��
�
Scholastic Projects
��
The obstacle avoidance program for the Intermediate Trekker uses the Ultrasonic sensor mounted to the top of the Trekker on a sweeping scanner bracket, a front bumper switch, and an IR detector mounted to the bumper switch.� The Ultrasonic sensor and the IR sensor can be switched if desired (it would require some code changes).� The bumper switch can also me moved to the rear if desired (again this will require some code changes).� Other variations could be redefining what the front of the Trekker is.� Currently the Front of the Trekker is defined as the end where the drive wheels are and the OOPic mounts.�
�
The infrared scanner sends an infrared signal out (invisible to the human eye) and times how long it takes for the signal to reflect off an object and return to the infrared receiver.� The time it takes to reflect is then converted into a voltage.� Using the OOPic code, an oIRRange Object converts the voltage to a distance.� An IR signal is good at reflecting off most surfaces that have some reflective properties.� The IR detector will detect obstacles and cause the robot to stop.� The IR detector can detect from a range of 4 inches to 30 inches.�
�
The Ultrasonic sensor is similar to the IR except it uses sound to reflect off objects.� The time it takes to return the sound is converted to a distance using the oSonarDV OOPic Object.� The ultrasonic sound is considered the "ping" and the returned sound is called the "echo".� The ultrasonic signal is good at reflecting off most hard surfaces.� Surfaces that absorb sound do not work as reliably.�� The Devantech SRF04 Ultrasonic detector can detect from a range of ~4 inches to ~10 feet.�� The Ultrasonic scanner is attached to a Sweeping scanner.� The sweeping� scanners is attached to a servo via a bracket and allow the scanner/detector to look with a field of view slightly greater than 180 degrees.� They can look without the robot having to rotate/drive.�
�
The Bumper Switch is as the name implies - if it bumps into something the switch contacts are closed and the OOPic gets the signal.� The Trekker will then stop once the bumper switch is activated.� The Trekker can be equipped with bumper switches on the front and back.
The Line follower uses 4 infrared photo reflective sensors.� White reflects light, black does not reflect.� The sensor will needs about a 0.25” to 0.5” black line on a white surface in order to work.� The Trekker Expansion card has a “pull up” resistor on each line follower output.� The pull resistor does exactly what it sounds like, it pulls up the value to 5 volts.� The reason you pull up is to eliminate the effects of a drifting circuit.� If the output is floating so could the value the OOPic reads hence giving erroneous readings.� So when no signal is present the output the OOPic sees is pulled up to 5V.� When the sensor does send a signal it has enough current to overcome the pullup resistor and ground (~0 Volts) the output.� The expansion board also puts a capacitor to each of the outputs to ground to eliminate spikes and any other spurious readings and smooth out the outputs.
�
The 4 line follower sensors should be positioned such that the middle two do the fine-tuning and the outside ones do the course tuning.� The trick is to what the Trekker should do when no sensors detect the line.� When no line is detected it could be in-between two sensors or it could be way off track.� The example line follower code provided with the Trekker eliminates some of this doubt by putting a program latch on the outside sensor that� keeps the robot turning until the inside sensor gets a reading (ie the line has moved back towards the center).�� The program simply does a large loop checking each sensor, performing the task if one of the sensors indicates a line, and continuing.� The loop also checks the Sharp IR ranger to see if any obstacles are in the way.� If an obstacle is detected the Trekker goes to a subroutine to stop the drive servos and loop until the obstacle is cleared.� The entire program just continuously loops until it is turned
off.�
Autonomous Sumo Wrestling is another sport the Trekker can perform.� It uses many of the sensors listed above.� The line following sensors can be used to warn the Trekker that it is about to go or be pushed out of the circle.� The Trekker uses its sensors to seek the other robots and simply tries to push it out of the circle.� This setup and program can also be used to push other objects out of the circle (i.e. house cleaning).
�
The Sumo wrestling program uses the same sensors as the Line Follower.� It uses the line followers to keep itself inside the circle.� Two of the sensors are moved to the front bumper switch, the other two remain on the line follower bracket, and the line follower bracket is moved to the back.
�
The programming of the sumo is more complex than the line follower.� The programming requires some strategy.� The big challenge is programming it to respond to being pushed out of the circle or pushing another robot out of the circle.
�
The Arena should be an all white surface with a black line around the perimeter.� The opposite can be used if the sensor values are inverted.� It would be better if all the out of bounds was black, but just a single line about 0.25 to 0.5” thick is sufficient for the sensors.� The IR can see about 30” so a 3 to 4 foot diameter circle would be a good size.� To eliminate the Trekker tying to attack things outside of the circle, the effective range of the IR can be detuned or the obstacles should far out of the circle unless you want to add an additional challenge.� The Line sensors will prevent the Trekker from leaving the arena.
Fire Detection is also a very competitive event.� The object of the fire detection is to navigate the robots through a maze of walls and look into the rooms and see if there is a fire.� Using a UV sensor, a flame the size of a single candle can be seen 5 meters away.�� The Trekker utilizes a Hamamatsu UV sensor that is mounted onto the Trekker sweeping sensor brackets.� The Trekker scans the area and finds an open flame.�
�
The Hamamatsu UV TRON Flame Detector� is lightweight, has low current consumption, and operates as high sensitivity UV Sensor.� The UV Tron is an ultraviolet detector that makes use of the photoelectric effect of metal combined with the gas multiplication effect.1t has a narrow spectral sensitivity of 185 to 260 fill. Thus it is solar blind, being completely insensitive to visible light. Unlike semiconductor detectors, it does not require optical Visible-cut filters, thus making it easy to use.
�
UV Tron Flame detector is small, but has a wide angular sensitivity (directivity) and can reliably and quickly detect weak ultraviolet radiation emitted from a flame due to use of the metal plate cathode (e.g. it can detect the flame of a cigarette lighter at a distance of more than 5 m.). The Flame detector is well suited for use in flame detectors and fire alarms, and also in detection of invisible discharge phenomena such as corona discharge of high-voltage transmission lines.� To minimize the area the sensor sees the flame, the field of view is masked using a sensor shields.� The shields are useful when you are trying to locate the location of the flame.
�
The driver for the UV TRON is operated by applying DC low voltage and outputs a high-voltage power supply.� It also contains a signal processing circuit on the same printed circuit board. ��Since background discharges of the UV TRON caused by natural excitation lights (such as a cosmic ray, scattered sunlight, etc.) can be cancelled in the signal processing circuit, the output signals from the C3704 series can be used without errors.
�
The Flame Detector Mask is a piece that slides over the UV TRON Detector to mask the detector so the sensor can only see the UV Flame if its directly in front of the detector.� This is ideal when trying to determine where the flame is coming from.� The sensor has a very wide viewing angle that is great for detecting the presence of a flame, but without the mask the detector will not be able to determine where the flame is coming from.� The Mask is 1” in diameter with a center hole machined out along with about a 1/8” slot machined through the side to let the UV in.� The field of view is narrowed to about a total of 15 degrees while not significantly impacting its sensitivity.� The mask is simply glued to the driver board to allow it to stay on.
�
The Robot that finds the flame the fastest is awarded the most points.
Soccer robots are also gaining popularity.� The object of the soccer robots is to work as a team and push a soccer ball towards a goal.� This is a very complex and competitive sport.� The Trekker can be equipped with brackets that attach to the front bumper switch.� The brackets will detect if it has caught a ball using a IR sensor that shoots across the front of the bumper switch.� The soccer robot works best with a Trekker that has a front scanner attached to the bumper switch and at least one sweeping scanner attached to the top of the Trekker on a scanner bracket.� The basic principle of finding the ball is to use the top scanner and scanner attached to the bumper switch.� If the lower sensor sees something the top scanner does not see, then it’s likely a ball.� The top scanner will not see the ball since it is below its field of view.� The Robot can then drive towards the ball, fetch it, and drive it to its goal.
�
The Trekker slowly scans the area with IR to detect objects. �When a change in the IR reading occurs, the OOPic "pings" the ultrasonic sensor and compares the two readings. If the readings vary by a value greater than the threshold set, the Trekker will move toward the object. �The Ultrasonic should not be able to see the ball since the ball is lower than its field of view.�
�
If during that time the variance changes to a value less than the threshold, the Trekker aborts its "capture" attempt and continues scanning. �When the Trekker does acquire a target, the IR emitter and collector beam located in the "catcher" will be broken by the object, thereby resetting the operation. �When the object is removed from the "catcher" the Trekker will resume the search for objects.�
�
Currently the Trekker will only operate in areas where the maximum distance from a ball is approximately 48".�� It will work with any ball that is about the size of a tennis ball or slightly larger.� The larger ball will be seen by the ultrasonic sensor.
�
