Lesson 2: Stacking Cubes

Previously, you learned about how to code the 6-Axis Arm to pick up and place Cubes onto a pallet. You then revisited that skill in the previous Lesson as you learned how to make and implement a plan for a VEXcode project.

In this Lesson, you will:

• Create a plan to stack Cubes on a pallet.
• Code the 6-Axis Arm to stack Cubes on a pallet.
• Change z-axis coordinates to account for the height of a Cube to create a stack.

By the end of this Lesson, you will plan and build a project where the 6-Axis Arm creates two stacks of two Cubes on the pallets.

While building the plan, many elements from the Lesson 1 plan were reused. You will notice as you build more and more plans that there will be common elements you can reuse. This is helpful when you get to more complex projects. You can look back through your engineering notebook, study the plans and related VEXcode projects that were built, and use elements of those successful plans in new projects.

After creating the plan for stacking Cubes on the pallet, we can prepare to implement this plan in VEXcode. 

The z-parameter in the Increment position block will lower the 6-Axis Arm the distance necessary to stack the second Cube on top of the first. To figure out what that value is, we need to know the location of the Magnet when the two Cubes are stacked on each other. This offset can be used to help us figure out how far the 6-Axis Arm needs to move along the z-axis to stack the Cube effectively. 

Using what we know about the height of the Cube and the height of the pallet, we can approximate the offset of the z-coordinate to be 65mm. Each Cube is approximately 25mm tall and the pallet is 15mm tall.

There are two ways to determine how far down on the z-axis to move the 6-Axis Arm.

1. To move from the starting position (100mm) to the desired position, you can determine the difference. 100mm – 65mm is approximately 35mm. To avoid any collisions between the bottom of the second Cube and the top of the first, you can subtract another 5-10mm. Moving the 6-Axis Arm in the negative direction along the z-axis for approximately 25mm will enable the second Cube to be stacked in the desired position. 
2. You can also use the Monitor Console to find the z-value at the top of the stack of Cubes. This information from the Monitor Console can be used to help figure out the relative movement needed to lower the 6-Axis Arm to place the Cube effectively. In the project we are building, the z-coordinate is set to 100mm when the 6-Axis Arm moves above the Cube on the pallet. This is the starting position of the 6-Axis Arm for this relative movement. The z-value of the 6-Axis Arm's position on the top of the stack in the example shown here is 73mm. This is the desired position of the 6-Axis Arm when the placing the Cube on the stack. 
   
   To move from the starting position (100mm) to the desired position (73mm) is approximately 28mm. Moving the 6-Axis Arm in the negative direction along the z-axis for approximately 25mm will enable the second Cube to be stacked in the desired position. 

The 6-Axis Arm picked up and moved two Cubes to the pallet, stacking the second on top of the first. 

Activity

Now that you have made a plan and coded the 6-Axis Arm to stack one Cube from the loading zone on top of another on the pallet, you will practice these skills. In this activity, you will build on your project from this Lesson to code the 6-Axis Arm to stack two additional Cubes onto the second pallet.

Setup: Place one Cube in the loading zone on Tile location 17.

Activity: Code the 6-Axis Arm to stack two Cubes on each pallet.

1. Follow the process you have learned to make a plan for how to code the 6-Axis Arm to stack two additional Cubes on the second pallet with your group. Be sure that you are all agreed on your approach before you begin building onto your project. You can build onto your project from this Lesson.
   1. Document your plan in your engineering notebook. Be sure you have decomposed each step into the smallest possible behaviors. 
   2. Once you have created and documented a plan, review your plan with your teacher.
2. Build onto your project in VEXcode to match the plan your group agreed upon. 
   1. Rename your project Unit 8 Lesson 2 Activity and save it before you begin editing the project.
   2. Use Comment blocks in your project to organize your project to match your plan.
3. Run the project incrementally to test it. Manually place each of the Cubes in the loading zone once the previous Cube has been moved.
4. Does the 6-Axis Arm successfully create both stacks of Cubes the way you planned? There should be one stack of two Cubes on each pallet. If not, continue to edit the project until you have successfully created two stacks. 
   1. Be sure to document any adjustments to your plan in your engineering notebook. 

Check Your Understanding

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

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

Select Next > to move on to the Putting It All Together activity.