This is an educational project I made and published on YouTube. It shows how much rain power (watts) is available from a residential rooftop and the best way to harvest that energy. Most of the parts are 3D printed from a CAD model I made in Fusion 360 which is available for download on GrabCad (search for Quint BUILDs). I did some machining and welding but I've seen others get away with all 3D printed parts or substituting with wood if necessary.

YouTube video part 2 showing construction and testing with details on rectifier circuit:

YouTube part 1 using off-the-shelf DC generator (simpler but less efficient)

Step 1: Fusion 360 CAD Model

This project pretty much requires access to a 3D printer. You don't need to be an expert at Fusion 360, but it's free to download and use and there are tutorials galore on everything you need to know to use it. I recommend starting with the rotor and seeing if you can get the magnets to fit in place to start.

Step 2: Winding the Coils

You don't need a lathe for this, a hand drill will suffice. The fixture is included in the CAD model and is two identical parts that mesh together. The hole in the center fits a 1/4-20 bolt that would easily fit in any drill for spinning and winding the coils. I used 26 AWG magnet wire, winding until the width across the coil approached 33mm.

Step 3: Install Coils in Stator

You'll have to 3D print the stator piece for this of course. Before removing the wires from the fixture you'll want to restrain it with zip ties or wire ties to keep the wires from separating. I applied a little glue where I could before removing the fixture but the ties proved sufficient by themselves. I used super glue or gorilla glue applied to the surfaces and added a little heat to speed up the drying process. Good old-fashioned Shoe Goo worked great to hold the coils in the stator.

Step 4: Assemble the Generator

Here are all the parts laid out on the bench. The stator with coils installed, rotors with magnets installed (magnets were tight enough fit I pushed them in with no glue), housing front and back with bearings installed and 1/4" aluminum shaft. I turned the shaft on my lathe to make it fit in the bearings but have seen people do this with a drill and sandpaper. The bearings are 6mm inside and 19mm outside that pressed right into the housing parts by hand as printed. I hand-tapped the printed parts for fasteners to hold it all together.

Step 5: Mount to Plate

There are a bunch of ways to mount the generator in front of a jet of water. I chose a piece of aluminum diamond plate I had lying around. You could use wood or plastic though the wood could easily swell with exposure to water (which it will get plenty of). I mounted the plate to my vertical pipe with stainless muffler clamps, but feel free to mount it anyway that works best for you and what you have access to.

Step 6: Mount to Vertical Pipe

There are lots of details not covered here that are included in the multiple YouTube videos I published on this project. If I included everything here it would be an entire book. Watch the videos, look at the steps and see if this is something you want to try to tackle. At a minimum you can figure out how much power you'd be able to collect from your roof depending on area and how much height (head) you're able to take advantage of.

Good luck!

Quint