Gear Trains and Ratios
Gear trains are very important in the world of robotics because they
provide not only a transfer of energy, but a translation of energy. In other
words, speed can be translated into torque and torque to speed. The
amount of speed and torque output of a gear train is measured in a
"gear ratio." In our case, Eddie is running a 1:1 (24: 24) gear ratio.
To understand gear ratios, just remember that the bigger the number
on the left is compared to the number on the right, the faster and weaker
the output will be. Conversely, the bigger the number on the right of the
ratio is compared to the left, the slower and stronger the output of the
gear train will be.
Right now, because we have a 1:1 gear ratio, our output is the same as
our input (minus friction and other nominal forces). Experiment with Eddie
by replacing the gears on the motors with tiny eight-tooth gears, and the
gears on the drive axles with
the large 40-tooth gears. This
will give Eddie an 8: 40 or 1: 5
gear ratio, meaning that he'll
have a lot more pushing
power. You can also try the
opposite — put 40-tooth
gears on the motors and
eight-tooth gears on the
drive wheels, and watch the
wheels fly!
A 1:1 (24: 24) gear ratio.
Remember, you can also
move the drive axle position
to fit even more gear ratios.
A 1: 5 (8: 40) gear ratio, geared
for torque.
A 5:1 (40: 8) gear ratio, geared
for speed.
66 SERVO 08.2010
Experiment!
Now that you understand the basics, do some
experimentation. Here are some ideas:
- Get Eddie to move forward, then stop.
Wrapping Up
We’ve taken a look at the LEGO MINDSTORMS NXT kit
as a whole, and built a basic driving chassis. Next time,
we'll take a look at how to program the NXT on a
computer, and learn all about touch sensors. From there,
we'll continue to add to our knowledge of the NXT,
eventually working with all the sensors from LEGO, and
some third party sensors as well, so stay tuned! SV
