This project started with the Ball joint articulated octopus by Ellindsey. After printing some tentacle segments with clear filament, I wanted to illuminate my octopus! I used Tinkercad to design and print an illuminated battery powered "rock" that the octopus can chill on. LEDs in the rock shine through his clear head and clear tentacle segments. The original octopus was scaled to 142% to be big enough to fit around a rock that could house an 18650 Li-ion battery.

This project offers lots of opportunity for creativity and customization:

Print and assemble the tentacle segments in different colors

Choose between four octopus heads:

Original
Alien
Steampunk
Skull

Customize your LEDs. examples:

Slow flash RGB
Fast flash RGB
Blue / Red flashing
Red / Green flashing (Christmas colors!)
Regular LEDs (current limiting resistors required)

Choose your favorite switch type

Toggle switch
Locking push button switch

Step 1: Print and Gather Parts

Download the 3D files from Thingiverse HERE

Feel free to copy and make changes to the TinkerCad file HERE

The Octopus and Rock Shell parts are 3D printed. The rest of the parts can be purchased from online sellers like Aliexpress, Ebay, or Banggood.

1- 3D printed Octopus Head. There are different versions available including a steampunk octopus, an alien head, and a skull. Print it so the area around the eyes uses clear or translucent filament.
1- 3D printed Rock Shell. Print it so the area around the LED holes uses clear or translucent filament.
16- 3D printed clear tentacle segments
24 (or more)- 3D printed tentacle segments - any color
8- 3D printed tentacle ends - any color

8- 5mm RGB or flashing LEDs. If you choose to use normal LEDs without a flashing chip built in, then current limiting resistors will need to be added.
1 - 10mm RGB or flashing LED.
1- Power Switch: locking pushbutton type or toggle switch
1- Salvaged 18650 cell from a laptop or cordless tool battery. Charged to 4.2 V
1- Battery holder. Stay away from the kind that uses soft plastic "ears" to hold the battery in. The ears end up holding the battery away from the electrical contact.
8 - 2 to 3" lengths of jumper wire - AWG 22 to 26

Step 2: Solder LEDs in Parallel

Refer to the schematic for an illustration of how I wired the LEDs in parallel. Since the flashing chips built in to the LEDs provide current limiting capability, resistors are not needed when used with voltages around 5V.

Since the LED holes in the Rock Shell are so close together, some time can be saved by soldering the legs of the LEDs together with jumper wires. My technique was to start with one jumper soldered to two legs, then twist and solder the second jumper to the end of the first. I held the twisted, soldered wires in the same fingers with another LED leg, and placed the second LED in a "helping hands" device. With a quick application of heat from the soldering iron, the four parts were quickly soldered together. After all nine LEDs are soldered, test them by holding the jumper wires to the ends of the 18650 battery. If they do not light up, try some troubleshooting steps: is the battery charged? Is the polarity correct on all the LEDs? Are two legs touching, creating a short circuit?

Step 3: Add the Power Switch

Solder a wire to one terminal of the power switch before threading it through the hole in the Rock Shell. If using a toggle switch, pay attention to which terminals are connected when the toggle is flipped UP. I added a piece of heat shrink tubing here for a bit of extra protection. Someday I'll learn how to shrink the tubing without scorching the wire insulation.

Step 4: Push the LEDs Into the Holes, Secure With Hot Glue

After pushing the LEDs into the holes, bend the pos+ and neg- LED legs away from each other. If you allow them to touch, it could create a short circuit that would damage the battery and perhaps start a fire. Secure the LEDs in place using hot glue. Solder the positive wire to the power switch.

Step 5: Attach the Battery Holder

I decided to mark the terminals of the battery holder because the molded impressions on the bottom are sometimes hard to see. Tin the terminals using a generous amount of solder. Attach the switch wire and the negative jumper from the LEDs. Push the battery holder into the Rock Shell and secure it with hot glue in four places. Install the battery, flip or push the switch, and all nine LEDs should light up! You're done!