Neopixel Bullet

Description

A rotating display of animated Neopixel LED matrix panels.

Details

The project started off with a desire to use the Neopixel matrix panels and motors lying around in my stash. I started searching for ideas and came across a cool project, ULTiM8x8 modular, no-solder, RGB LED half cube, by jasoncoon. So, I decided to replicate it but with some changes to add motion.

The body was designed in Fusion 360 and includes a display with 3 Neopixel panels mounted on a turn table like platform. The display cycles through some animation sequences that can be changed over WiFi using a phone or any PC.

Below is the list of parts to be 3D printed and the required electronic components:

• a canopy which has 3 square faces to install the Neopixel panels at right angles to each other.
• a base which is a cylindrical housing to situate the electronics including the microcontroller, DC motor, slipring and the buck converter. The power input and the switch is also located here.
• a slew bearing with 90 tooth which is printed in place. The spacing between the inner and outer ring is 0.5 mm and could be a tight fit. So, make sure that the printer is tuned accordingly.
• a mounting bracket which keeps the DC motor and the slip ring in place. The rest of the electronics can be mounted on or around the bracket.
• a 15 tooth spur gear which is mounted on the motor shaft and mates with the slew bearing with the gear ratio 6:1 to reduce the speed and increase the torque.
• the Neopixel LED panels and the corresponding lids. The lid serves to unify the final look and diffuses the light from the otherwise very bright LEDs.
• For the microcontroller, I decided to stick with ESP8266. It has WiFi which can be used to remotely change the display patterns or update the firmware over the air. It is inexpensive and generally packs in a lot of punch in a small package.
• A slipring to join the upper and lower sections. More about this further in the builds logs.
• A switch and a barrel jack for power input from a DC adapter.

All parts were printed in PLA with 0.28 mm layer height and a 4 mm nozzle on an Ender 3. The STL files can be found on Thingiverse.

Click on the github link for changes to the code on top of the original repo.

Design choices

One unique challenge I faced in the beginning of the project was to transfer the power and signal from the base to the moving canopy. I searched up and found a few solutions including the use of hollow core motors or simply use an independent power source. The former was a bit expensive for my taste and the latter was a little inconvenient. So, I decided to go with an easy and relatively inexpensive option i.e. a slipring.

A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. However, after digging a bit deeper, I noted that there was some concern around the electrical noise that is introduced with the use of a slipring. It was a bit of  a leap of faith since the control signal for the Neopixels has a rather strict timing requirement but it turned out ok. May be the quality of sliprings has improved and the noise effects may not be pronounced for small voltages and current.

Another tricky part was to figure out the mechanism for moving the canopy. All I knew was that I have to use gears but wasn't sure of the actual design. After some bit of thinking and tinkering, I designed a simple mechanism to have a gear in the center colinear with the slipring and transfer the power to this shaft from another gear and the motor installed next to it. However, then I came across a clever bearing design in the project Arduino controlled photogrammetry 3D-scanner, by Bribro12. So, I redesigned the part for my requirements and decided to use that instead.

A bit about the power requirements. The LEDs, microcontroller and the DC motor supply are all in parallel. The main supply comes from a 5V DC adapter capable of sourcing at least 3A of current. A single neopixel draws around 60mA of current to display white (red + green + blue) with full brightness. So, in theory, 192 pixels (64 x 3 panels) alone will take about 11.5A current. In practice, however, not all the pixels are illuminated at the same time and they are all be white either. The DC motor doesn't need too much torque to drive the canopy and as such doesn't draw excessive current. So, I figured 3A adapter should be enough.

A buck converter is used to step down the input voltage to the DC motor to the desired value based on the required speed using an onboard potentiometer. Alternatively, a common driver, L298N can be used to modulate the speed of the DC motor using Pulse Width Modulation (PWM) and additionally its direction using the H bridge.

Tips

• If the slew bearing is having a tough time turning, then apply a little lubrication. It should help reduce any friction. Let it run for some time for it to get dialed in.
• Adafruit suggests adding a 300-500 ohm resistor and a 1000uF capacitor to buffer any spikes from the initial current.

Build instructions

Step 1

• Secure the motor and slipring to the mounting bracket using 3mm screws and nuts.
• Attach the mounting bracket to the standoffs in the base.
• Insert the barrel connecter and the power switch to the appropriate openings in the base.
• Before wiring up the motor and slipring with the supply, make sure that the slipring is installed with its collar resting on the mounting bracket.
• Situate the ESP8266 and wire it up as per the connection diagram in the instructions.
• Install the slew bearing after lining up with the tab on the side of the base. The bearing will rest on a small ledge located on the inside perimeter of the base.
• Test and make sure that the motor can drive the slew bearing without binding.

Step 2

• The Neopixel panels go on the 3 faces and have to be installed in a specific pattern and orientation for the display to work as per the default software configuration. The illumination patterns are achieved using a pixel map derived from the coordinates of each pixel in the 3D space. You can think of the 3 panels as 3 orthogonal faces in the cartesian space joined together at the origin. As such, the faces can be treated as XY, YZ and ZX. Refer to the picture in the project instructions.
• Each panel has an input port and an output port with voltage, ground and a control signal line. The panels have to be connected in series with the output of first going into the input of second and the output of second going into the inputs of 3rd.
• The panels have LEDs in a non-serpentine pattern. It is easily configurable in the software if the pattern is opposite. Note that a panel can be installed in 4 different orientations on a given face. Again refer to the instructions to ensure the correct orientation. I will admit that it was a bit tricky to orient them the first time. Of course, it is not the end of the world if you get it mixed up. As long as you know, what you have and how you have installed it, you can change the pixel map in the software and get it to work.
• Clip the wires long enough so that they can be brought outside from the small opening in the bottom face of the canopy. Color coding can make the life a lot simpler. I chose to go with Red for Vcc, Black for ground and identical color for a given pair of input and output signals that have to be connected together. I then twisted the 3 wires from each port and brought them out. Next connect the input and output stages. At the end, it will leave one set which has to be connected to the turning portion of the slipring. The fixed portion of the slipring is connected to the output from the base.

Refer to the following layout for connecting the Neopixel panels.

Refer to the following circuit diagram for wiring.

Step 3

• Snap the base and canopy together after lining up the 4 slots.
• Turn it on and enjoy!