OT? expression for position controller

Hi all, I'm totally illiterate on scripting, I'm just trying to teach my 8 years old nephew a couple of tricks applying some math to graphics, I'm here searching for little help from some guru and hoping not to be too much OT!

I assigned a position expression controller to a box moving upward along an helix

[100*cos(720*NT), 100*sin(720*NT), 100*NT]

I want to modify this expression (or create a new one) so the box continues to move as previously, but also - if you see it from top view - it moves linearly on the XY plane: ie, from point 0,0,0 to 100,100,0 and then to 200,100,0. I want to include this movement in the expression, not animating by hand, path, etc. To be useful for the kid, I would like to apply vectors theory shown here:


I accept any type of advice, thank you!