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In the summer of 1999, we had used the bottom two layers of 3T to provide autonomous control for a single subsystem--a second-generation biological water processor--during a 450-day, 24-hour-a-day, 7-day-a week test. Then in January 2000, the Advanced Water Research Group received ALS funding for the year-long IWRS test, involving four advanced water-recovery subsystems (Bonasso 2001) (see Advanced Water Recovery System sidebar).BuildupUsing 3T allowed us to develop the control for the IWRS in a modular fashion in two ways. First, moving from bottom to top (figure 4), each layer has its own data structures, timing constraints, and development tools that allow for parallel development of the software. Thus, we were able to develop skills sets based on the evolving hardware specifications and simultaneously develop the sequencer procedures. Early on, as the water research team developed the design for each subsystem, one part of the 3T team wrote the sequencer procedures for each subsystem in the RAPS language (which, in turn, is written in Lisp) (1) using virtual skills, that is, Lisp skills connected to a Lisp simulation of the expected hardware. A virtual simulation of, say, the reverse-osmosis subsystem could then be shown on a laptop to the WRS engineers and the control design refined in an iterative process even before the actual hardware was available. The primary result of this process was a set of skill specifications for each subsystem (figure 5).

"The three new machines are aimed at different sections of the backhoe loader market," said Kevin Hershberger, senior marketing engineer backhoe loaders. "The 416D is targeted to the rental services, utilities and DCA. The 420D/IT is targeted to the owner/operators and building construction markets while the 430D/IT is targeted to the owner/operators, building or construction contractors as well as the sewer and water contractors." The new loaders are similar to the C-Series in many areas and in some cases use the same components as the C-Series machines. For example, the frame and many drivetrain components are either very similar or direct carryovers from the earlier machines. "The main area of difference between the new D-Series and the old C-Series is the hydraulic system and the cab interior," said Jon Carman, commercial marketing manager for backhoe loaders.