Dreaming Tree (3dsvg.com) has a lovely Light Up Windmill project.   This article tells how I motorized it.

With my husband's help, I added a motor to it.  He designed a 3D-printed motor mount for it, and I added a switch.   

It will take a couple of small modifications to the windmill project:  (see the image below) 

1. Change the top of the turbine housing: Remove the  tab from the top of the rightmost section, and add a small tab to the topmost part of the middle section.  This will let you open and close the housing from the top for battery access.  

2.  Cut a hole in the back to accommodate your switch.  You will also need to cut the same hole in the reinforcing piece that strengthens the wall.

3. Cut 4 extra trim pieces --  the thin ones, not the folding ones,  Since the top will open for battery access,  you need single strips.

Then insert your motor, wire it up to your battery holders and switch  and put into the housing.  Push the dowel piece onto the shaft. Add a pipecleaner 0r paper spacer, and glue on the propeller.  TEST THE ANGLE. 

Here's a link of some  suggested supplies and my notes about future versions...

 The Dreaming Tree Windmill Light Up

3D Print Files for motor and shaft dowel   (zip file - download)

Motor (AliExpress)      --   (Using this one as a replacement in next version --it appears to be the same size-- because the original seller added insane shipping charges,  Also, am going to use a 15 rpm as 30 rpm  was a bit fast for my liking.)

Battery holder (AliExpress)  (my next version I am going to try this one with an integrated switch, hopefully will just be able to pull in and out without any need for a top opening.

 Switch (AliExpress)  -- Not needed if you use a battery holder with a switch, which I plan to do next version. 

Here's a screenshot of the pieces you will need to modify.   

Note: My next version probably will eliminate the back hole and will make the slot large enough to accomodate the cell holder and switch, but still figuring out how to best hold it in place.  May need to ask my husband to modify the 3d file...    I'll post here if that happens.