Secret-Knock Gumball Machine

Hi!

This is the gumball machine project I worked on this year in Advanced Engineering. The full instructions for building this project can be found in the Make Magazine December 2012 edition (online version linked here). This Instructable is mainly for detailing the changes I made to this project and describing some advice for building your own secret-knock gumball machine.

All of the supplies that are required for this project are listed in the Make Magazine article linked above. However, these were some of the additional supplies that I required for my modifications to the design:

• A 3D-printer with filament
• A laser cutter
• A piece of 3/16" plywood, at least 25mm x 25mm
• Wood glue
• Hot glue gun
• At least 4.5' of 1" square wood rail
• Masking tape

For this project, I chose to laser cut the wood pieces I needed instead of cutting them by hand. Because of that, I had to first design each piece on Fusion 360. I then converted each design into a DXF file. Pictured above are the DXF files for this project (linked here).

Next, I laser cut all of my parts out of 1/4" plywood or acrylic (pictured above).

Next, I cut and glued on wood rails to the ends of each side plate. I also glued on the funnel rails. For both of these, I used Gorilla wood glue.

Next, I 3D printed the dispensing wheel and glued on the wood stir plates (again using Gorilla wood glue) at the correct angle (indicated in the Make magazine). I also assembled the funnel. This step was largely similar to that indicated in Make magazine. However, rather than use nails to connect the funnel together, I used wood glue. The rails mentioned in the supplies section were glued on first for additional support.

This step is by and large the same as the one indicated in Make Magazine. The only differences are:

1. Since I used plastic for the dispensing wheel instead of wood, I had to tape around the gumball hole to prevent cracking and shifting when the assembly was clamped.
2. Two wood rails were added for support on either side of the assembly (as pictured above)
3. I used a 7/32" screw as the axle rather than brass tubing.

This was the last step that differed from the instructions shown in Make magazine.

For this step, it's useful to refer to the layout and schematics diagrams in the Make magazine article. The primary difference in my project was that I never soldered my connections. Instead, I just used the breadboard on the Arduino Uno. This was much quicker and didn't lead to any problems for me.

Pictured above are videos of the wiring in the machine working. One displays its reaction to the correct knock pattern (notice the motion of the servo motor). The other displays its reaction to the incorrect knock pattern.