Laser cut plywood

2D cut

2D cut assembled

Bendable object

In order to create shapes that follow a curve, laser cutters can also be used to generate 3D shapes. A simple example is the following shape which can be bend around one axis. This is achieved by cutting away only parts of the material. The resulting radians are however hard to predict. To use this technique in product design takes some trial an error.

In order to cut plywood of 3 mm thickness, speed was turned up to 8 %. All other settings were kept the same as above.

Bendable shape

Flexibility demonstrated

3D design - first part

Here is the first model I did with Fusion 360. It is a box which is going to contain the camera and its gimbal later on. The final result looks like this:

Camera housing design

By the way, to find out how to embed Fusion 360 files, follow this link.

The precise design of the gimbal will come later, as there is a variety of solutions. However, here is the first draft.

The manual sketch

First part: housing for the gimbal

First CAD sketch - Photobot

Let's start with the housing design. Within Fusion 360 Model, I'll start with 200 mm by 200 mm box with a height of 150 mm. This leave enough space for the electronics, the flashlight and the gimbal, it is work in progress anyhow.

Step 1

Camera hole draft: Draw two circle with diameter of 70 mm. Create a center line (press x to change line style). Connect the circles with a tangent and trim unneeded edges to make the design more accurate. Mirror the left side over. The oval shape will allow the camera to pitch without hitting the housing.

Step 2

Shell box: Before creating holes are created, the box has to be a shell. Let's create a shell with a wall thickness of 4 mm. The final box will most probably be from plywood.