The networking power of Raspberry Pi drives LED lights to liven up acrobatic dance routines. Lucy Hattersley gives PoleFX a twirl in the latest issue of The MagPi, out now.
Billing itself as the world’s most advanced dance pole, PoleFX uses thousands of LED lights embedded inside a network-connected pole. On the sidelines, a Raspberry Pi-powered network box is using OpenCV to image match videos and turn them into light-based visual animations.
“Our goal is to create functional pieces of art and embed show technology into new places,” explains Spencer Hochberg, inventor and owner of PoleFX.
Amongst the dazzle and display, it is easy to overlook the technical requirements of this build. The pole itself needs to be “structurally strong” explains Spencer, to withstand the dynamic moves of acrobats, “while protecting and displaying an array of thousands of integrated pixels.”
Those thousands of pixels create an LED screen inside the pole structure. “The pole acts as a canvas for digital art that complements the performer,” explains Spencer.
Inside PoleFX sits a Raspberry Pi acting as the system’s content server and control interface. Each pole is connected to PoleFX via an Ethernet cable, and the poles receive frames of data “on-the-fly” from Raspberry Pi.
The control surface is a local web interface. “We also support simple control using a USB keyboard, encoder with OLED display, as well as DMX [Digital Multiplex lighting controller],” Spencer tells us.
“Raspberry Pi made it easy for us to put a flexible, low-cost brain in the middle of our system. The giant community of users has made it easy to find tutorials to get started and configure everything,” he notes.
The low power requirements for Raspberry Pi were also a consideration, and the “huge amount of online resources” made it quick and painless to implement.
The current poles are powered using a Raspberry Pi 3 Model B, which is processing and sending frames out at 60 fps.
The poles had to be specially designed and custom-built for purpose. The outer shell of the pole is made using “extruded black polycarbonate tubes.” Spencer tells us this material is “resistant to cracking and hides the LEDs.” They allow the light to shine through.
Inside the pole, 3D-printed parts are used to mount non-structural components, and an internal slip ring that enables the wire connections to spin as the pole rotates.
PoleFX is “mostly built from off the shelf components.” The main mounting plate inside is a custom PCB (printed circuit board), which is an “easy way to fabricate a mounting plate and simplifies the internal wiring.” The back panel of the enclosure where the ports are exposed is also a PCB, used only for mechanical and cosmetic qualities.
The main code is written in Python and the patterns are encoded as H.264 video files. The video frames are read using OpenCV to sample the pixel values. “We then composite and make other post-processing adjustments before sending the pixel data out over the Ethernet network in multicast sACN/E1.31 packets,” Spencer reveals.
Raspberry Pi is configured as a wireless LAN hotspot that hosts an Open Stage Control server, so the user can connect to the network and load the control UI without having to install anything.
Apart from controlling dance poles, the content-server side of the project is generally useful for storing, generating, and playing back LED animations for a wide range of installations where a whole PC would be “overkill”, and “a microcontroller alone is too limited.”
An early motivation for building load-bearing, pixel-mapped poles was to then use them to build larger structures. “Touch-reactive LED handrails and jungle gyms may be just around the corner!”