03 Design principles: why we made it this way

Design principles

The FoamyQuad is build in an H-configuration, rather than the more commonly-seen X configuration. This is to provide you with a nice, big, floating platform upon which you can mount stuff. You can mix and match components a lot more this way, including putting larger batteries, different cameras, video transmission gear, or perhaps a small dog. An X-quad usually has less space available, and it's harder to change things around.

It's built using bamboo spars, which have extraordinary strength and stiffness per weight (somewhere in between fiberglass and carbon fiber), and are easily sourced in most places in the world. In a pinch you can use 20mm wooden doweling, 15mm aluminum tubing, or 15mm carbon fiber tubes (great if you can get them, but expensive and hard to replace). Less than the suggested diameters are not a good idea; 10mm carbon fiber or 15mm wooden doweling may look like a great idea (and look like a nice cost savings) but vibration will cause things to shake apart when you actually try to fly! Don't do it.

The secret sauce here is the 3D printed parts. Basically these solve the problem of mounting things that require a flat surface (like motors) on parts that are strongest if they are round (like spars). This would all be easier if you just used spars with a square cross-section; people have made good quads with square spars made from wood, aluminum, and carbon fiber, allowing them to simply bolt the spars to the fuselage and the motors to the spars. However, round spars give the best strength and stiffness (which is very important for vibration resistance) per weight, so it may be worth the added complexity of round spars, which anyway are pretty easy to use with these 3D printed parts. If you don't have a 3D printer, find a local makerspace or fab-lab, and get someone to print them for you! Most makerspaces, even in poor countries, will have one or two 3D printing enthusiasts who will be delighted to work on this kind of neat project, often for the price of raw materials which is only a dollar or two for the whole quad. The 3D printed parts are also designed to fail in the event of a crash; this is to protect the more expensive and difficult-to-replace parts! Much better to break a motor mount, which can be replaced quickly and cheaply, than to bend a motor shaft.

The quad is held together using elastic bands. This seems a little odd; you might expect something a little more solid! However, this quad is designed to be easily rebuilt after crashes. It's small, light, made from foam, with breakable 3D printed parts, and held together with elastics. Most of the kinetic energy of a crash goes into stretching or snapping elastics, crumpling foam, and snapping 3D printed parts. Your motors and electronics are thereby protected from a lot of potential damage. You can, if you choose, bolt the spars onto the fuselage (there are holes in the mounting brackets to do so), but if you stick with the elastics your quad is more likely to survive your attempts to learn to fly, which we trust will be in a safe environment far from unwary bystanders!

The quad is designed to use the APM-Copter software and flight controller, and configuration settings are provided that will work pretty well right away, provided you use the recommended motors, battery, propellers, and spar lengths (if you want to improvise, go ahead, but you may have to do some tweaking of the flight controller parameters before your quad flies in a stable fashion; our recipe is likely to get you a relatively tame and controllable machine right away). There are plenty of other options for a flight controller, including some VERY inexpensive ones. If you don't need any of the autonomous mission capabilities, you may be better off with a much less expensive flight controller (most of the cost of the FoamyQuad is the flight control gear) without a GPS, telemetry radio, and so forth. The current electronics setup is about $170 worth, and basically gets you an incredibly powerful autonomous flying robot that easily equals or beats the performance of $1000+ commercially-available drones, but if you just want basic stabilization you can go as low as $10 (which will get you something like this which is sufficient to get started manually flying).