The engineering work starts here as you bring your creative concepts into reality. Your design assumptions and calculations are part of your Phase I submission. What safety considerations were made, for the construction phase as well as the operations phase, including how to handle the heavy rock sample.
Why did you make certain choices? What initial assumptions did you need to correct? How did you decide between options with greater functionality but higher costs? The judges will look for how much you learned, not just the machine you created.