Servo - January 2013

GEERHEAD

A student from Hiram Johnson High School is testing code for the minesweeper Mobot configuration.

Replacing the batteries in a minesweeper configuration.

The platform supports Windows XP, Vista, and Windows 7, and also the Mac OS X, a Graphical User Interface (GUI) robot controller, and a C/C++ interpreter channel for processing and motion control.

“The Mobots are useful in teaching pre-algebra, algebra I, geometry, physics, physical science, computer science, and really anything where abstract concepts can be realized in the physical world to create a greater understanding for students,” according to UC Davis. Each unit is individually useful since there is no minimum assembly/setup that needs to occur to get started in the classroom.

Engineering Professor Harry H. Cheng of UC Davis with one of his Mobot modules.

Engineering the Mobot's Wheels — a Lesson in Design vs. Cost

The engineers at Borabo Robotics decided the Mobots needed their own special wheel accessory to make the robots mobile. The eventual design included rounded edges, cut-outs, and extrusions to make sure the wheels had good tread and traction, and remained in contact with surfaces in a way that enabled the robots to continue to be locomotive — even when the module’s joints were bent at an angle.

One approach the engineers considered was a two-sided shell design with dead space inside which could be plastic injection molded with snap connection joints to connect it to the Mobot’s rotating interfaces. However, the Borabo design engineers found the injection molding approach challenging since the molds required to create the snap-on features were pricey. Even a less expensive bump-off process that adds the overhang features during removal from the mold could not be applied to the entire wheel, so another approach had to be found.

A single-sided design approach was then considered. This led to several iterations including a treaded wheel with a central rib, enabling even rolling. The design could be easily molded in an inexpensive fashion with no overhang or special procedures. Still, the engineers had to reduce the width of the wheel in an attempt to come in under budget. This helped but was not enough.