3. Computer Aided design

This week I worked on 2D and 3D Design yousing the Tool FreeCAD. You can download here and install it with standard settings.

2D Design

To get started, I sketched a 3D-model of my final project by hand: FOTO FROM DRIVE

I will start with the top and bottom of the casing of the drone. Therefore I open FreeCAD and open a new document by pressing CTRL+N. Then I pick the “Part Design” workbench and click “create body” in the Task-Tab in the combined view window.

Afterwards, I have selected the newly creaty body and create a new sketch.

Now I create the sketch in the XY-plane, which resembles the flat ground. I select the rectangle tool and create a basic rectangle, click to start and click again to finish the shape.

I select the lower left corner of the rectangle and the origin point and click on the coincidence constraint button to make the shape align with the origin.

Now I can drag the top right corner of the rectangle and move the point, but the lower left point will stick to the origin. By using more of those contraints, we will design our shape.

In the next step, I create a spreadsheet, for that I will go to the Spreadsheet workbench. But first I need to close the sketch using the ESCAPE-key. Then I click the button in the symbol bar for creating a spreadsheet and double-click it in the hierarchy. In my example i create a parameter i call baseSize and give it a value in the column to the right. Right-click - Settings - Alias - and type my parameter name. This way I can reach it from within a sketch.

In the next step, I navigate back to my sketch and double-click it in the hierarchy to open it. I select a line and click the symbol to set its length. I click the small round icon in the line and enter the name of my spreadsheet and the name of my parameter.

I apply this to one of the orthogonal lines too and now I have a perfectly constrainted sketch. I want all of my models and designs to be perfectly constrainted. This way I can prevent a lot of errors and mistakes.

In the next step, I navigate to the Part Design workbench and select the body. Then I click the extrude button. I enter the thickness I desire (in my case 3mm) and click OK.

Now I have a 3D object. I click on the upper surface and create a new sketch.

I create a circle and choose the center of it and the origin and set a coincedence constraint. I create a new parameter in the spreadsheet that holds the size of the circle and connect it to its diameter. I want one cirle at every corner. I use the edge of my external geometry by using the tool in the upper right, then I set coincidence constraints with new circles to each corner. Afterwards, I use an equality constraints with all circles, to make them have the same size.

I will exit this perfectly constrained sketch and select the pad in the hierarchy to intrude it. I choose 3mm for thickness again and am already done with the first part!

After saving it, I create a new document for my next part. From now on, I will only document a new method or tool.

For the next part, I create the cross that holds the rotors. I will make it 1cm longer at each side than the diagonal distance between two rotors. for my 10x10 cm case the distance should be 16.14cm. So I start by creating the rectangle and set the sizes using a spreadsheet. Then I extrude the rectangle by 3mm and create a new sketch on its upper surface. There I add circles on the corners again, set their diameter in the spreadsheet and intrude them. I created additional circles to intrude at the tip of every arm. They are positioned 1cm from the edge with a diameter of 0.5cm.

The next part I create is the connection between top and bottom. Afterwards I will assemble them together for a test.

Using the plugin A2plus for assembly, which you can get in Tools - Addon Manager, I used the various constraint tools to align the edges and planes at each other. I think it’s best to play around a little with those tools, maybe with some test objects to get to know with the assembling. The outcome is the following:

Clicken the transparency button on top shows all the assembled parts in transparent. Final Assembly: