Arduino Meets Lego: The Ultimate DIY Robotics Project

Cyrus Tabrizi, 8/29/13
Step 3: 3D Modeling in Autodesk Inventor

      For those of you ARE going to laser cut (or 3D print) your own design, our journey continues into the world of CAD. I used Autodesk Inventor to create my enclosure digitally, because it is a powerful tool that is available for free as a student. While many other CAD programs are available (like SolidWorks, or, for free, Google Sketchup, 123D and plenty of others), I will be showing you how to do everything using Inventor.
      The first step is to open Inventor and create a new Assembly (a Standard.iam). From here you’ll want to click the “Create” button in the “Assemble” window. Type in the desired name for your first part under “New Component Name” and the desired storage location for it (keep all your parts in the same folder), and then click OK. Click anywhere on screen and then click “Create 2D Sketch” and click somewhere on the screen to select your drawing surface.
      For each part you will need to make, this and the rest is basically the same. You start by creating a 2D sketch with lines and different shapes. In doing so, you’ll use such tools like Dimension, Trim, and the different Constraints a lot, so try to become familiar with them—trust me, it’s worth it.
      When drawing your part, it’s important that it be formed in a closed loop. An example of a closed loop is if I were to take a piece of string and attach each end to the other to form a circle. If the two ends were not attached, the string might still have a shape, but it wouldn’t be in a closed loop.
      When your sketch is ready, click “Finish Sketch” and then head over to the “Extrude” command under the “3D model” tab—this is what turns your 2D surface into a 3D model. Once you’ve opened the Extrude window, hover your mouse over the body of your sketch. If you’ve done your sketch correctly, the surface of it should change color (mine appears light gray). If not, you need to go back and edit your sketch by clicking Cancel, right clicking on your sketch, and clicking “Edit Sketch.” If it does change color, though, you’re set. Click on the sketch and Inventor will show it as a 3D part. Chances are, though, that there are parts of your sketch that aren’t meant to be extruded. If that’s the case, click on them again while holding the CTRL key. You can go back and forth selecting all the closed loops until your part is exactly as it should be, minus its thickness—that comes next. Since we are primarily laser-cutting the various enclosure parts from a single sheet of plastic or acrylic, all the parts will have the same thickness (mine was 1/8”)—that thickness is the amount we will want to extrude our 2D drawings. This is under the “Extents” and “Distance” form in the “Extrude” window. Type in the thickness with the right unit of measurement and then click OK. Once its extruded you’re set! That’s your first 3D piece! Now click “Return” on the right and you’ll be back in your assembly and able to make another part.

Inventor Parts Coming Together
      This is all you’ll need to make your parts, but if you want to see your parts come together (which makes it a lot easier to visualize and plan out things), you’ll have to do a little more work (but I highly recommend it and its actually quite simple once you get the hang of it). Basically, you have to tell Inventor how the parts should stick to each other—this relationship is called a Constraint, and there are many different types Inventor has to offer. It would take a while to explain each and every one of them and their different options, but you can figure it out just as effectively and much more quickly by just playing around with it on your own (and its fun too). All you have to do is open the Constraints window (or press CTRL + C), select a type of constraint, click the little number “1” button under "Selections" and select the surface of one object, and then click the little number “2” button and select the surface of a second object. If everything is okay, the two objects should now move together and be constrained, but for the constraint to remain, you have to click OK or APPLY. By using different constraints on different parts of the objects, you can make it so that they all fit together without any freedom to move around. The best part of this is that you can edit your parts while they are together (be careful, though, because this may remove one or more of your existing constraints, but you can easily redo them).

Overall CAD