A project by Tom Weber and Daniel Buschek.

What is it?

Our project idea was to develop a spherical plotter, i.e. a device to draw on a sphere. The concept may also be described as a metaphor on pottery making: A rotating “raw” object is altered in appearance by the user’s hands. In comparison to traditional pottery, the Sketchball offers an additional second degree of freedom regarding rotation. Moreover, the user’s hands are not in direct contact with the sphere. However, instead of changing the shape, the artist changes the design or colour of the object.

The following video captures some impressions over the course of the whole project:

How does it work?

The Sketchball concept consists of three basic parts: The ball socket, the drawing arm and the input device. They are described in more detail in the following paragraphs.

Ball base: The socket follows the idea of an “inverted” ball mouse technique. Classical ball mouses use two cylindrical sensors to capture the force of the ball and a third wheel to provide stability. We too use two cylinders and a third passive resting wheel. However, in our project, force is applied the other way round – from cylinder to ball. That way, we are able to rotate the ball so that every possible surface point can be reached by the pen. The pictures below show our first rough sketch and the construction process of these parts.

First sketches

A powered cylinder

Drawing arm: The pen itself is resting on a gallows-like arm and can be raised or lowered down to touch the sphere in changeable intervals. This interval is controlled by physically turning an arrow on a wheel (see final image below). Thus, it is possible to draw full or dotted lines. The arm also applies pressure on the ball from above, using a simple screw with a knob on the end. This ensures that the ball is kept in place and doesn’t “jump” too much from the cylinders, which is important for rather light-weight balls, like polystyrene. The development of this part of the device is pictured below.

Base with arm

Controllable pen

User input: The input device captures the user’s commands, which are expressed with their hands, to follow the pottery-metaphor. Therefore, we created a special pair of cuffs. We first wanted to use bend-sensors on those, but then settled for tilt-sensors instead, because the first were already in use by another group. Therefore, tilting the cuffs is registered by the arduino, which can then send signals to the motors accordingly. Logically, we mapped each glove to one cylinder, so that the user can take influence on the sphere’s rotation in an easy and intuitive way. The image below shows a cuff attached to the rest of the device.

Connecting the input cuffs

Now that all three parts have been presented, the following paragraphs discuss some more details about their construction and implementation.

To power the cylinders, we used two stepping motors. They required a special “motor-shield“, which we assembled and plugged on top of the arduino uno. This shield allowed us to control the steppers rather easily code-wise. However, the shield became quite hot when the motors were running for some time. To counter any possible overheating, we created an active cooling device by glueing a small fan to a short metal pipe-end. This was then used to apply a steady stream of cool air between the motor shield and our own additional “shield” on top of that. This second custom-built shield served as a plug-point for the cuffs and minimized the total space needed for our circuits. The cuffs consisted of the aforementioned tilt sensors, one per glove, and an additional LED to allow for some simple visual indication. Although the LED can be used for to signal anything, in the current implementation it indicates the cuffs’ states (tilted or not).

In our programming we used the AFMotor-Library, which acts as the software counterpart to the motor-shield. With this library, control of a stepper motor can be realized by simply creating a certain motor-object and calling its functions. To sum it up, our program’s main loop reads the input from the cuffs, sets the motors’ speeds accordingly and finally tells the steppers to start turning. The pen is controlled in a similar fashion: Within the loop, the value of the control wheel’s potentiometer is read and administered to the servo motor attached to the pen.

The following graphic pictures the final state of the project, including captions for its various parts. You might want to click on the image to view a larger version.

Final project

Values and Potentials

In its current state, the Sketchball mainly serves artistical purposes. One of its values lies in its ability to provide a rather unusal and unique spherical “3D”-canvas. It has therefore the potential to facilitate the creating of interesting new pieces of art. Moreover, it can be controlled by two users at once (one cuff each), thus offering a possibility for cooperative and communicative design. For example, a ball’s design might be the result of two people shaking hands, dancing and so on. In addition, multiple Sketchballs would have the potential to serve as a new distinct communication device. Just think about a kind of “ball fax”, where one user’s designing actions are recorded and sent to another person for replay. The receiver would then not only be able to recreate the resulting ball, but also relive the sender’s creative process.

For whom is it?

The Sketchball is a creative gadget with a wide range of possible audiences: It can be used by a single person in an “at home” context to create personal gifts, art or decoration. On the other hand, it might also be used as a public interactive installation. In this context, one would typically want to allow multiple people to interact with the device, after another or even at once, creating a ball to represent a group of people, a timespan or something similar. Moreover, art and design related schools, universities or companies may use it as an unusual form of interactive advertisement, maybe on exhibitions. Since the input sensors may be put on other parts of the body as well (feet, legs, …), the Sketchball could also offer a creative outlet for disabled people. Finally, if extended by a high precision plotting/printing head, it could be fitted to produce astronomical models of planets or the like.

Next steps

The current version of the Sketchball could benefit from increasing its power and precision. This would allow to use larger and heavier balls and also enhance the degree of control over the designing process itself. A good first step towards these goals would be to exchange the stepper motors for two similar motors of the exact same type. At the moment, they do not provide exactly the same power. The grip on the cylinders could also be improved with appropriate materials. Some experiments would be required to identify the optimal adherence. With increased precision, it would make sense to develop an action-recording system (see above) to store and replay designs. Further ideas include various switchable colours and finally the mapping and plotting of whole images, received from a computer.

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