Hi Deepa,
I am a head judge at tournaments each year and this comes up frequently. First, many teams don't do any type of model. It's not "required". However, as you have looked at the rubric, you have seen that indeed models are mentioned. In the CREATE Category we have this:
CREATE – Team developed an original idea or built on an existing one with a prototype model/drawing to represent their solution.
Level 1 (Beginning) states "Unclear model/drawing of solution"
Level 2 (Developing) states "Simple model/drawing that helps to share the solution".
Level 3 (Accomplished) states "Detailed model/drawing that helps to share the solution".
Just like the statement says, drawings are fine. They can be hand drawings, or CAD, or something in between (MS Paint, powerpoint, you name it). Models are also fine. They can be Lego, cardboard, plastic, baling wire and gum, cloth, you name it. My team actually used concrete a few years ago! Whatever works for your team. It doesn't have to be a working prototype. Anything that helps clarify or visualize your team's solution.
Again, none of this is required.
I hope that helps!
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