I am sure I am not the first one facing the dilemma – plastic vs. carbon – when choosing multicopter props. Carbon fiber is twice as expensive. On the other hand, props are the key moving part and may significantly affect your rig’s performance, battery life, and most of all video quality. To put the issue to rest once and for all I did my own test using an iPhone vibrometer app and two sets of 10x45 plastic and carbon fiber props, 12 vs 8 grams a piece respectively.
Both sets (hexacopter) have never been balanced before and ran at the same minimum throttle speed. Plastic props vibrated at 1.6-1.8 m/s2. They also produced more noise.
Carbon fiber props ran at healthy 0.2 - 0.3 m/s2 and sounded much better. Also, they are significantly lighter and stronger than plastic.
Cautionary note – carbon fiber props are very stiff and sharp. Carbon fiber is 100 times stronger than aluminum and can cause bodily harm at high speeds. You should handle them with extra care.
See for yourself
Great post. I think you're right on. I imagine that it makes a difference if you are using high-gloss CF (lots of resin) or matte finish (low resin). I think most people don't think matte looks nice, so the manufacturers only interested in appearance will use glossy material, which is actually weaker.
Those black "CF Reinforced" plastic props are the one that snapped mid-air on my quad, leading to it's death.
I work for a contract manufacturer specializing in composites manufacturing, and I can tell you that properly engineered products made using carbon fibre products are not only lighter but far stronger than when made using conventional materials. If it's cheap it's defiantly not a true composite product. By the lb or linear yard CF is far more expensive than any other common material. Besides the advantage of weight the primary and often most forgotten benefit of manufacturing with composites id the fact that you can align the materials to best suit the stress points of the design and you can provide maximum strength and stiffness on the axis of load. Much of what we see in hobby related products are purely cosmetic application of carbon or carbon look materials. Carbon in thin unidirectional layers is very fragile and susceptible to breakage, however if properly designed it can be both strong in the long axis as well as in torsion. That said, it's a lot like building and flying a plane, we build them to fly not crash. If that's part of the design intent and survivability isn't a factor then we can use a very thin, lightweight design (less rotational mass = better efficiency and higher performance) and reap the benefits of the material to the max. A reinforced nylon prop usually consists of nylon with randomly oriented short fiberglass strands this helps bond the prop together and helps when an edge or tip becomes chipped but does little to add any real strength or stiffness to the prop. It's always a compromise when choosing the materials for any design, and as always we must choose our props based on our use. If we looking for durability and low cost we might be on one end of the spectrum and if we are looking for higher performance and cost or durability isn't as much of a factor we might be on the other end of the spectrum. On a side not I have played around with a large variety of props and can say that the right prop can yield 20% or greater increase in performance and or efficiency. The search for the Holy Grail is a full time job!
I've never had that happen with these using the smaller diydrones motors but I've had that happen to diydrones props that I got a couple of years ago. I think it was from a slight hit they took on a soft crash or hitting something and since I didn't notice, it then failed in the air. Also it can happen if you crank down too much on the collet. Things from my learning days that I'm sure didn't happen in your case but it can happen if you don't check them carefully after a soft crash where nothing really broke but a prop took a hit that weekend it's hub.
I find the weight of the Prop to be a big issue. I have spent some time working on vibration in my quads with different motors. I have changed the motor bearings for abec 5 quality and balance the props. when I try a CF prop compared to a light electric the lighter prop is always significantly less vibration.
Rob, I think you are onto something close to what I have felt for a while now about CF props in comparison to good quality plastic props. The one main dislike I have for CF props is they can fracture at the motor shaft collar while tightening the nuts and you wont be able to tell this until after it breaks off completely while in flight.
I have a theory that the rigidity of the CF props might in fact be less energy efficient. Ive yet to put this to some good testing to prove it, but since Ive switch a lot of my copters back over to plastic props, they do seem to fly more easily and I get slightly better flight times out of them.
Here is where the foundation of my theory comes from. There is a big Eagles nest in the forest just out front of my apartment building and I often watch them catch thermals out the front of the building to go of hunting for the day. They often come within 5-10 meters from my balcony.
I noticed while watching them, they have long flexible wing tip feathers that seem to act like shock absorbers as they hit uneven pockets of air as they fly in and out of the thermals.
I could imagine how much easier this would be for them to manage those sudden changes in air movement and density and it would require much less energy fighting this say than if they had very rigid wings. Sudden gusts and change in air movement would be very tiring and hard to mange much like riding in a car without shock absorbers.
I feel the flexibility of plastic props might work in the same way where they give a slightly easier forgiving ride and as such likely they don't expend quite as much energy in doing so.
When I have some more time I'm going to work out a method to put this theory to test and see if it proves me right or not. .
Interesting, while doing battery testing on my basic 450 quad - hovering in one place - i noticed I get consistently slightly less flight time with CF props than I do with plastic props - 16mins vs 18mins and it's more exaggerated in a breeze/wind.
Also interesting that airplane manufacturers interested in efficiency make wings that are disconcertingly flexible (to a nervous flyer!).
Nice observations Dom.
It sort of make me ask the question where did the idea to use carbon fiber come from for use in multirotor props to begin with? Was it simply to have stronger more damage resistant props? Was it just from an assumption CF is so good in many other areas it should automatically be a given it would be the best material for multirotor aircraft props as well?
I have never seen any significant test data to prove they are more efficient or not eitherway. But just going on my own observations and experience with using the exact same aircraft, I actually get less flight times using CF props. Seems you have now found the same which support the same as my findings. .
There are a couple of other things to take into account:
First the fabrication methods. You can make plate by layering sheets one upon another, and even if you angle the weave for the best strength, and squeegie the final product, it may not be as strong as a sheet made well. A sheet should be cured with pressure, and the resin is very important. Even though it isn't the strongest element in the process.
Second. CF doesn't resist abresion well. Care has to be taken around holes or any surface where one element rubs on another.