Thanks, I hadnt looked in detail at the design calculator, I will give that a shot. The biggest thing is that I want them to UNDERSTAND it, rather than just throwing some numbers in a spreadsheet...
So I think I will try to borrow the formulas and explain it to them before I show them the sheet.
Richard - thanks for the reference to the post, I will see if that helps them make more sense of it!
And as for the bathroom scale, they have come up with ways of "testing" but Im trying to get them to do the true engineering... DESIGN it first, then see if your calculations match what the real measured values are... if not, why??
Thanks for the help so far!