| Gears
and Drivetrains
Gears
are
used
for
two
basic
purposes:
1)
increase
or
decrease
rotation
speed
2)
increase
or
decrease
power
or
"torque"
Torque
is
inversely
proportional
to
speed.
You
can
calculate
the
"gear
ratio"
by
using
the
number
of
teeth
of
the
"drive
gear"
divided
by
the
number
of
teeth
of
the
"driven
gear.
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|
To
increase
speed
and
reduce
torque
use
a
large
drive
gear
coupled
to
a
smaller
driven
gear.
In
this
example
we
use
a
40
tooth
drive
gear
to
turn
smaller
gears
to
get
the
illustrated
gear
ratios.
So
the
8
tooth
gear
will
turn
5
complete
rotations
for
the
every
rotation
of
the
40
tooth
gear.
The
motor
has
been
geared
up. |
|
|
To
reduce
speed
and
increase
torque
use
a
small
Lego
gear
turning
a
larger
gear.
For
the
40
tooth
gear
in
this
example
the
gear
ratio
is
8/40,
or
1/5.
This
gear
ratio
can
also
be
written
as
40:8
or
5:1.
So
for
every
five
rotations
of
the
8
tooth
gear,
the
40
tooth
gear
will
have
turned
only
once.
The
motor
has
been
geared
down. |
Notice
that
you
can
combine
gears
in
a
chain
or
series
to
achieve
different
gear
ratios.
The
gear
ratio
of
a
gear
chain
is
calculated
by
multiplying
the
successive
ratio
of
drive
gears
divided
by
driven
gears.
Here
that
would
be:
(8/20×20/24=
160/480=1/3
or
3:1)
|
|
Extreme
gear ratios
can be
achieved
by stacking
gears
in a gear
box. Incredible
changes
in both
speed
and torque
can be
accomplished
with a
little
ingenuity.
|
Pulley
Based
Drive
Trains
|
|
Changing
the
Axis
of
Rotation
 
|
You
can use
a gearbox
like this
along
with a
"worm"
or "screw"
gear and
a toothed
gear to
change
the axis
of rotation.
The Bionicle
line also
has several
types
of gear
boxes
that split
the motion
along
two axis.
|
|
You
can also
use the
bevel
gear,
the new
style
bevel
gears,
or the
"crown
gear"
to change
the axis
of rotation.
The new
style
bevel
gear gives
the easiest,
most powerful
transference.
the other
two are
more prone
to slippage
under
strain.
|
|
|
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Rotation
To
/
From
Linear
Motion
Rotation
to
Reciprocal
Semi-Linear
Motion
Rotation
to
Intermittent
Rotation
Constant
Rotation
to
Reciprocal
Moti
|
Use
the
"rack"
gear
to
change
between
linear
and
rotational
motion.
You
can
also
use
the
worm
gear
(aka
screw
gear)
to
change
between
rotational
and
linear
motion.
|
Gearing
related links:
Texbrick
A
great introduction to
gears and how to use them.
Wellesley
Another
introduction to gearing.
Shows how to build a very
basic gearbox.
Gears
An
in depth discussion of
gears. Discusses the lego
"spacing problem"
or how to get the gears
to mesh when using different
size combinations - a
very important skill.
Also discusses the differential,
intermittent motion using
offest gears, a simple
transmission and even
steering.
Types
of Gears
What
is a rack, pinion, bevel
gear etc..
Art
of Lego
Some
neat modules, well illustrated
with pics.
Robot
Games
A
more technical introduction
to gears.
Manual
Transmission
Although
it uses no RCX, and is
strictly manual, this
transmission gives a good
idea of how a transmission
works.
Shiftable
transmission
Uses
a "stickshift"
to select from multiple
gears.
Directional
Transmission
Drive
two different drive trains
- one for each direction
the motor spins. Could
be very handy.
The
Brick Bakery - some great
info
From
how to get gears to mesh
well on defferent stud
spacings to a modue for
discontinuous motion.
Gear
Ratios
What
is a gear ratio and how
do you calculate them.
Tables
of Gear Ratios
Includes
some great tables on how
to achieve specific gear
ratios
Build
a basic geartrain
Simple
instructions for building
a gear train (aka gearbox).
Another basic gearbox
Another
basic gearbox - duh.
Motors
- a comparison
A
great introduction to
all the avaialbale Lego
motors, their characteristics
and capacities.
-
and of course -
Bricklink
The
place to buy extra gears
- and anything else lego. |
