This has also been published on our MakeItZone forum.


I bounced the LockBox/Safe idea around with a few people of different ages, interests, and skill-sets, and got general agreement that this has potential.


The next step was to design it.


I opted to use Fusion360 to design it in 3D, even though it will be laser-cut out of 3mm birch plywood sheets. I'm learning that the parametric modelling and timeline features are amazingly powerful- especially if you think of the design as a series of programmed geometric operations.


However, there are two caveats/"Gotcha's" that regularly catch me up:

  1. Rolling the timeline back to a feature, editing it, breaking later steps, and not noticing the yellow exclamation marks that appear on the timeline. These indicate that your design 'program' is 'not compiling'. Unfortunately for me, Fusion360 will try and use cached data from before I broke the design. I have to diligently keep checking for these issues. I would like to have these more prominently highlighted in the UI.
  2. You can set up a table of parameters (eg sheet_thickness) and base your design on these variables. Change one, and if your design is well built, the final geometry will magically update correctly. However you can't keep the parameter table window on screen as you edit, nor can they be shared across sub-assemblies/designs. To help with the later I use the ParameterIO add-on.

I modelled the door as a sub-assembly and then imported it into the final fully assembled model.


As a rendering it looks something like this:

Rendering of MicroBit LockBox design


The box on the left of the door is the AAA battery pack for the MicroBit. The servo is mounted on the inside of the door, with the circle-with-a-side-chopped-off latch attached to a servo horn. Hidden in this view is a cutout to run the servo wires from the inside to the MicroBit, and mounting holes for bolts to run through the door and attach the MicroBit. The servo can be attached to power and `Pin 0` by soldering or looping under a mounting bolt. The MicroBit is on the outside of the LockBox so it can be configured, reset, and so the screen can display status messages.


Next step is to export the flat surfaces into `SVG` files ready for laser cutting. I've found the Shaper Utilities addin to be the most reliable way to do this.


The SVG files are then imported into Inkscape where the final required tweaks were made to match our laser cutter's requirements.


The parts were cut and packed, ready for our trip to Hornby Island and a session at a new Makerspace- the Hornby Island Spark.


The final assembly was done at a small cabin in the woods:

Close up of servo and latch

Very happy it went together with only one minor issue- the door should be slightly narrower to have a little more clearance so that it can be more easily opened and closed.


Note: the door is 1mm narrower in the latest version of the design on Autodesk's design sharing site.


The design files have been shared publicly:


Next post- the MicroBit Code.