Choosing an Airframe for Your Quadcopter Drone
The main project of the book is a four-bladed helicopter (pictured in Figure 4.1) called a quadrotor or quadcopter. You’ll begin the project by choosing a chassis, which in the plane world is called an airframe.
FIGURE 4.1 Build this quadcopter yourself!
This chapter begins by presenting you with a number of chassis options, but ultimately (spoiler alert!) I went with a set of MakerBeam aluminum girders that I bolted together into a fine airframe. I then topped this off with a handy wooden platform that will eventually house the quadcopter’s microcontroller, battery pack, and other electronics.
I’m getting ahead of myself, though! Before we get to the MakerBeam build, let’s check out a bunch of other options, including commercial products and DIY possibilities. Once we check those out, I’ll guide you through assembling your own MakerBeam airframe.
The funny thing about a drone or robot’s airframe is that it’s mostly just there to hold everything together, so consequently any reasonably rigid, strong, and lightweight material could be (and has been!) used to build a chassis. Sometimes this is done to hilarious effect, with all manner of odd things—recall some of the projects from Chapter 2, “Showcase of Cool DIY Drones.”
There are wood airframes, plastic ones, and metal ones. If it’s reasonably strong, light, and you can bolt stuff to it, chances are it will work as a chassis. That said, some airframes do offer considerable advantages.
For instance, the airframe pictured in Figure 4.2, from Parallax’s ELEV-8 quadcopter, features lightweight aluminum tubes for the motor booms, with plastic mounting lugs designed specifically to mate with the motors and other components that come with a kit. It’s to be expected, but it’s kind of nice knowing everything will fit together.
FIGURE 4.2 The Parallax ELEV-8 features a lightweight airframe made out of plastic and aluminum.
This effortless compatibility and more polished appearance are a couple of advantages offered by commercial airframes. In the next section, we’ll go over a number of features of these products to take into consideration when making a purchase.
Choosing Between Commercial Options
Let’s go over the criteria one might consider in choosing an airframe. The following list discusses some of the features to take into consideration:
- Appearance—Anyone can make homely. If you’re paying money for a chassis, it should look like it was designed and machined by professionals. It should look better than what you’d whip up in your basement.
- Configuration—How many motors will your copter feature? The number of motor booms is not the only configuration-related question to think about. Will you want to mount a camera on it? Depending on where you put the camera, you might need landing struts. The most common airframe is the now-classic quadcopter, featuring four motor booms with a central plate that supports the controller and batteries.
- Dimensions—How big of a quadcopter do you want? My Parallax ELEV-8 is over 2 feet across, and it’s considered only typical by quadcopter standards. Keep the overall needs of your project in mind, as well as the technical specifications of your motors and props. Don’t be hesitant to try out a smaller project first—the motors and other components may be cheaper because their technical requirements are less demanding.
- Material—As I mentioned, pretty much any reasonably lightweight and sturdy material can be used for an airframe. That said, aluminum and plastic—or a combination of the two—are the most popular.
- Mounting hardware—This one is huge for me. What use is a cool airframe if you can’t easily bolt your components onto it? Wanting to have motors that easily bolt onto an airframe often means having specialized plates and attachments, although this isn’t required. Many quadcopters have been built that are held together mostly with duct tape and zip ties.
- Price—I see a big difference in prices, but sometimes it’s not so apparent what you’re getting for the extra dough. With all hobbyist hardware, there are some categories of product that have cool screen-printing on the housing and cost twice as much, but ultimately aren’t all that impressive.
- Strength—The dirty secret of quadcopters is that they crash—a lot! They’re constantly plowing into the turf after batteries run out or a technical glitch occurs. How durable of a drone are looking to build? On the other hand, with strength often comes weight, and what good will it be to have an indestructible quadcopter that can’t make it off the ground? Which brings us to...
- Weight—The final criteria to consider is weight. The lifting power of your motors offsets the weight of the chassis, and if you have monster motors and props, you can get away with a more robust airframe.
Making Your Own Airframe
Although buying is always an option, it’s definitely best to build an airframe if you have the time, the tools, and the materials. That way, you can have the perfect airframe for your needs, and you can take pride in having created something!
The following sections discuss the three basic ways to create your own airframe.
With a building set, instead of designing anything, you simply build your airframe out of plastic or metal beams. Most DIY kits involve the bolting together of parts anyway—granted, custom parts rather than stock parts—but you can still see how easy it would be to build your own airframe.
In this chapter, I show you how to use a convenient and clever aluminum building set called MakerBeam to build a chassis, as seen in Figure 4.3.
FIGURE 4.3 Build an airframe just like this with the steps shown later in this chapter.
Another option is to print your own airframe using a 3D printer, a tool that creates three-dimensional objects out of melted plastic. There are already a bunch of quadcopter parts on Thingiverse, a site featuring 3D-printer files that can be freely downloaded. Take, for example, the T-6 Quadcopter, pictured in Figure 4.4. Its creator, Brendan22, designed and printed the booms and enclosure, and you can download his designs on Thingiverse at http://www.thingiverse.com/Brendan22/designs.
FIGURE 4.4 The T-6 Quadcopter has a 3D-printed body and six motors (credit: Brendan22).
If you aren’t content to download someone else’s work, you can use 3D-design software such as SketchUp (sketchup.com) or Tinkercad (tinkercad.com) to build the part you need for your project, and then print it out on your handy 3D printer. If this sounds a little expensive, that’s kind of true. 3D printing is a new industry, and prices haven’t come down to the point where everyone has a 3D printer at home. Don’t worry: There are plenty of other ways to build an airframe!
Wood makes for a very lightweight and sturdy airframe material, especially for smaller and lighter quadcopters. A lot of model gliders use balsa, a super light and easily-shaped wood. However, quadcopters have the capability to carry a decent amount of weight, and that makes wood’s relatively unimpressive strength-to-weight ratio less of a problem.
One fun aspect of wood airframes is that you can laser-cut the frame out of thin slats of wood and then piece them together like a puzzle. Figure 4.5 shows one example of this type of creation. Called the Flone (http://www.thingiverse.com/thing:113497), it’s an airframe for a smartphone-controlled quadcopter. It looks great and is easy to make—if you have a laser cutter, that is.
FIGURE 4.5 The Flone airframe is easily laser-cut out of a piece of wood (credit: Lot Amoros).
Another advantage to wood is that it is a cinch to modify it on the fly—just drill a hole in it! Unlike commercial frames, or even metal and plastic ones, it’s super easy to cut or drill into a wooden chassis. If you mess up, all you have to do is laser out another one!