This work is interesting to us because of its implications for the design of physical social interfaces. There has been substantial work in the field of haptics around using vibration as a way to add more interaction modes to existing communication systems. The basic problem with vibration is that it requires some sort of mapping; because humans can't create vibration, haptic projects tend to map some other variable onto vibration. Part of why we thinking tugging as a new physical interface modality is so exciting is that it is a natural tangible experience that can be both an input and output method. We call this a coincident input/output space - it avoids non-obvious mappings while also avoiding the challenges of competition in fully symmetric input/output spaces.
To explore the Tug and Talk concept, we built a series of prototypes. The first prototype was built using the Vex Robotics Design System. It only allowed tugs to be sent in one direction and was quite large.
Our second prototype was designed to fit inside a belt buckle form factor. For the most part, we used simple off the shelf components in our design. For actuation, we used a small servo with sufficient torque to feel like a "tug." For sensing, we used the potentiometers from inside a PlayStation 2 game controller. These potentiometers are already biased with a spring, providing tension to the "sending" chain. To control the system, we used a Robostix controller board. These boards have an ATmega128 chip as well as breakout pins for driving servos, analog to digital conversion, digital input/output, and serial communication. While these boards are somewhat bigger than we really needed, they made prototyping relatively easy. To communicate between the devices, we used a four pin serial cable. The protocol was quite simple - if a buckle sensed that it was being tugged, it would send a single byte over the serial cable from 0 to 255. The buckle receiving the signal would convert that value into a PWM waveform and drive the servo, provided the interrupt button wasn't down.
Packaging issues were addressed with a focus on component placement in relation to the actuation, sensing, and user interaction requirements of our design. For simplicity, a single mounting surface was chosen to arrange the hardware on a common plane. A two dimensional plywood lay-up was implemented to create the controller box and spacers which insulate hardware housing from the copper belt buckle enclosure. The completed hardware housing consists of 8 unique parts, laser cut from 1/8 inch Baltic Burch plywood, for a total of 31 individual parts laminated in 13 layers. Plywood was chosen for the insulating hardware housing as an ecological alternative to acrylic and because its material properties coincide with manufacturing processes available.
The belt-buckle case was fabricated out of copper using traditional metalsmithing techniques. The pieces were precision cut and carefully soldered together, creating the box that contained the wood packaging. We used a copper penny and attached it to the button that was used to stop the tugging motion. A patina was added to create an antique-like finish to the piece, which was then carefully brushed for effect. The whole device was then mounted on a strip of leather that fastened at the back.
If you have any questions or comments, please feel free to get in touch. I can be reached at dharry at media . mit . edu.