Road wheels:
The main points about a road wheel are its diameter and the nature
of its tread. A larger diameter is better on a rough or uneven surface because
the wheel can more easily rideup over ridges and is less likely to get stuck in
grooves. Also it allows there to be a larger clearance between the surface and
the underside of the chassis.If the surface is smooth and even, for example the
rails of a gantry, small wheels have theadvantage of light weight. It is all too easy
for a robot design to finish up by beingheavier than the motor can drive. Using
small wheels helps to avoid this. Tyres help the robot to run without slipping.
The simply programmed robots usually start and stop abruptly. This leads
to skidding or slipping. We rely on a robot being able to run in a straight line
but slipping makes it run in irregular curves. Unless it is continually taking
its bearings from a fixed landmark, it soon gets lost. Wheels slip, even when
they have tyres, but tyres help to avoid serious slipping.
of its tread. A larger diameter is better on a rough or uneven surface because
the wheel can more easily rideup over ridges and is less likely to get stuck in
grooves. Also it allows there to be a larger clearance between the surface and
the underside of the chassis.If the surface is smooth and even, for example the
rails of a gantry, small wheels have theadvantage of light weight. It is all too easy
for a robot design to finish up by beingheavier than the motor can drive. Using
small wheels helps to avoid this. Tyres help the robot to run without slipping.
The simply programmed robots usually start and stop abruptly. This leads
to skidding or slipping. We rely on a robot being able to run in a straight line
but slipping makes it run in irregular curves. Unless it is continually taking
its bearings from a fixed landmark, it soon gets lost. Wheels slip, even when
they have tyres, but tyres help to avoid serious slipping.
Pulley wheels:
A pulley is a wheel with a grove around its rim, known as a race. Pulley wheels are
mainly used for the transfer of force. In the Gantry, for example, they transfer the force
of gravity to the chassis to pull it along the tracks when the winch unwinds.
They are also used in the pulley system that raises and lowers the hook and
some other tools. Another way in which force is transferred is by a belt drive
between two pulleys. A pair of pulleys of equal diameter simply transfer force over
a distance. If their diameters differ, the result is similar to that of a gear chain. A larger
pulley driven by a smaller pulley rotates at a slower speed but with increased torque.
Pulleys are connected by the drive band, but gears have to be in contact. This makes
pulleys useful for transferring force over a distance.A further advantage of using
pulleys is that drive bands are slightly elastic so the exact distance between the
wheels is not important. With gears it is essential for the teeth of the two wheels
to mesh accurately together.
Fig:wheels 01Gear wheels:
Gear wheels are often needed for drive transmission and for moving arms and grippers.
They are available as packeted kits of plastic gear wheels of a range of diameters from
various manufacturers. Tamiya produce sets of gears, including motors, that can be
assembled into gearboxes of many different ratios. Meccano and Lego produce gear
wheels too, and the kinds of mechanism that can be built from them are shown in the
photos overleaf.Gear wheels transmit turning force by engaging their teeth.
The number of teeth on thewheels matters more than their diameters. When talking
about gear wheels we speak of‘24t’ wheels and ‘36t’ wheels, meaning wheels with
24 and 36 teeth. When one gear meshes with another, the speed (or rate of rotation,
or angular velocity) of one gear relative to the other depends only on the numbers
of teeth on each wheel. For example, wheel A, with 10 teeth, is driven by a motor
and engages with wheel B, which has 40 teeth. As A rotates one revolution its
10 teeth mesh with 10 teeth of wheel B. But B has 40 teeth, so has turned only
a quarter of a revolution. Meshing a wheel with few teeth against one with more
teeth gives a reduction in speed.
Fig:Wheels 02
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