2002: The Plank: Designing a Simple Haptic Controller

Abstract

Active force-feedback holds the potential for precise and rapid controls. A high performance device can be built from a surplus disk drive and controlled from an inex- pensive microcontroller. Our new design, The Plank has only one axis of force-feedback with limited range of motion. It is being used to explore methods of feeling and directly manipulating sound waves and spectra suitable for live performance of computer music.

Appendices

Author Commentary: Personal Reflections on The Plank

Michael Gurevich and Bill Verplank

The Plank was a direct outgrowth of research and experimentation by Verplank and Mathews at Interval Research that was in many ways a prototype for NIME itself: we were interested in developing new, interactive, audiovisual hardware/software technologies with primarily open-ended, creative applications.

The project can also be seen as an extension of Max Mathews’ vision for computer music evident in his first real-time interactive computer music system—GROOVE—and ultimately of course in his Radio Baton. Max was an amateur violinist, but he didn’t think the computer would make him a better musician. At Bell Labs, Max was among the pioneers to use the computer as a tool for simulation—initially to simulate telephone transmission systems; elaborating on this premise, he thought the computer could allow him (or anyone else) to simulate the experience of a great musician. Of course, there are many kinds of musical experiences, each of which is multi-faceted, and it ultimately occurred to Max and others that one aspect that was missing in many digital music systems was feel: the tactile, tangible relationship a performer has with their instrument; the ways an instrument pushes back on you when you push on it.

Others had certainly explored the intersection of haptics and music before The Plank. Brent Gillespie and Sile O’Modhrain preceded us at CCRMA (Gillespie and O’Modhrain 1995), and Claude Cadoz’s group had been working on the problem since at least 1978 (Cadoz et al. 2003). Charles Nichols presented his sophisticated haptic vBow at the same NIME (2002) as The Plank. But in what we feel would become the essential spirit of NIME, and indeed the nascent “Maker” movement, The Plank sought to make haptics “easy;” the paper was really intended as a catalyst for others to try the same thing. It employed easily-obtainable, inexpensive, and largely open-source tools, and emphasized that the underlying principles could be implemented with little effort.

It is worth noting that The Plank marked the first documented use in NIME of an Atmel AVR microcontroller (for which we owe an eternal debt of gratitude to Pascal Stang), which would become the core of the Arduino, now probably the most popular development board for physical computing in the world that powers much “making” and much of NIME. As it turns out, this is no accident: Bill Verplank brought Pascal Stang’s AVRmini development boards and AVRLib library (as well as The Plank) to the Interaction Design Institute Ivrea; when Massimo Banzi and others were frustrated they couldn’t easily get their hands on more AVRmini boards, Arduino was born.

One of the perpetual problems with experiential phenomena such as music is the difficulty in communication around the experience through the written medium. We are fortunate with music both to have a centuries-old discourse to draw upon, but also that it is relatively easy today to embed and distribute audio alongside or within written forums. We do not have either of these luxuries with haptics; for now, the best way to communicate about haptics, as well as to generate interest in musical haptics, is to “feel it.” For this reason, Verplank has remained committed to conducting courses and workshops on music and haptics, and to elaborating on making accessible tools like The Plank readily available. These efforts include a “Music and Motors” workshop that has run at the Copenhagen Institute of Interaction Design since 2011, which has produced numerous inventive projects, as well as a dedicated development board built on the Teensy 3.1 platform (Bak et al. 2015). Several alumni of our workshops and courses have not only made substantial subsequent contributions at the intersection of music and haptics, but have also been responsible for expanding the incorporation of haptics into consumer products at companies including Apple and Immersion.

Haptics remains a vital topic at NIME. Bill Verplank has continued to develop The Plank with a similar emphasis on helping to understand and emulate the “feel” of playing an acoustic instrument. Some of the most exciting work on haptics in NIME has come from Edgar Berdahl, who fulfilled one of our initial objectives for The Plank by creating a direct haptic interface to a computational acoustic simulation of a musical instrument—effectively unifying the haptic and sound synthesis models (Berdahl et al. 2009a). Berdahl has also expanded on O’Modhrain’s work to examine ways that active force feedback may improve musicians’ abilities to perform with digital and electroacoustic instruments (Berdahl et al. 2009b).

Expert Commentary: Haptics for Sonic Interaction Design Using Recycled Motors

Edgar Berdahl

Bill Verplank was a pioneer of NIME even before NIME became a recognized field. In the mid-1980s, he co-coined the term interaction design, and he helped introduce interaction design into digital musical practice by leading the NIME course at Stanford University for many years (Berdahl and Kontogeorgakopoulos 2013). He introduced valuable concepts to the NIME community such as distinguishing between musical “buttons” and musical “handles,” sketching and critiquing project ideas using his Interaction Design Framework, and designing haptic controls for music, which is the subject of this commentary.

In their seminal paper, Bill Verplank et al. described the first work on enabling students in a NIME course to experiment with haptic force-feedback controls. This work included the development of The Plank haptic device. The ingenuity of The Plank lies in the high-fidelity force feedback that a hard drive motor can provide (low inertia, low friction, relatively large peak torques) while concurrently emphasizing the value of recycling used electronics due to the large number of mechanical hard drives discarded every year, these motors can be obtained at very low prices. Therefore, pedagogical exercises with The Plank not only inform about new sonic interactions enabled by force-feedback devices, but they also build connections with important ideas from found art and circuit bending (Bak et al. 2015; Ghazala 2005). New technology is mass-produced by capitalist interests, yet haptic musical interactions can be enabled by recycling and rewiring old hard drive motors.

Although exercises with The Plank could convince students to think more holistically about recycling electronics and reducing waste, the process for creating Planks is somewhat daunting as it involves many steps. Consequently, other NIME researchers and musicians will likely prefer to obtain Planks directly from Bill Verplank himself, who has finely crafted the art of building them and distributes them via a series of open-source workshops. These workshops have been conducted in conjunction with Jakob Bak and David Gauthier. Their expanded series of haptic exercises emphasizes precise motor control via embedded programming using integers. Various schemes are employed for embellishing the firmware models with synthesized sound. Participants in these workshops have created an impressive array of beautiful project designs that point toward the future of haptics in NIMEs (Verplank et al. 2001).

These open-source workshops were preceded by my related work in open-source haptics, which has now culminated in the repository called Open Source Haptics for Artists. My work lies closer to computer music than to design. I aim to create software models for haptic control of high fidelity musical sound generated by floating-point algorithms. My personal goal is to create each model once, and then be able to render it using a wide array of future devices (Hertz 2012). In support of this goal, I focus on algorithm design and use embedded electronics only to interconnect haptic devices with powerful computational hardware.

In homage to the legacy established by Bill Verplank et al.’s work and vision, I am providing a way to connect The Plank with the Open Source Haptics for Artists repository.¹ This is most easily accomplished with a capacitive sensor, which can be implemented by soldering a wire to a piece of copper tape, using double-stick tape to fix the copper tape against the backside of The Plank handle, and then connecting this wire to the FireFader microcontroller board. Then, any of the models developed for my open-source FireFader device can also be rendered using The Plank.

Overall, the mechanical performance of The Plank is very good. However, according to my informal tests, the position sensor is noticeably nonlinear, yet it is monotonic and close enough to linear that most of my models produce the desired result if sometimes with a slightly warped perspective.

One of my models contains a series of force profiles that can be customized by the user drawing into a table with the mouse. The force profile concept is described in Bill Verplank et al.’s featured original paper, and the equation below describes the physical relationship mathematically. The height h(x) of a virtual mass m on a frictionless terrain at position x can be related to the force profile F(x) by way of an integral:

$$\begin{aligned} \mathrm {Work} = -\int _0^x F(x_m)dx_m = mg\Big (h(x)-h(0)\Big ). \end{aligned}$$

(1)

In closing, it is hoped that open-source haptics will continue to flourish within the community and enable Bill Verplank’s goal—that NIME community members have the access and knowledge to tastefully incorporate haptic force-feedback control into their projects. The greater the depth and breadth of open-source resources, the more new possibilities are enabled.