View the high-level schematic (PDF) of the robot's sensors, power, motors, and microcontrollers.
Hardware. The robot design is a two-platform differential drive robot with a caster. The drive motors are servos modified for continuous rotation. The robot has two additional servos, one to control a large gripper on the bottom platform, and one to tilt a CMUCam2 camera on the top platform. The gripper is recessed into a "gripper well" on the bottom platform to keep it from snagging on objects. The top platform also has a flat front to allow for pushing of taller boxes.
Power. The robot has a removable 5-A-cell NiMH battery pack and a rocker-style power switch. The battery pack was intended to provide sufficient power for two hours of hard labor, but we have found the battery life to be much longer than that.
Sensors. The design allows for up to five Sharp IR distance sensors and can sense objects up to two feet away. A bump sensor in the gripper well indicates the presence of a grippable object, and a bump sensor on the top platform indicates that there's something to push. Both wheels sport WheelWatcher shaft encoders for dead reckoning. The CMUCam2 camera permits simple image recognition, color tracking, and other basic facilities.
Microcontrollers. The motors, IR sensors, and bump sensors are presently controlled by an Acroname Brainstem GP motor controller, which in turn is controlled via I2C or serial from a Gumstix linux computer. The Brainstem can control up to five digital ins/outs, five analog ins, and four servos. The CMUCam2, attached to the Gumstix via serial, can control an additional three digital outs and five servos (power permitting). The Gumstix can control additional devices via I2C. Notably, the robot was designed with the intent of attaching CrossBow Mica-2 and Mica-Z sensor motes.
Purchase. All the parts were purchased off-the-shelf from existing hobbyist robot companies or other vendors. We tried to minimize the number of custom items. At present the robot has four custom parts: the two platform decks were cut to specification by Budget Robotics, the mount connecting the CMUCam2 to its servo was cut out of scrap aluminum, and the bracket holding the Sharp IR sensors was fabricated from aluminum flashing. At left you can view our parts list, including purchase costs.