Introducing PUSH-UPs, an articulated display panel.
This is a 8 “pixel” prototype of a animated surface display system. The final goal is to create a surface with a hundred or more separately articulated “pixels” to create a dynamically changing topography. Stimulus for the larger unit may be from a camera, an arrays of sensors, or purely from software that simulated different surface topologies.
I’ve been talking about designing an articulated tabletop for sometime now – taking my inspiration from TRANSFORM, from the Tangible Media Group at MIT Media Labs. While I am not trying to copy their design, the key to this idea is in the design of a moving “pixel” that is small, provides several inches of “travel”, is able to be illuminated and, most importantly, cheap! This allows the design to be scaled to whatever size is desired. As this “pixel” element is actually a linear actuator, I have considered and experimented making all sorts of actuator designs but nothing I came up with is satisfying these criteria. In the video we can see that the table-top part of each pixel is a small square-section plastic tube connected to a wire or plastic linkage that connects to the control box below. But what is this control element and how does it provide the 4″ of travel that the video shows?
In a telephone discussion with Doug, an engineering colleague of mine, we noodled through some simple design ideas that would use cheap and readily available servo motors to articulate acrylic rods that can pass light.
So, the seeds of this prototype design were sown.
So, voila. PUSH-UPs.
I have made many designs using servos (see PopUp Clock, and Flipper) and I had plenty of the small metal-geared MG-90s on hand. In addition, I have created lots of clocks recently (yet to be posted) that use acrylic rods as light pipes for colourful displays so I had lots of 1/4″ and 3/8″ rod stock. And of course, I always have yards of addressable LEDs.
The original design idea came from a video clip online of an amazing articulated table top that reacted to gestures and hand movements. It was called TRANSFORM from the MIT Media Labs (see “Crazy Morphone Magic Table Surface” ) and several of us have been discussing how it was designed. I think the consensus is that each of the 30×30 table top “pixels” is actually driven by thin steel cables running in individual plastic pipes down to some type of linear actuator in the control unit below. When you see all of the fans around this control unit, something is clearly putting out a huge amount of heat and we are stumped as to what this actuator is and how is operates.
Now, while the idea of separating the top “pixels” from the control unit is smart and would be needed to get the desired pixel density, I wanted something that I could start experimenting with quickly. I thought of using the servos to lift and lower the pixel rods but I did not have any stiff piano wire so I settled on designing a simple linkage, cut from 6mm HDPE.
So, this prototype consists of 8 servos mounted on a plate. The servos are arranged as 2 columns of 4 servos and are mounted “back-to-back” to minimize space requirements. A servo “horn” and connecting rod connect each servo to a length of 3/8″ acrylic rod installed in a hole cut in a 12mm thick top plate. As the servo horn rotates through its 180 degrees of travel, the acrylic rod rises over 45mm (1.8″). Although there were other design constraints, the servos are close to being as tightly packed as I can get them in this simple design.
In this design the “pixels” are in rows about 33mm apart, while the two columns are 50mm apart. By pocketing one row of servos into the upright plate, and by making the servo horn and linkages from thinner material (e.g. fibreglass board), the columns could be placed about 35mm, making the design pretty symmetrical. Separating the control unit from the table top would allow for even more closely spaced “pixels”, approaching the 25mm grid that I was aiming for.
The underside of the top plate is machined to accommodate two strips of addressable LEDs to illuminate the rods. The distance between adjacent rods was designed to fall on the 16.67mm pitch of the commonly-sourced addressable LED strips that mount 60 LEDs per metre. Abrading the inside of the rods allows light to enter the rod, illuminating its entire length.
Cables from the LED strip in the top plate and each servo pass through the base into the cavity below and connect to the rest of the electronics.
The base unit consists of an Arduino Nano connected via I2C to a 16-channel PWM & Servo driver multiplexer (based on the PCA9685). Software on the Nano allows independent articulation of each of the servos to control the topology of the top surface.
The unit is powered by 1 12V “wall-wart” and an internal DC buck converter provides a stable 5V supply for the servos. As they can all be active at once, I designed in a converter that can deliver peaks of over 3A.
All design parts are cut from 6mmm and 12mm HDPE and connected together using M2.5 and M3 stainless steel hardware.