VEX CTE - Unit 4 - Controlling the Path

In the previous Units, you have had the Magnet Pickup Tool attached to your 6-Axis Robotic Arm and used that to pick up and move Disks on the CTE Tile. In this Unit, you will change the end effector to the Pen Holder Tool and use a dry-erase marker to draw on the Tile with the Dry-Erase Surface.

In this Lesson, you will:

follow build instructions to change the end effector and add the Dry-Erase Surface.
learn about how to use the Pen.
draw a line on the Tile.

Watch the video below to see the 6-Axis Arm draw a diagonal line across the Whiteboard surface using the pen.

Changing the End Effector

In the previous Unit, you learned about different end effectors that can be used with the 6-Axis Robotic Arm. Follow along with the steps below to change your build.

Open and follow along with the steps in the 3D Build Instructions to build the Direct CTE 6-Axis Arm Base + Whiteboard.

6 Axis Arm with pen attachment and whiteboard attached to the tile.

Coding the Pen

In order to code the 6-Axis Arm to move the Pen and draw on the whiteboard, there are some things we need to consider and build into a project. In this Lesson, you will get started coding the Pen.

Setting the End Effector in VEXcode

In the projects in this Unit, you will notice a new block, the Set end effector block.

VEXcode EXP project with a red callout box around the Set end effector block. The parameters in the block are set so it reads, 'set arm end effector to pen'.

The Set end effector block is used to communicate to the 6-Axis Arm what end effector is being used so that it can set the new Tool Center Point (TCP). The end effector can be changed by using the dropdown option on the block.

Set end effector block with the dropdown menu open showing the choices 'magnet' and 'pen'. There is a black checkmark beside 'pen' to show it has been chosen.

In Unit 1 you learned that the (x, y, z) coordinates of the 6-Axis Arm are determined using the distance from the origin to the TCP.

Top down image of the 6-Axis Arm with the Pen Holder tool attached. A red dot is placed on the top of the Pen Holder Tool with a red arrow pointing to it. A pop out side view image of the 6-Axis Arm shows the marker tip facing down in the Pen Holder Tool with a red dot on it, and another red arrow calling it out.

The TCP of the Pen is at a different z-value than the Magnet. If the Set end effector block is not used to adjust the end effector, the 6-Axis Arm may provide inaccurate coordinates or move to an unintended location.

Close up side view of the Pen Holder Tool with the marker, and the Magnet Tool to compare the TCP of each end effector, showing the difference in height.

Drawing a Line

Now that you conceptually understand the parts of the project, follow the steps below to create and run the project and see a line drawn on the whiteboard.

Open a New Blocks Project and recreate the project shown here.

VEXcode EXP project beginning with a When started block, followed by: set arm end effector to pen, a comment reading 'Move to point A', Move arm to position x: 150 y: 50 z: 0 m m , Wait one second, a comment reading, Move to point B, Move arm to position x: 50 y: 150 z: 0 m m.

Look at the blocks in the project. How do you think the 6-Axis Arm will move based on this project? Record your prediction in your engineering notebook.

The project from above with a red callout box around the blocks below the When started block indicating that the blocks should be used for making a prediction.

Be sure the 6-Axis Arm is connected to VEXcode. Run the project.

Observe as the 6-Axis Arm uses the Pen to draw a line from the first coordinate to the second on the whiteboard.

The upper right corner of the VEXcode EXP Toolbar with the Run button highlighted with a red box.

Stop the project once the 6-Axis Arm has stopped moving.

How does the movement of the 6-Axis Arm compare to your prediction above? Record these comparisons in your engineering notebook.

The upper right corner of the VEXcode EXP Toolbar with the Stop button highlighted with a red box.

Check Your Understanding

Before moving to the next Lesson, ensure that you understand the concepts in this Lesson by answering the questions in the document below in your engineering notebook.

Check Your Understanding questions > (Google Doc / .docx / .pdf)

Select Next > to learn about coding the movements of the 6-Axis Arm to avoid obstacles.

Lesson 1: Using the Pen