Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 5 Tracked Vehicle Suspensions and Drivetrains 171
lem. The steel eliminates stretching, and adds little weight to the system.
For even greater strength, hardened steel crossbars are molded into the
track. These bars are shaped and located so that the teeth on the drive
sprocket can push directly on them. This gives the urethane track much
greater tension strength, and extends its life. Yet another modification to
this system is to extend these bars towards the outer side of the track,
where they reinforce the treads. This is the most common layout for urethane
tracks on industrial vehicles. Figure 5-4 shows a cross section of
this layout.
TRACK SHAPES
The basic track formed by a drive sprocket, idler, and road wheels works
well in many applications, but there are simple things that can be done to
modify this oblong shape to increase its mobility and robustness.
Mobility can be increased by raising the front of the track, which aids in
getting over taller obstacles. Robustness can be augmented by moving
vulnerable components, like the drive sprocket, away from possibly
harmful locations. These improvements can be applied to any track
design, but are unnecessary on variable or reconfigurable tracks.
The simplest way to increase negotiable obstacle height is to make the
front wheel of the system larger. This method does not increase the complexity
of the system at all, and in fact can simplify it by eliminating the
need for support rollers along the return path of the track. This layout,
when combined with locating the drive sprocket on the front axle, also
raises up the drive system. This reduces the chance of damaging the
drive sprocket and related parts. Many early tanks of WWI used this
track shape.
Another way to raise the ends of the track is to make them into ramps.
Adding ramps can increase the number of road wheels and therefore the
number of moving parts, but they can greatly increase mobility. Ramping
the front is common and has obvious advantages, but ramping the back
can aid mobility when running in tight spaces that require backing up
over obstacles. As shown in Figure 5-5 (a–d), ramps are created by raising
the drive and/or idler sprocket higher than the road wheels. Some of
these designs increase the volume inside the track system, but this volume
can potentially be used by other components of the robot.
More than one company has designed and built track systems that can
change shape. These variable geometry track systems use a track that is
more flexible than most, which allows it to bend around smaller sprockets
and idler wheels, and to bend in both directions. The road wheels are