Simple NXT Calibration:
Look Ma! No Tools!
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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 firstname.lastname@example.org
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.