jBot: A fully Autonomous, Self-Guided, Mobile Robot

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The Journey Robot is an outdoor robot designed to run offroad in unstructured environments. It was inspired by the DARPA Grand Challenge and built as a prototype vehicle for that competition, in collaboration with Ron Grant and Steve Rainwater of the Dallas Personal Robotics Group, Mike Hamilton, Mark Sims and myself.

jBot is a fully autonomous, self-guided, mobil robot, capable of navigating on its own to an arbitrary set of waypoints while avoiding obstacles along the way.The concept for the robot was hashed out over the summer of 2004 in a series of RBNO meetings at the warehouse of the DPRG. The platform was designed by Mike during the fall and winter of 2004 and I built the vehicle in my home machine shop in the spring of 2005. jBot moved under its own power for the first time on April 9, 2005 (3.5M mpg).

The robot was designed to meet the twin requirements of off-road stability and zero turning radius. The present platform is a differentially steered 6-wheel vehicle, with all-wheel drive and all-wheel independent suspension. Power is provided by two Pittman 24 Volt DC gearhead motors and a 24 volt, 4 amp/hour NiMh battery pack. Total robot weight is about 20 lbs. The robot's tires, wheels, and suspension were scavanged from a Traxxas E-MAXX 4-wheel-drive 1/10 scale R/C monster truck. These are very nicely engineered suspension and drive parts, with a full set of factory parts available, as well as lots of after-market components from various manufacturers. Mike designed a custom drive train to interface with the suspension parts, giving us an all-wheel-drive vehicle with zero turn radius and full independent suspension. The only aftermarket parts used were the addition of MIP CVD steel constant velocity joint drive shafts to replace the factory plastic parts, which were not able to handle the torque, and a set of aftermarket Road Rage tires.

The robot's "brain" is a Motorola 68332 micro-controller running in one of Mark Castelluccio's Mini Robomind controller boards. The current suite of sensors includes quadrature shaft encoders on the motors, an array of four Polaroid (Senscomp) sonar transducers, a Microstrain 3-axis inertial measurement unit, and a Garmin Etrex GPS receiver. A pair of Devantech H-Bridge intelligent electronic speed controllers are used to drive the DC gearhead motors.

The robot's operating system and control and navigation software were developed and written by the author based on algorithms originally developed for the SR04 and the nBot robots. The robot uses a small cooperative multi-tasking executive to run a set of behaviors. The behaviors are prioritized in a behavior-based or "subsumption" architecture. The powerful TPU subsystem of the Motorola 68332 provides interrupt-driven hardware interfaces for user I/O, motor drivers, quad encoders, PID speed controller, sonar array, and radio PWM decode for a remote emergency override. It also supplies four RS-232 communication channels for the control terminal, IMU, GPS, and an optional serial video camera.