What is a good alternative to carbon fibre for a quadcopter frame?

Question

I am making a diy quadcopter and I need a strong and light material for its frame.

Carbon fibre is not available in my area. I have tried aluminium but it's too soft and so needs repairs. What alternatives are recommended?

Answer 1

There's no denying the fact that when it comes to materials that are strong, stiff and light at the same time, carbon fiber is king. If you're looking for performance, there's no way around it. If performance is not the most important thing in the world, however... Well, there are several options.

Before I start listing these, I must point out that all frames break. Some break more easily than others, but you can't have an unbreakable frame. The question is how you repair it when it breaks, and the answer depends on the material.

• Plastic frames are actually a very popular option in micro-sized quadcopters that only weigh tens of grams. These frames usually feature a non-flat shape, prop guards and other features built into them. A subset of those, 3D printed frames, are also quite widely used in DIY designs of larger sizes, and, as everything 3D printed, are a good way of prototyping your design before moving on to other materials. In some cases, where performance is not a concern (for example, if your main focus is having a platform for testing algorithms for which flight time or range is not important at the time, or just want to play around with a design) you may even never move on from a 3D printed frame. While these tend to be heavy and/or brittle compared to other materials, there are some exceptionally light designs, and depending on the intended applications, durability might not be a concern. Besides, if you do break one of these, you can always just print a new one. Also keep in mind that there are many different specialized 3D plastics available, such as carbon-impregnated ones, lightweight foaming PLA and others, which, along with clever design, can in fact give you a fairly performant, stiff and/or light frame. All of these have tradeoffs, however, so do your research.
• Wood and metal/fiberglass is a staple of "oldschool", large (8"+) DIY drones from the KK2/Naze era. As the drone gets larger, heavier frames tend to impede it less, and any crash could easily break an arm just due to the sheer weight of the drone, no matter what the arm is made of. So this kind of design focuses on repairability instead: one can easily make tens of wooden arms in their workshop for very cheap and swap them when they break. Potentially, one could try to make a smaller wooden frame as well, although at this point lightness becomes important, so I'd advise to stick to lighter woods if you do, maybe even balsa.
  • Full-metal frames are not unheard of as well; Aluminium and titanium are widely-accepted building materials in aviation and actually tend to have better performance than wood. You'll have to use tubes/other non-flat shapes, though.
  • Even though you've ruled out carbon fiber, you may be referring specifically to CNC machining of frames out of flat sheets. Premade carbon fiber elements such as strips and tubing are readily available for order online and are easy to work with using basic tools. A lot of larger drones today are made using the same basic technologies as the wood/metal drones of old, but with arms out of carbon fiber tubes instead of wooden planks. If you're building a large drone, this is a very feasible yet high-performance option.
• Finally, Pure fiberglass composite. Glass fiber composites are in fact even stronger per unit weight than their carbon fiber counterparts, but significantly less stiff, which is why you don't usually see them in performance drones: In flight, dynamic and resonant characteristics are more significant than pure strength, the latter coming into play only when you crash. But if the drone flies better, you're less likely to crash in the first place. Still, the difference in stiffness of the material can be overcome with clever profiles, and glass is generally easier to work with than carbon, so there are some niche uses even in performance designs.
  • The first of them is very large drones, which tend not to care as much about neither weight nor aerobatic performance. Here, glass fiber can shine if you've got the facilities to manufacture it. That said, if you're building a very large drone, the frame is likely to be a very small fraction of its cost, so you might just as well order a custom carbon design (or use premade carbon parts like the previous option).
  • The more interesting option, however, is a PCB frame, in which the frame is not just a structural component, but also carries all the electronics that the drone needs to fly. Some fantastically lightweight designs have been made using this technique: even though the glass fiber itself does not perform as well as carbon, the design makes up for it by ditching all the other PCB and wiring weight that would otherwise be carried on top of the frame in a traditional design. While not optimal for sporty flying, this is the perfect option for a long-range/long flight time autonomous design... if you can lay out the PCB, as all of the components (flight controller, ESCs, vTX, etc) have to be integrated into it.

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Some examples for inspiration:

Plastic frames

Brushed micro quadcopter (tiny whoop) with molded plastic frame:

2" brushless copter with molded frame:

Brushless quadcopters with 3D printed frame:

Foldable brushed 3D printed frame:

Wood/metal homemade frames:

Typical fully wooden H frames of the KK2/Naze era:

Classic X frame with metal/plastic center plate and wooden arms:

Very simple wooden X frame:

Small drone with laser cut wooden frame:

Frame with metal arms:

Full-metal frame:

H frame out of carbon tubing with 3D printed brackets holding it together:

Glass fiber frames

Molded fiberglass tricopter:

PCB frames:

Answer 2

It depends on what kind of airframe you want to build, what size it is and what you intend to do with it.

Early DIY drones often used moulded plastic, for example he immensely popular DJI Flamewheel. Many camera drones, such as the DJI Phantom, still use that plastic construction to this day.

It was also fairly common to build airframes out of wood.

However, in more recent years, carbon fibre has become the gold standard in terms of weight, strength and price.

Smaller drones, such as Tiny Whoops, as well as toy grade quads may still use plastic as they often don’t have the mass to break plastic frames during a crash, and if you are okay with the risk that a crash at sufficient velocity could destroy your airframe, moulded plastic may be a good option (I say moulded as 3D printed is unlikely to have the required strength).

You say you have tried aluminium, however there is an important distinction to make. Thin aluminium sheets would be fairly malleable, however a section of aluminium extrusion or a rectangular aluminium pipe (or even a circular aluminium pipe if you can find a way to mount the motors) will probably provide enough strength for low-impact activities.

You could, of course, construct your airframe out of wood, however finding sufficiently light and strong wood may prove to be a challenge.

Companies like Banggood and Hobbyking carry carbon and ship to most of the world; if you haven’t tried these I recommend giving them a look.

It is also important to keep in mind that modern flight controllers have filtering to make almost anything (including a taxidermist cat - it’s real) fly.

Answer 3

Polycarbonate frames can work quite well, but they will flex more. I have made a lot of them and they get a lot of flying time in carpark racing locally.

Answer 4

Before carbon fiber frames became popular, I was building my frames with wood. This worked quite well for cruising around, but if you are building a racing drone, then carbon is your best option. If you can't get carbon, try plywood as it is layered and the layers will add a bit more durability. I'm referring to hobby grade plywood that ranges in thickness.

Answer 5

It would indeed be helpful to know what kind of quadcopter you are looking to make.
I have made several quadcopters and one octocopter, but all with the purpose of aerial photography, not racing. Always used aluminum frames. Here is why.

Plenty and cheap availability. Most DIY stores have the 10mm square section tubes needed for the arms. The price was under 2 euros for 1 meter piece. Bought plenty.

I have tried aluminium but it's too soft and so needs repairs

Indeed, in case of crashes. And that is a plus for aluminum. In case of a crash it will bend. This means that part of the energy of the hit will be absorbed by an aluminum frame. Whereas on a rigid frame you risk that most of the energy will be transferred to the precious electronics. For this purpose I weaken the arms a bit by drilling holes in them just before they get under the plate that holds the electronics. After a crash you just discard the torn arm and put a new one in place. Because, you know, it's cheap.

Aluminum, on the other hand, is plenty rigid for flight, even in case of acrobatics.
Many of the other materials suggested (woods, plastics) are not quite as rigid. This will likely cause flutter of your arms in flight leading to an overall less stable airframe.
Normally I use wood for the plate holding the electronics (attach it with dampeners, to reduce vibrations as much as possible) and the camera gimbal.

Answer 6

Bamboo is surprisingly close to carbon fiber rods and tubes in all properties except cost.
For more complicated shapes, wrap fiberglass cloth around a removable mandrel, or over a lightweight core such as foam (which you can even dissolve away after the fiberglass has hardened, for extra lightness).

Answer 7

Depending on your application, a wood frame with a fiberglass wrap may be an option. Many balsa wood r/c airplanes and gliders have their wing center section wrapped with fiberglass and epoxy. When done right it's incredibly strong for a modest weight gain. Obviously, this wouldn't be the best option for all situations but may be worth a look.

Check youtube and the usual r/c forums on how to do it if you are unfamiliar.

Answer 8

I would personally shy away from PCB frames as PCBs are not intended to have the stresses which quad flying, and crashing, will ultimately inflict on the frame. The traces and solder points are prone to failure with these stresses. I would stick with a separate pcb which is smaller and and can be located in a protected part of the aircraft.