STEM Robotics 4 All

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Lesson 2: Motion with no Sensors (Scratch)

The RoboMentors will introduce you to use of EV3 motors using Scratch without sensors.

What You’ll Learn:

  • Measure distances with Port View
  • Analyze the mechanics of the mission
  • Construct a passive mechanism sliding on the wall.

What you might want to review how to use :

  • the Port View on your brick
  • the basic motion blocks to write a Scratch program

Lesson 2 Preliminaries contains a series of of videos from the Carnegie-Mellon curriculum. If you want to learn more about it and watch more similar videos please check it.

Let’s Get Started!

The Mission 02 Step Counter

Robots need precise, step-by-step instructions to complete a task. Such a set of detailed notes that the programmer can use to write the code when they are ready is called pseudo-code.

  • use the mat drawing + post-its 
  • each season FLL provides a mat (jpeg) that you can import in your phone and start scribbling on it

Position your robot in the base, open on the brick PortView, check that the motor readings are in degrees (deg). Slightly push down the robot to ensure that both wheels are moving and read the numbers in the end.

Passive Mechanisms

Analyze the position and the mechanism to identify the challenges and advantages. Create a mechanical alignment to square up against the mission model and consistently align your attachment against the structure of the mission.

Advantages of M02

  • it is close to the wall
  • there is an almost straight path to the swing
  • it is not too far away from base, and not in a crowded space

Challenges of M02

  • while pushing it get can stuck if the side white-grey pendulum swings too wildly 
  • while pushing it the side white-grey pendulum needs to swing a little
  • the white-grey pendulum is very small

Analysis Results:

  • Close to the wall
    • can be solved with a wall following mechanism
      • Mechanics: use wheels to roll on the wall, make sure that you mechanism does not buckle
      • Programming: do not drive straight, drive slightly into the wall
  • An almost straight path to the swing
    • Very easy Programming suitable for beginners: you can use dead-reckoning by driving straight without sensor control
  • Not too far away from base, and not in a crowded space
    • you can use a passive attachment, that you can leave in place
  • The side white-grey pendulum should not swing too wildly, but it should be free to swing a little 
    • create a channel to constrain the position of the white-grey pendulum into it
  • The white-grey pendulum is very small
    • it would be difficult to be precise, so use a funnel the white-grey pendulum
Passive Mechanism

A video summarizing the lesson and including the Scratch code as well as a demonstration:

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© The Robo Mentors (Marc and Anne-Sarah)

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