Page 75 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Throughout this text, we’ll refer to pillow block bearings as those with a rigid
mount or base mount that supports the shaft in a position parallel to the surface
on which the bearing is mounted. We’ll use the term “flange mount” bearings for
those that have two or four holes, and mount the shaft perpendicular to and penetrat-
ing the surface upon which the bearing is mounted. Most of the ball bearing varieties
of these mounted bearing assemblies cannot change the axis of rotation of the
shaft. Certain non–ball bearing types have a bronze bushing or bearings mounted
in a spherical “ball” assembly that allows the shaft to rotate from 20 to 30 degrees
or more off-center. These types of bearing assemblies are useful when mounting
drive components that are not quite aligned with other shafts and components.
The Pillow Block Bearing The pillow block method of mounting wheel shafts is
probably the most popular way to attach wheels to a combat robot. The pillow
block bearings can be mounted below the bottom surface of the robot with the
shafts exposed, or the same bearings can be placed above the bottom plate with
the shafts enclosed in the interior of the robot. In the second configuration, the
outside bearing can be a flange mounted bearing on the wall of the robot’s chassis.
The advantage of using these types of bearings is the ease of mounting. A typical
ball bearing race assembly still must have a machined hole in which to insert the
bearing. Either the bearing must be tightly pressed in and held in place by friction, or a
small slot must be cut into the circumference of the hole in which to insert a retain-
ing ring. The ready-made assemblies of the pillow block or flange mounted bearing
are far simpler to install. In most cases, the builder will want the shafts used with
these bearings to be securely held within the rotating part of the bearing, so bearing
assemblies with set screws are recommended. Grainger, McMaster-Carr, and other
suppliers have many varieties of these bearings in stock. These and other suppliers are
listed in Appendix B of this book. The McMaster-Carr catalog also has useful data on
maximum dynamic load capacities in pounds, as well as maximum rotational speed
in RPM.
Either of these types of bearings has applications in other areas of robot design.
Large swivel joints that may be used for weapons can make use of pairs of these
bearing assemblies in conjunction with a high-strength bolt or multiples of bolts
as the “hinge pin.” Configurations like these make for high strength hinges and
are preferable to standard door hinges for applications of high stress. Such a hinge
mechanism is shown in Figure 3-10. In this figure, a flipping mechanism is sup-
ported by two pillow blocks. The left-hand side of the figure shows the robot prior
to a combat match and the lifting prongs have not been attached. The right-hand
side of the photo shows the robot after a round of combat. Note how much damage
this robot took, but the shaft and pillows blocks are still intact. This is one of the
great advantages of pillow blocks—their durability.