Thames & Kosmos AIR Plus Water Power Experiment Manual page 6

AIR+WATER power |
The big gear has more teeth than the small
gear. Despite the number of teeth or the
size of the gears, all of the teeth on all of the
gears in the same gear system must all be
the same size. In simple gear trains, the driver
and driven gears will rotate in opposite direc-
tions. When a third gear is inserted between
the driver gear and driven gear, and makes
them rotate in the same direction, it is called
an idler gear.
The gears in this construction system come
in five different types: 20T, 40T, 60T, 80T, and
160T, the extra large gears. This particular kit
only contains 20T and 40T gears. The other
gears can be found in other kits.
The gear system contains both spur and
bevel gears. This kit contains "spur gears,"
which mesh in the same plane and regulate
the speed or the turning direction of the
shafts, and "bevel gears" (the beveled edges
of the gears) which mesh together at right
angles to the initial turning plane of the gears
and shafts to change the plane of rotation.
The pitch diameter of the gears in this gear
system is proportional to the number of gear
teeth. In other words, the pitch diameter of
the 20T gears is 20 millimeters while the
pitch diameter of the 40T gears is 40 mil-
limeters. Again, the pitch diameters are the
imaginary circles between the meshed gear
teeth as shown in Figure E.
The gears are easy to install on the rods
and frames in this kit, because the rods and
frames have holes positioned in increments
of ten millimeters. The pitch diameters are
in multiples of 20 millimeters, and thus the
distance between the center points of the
gears is in multiples of ten millimeters.
In Fig. E, the distance between the centers of
the two gears is calculated like this:
20 mm 40 mm
R1 + R2 = +
2 2
Therefore you can easily place the two gears
on a rod or frame so that they mesh together
smoothly. The other sizes of gears are de-
signed with the same elegantly simple con-
cept, so that all of the gears can easily be
assembled into working gear trains.
According to the instructions above, can
you figure out how many holes there are be-
tween a 40T and a 60T gear when they are
meshed?
Learning about Gears
= 30 mm
4
160 T*
20 T
40 T
60 T*
80 T*
Fig. C Gears (T = Number of teeth)
(*Not included in this particular kit.)
Fig. D Characteristics of gear teeth
R1 R2
Fig. E The transmission between the pitches
during the meshing of two gears