Evo OzoBlockly Lesson: Emergency Automatic Breaking

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1 OZO AP P EAM TR T S BO RO VE D Evo OzoBlockly Lesson: Emergency Automatic Breaking Created by Richard Born Associate Professor Emeritus Northern Illinois University richb@rborn.org Topics Robotics Computer Science Programming Ages Grades 7-12 Duration 40 minutes

2 Evo OzoBlockly Lesson: Emergency Automatic Breaking By Richard Born Associate Professor Emeritus Northern Illinois University Introduction Systems that can help drivers avoid front-to-rear crashes are becoming more and more common, with the number of such systems for cars doubling in the past four years. These systems use sensors to detect when a car is getting too close to a car in front of it. The simplest systems provide warnings to the driver, while some go further by providing the capability of emergency automatic breaking. The goal is to save lives, and at the very least, to reduce the severity of injuries by lowering speeds involved in a crash. In this lesson students will investigate an OzoBlockly program that makes use of Evo s IR (infrared) sensors to provide automatic emergency breaking. The program is only twenty blocks in length, but the logic involved is subtle enough that a careful discussion of the program with students is encouraged. The EvoMap for This Lesson Evo will be doing line following, not free movement. Figure 1 shows the EvoMap in reduced size for discussion purposes. A full size version of the map for duplication and use with Evo can be found on the last page of this document. Figure 1 1

The large circle is the road on which the Evo s will be traveling. At least two Evo s are required, but the author has used three as well, all traveling at different speeds.

3 The large circle is the road on which the Evo s will be traveling. At least two Evo s are required, but the author has used three as well, all traveling at different speeds. In makes no difference if the Evo s are traveling clockwise or counter-clockwise, but they should all be going the same direction. The Evo s can be placed anywhere along the road before starting the OzoBlockly stored OzoBlockly program. The purpose of the short spokes along the road will be explained during the discussion of the OzoBlockly program. It is suggested that the video be viewed at this time to clarify what the OzoBlockly program accomplishes. You will notice that when Evo is moving, the LED is green. When one Evo approaches another within a distance equal to that between adjacent spokes on the road, the Evo in back stops on a spoke and changes its LED to red. It remains red and stopped for a few seconds before continuing its journey along the road. Meanwhile, the Evo in front continues its journey without experiencing a read-end collision. See the photo of Figure 2 for a still shot. As indicated by the arrow, all Evo s are traveling clockwise along the road. The Evo with the RED led has stopped on a spoke so that it wouldn t collide with the Evo on the far right of the image. Meanwhile, the Evo on the far right has continued moving around the circular road without having experienced a rear-end collision. The OzoBlockly Program Figure 2 Figure 3 shows the OzoBlockly program that is running on each of the Evo robots. Initially, each of the LEDs is set to the color white, the speed of Evo is set, and then there is a two second delay before Evo starts moving. The author found that with three Evo s traveling around the circle, speeds of 30 mm/s, 40 mm/s, and 50 mm/s worked very well. You don t want the speeds to be identical, as this would tend to keep the Evo s equally 2

4 spaced as they travel, seldom experiencing near collisions. The two second delay makes it easy for the student to press the start button once to turn Evo on, and then press the start button two more times to start the stored program. Figure 3 The outer repeat forever loop is intended to keep the Evo s moving until they are turned off or until their batteries runs out of power. The LED is set to the color green, and Evo is instructed to follow line to next intersection or line end. Since there is no line end, it will follow the line to the next intersection, i.e., the next spoke on the circular road. The red LED then turns on, but ONLY for a short, unnoticeable instant of time, unless Evo is delayed in the inner repeat forever loop. Evo will be delayed for 4 seconds in this inner loop if either or both of its front sensors sense another Evo in front of it. Otherwise Evo will break out of loop very quickly and continue the next iteration of the outer loop, where the LED is set to the color GREEN again. So we see that we can end an infinite loop by breaking out of the loop when desired. By reading both the right front and left front proximity sensors, it makes no difference if the Evo s are moving clockwise or counterclockwise (as long as they are all moving in the same direction). When moving clockwise the right front sensor is more sensitive to a nearby Evo, whereas when moving counter-clockwise, the left front sensor is more sensitive. Classroom Activity After discussing the OzoBlockly program with the class, the teacher can have different students or student groups create the program in OzoBlockly, and then load the program onto Evo. Once again, speeds of 30, 40, and 50 mm/s worked the best. Higher speeds are much more apt to result in rear-end collisions, but they are quite rare with the recommended speeds. Students should be encouraged to explain why collisions are more likely at fast speeds, and how the program or the EvoMap could be adjusted to reduce the risk of rear-end collisions at high speeds. 3

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Ozobot Art OzoArt! Created by. Richard Born Associate Professor Emeritus Northern Illinois University Topics

Ozobot Art OzoArt! Created by. Richard Born Associate Professor Emeritus Northern Illinois University Topics OZO AP P EAM TR T S BO RO VE D Ozobot Art OzoArt! Created by Richard Born Associate Professor Emeritus Northern Illinois University richb@rborn.org Topics Robotics, Computer Science, Programming Ages Grades