I'm a physics teacher, and I am for the first time (thanks to the efforts of our team) teaching an "Introduction to Robotics" course next year in the high school, tied to the efforts of Team 1551. This is exactly the kind of thing I was hoping to find online somewhere.
Vocabulary is *key* when writing a textbook that you want to be transparent to students. I suggest that you (literally) give the chapters to a convenient seventh or eighth grader who is rather average in their overall science/technology background, and ask them to highlight/ask about any words they do not know. Make a glossary including those words, plus any others you might think prudent (like 'stall' in the concept of a motor).
If the intent is to publish this as a .pdf file, then make all vocabulary works linkable to the glossary.
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And on a side note, when not hurriedly typing forum posts before my dinner gets cold, I'm pretty good with English. It was one of my minors in college, and I have some published work floating around out there. I would be more than happy to help edit anything you do.
...that said, I do *not* have time to do raw creation stuff. As FIRST winds down to summer levels, beekeeping picks up, and I'm just as busy as ever! (Oh, and did I mention that I have a brand new class to create from scratch by September, in my nonexistent free time?
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But anyway, I pledge my services as an editor to this enterprise.
Good luck, and thank you so much for doing it. An absolutely fantastic idea.
Patrick