I was looking for a Duplo helicopter for my nephew for Christmas but couldn't find one with just a helicopter so I made one. He's 3 so I wanted to keep it simple and only put 2x2 Duplo sized studs in the cockpit for a Duplo figure and made the rest kind of fisher-pricey. Works well with all the Duplo bricks I have tried with it so far. I was having some printing issues with larger objects so I also tried it at 1/2 scale which makes the studs regular lego size. I guess the printer isn't up to the tighter tolerances needed for lego because at this scale the lego parts are a bit hard to get on though they do work.

I think of my self as an artist and not an engineer so the tolerances are less than great and it may have some pretty big design and structural issues. My 1:1 Duplo print mostly clicked together and holds without glue but I had to clean and sand some of the parts a little bit more than I would have liked to make it work. Had to really sand the holes for the rotors so they would spin freely. I printed these on my UP! with the normal and .25 mm settings. Maybe with fine and .20mm settings it would work a bit better?

Print and clean up parts. Sand top, bottom and inside of rotor holes and the post part of the rotor pegs till they slide on and spin freely.

Snap together.

Mine all clicked together and held. Might be a good idea to add a little glue before snapping together to make it a bit stronger.

Oh, there are two rotors. I liked the original slightly larger rotor I made but it didn't fit on my UP! so I made a slightly smaller version. Either will work and the smaller UP! version is in my photos on the Duplo 1:1 print while the 1/2 scale print has the full size rotor since it fit on the printer at that size.