Power transmission devices support a load,
permit movement of the load, and transfer mechanical energy from the
actuator to the load. One family of power transmission devices
contains belt drives and chain drives. Three
classes
of belt-type drives are in common
use.
- Rubber-type belts that do not enforce synchronization
(slippage is possible) between the driving and driven wheels. This type
includes the round belts (shown in the photos above), v-belts, and flat
belts. The wheels they run on are called Pulleys.
- Rubber-type belts that DO enforce synchronization
(slippage is NOT possible) between the driving and driven wheels. These
belts are usually flat with precisely spaced teeth which engage slots
in the pulley. These are called Timing
Belts and Timing Pulleys, or
Gearpulleys.
- Chain drives, which may be metal or plastic. Slippage
cannot occur, but there is enough play in the coupling that it cannot
be referred to as synchronous. The wheel upon which the chain rides is
called a Sprocket.
Belt-type drives can be used along with bearings and axles to couple a
motor to a
load. In the process speed and torque can be traded off by choosing
different diameters for the driving (motor side) and driven (load side)
pulleys or sprockets. This should be familiar from shifting the gears
while riding 10-speed (or
more) bicycles. More on this subject can be found on the Drive Ratios page.
Pulleys, timing pulleys, and chain sprockets will not function properly
unless the outside contour of the belt matches the contour of the
pulley's rim. See the Timing Belt and
Pulley page for further discussion of belt drives.
The belt stock shown in the demo above is PRB-03 POLYCORD 3/16" DIA
from Small Parts, Inc. To use the material, first cut the appropriate
length of belt stock, then weld the ends together with a lighter. Full
instructions are in the catalog.
The black pulleys are from Small Parts, Inc., and the white pulleys are
made of Delrin® machined on the metal lathe.
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Small power transmission devices are best
not purchased surplus because it's hard to find pieces that actually
fit together. Two sources for these components are SDP-SI and Small
Parts, Inc. They are listed in the sources
page.
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