so they would not bind when trying to slide along the main tracks.

I made two brackets to attach the ¼" carriage track rod to the square tubing of the carriage frame and slipped on a matching internal-diameter linear bearing from Skycraft to hold the stylus. With the carriage completely assembled and sliding along the main track, the Scribbler Bot’s framework was complete.

I looked at the ordinary plastic straw in my soda and realized it was the same diameter as the inside diameter of the sprocket, so I stuck it into the sprocket, cut it off, and filled it with JB Weld. Once it cured, I drilled a new, smaller hole in the center, which fit over the motor shaft perfectly.

Finally, it was time to hook up the controller board and start testing. I soldered motor wires to terminals on the controller board and, after some trial and error, got everything to work. Since then, the Scribbler Bot has drawn dozens of portraits, including many at last year’s TED conference in Monterey, Calif. ( ted.com). Meanwhile, I have improved things by putting all of its electronics into a detachable project box that the control board and motors can easily plug into.

Attaching the Motors and Pulleys

The stepper motors use pulleys and belts to move the carriage and stylus into position. Getting the carriage to move along the main tracks (x-axis) is the heavier problem; the tracks are far enough apart that the carriage needs to be pulled along both sides. I decided to use an axle to connect two pulleys on the side opposite the motor. The force would transmit in a “C” shape starting from the motor: motor to belt, to pulley, to axle, to opposite pulley, to opposite belt.

I used a ¼" automotive timing belt for the belts on both sides. For the first three points in the drivetrain, the motor and the two pulleys on the axle, I attached sprockets to mesh with the belts; the last point in the drivetrain is just a smooth drum. I attached all 3 pulleys to spin on bearings from an old skateboard. For the axle, I used more ¼" aluminum rod.

I mounted the x-axis motor and the last pulley onto the baseboard using some shelving brackets and random bolts. For the pulleys on the axle, on the opposite end of the main tracks, I fabricated custom brackets to attach them to the board. The belts travel directly over the main tracks and attach to the carriage frame underneath, in order to pull it along. To make this connection, I drilled holes through the underside of each belt and the top of the carriage frame, and secured them together with small bolts.

The carriage uses just 1 belt to move the stylus. I mounted the y-axis motor on one side of the carriage and a pulley on the other. I attached a sprocket onto the motor shaft using my plastic-straw trick (described next) and fitted more ¼" timing belt around the motor and pulley.

With both motors, I ran into a problem attaching Douglas McDonald is a multimedia developer from the sprockets to the motor shafts. I couldn’t find Orlando, Fla., who enjoys working on art robotics in his sprockets that matched the belts and had the spare time. For more information on his projects, please right internal diameter to fit over the motor shaft. visit tek-tonic.com.

Future Directions

The Scribbler projects are constantly evolving. I am currently working on a web version that will allow users to scribble images and watch them be drawn on the Scribbler Bot via webcam online. Also in the works is a wireless sidewalk-chalk bot that will drive around and draw images based on input from users over the internet.

 

The Scribbler

The Scribbler Bot’s software derives from an online drawing toy called the Scribbler ( zefrank.com/ scribbler), written in Flash by Ze Frank. Since the Scribbler, Ze and I have collaborated on other projects based on its algorithms, which generate complex line drawings out of any image.

With Scribbler Bot, we wanted a machine that creates keepsake drawings of people’s faces quickly and recognizably, while maintaining a sense of originality and surprise. “Analog distortions” from motor vibrations, broken pencil lead, and other causes are part of the fun. For the Bot version, I ported the original Flash code to Director, for better speed, motor control, and camera integration.

The Scribbler was influenced by the artbot scene ( artbots.org). For more information on the Scribbler project, please visit lotsofwires.com.