Specialized Gears
In addition to the standard shaped gears, there are lots
of other ones which will enable you to build varied Technic
models.
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 Crown
Gear
This gear is so called because the edges of it turn
upwards like a crown. It is the same size as a standard
sized 24-tooth gear, but its unusual teeth shape allow
you to mesh it with other gears at right angles. The
disadvantage of a gear like this is that is will provide
a lot of friction and must be backed up against a beam
or bushing to stop it slipping out of place. Despite
this, it is still an important gear and very useful.
It can be used in place of a normal 24-tooth gear but
this is not advisable.
- The Crown gear meshed with a small, 8 toothed gear.
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 Bevel
Gear
This gear is like the second incarnation of the Crown
Gear, but it still has some differences. The first,
and most important, is that it can only mesh with
other bevel gears. It has 12 teeth and is more compact
than the crown gear. It is only slightly more efficient,
and can also be used in the Differential (three bevel
gears are the only gears that fit inside it).
- Two bevel gears meshed at right angles.
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 Worm
Gear
This gear is very unusual, but also very useful. For
one full rotation of the worm gear, the gear that it
is meshed with will move along one tooth. For example,
the model on the left reduces the speed of the gear
by 24:1 - a very compact and efficient way of gear reduction.
Another bonus is that it is a one way function only,
no amount of turning will make you turn it the other
way (a useful feature in cranes, for example), although
it will wiggle slightly as the size of the gear is just
smaller than 2 large bushings. This wiggle can be eliminated
by positioning the worm gear vertically in a structure.
Have a look at the TOP TIP! for more info.
- A small structure connecting a worm gear and 24-toothed
gear |
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 The
Rack
The rack is a small, flat gear the size of a 4x1 brick.
It can be used to convert gears into linear movement
and is often used in car mechanisms. The rack must be
able to slide freely, and there are generally three
options for this. Up-turned beams (on the left), half
beams (picture below) or smooth tiles. My technic Lego
doesn't include any smooth tiles (and I cannot be bothered
to get some from my other Lego to combine it) so I do
not have an example of this. You must make sure that
the cog is raised sufficiently from the edges of the
rack otherwise the rack will not slide properly. That
cog can be any sort of cog, but to make the structure
more compact and to allow finer control, an 8-toothed
cog is normally used.
It will not take much turning to get the rack out of
the mechanism, so longer racks can be made by joining
them together at the bottom.
- (above) A rack sliding on upturned beams
- A rack sliding on a yellow half beam (it that its
name???) |
