Simple NXT Calibration:
Look Ma! No Tools!
Featured on
thenxtstep.blogspot.com
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As we all know, one of
the endearing qualities of LEGO
robotics is its inherent
lack of precision.
As good as the NXT motors are
(and other components), they
are, at their core, basic DC
motors with gears. All of our
motors (about 20 of them) all
work slightly differently in
terms of acceleration, power,
braking, etc. |
Yet it is essential that your
motors (particularly paired
driving motors) be as close as
possible in performance specs.
So how do you do this without
torque gauges, tachometers,
etc.? Leu Beach, one of our mentors, along with our
programmers, Jonathan, Doug,
Nate, and Cole, came up with the
most amazing, simple,
calibration system ever.
It took us about 15 minutes to
test all our motors. The
resultant matched set vastly
improved the robot's directional
consistency and performance.
Important Note from a
Fan: You may
want to make it clear that you have to
use MOTOR
blocks to do this testing and
not MOVE
blocks. We first tried this
with MOVE blocks and all the motors
seemed to be in sync. Then I remembered
that MOVE blocks automatically adjust
for differences. So, we changed the
program to use 2 MOTOR blocks running in
parallel and it showed the differences.
Ready to be amazed? Read on.... |
LET US KNOW HOW THIS WORKED FOR
YOUR TEAM. Please send a short
note to
marco@techbrick.com |
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First, all you need is a
setup as shown below. One NXT, two long wires, all
your motors, and an axle.
Lay the motors flat as
shown. Make sure the cables are loose and do not
restrict the motors.
Then simply run both motors
at the same rate. If one accelerates faster, runs faster,
or breaks harder (on stop) it will kick up as shown. Pull off
the second motor and try the next one.
Continue until both motors
stay flat at all speeds and startups. Then try
the paired motors at various speeds and ramp ups
and breaks to confirm.
The second test is
rotational accuracy. Take one motor and attach a
gear with a peg. Run it for 10, 20, 50
rotations.
See if it ends up in the
same place that it started. Make sure your
matched motors are accurate in this test.
Lastly, mark your motors legally. FLL says
there can be no markings on the LEGO pieces that
are visible. So, Linda Barrington suggests using
permanent markers to identify matched pairs by
making a dot inside the plug outlet by color or
other marking.
That's it. It works. |
