Exploring Velocity - Python

• Activity Outline
  This exploration will first introduce students to setting the velocity for driving and then ask them to explore how the velocity of the robot affects its momentum. Click here (Google / .docx / .pdf) for the outline of this activity. Understanding the momentum of the robot will be an important concept to apply to the Strike Challenge bowling game.

• What the Students will Program
  Using the Speedbot (Drivetrain 2-motor, No Gyro) template project allows the students to change the velocity settings of the Speedbot simply by adding set_drive_velocity to the drive_for instruction. The guided part of the activity has students moving the Speedbot at different velocities and the end of the activity asks them to apply their skills for programming velocity to tests of momentum and energy transfer.

Here is an overview of the User Interface of VEXcode V5. Students will be introduced to these tabs/buttons during the activities in this Momentum Alley STEM Lab. Links are also provided throughout the STEM Lab to provide more information about these tabs/buttons.

If this is the student's first time using VEXcode V5, they can reference the Tutorials at any time during this exploration. The Tutorials are located in the Toolbar.

Model each of the troubleshooting steps for the students.

• Project Names can have spaces between or after the words.

  

• You can ask students to add their initials or the name of their group to the project name. This will help differentiate the projects if you ask the students to submit them.
• Because this is the first activity with programming your students may attempt, you should model the steps, and then ask students to complete the same actions. The teacher should then monitor the students to ensure that they are following the steps correctly.
• Make sure that the students have selected Open Examples from the File menu.
• Make sure that the students have selected the Speedbot (Drivetrain 2-motor, No Gyro) template project.
• You can point out to the students that there are several selections to pick from on the Examples page. As they build and use other robots, they will have a chance to use different templates.

• Point out that when they first opened VEXcode V5, the window was labeled VEXcode Project. VEXcode Project is the default project name when VEXcode V5 is first opened. Once the project was renamed Drive and saved, the display was updated to show the new project name. Using this window in the toolbar, it is easy to check that the students are using the correct project.

• Tell the students that they are now ready to begin their first project. Explain to the students that by just following a few simple steps, they will be able to create and run a project that will move the Speedbot forward.

• Remind students to save their projects as they work. The Python section from the VEX Library explains saving practices in VEXcode V5.

This is a good point to pause and have the students review the steps that were just completed on starting a new project in VEXcode V5 individually or in groups. Ask the students to reflect individually before sharing within their group or to the whole class.

Notice that the second and third instructions (Lines 33 and 34 in the image above) are the same as the fourth and fifth instructions (Lines 35 and 36 above), but with a different velocity parameter. After adding the third instructions, students can highlight the lines to be repeated and copy and paste them to complete the project. They can then change the velocity in the fourth line to 75 percent. 

• Remind the students to disconnect the USB cable from the Robot Brain. Having the robot connected to a computer while running a project could cause the robot to pull on the connection cable.

• Stop and Discuss
  Ask the students to predict what they think will happen when this project is downloaded and run on the Speedbot robot. Tell the students to record their predictions in their engineering notebooks. If time allows, ask each group to share their prediction.

  Students should predict that the Speedbot will first move forward at its default velocity (50%), then slower (25%) than the default velocity, and then faster (75%) than the default velocity.

• Model First
  Model running the project in front of the class before having all the students try at once. Gather the students in one area and leave enough room for the Speedbot to move if it is placed on the floor.

  Tell the students it is now their turn to run their project. Make sure that they have a clear path and that no Speedbots will run into each other.

• To change the drive_for command from forward to reverse, simply change the first parameter to REVERSE. This will have the motors in the drivetrain move in the opposite direction.

• The number of mm can be changed, but for this example we will leave them at 150 mm as set in the previous step.

• Remind students to disconnect the USB cable from the Robot Brain before running the project.

• Remind students to save their projects as they work. The VEX Library has a section for Python that explains saving practices in VEXcode V5.

Ask teams to share the testing area and ball if necessary, but multiple testing areas each with their own ball could also be set up. Decide whether you want to set the testing area(s) up, or if you want students to do so.

• Data collection and analysis, even simple pattern recognition, are fundamental science skills. This activity adds structure to that data analysis by preventing common missteps.

• Notice that the instructions do not tell students to vary the driving distance of the robot along with varying the velocity of the robot. This is an intentional application of what learning scientists call the Control of Variables Strategy. Teaching novice investigators to manipulate one variable at a time (i.e., the velocity in this case) to determine its influence on a second variable (i.e., the distance the ball travels after collision) is important because it is not necessarily an approach students will adopt spontaneously over a guess-and-check approach. Typical guess-and-check approaches often manipulate more than one variable at a time (i.e., changing both the velocity and the distance the robot travels) and observing the confluence's impact on the distance the ball travels after rotation. This activity tries to guide students away from that because the relationships between the variables are then ambiguous. Is it the higher velocity of the robot, the farther distance the robot drives, or both that lead the ball to travel farther? We can't answer that when we manipulate both variables at the same time.

• However, teams might spontaneously try driving the robot different distances. If you observe this, ask them only to change the distance but keep the velocity the same as it was in a trial with the original 500mm distance. That way, they can compare the same velocity with different driving distances to see if the robot's driving distance also factors into how far the ball travels.

• Prepare the area for the ball to bounce in varying directions for varying distances. Close doors and/or windows as needed.

• The table for Exploring Velocity can be saved from below, or students can recreate the table in their engineering notebooks.

• A rubric for evaluating team engineering notebooks can be found here (Google / .docx / .pdf), and a rubric for evaluating individual notebooks can be found here (Google / .docx / .pdf). Whenever you plan to evaluate student work with a rubric(s), be sure to share the rubric with them before they begin to work on the project.

1. The movement of the ball is evidence that the robot transferred energy during the collision. Students might also describe the speed of the ball after impact or its direction of travel as evidence.

2. The distance that the ball travels depends on the mass/weight of the ball used and the velocity set for the robot.

3. Students should recognize that higher velocities lead the ball to travel farther than lower velocities. Explicitly connect this to the momentum of the robot. Highlight that the weight of the robot has not changed, only its velocity, but that both contribute to the robot's momentum. Ask them if they think the ball would travel as far if the robot was heavier. It presumably would. There is more about the effects of the mass of the ball during the collision in the next reading.

4. Student groups might have selected widely variable velocities but the overall learning objective is for students to recognize that higher velocities lead to greater momentum which transfers more energy to the ball during collisions.