VEX Workcell - Capstone Project - Lab 13

Teacher Toolbox - Facilitating the Cartesian Coordinates page

What the Teacher Will Do:

Instruct students that they will be working together in their groups to read and discuss the information on this page.
- Students can work in the same groups from the previous page, or get into new groups.
- Groups should be discussing the contents of this page with each other, but each student should be individually reading in order to contribute.
- Tell students they will be asked to sketch and label a possible layout design for their Workcell.
  - Remind students that they can have different individual designs ideas.
  - They should discuss the pros and cons of each within their groups in order to decide on which ideas should be included in the group layout.
  - If desired, you can print the image below and have students paste this directly into their Engineering Notebooks while sketching the layouts.
Ensure each student has their device to view this page in the Lab.
Tell students to check in with you at the end of the page.
Once all groups have checked in, bring the class back together and lead a whole-class discussion to wrap up the page before moving on. Guidance for the discussion is provided in a Teacher Toolbox at the bottom if this page.
Circle the classroom as students read through this page and answer any questions that arise.

As you get ready to design your Workcell for the Capstone Project Competition, you have to consider how to code the arm to move to specific locations, such as the Start and End Zones, autonomously. In order to code the arm of the Workcell for autonomous movements, you have to understand the arm’s reachability and the associated (x, y, z) coordinates that the arm will move to. The overlay of the coordinate system changes depending on the location of the arm, and is crucial to understand in order to code the arm to pick up and place disks. Understanding how the Workcell and its arm moves in 3D space was covered in Workcell Lab 3’s Play section.

However, what will the coordinates be if the arm was moved to a new location on the Workcell? On this page in the Play section, you will explore the Cartesian Coordinates of a moved Workcell arm.

Workcell Orientation Activity

As you read through the page, complete the following activity to practice understanding the orientation of the Workcell and how the Cartesian Coordinate system is related to the orientation:

Sketch a placement for the arm of the Workcell in addition to the Start and End Zones.
Label the approximate X, Y, and Z-coordinates of the Start and End Zones on your sketch depending on the orientation and placement of the arm.
Use this image from the Capstone Project Competition rules document (Google / .docx / .pdf) to plan out your layout ideas.

Note: Orientation is the physical position or direction of an object relative to other objects in its surroundings. Remember to think about the placement of the arm relative to the Start and End Zones to determine its orientation.

Cartesian Coordinates of a Moved Workcell Arm

As mentioned in Workcell Lab 3, the (0,0,0) location is found at the center base of the turntable, and is measured to the center of the tool plate on the end of the arm.

This means that the origin is located wherever the center of the turntable is.

If the arm, and more specifically the turntable, is moved from its current location on the Workcell to a new location, the (0,0,0) location also changes.

Image showing the center location of the turntable and the tool plate on the arm

For example, you can see that the origin is still located in the center of the turntable, even though the location of the arm has moved. Furthermore in this image, each tick mark on the X and Y-axes represents one inch.

This is important, because the X, Y, Z-coordinates that the arm can extend depend on the actual location of where the arm is mounted. This means that the coordinate system changes if the placement of the Workcell arm is moved.

Lab 13 build with the X and Y axes grid overlay

The orientation of the turntable, more specifically the potentiometer inside the turntable, is what designates the coordinate system.

Rotating the potentiometer will change which direction the X and Y-axes face.

In this example, the arm, and more specifically the potentiometer, are facing the V5 Brain. This orients the positive X-axis towards the V5 Brain.

In this example, when the arm is rotated 90 degrees, the potentiometer also rotates 90 degrees.

This orients the positive X-axis towards the End Zones.

Lab 13 Build Layout showing the cartesian grid rotated 90 degrees

Potentiometer orientation facing the End Zones

The Z-axis always remains the same no matter where the position of the arm is mounted on the Workcell.

This is because the Z-axis is 0 when the tool plate is touching the base plate of the Workcell.

The positive Z-axis is above the base plate and the negative Z-axis is below the base plate.

When planning out where elements will go on your Workcell, one helpful piece of information is using the Manual Move example project in VEXcode V5. This example project will display the current X, Y, and Z-coordinate values of the end effector. For more information about this example project or how it works, view Workcell Lab 3’s Play section.

This is helpful to map out the coordinate grid and where certain elements can be placed in order to ensure the arm can reach them.

V5 Brain screen showing the current X, Y, Z-coordinates

Teacher Toolbox - Solution

Below is an example solution to the following prompts that students were asked to consider at the top of the page:

Sketch a placement for the arm of the Workcell in addition to the Start and End Zones.
Label the approximate X, Y, and Z-coordinates of the Start and End Zones on your sketch depending on the orientation and placement of the arm.

Again, this is just an example. The labeled (x, y, z) coordinates here are not labeled to exact scale. The example is used to show how a placement of the arm of the Workcell can be used to establish the coordinate system and the associated (x, y, z) coordinates of the Start and End Zones.

Discuss with students the different quadrants associated with a new placement of the arm. For example, the red disks and half of the blue disks are in quadrant I in this example. That means that both the X and Y-values will be positive.

Teacher Toolbox - Check in

After students have reviewed the entire page, bring the groups together for a discussion.

Ask students to demonstrate how each X, Y, and Z-axis is associated with the arm of the Workcell, or more specifically the potentiometer.
- Students should be showing that no matter how the potentiometer is oriented, the X and Y-axes will remain relative to the position of the potentiometer (the X-axis perpendicular to the long sides of the potentiometer, and the Y-axis perpendicular to the short sides of the potentiometer).
Ask students to share their sketches for the placement of the arm in addition to the Start and End Zones. Being able to see how other groups are already thinking about their Workcell design can help students see different perspectives and gain inspiration from others. It's also a great way to help correct any misconceptions or incorrect labeling of (x, y, z) coordinate values before students move on.

Teacher Tips - Labeling the X, Y, and Z-axes

When students are trying to remember the coordinate axes on the Workcell, especially when the arm is moved around the base plates in new orientations, it may be helpful to label the axes. You can label them using tape, sticky notes, or even dry-erase markers.

This image shows an example of the axes labeled on Lab 2's build using tape, however, this method can be applied to the Workcell no matter the layout or marking materials.