Assignment #17
Mechanical design

The seventeenth Fab Academy assignment is mechanical design. The COVID-19 emergency makes collaboration difficult, but I teamed up with students from Open Dot Fab Lab in Milan. We’re going to build a soap bubble machine.

1 – the idea

The machine will consist of a semicircular tank, a DC motor, a servo motor, and an ultrasonic sensor. The mechanism is straightforward: a motor moves a bubble wand into the tank and then in front of a fan at the top of the machine to produce bubbles. The mechanical design has four main parts:
- 1 - a soap tank that will keep the soap and the proximity sensor
- 2 - a support to keep the motor that will move the fan
- 3 - Support legs to hold the machine upright and carry the circuit - 4 - A servo motor support and an attachment for the bubble wand

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2 – 3D modeling

I began by modelling the semicircular tank and motor supports in 3D. The sensor will sit at the front of the tank, but we’ll explore that in the next assignment.

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3 – manufacturing the basic parts

With the models ready, I began making the parts. I 3D-printed the tank and milled the wooden motor supports on the CNC machine. We then put the parts together to check the fit.

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4 – preliminary assembly of the mechanism

Once the parts were ready, we tested whether the bubble wand’s rotation brought it into line with the fan. We used Plasticine and wire to explore the mechanism, including the wand length needed to dip into the soap solution.

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5 – further 3D modeling and assembly

Once I was happy with those tests, I returned to FreeCAD and modelled additional supports for the motors and bubble wand. I then printed and assembled the parts, using some models downloaded from the web to help with the design process.

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We assembled everything and moved the parts by hand to check the mechanism. It seems to work! Next, we’ll add and program the electronics so that the machine can start making bubbles.

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Source files

Here are all the source files for the mechanical design assignment:
1 - FreeCAD file for parts
2 - STL file for tank
3 - STL file for servo support
4 - STL file for bubble stick support
5 - STL file for bubble stick support
6 - STL file for DC support