27404 Parallax Inc, 27404 Datasheet - Page 106

• Manufacturer Part Number: 27404
• Description: COMPETITION RING FOR SUMOBOT
• Manufacturer: Parallax Inc

Specifications of 27404

• Accessory Type: Hobby and Education
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: SumoBot®
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Your Turn - Detecting Tilt
What if the QTIs were to give you a unique signature when the SumoBot is tilted
backward?
ACTIVITY #3: SELF CALIBRATING QTI SENSORS
As mentioned earlier, different lighting conditions and different competition rings will
cause the QTIs to give different measurements. If you selected a value to discern
between the black ring and the white tawara line based on your own practice ring, you
might be in for a surprise when you move your ring to a different location or use a ring
made of different materials. Reason being, the value you chose for your practice ring
might not work with the new conditions. When this happens, your SumoBot will drive
right out of the ring, maybe before it's even had a chance to engage with its opponent.
The solution to this problem was first introduced in the SumoBot text - a QTI self-
calibration routine. In this activity, you will take a closer look at how this kind of self-
calibration routine works.
QTI Self Calibration Code
Making the QTIs self calibrating isn't difficult if you start with the example program
from this chapter's Activity #2 - TestFrontQtiLineSensors.bs2. The first step is to add a
word variable to store a threshold value.
Since the SumoBot will have to start off in the middle of the ring, the only piece of
information it will have is the QTI measurements for the black surface. The program
√
√
√
Try tilting the SumoBot while it's sitting on the sumo ring.
Are the readings different from black and white?
How does the light level in the room effect tilt measurements?
qtiThreshold
Strategy tip
While it seems like this might be a great way to detect whether your SumoBot is at a
disadvantage, it tends not to work in practice. Whether the SumoBot's plow is under or over
its opponent’s, both SumoBots may tip upward for a moment as they push against each
other. Therefore, detecting a tilt does not necessarily indicate that your SumoBot is winning
or losing, so these measurements would not necessarily be helpful in deciding what type of
maneuver to do next. While QTI tilt is probably a blind alley, similar experiments may lead
to more useful sensor data and new strategies.
VAR
Word