BeagleBone Black project spotlight:
By Tara Stratton
If you went to Maker Faire New York this year, you could not have missed the Orbital Rendersphere. This “Big Giant Spinning Limb Slicer,” as the Hoboken MakerBar team affectionately calls it, displays images and videos on a four-foot diameter spherical surface using persistence of vision (POV) spinning at 450 RPM. It had a constant crowd surrounding it and earned five ribbons at the faire: four Editor’s Choice ribbons and one Educator’s Choice ribbon.
The Orbital Rendersphere started out as an idea for an entry into the 2013 Red Bull Creation Contest in April 2013. Red Bull sent the crew at Maker Bar a number of LED strips and asked them to build something cool out of it. They developed the idea, and then started building only a few days before the contest deadline. After spending a crazy weekend working like madmen on the project, the Orbital Rendersphere didn’t orbit! The team decided that the project was too good to let die, so they set their sights on having the project done by Maker Faire New York. The team also decided to set their sights higher for what they wanted the display to do. They increased the size and resolution of the display and redesigned it to be able to display video at 30 frames per second by spinning four vertical LED strips spaced 90 degrees apart at 450 RPM, or 7.5 rotations per second!
After first experimenting with microcontrollers, the team selected BeagleBone Black, to power the Rendersphere’s 36 feet of WS80211 LED strips. BeagleBone provided much more memory to accommodate larger image data and was able to update the LED strips extremely quickly through the use of Trammel Hudson's LEDScape code. The LEDScape code uses the programmable real-time units (PRU) on the Texas Instruments Sitara AM335x processor that powers BeagleBone Black to update multiple LED strips simultaneously with very little burden on the CPU. The team also uses a custom circuit board to buffer and connect GPIO outputs to the LED strips.
The main controller is a Mac Mini mounted in a custom arcade console. Every frame of video is rendered on this console and streamed over Wi-Fi to reduce the number of wires needed—normal wires don’t work for a POV display because they would get tangled up from all of the spinning. Because of this challenge, all of the brains required to run the display are mounted to the spinning part and spin along with the display.
The only wires the team required between the spinning and non-spinning part were for the power and ground connections. The team ran these lines from the power supply (3 10-amp 5V power supplies), one to the top and the other to the bottom of the axle where they contacted copper slip rings, and then distributed power to everything on the spinning part.
The Orbital Rendersphere frame presented the team with another challenge. The team needed to create a frame that offers structural stability, provides good visibility to the display and can be quickly assembled/dissembled for transport. The team created a modular frame design that provides unobstructed views of the display from three sides, bolts together quickly, and fits in a single van.
Now that the team had a desired rotation rate for the display and a frame to offer stability, they had to figure out how to actually spin the display. They tried a number of different configurations, but in the end, the simplest idea was the best. They mounted an electric heavy duty hand drill (Harbor Freight) to the top of the frame and used it to spin the axle. This provided a nice solution since hand drills have built-in high-torque axial transmission, which allows the Orbital Rendersphere to spin up gradually from a dead stop without slipping or burning out the motor.
We asked Travis what his team at MakerBar has coming down the pipe. He said that they going to scale up the concept they’ve started. “We don’t want to spoil the surprise, but it’s going to be BIG!” Travis said. He also invited others with a love for electronics and a passion for making cool projects to “come down, share your projects or ideas, have a beer with us, and share in our passion for all things electric!” Whether you make it to Hoboken or not, hopefully we’ll see more of the Orbital Rendersphere (or the big next generation) at Maker Faire 2014!
Video credit: Andrew Fustini, element14