Merge pull request #155 from orionrobots/freecad-assembly

FreeCAD assemblies post

Author: dannystaple

Diff for: content/2025/02/12-freecad-assemblies/2025-freecad-assemblies.md

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+---
+title: Trying out Assemblies in FreeCAD 1.0.0
+date: 2025-02-12
+tags: [3d cad, robotics cad, robot building, robotics at home]
+description: Using the FreeCAD Assembly workbench in FreeCAD 1.0.0
+thumbnail: content/2025/02/12-freecad-assemblies/robot-chassis-front-assembly.png
+---
+I've been working on a robotics mentoring project for [Coder Dojo KU](https://www.coderdojoku.org/). There will be a fleet of 10 of these robots. The current task is to model a sensor bracket that I can print for some RCWL-1601 ultrasonic distance sensors.
+
+The specific sensors are always 3.3v compatible, and quite cheap. Awkwardly, they do not fit where the more frequent HC-SR04 ultrasonic sensors fit. So I'm designing a bracket to hold them in place on the Adafruit Mini-3-round chassis that I'm using as a base for the robot.
+
+I wanted to ensure it fit, and modelled part of this chassis in FreeCAD. I've been using FreeCAD for years, but today I got into what the 1.0.0 version could do for me.
+
+## Fasteners workbench
+
+The first thing is to try the Fasteners workbench if you haven't. Screws and standoffs are there, and people who know my building style know that I like to use PCB standoffs for lots of construction since they are cheap and fairly easy to get hold of.
+
+If you want to model nuts, bolts and washers, this is the workbench for you.
+
+The stand-offs are in a slightly odd selection in the workbench - look under the "Inserts" toolbar section for them. You can then set a standard diameter (M3 or M2.5 are what I use) and length.
+
+## Assembly workbench
+
+I've been burned a bit by FreeCAD assemblies workbenches - with assembly 2, 3, and 4 all behaving very differently, being incompatible, and a bit unstable.
+
+This one however, has been a joy to use.
+I provoked one crash sadly, probably by trying to do too much and change things while inside a mate dialog.
+A top tip is to save often, and finish a dialog based step before doing anything else.
+
+### Adding parts
+
+You can create an assembly, and starting adding parts. The transform UI appears after adding one in, so you can put it close to where you might need it.
+
+![Placing a fastener in the assembly](/2025/02/12-freecad-assemblies/placing-screw-for-assembly.png)
+
+I tend not to try moving them exactly into place, but give them the right orientation, but clearance to access the features needing to mate the parts together.
+
+### Mating parts
+
+![The Fixed Joint icon in the Assembly workbench in FreeCAD](/2025/02/12-freecad-assemblies/fixed-joint-freecad-assembly-icon.png)
+I was most often able to use the simple Fixed Joint style to mate items together.
+
+![Selection ready to join together](/2025/02/12-freecad-assemblies/fastener-hole-selection-ready-to-assemble.png)
+
+I select one parts feature - this case the top round edge of a screw hole on the chassis (the part that will remain still), and then a round edge of the part that would move, the lower rim of the screw head. When I then select fixed joint, that screw will be aligned so that the head is touching the chassis, and the screw is aligned with the hole.
+
+This seems far simpler than linking in separate documents, making reference geometry everywhere and aligning their axes.
+
+## The current result
+
+I'm first making a reference assembly to see that my design for the sensor will fit.
+
+![Reference assembly of the front of the robot](/2025/02/12-freecad-assemblies/robot-chassis-front-assembly.png)
+
+I've only modelled the front of the robot chassis and it's holes, a little lazy, but it's all I need for this current step. I'll be then adding in the sensor bracket, and making a low-effort model of the sensor itself to see that it fits well.