Figures 1 & 2 depict the vehicle-to-guideway mechanical
interface to both the upper and lower rails. Two of these suspension interfaces
occur per vehicle, with 18-foot wheelbase separation on the 28-foot long
vehicle. Primary suspension elements consist of an outrigger attachment to
the upper rail, a main drive wheel/gearing/motor configuration riding along
the lower rail, and a load leveling suspension unit. The dual-flanged, 26-inch
diameter main drive wheels have a concave profile to operate with the specially
crowned rail head.
The outrigger is unique to System 21, with its primary
functions being to carry tension loads to prevent vehicle overturning, and
to serve as a mount and conduit for a contact shoe used to draw DC power
from the guideway-mounted contact rail. The interface between the outrigger
and the top rail is shown in Figure 3. The outrigger surrounds the upper
rail head to provide a guide for the outrigger rollers. Each outrigger has
four rollers above the web of the rail, and four below. An "in-line skate"
mounting arrangement for the rollers, a configuration of interconnected hydraulic
cylinders, and a cam track mounting of the outrigger to the carbody allows
the outrigger suspension to conform to guideway transitions through curves,
switches and stations.