In the custom drone community, there are fun body modifications made of styrofoam called “foamies.” These are shaped, lightweight bodies that slips over your drone to give it a stylized appearance. We’ve seen everything from imaginative one-off aircraft to crazy recreations of ships from Star Wars.
To build your own foamie for your drone, you’ll need to know how to cut, glue, and finish foam. These guidelines are useful not only for drone modifications, but for any forms you’d like to create with foam.
Choosing a Foam
Walk into a hardware store, and you’ll be faced with two main types of foam: extruded polystyrene and expanded polystyrene.
Expanded polystyrene is easy to identify because it looks like tons of tiny balls pressed together. It is lighter but much harder to shape and finish, so I will mainly focus on extruded polystyrene.
Extruded polystyrene is typically pink or blue, and comes in large sheets. It cuts easily and can be sanded and painted very well. It can be slightly heavier, but much easier to work with at home.
Cutting and Shaping
For any custom body type, you’re going to have to cut some foam. For extruded polystyrene such as the blue foam board insulation, you can cut it well with any sharp blade. Often it isn’t even necessary to cut all the way through, you can simply score it and then snap along the scored line.
If you’re going to cut a lot of foam, or desire to work with expanded polystyrene, you’ll want to get a hot wire cutter. (Build your own with these instructions.) These use a bit of electricity passed through a wire to produce enough heat to cut smoothly through the foam. Cutting expanded polystyrene without one is a nightmare — the knife will rip the tiny balls loose, resulting in a jagged and messy cut.
In many cases, you’ll need to glue several bits to get a large enough block to start with. Sticking two pieces of foam together can be more difficult than it sounds. Do not use any glue that contains a solvent. Solvents will eat through your foam, leaving visible dents and craters. Some glues also struggle to dry when not exposed to air, which is exactly what happens when you’re sticking two sheets of foam together.
Gorilla glue dries quickly and adheres foam together quite well. It expands as it dries, so expect to clean up some edges. Don’t be surprised if you have big bulging yellow globs around the perimeter after a few hours.
A neat trick that has surfaced in online forums is to use a paint primer called “Gripper” by Glidden. It dries quickly and bonds sheets of foam together as well as any glue. The resultant bond can be sanded and cut just like normal.
No matter the method, you should apply pressure to the two pieces of foam being joined to avoid any gaps that will become visible as you cut shapes from your block.
After you’ve cut the foam to your desired shape, you can further refine things with simple sandpaper. You can get very nice results sanding extruded polystyrene with medium grit sandpaper. Start with a low grit, like a P100 to shape the body, then work your way upward to a higher grit to get the surface smoothness you want.
After your surface is reasonably smooth, you can apply a material to it for proper aesthetics and protection from bumps and bangs. While a prop builder might go at this job with Bondo or other automotive body putty, a drone customizer needs to consider weight above all else.
Pen/marker — Sometimes you’re perfectly fine with it looking like a piece of foam. Sometimes the shapes themselves are enough to convey the custom form you want.
Paint — A layer of paint can give the visual appeal you’re after without much addition to weight. This option offers the least protection, so rough
landings may leave your custom drone with some battle scars that aren’t easily repairable.
A layer of glue or resin — Painting on a layer of PVA glue and letting it harden will create a shell. This won’t be unbreakable armor, but will be slightly more robust than a simple layer of paint, at the expense of a tiny bit of weight. You can then paint on top of this.