is a kind of motor that instead of a chain uses 2 wheels on
the engine to spin the main wheel. This kind of engine is
often used on scooters, mainly go-peds, in place of a chain.
Friction drive units provide very smooth motion as the mechanism
is designed to virtually eliminate mechanical backlash and
a friction-drive mechanism the friction elements are mostly
like cylindrical, conically tapered or globoid wheels which
are pressed together so firmly that the frictional force developed
at this point or line of contact transmits power. The power
that can be transmitted in this way will depend on the magnitude
of the contact pressure and the coefficient of friction of
the surfaces in contact.
every friction drive a small amount of slip develops between
the friction elements: i.e., at the point of contact the driven
wheel always has a slightly lower circumferential velocity
than the driving wheel. The drive is therefore not a fully
positive one. Such forms of drive have the advantage that
the effective radius can be varied quite simply by a shifting
of the point of contact of the friction wheels toward or away
from the axis of rotation, so that infinitely variable control
over the transmission ratio is obtained.
can say the simplest form of friction-wheel drive, cylindrically
shaped wheels which roll against each other. The resilience
of the (often rubber-covered) wheels, spring pressure or weights
produces the necessary contact pressure and thus develops
the friction through which power is transmitted. Some Examples
are record-player drive, tape-recorder drive. Every powered
traction wheel of a road vehicle or rail-mounted vehicle is
in effect a friction drive. The contact pressure due to the
weight of the vehicle enables the wheel to develop friction
and thus get a grip on the road or rail surface.
This combination is comparable to a rack and pinion, the wheel
being the pinion and the road or rail the rack.
Fig.1 we can see a friction drive that is similar in construction
to a planetary gear and is of the type used for the tuning
mechanism on some radio receivers. The balls correspond to
the planet wheels; they roll on the inner shaft, which corresponds
to the sun wheel. When the fine-adjustment knob mounted on
the inner shaft is rotated, the cage formed
by the hollow shaft will rotate at a lower speed and thus
make possible precision tuning.
friction drive present for infinitely variable speed control
comprising two conically tapered friction elements and an
intermediate ring is illustrated in Fig.2. When the ring is
in the right-hand position, the upper shaft will rotate faster
than the lower shaft, which is the driving shaft, because
in this position the driving radius R is larger than the driven
the ring is being moved to the left-hand position, the driving
radius r will be smaller than the driven radius R, so that
now the upper shaft will rotate more slowly than the lower
shaft. Fig.3 shows a friction drive comprising a large flat
wheel and a small friction wheel which can be slid to different
positions on the driving shaft on which it is mounted.
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