Quadcopter frame design: is square or tube better to reduce vibration? Aluminum or carbon fiber?

I may have missed previous posts, but could not find a definite answer concerning Quadcopter frame design: are square or tube type arms and/or frame better to reduce vibration? Which is better when it comes to vibration: aluminum or carbon fiber?

Thank you for your tips.

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Could some one with some practical experience chime in? A simple word will do:

 LESS  Vibration = square arms or round tube?    aluminum or carbon fiber?

mu quad is an h-frame all in wood (balsa). wood is the best for non vibration.

since you prefer alum or carbon, this is my understanding.

Alum has the highest vibration rate comparing to carbon. If you want to reduce the alum vibration (arms vibration) I would suggest you use square alum, but the U shape, not rectangular. Then fill that U shape with a balsa stick. Some people did sugest to fill the sqare arm with polystiren (expandable, as can insulation). this will reduce vibration. Important is you to try to reduce vibration where the APM2.* is install, even arms are vibrating. I am using the old mouse pad (rubber) and add a layer under the APM. Works fine for me.

Fibre carbon is good because is not benting as alum. But if you fly FPV with at least 3 different frequency, you could notice some radio interference since carbon is electrical conductive (as aluminum).

Round arm could twist and need to be fixed against twisting.

As I said, I do prefere wood. My H-Frame (see below) is all balsa wood, is lighten then alum or carbon and no radio interference. If you add multiple layers (3 in my case), it is strong as alum or carbon.

If I crash, I prefere the wood arm to be broken (3$) and save the motor, instead of safe arm or bent, but broken motor.

 

Flying the Quad H-Frame

Quad H-Frame

 

Thank you very much for the comprehensive tips and the links.  I am rethinking now if I should try something similar, with balsa wood. It makes sense as far as vibration, radio interference, replacement part sourcing, and price.  Thanks again!

I would say that the frame type, prop balancing, and fc mounting type is more important to vibration control than the material type.

H frame has no direct path from motor to FC, so it's reduced compared to an X frame, also the diameter of the arm and the cross sectional area play a pretty big factor. Carbon fiber and alunium are both hollow which concentrates vibrations, but reduces the capability of low frequency waves to travel 3 dimensionally through the arm. This is good because it will reduce total deflection angle, but increase the cycle of vibrations and reduce the chance of amplifying sympathetic frequencies. So larger pancake motors will cause little vibration on hollow arms. 

Wood has a lower density and lower density means lower frequency waves will propagate through it easier, vice versa for the aluminum. Carbon fiber however, will really vary on stiffness and thickness, because it's a inhomogeneous material and might have specific frequencies through out the bandwidth that can propagate, depending arm length that can completely dampen vibration, but given the law of conservation energy, might weaken the arm over time by internally breaking the carbon stands like worn out jeans.

As for strength, of course carbon fiber has the highest strength per gram, but once it's hit it's limit it breaks. Aluminum can be be bashed with almost the same force with the same cross sectional area, but it might yield a small amount which might not be as devastating. Wood really depends on the tree for definite test strength, but there are general tables on the web about balsa and bass wood. I prefer a plywood base, as it is much stiffer and has no singular grain to transmit vibrations on or week lines on it. It's a bit heavier, but you can get away with using less.

Mixing wood and aluminum, like wood base with Al tube arms will give you more vibration dampening, as it will act as vibration gate. High frequency from the motor is passed to the arms, then transferred into the base which will dissipate quickly through the wood.

Moongel under a flight controller with eliminate a ton of vibration unto itself, but mounting it can be tricky, I use some 1/" dia bungy cord across the top to compress the board on moongel. this will increase the normal force, and the coefficient of friction of moongel is pretty high, so very little slipping, unless there's a big crash.

A square tube will give you more angles that will strengthen any sheet material and it limits the vibration deflections into 2 axis motion, as where a round tube can deflect in any direciton an create an oval ocilation at the motor end. Also, square tube will weigh slightly more because of increase in cross sectional area vs. a round tube of the same diameter.

How about pvc (sprinkler pipe).

I have used it on a T-copter and a V-tail copter. I use 1/2" for the arms and 3/4" for the tail. Lexan for the platform.

I also slide a styrofoam noddle over the arms for flotation.

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