FreeCAD – Part 3: Parts & Assembly

In this lesson, we transition from modeling individual bodies to organizing them into Parts and assembling the Millie Mini AI robot structure in FreeCAD.

This lesson focuses on preparing the project for real assembly workflows. Instead of creating new geometry, we take the bodies already built and structure them correctly so they can be positioned, repeated, and assembled as a system.

Reviewing the Existing Bodies

We begin by reviewing all of the bodies created in Parts 1 and 2 to ensure the project is clean and ready for assembly.

Steps covered in this lesson:

• Opening the existing FreeCAD project

• Reviewing all previously created bodies

• Confirming orientation and alignment

• Checking that each body is clean and fully defined

Getting the model organized at this stage prevents confusion later and keeps the project maintainable.

Converting Bodies into Parts

Next, we convert each existing body into a Part so it can function as a reusable component within an assembly.

In this lesson, we:

• Create Parts from previously built bodies

• Organize each component into its own Part container

• Ensure each Part contains the correct geometry

• Rename and structure Parts clearly for assembly work

This step is essential because assemblies work best when each physical component is represented as a Part rather than a loose Body.

Adding Local Coordinate Systems

Once each component is organized as a Part, we add local coordinate systems to define how parts align inside the assembly.

In this lesson, we:

• Add a local coordinate system to each Part

• Place coordinate systems intentionally for alignment

• Use consistent reference directions across parts

• Create predictable reference frames for repeated components

Local coordinate systems allow parts to be placed accurately and consistently without manual positioning or rotation.

Building the Assembly

After all parts are prepared, we bring them into an assembly workspace and begin building the robot structure.

In this lesson, we:

• Create a new Assembly

• Insert all Parts into the assembly

• Align parts using their local coordinate systems

• Position repeated components consistently

• Begin forming the robot structure as a system

This is where the robot starts to take shape as a real build, not just a collection of separate bodies.

Result So Far

By the end of this lesson, you will have:

• Converted all existing bodies into organized Parts

• Added local coordinate systems to each Part

• Created a working assembly with multiple components

• Built the first full structural layout of the robot

• Prepared the project for repeated components and real build planning

At this stage, the robot is now structured for real assembly work in FreeCAD.

What’s Next

In the next lesson, we’ll continue refining the assembly into a more build-ready design.

We’ll:

• Adjust part placement based on real-world fit

• Identify alignment issues early

• Begin planning hardware mounting and fastening logic

This is where the CAD model starts behaving like a real robot you can actually build.