Thinking of building your own quadcopter from scratch or with a frame kit? Then you certainly are not a beginner. While some folks who are just getting started with quadcopters or multicopters - and may never ever have flown one in the past - do attempt to build one from scratch, these projects seldom end well. While building your own drone either from a kit or from scratch can be tons of fun, it is certainly not for beginners.
While it is possible to build a working quadcopter that flies with sticks, these "barebones" models can't be expected to fly well. You would not expect professional grade drones to be built from plywood and dowels or sticks. No one should attempt to build their own quadcopter thinking they can save some money this way. When you factor in everything, ready to fly drones are perhaps less expensive and perform better. Quadcopters that perform well need good quality components that are matched right and perform well together.
Your best bet if you want to build your own quadcopter or multicopter is to use frame kits that come with highly detailed guides and there will be no way you can go wrong following these.
That said, selecting a frame that's right for your application does require quite a bit of thought...
Many folks who are relatively new to this hobby place a lot of emphasis on the electronics and seem to neglect the rest. While having good electronics is certainly important, what's the point of having even the best electronics money can buy if your frame is third rate? If your frame warps or bends then even the best 4K camera will be pretty much useless.
This is why you would want to select a really good frame for your diy quadcopter or multi copter.
The frame should be stiff, strong yet light. It should not warp or bend if you want your multicopter to have a stable and smooth flight. The frame should not be brittle either. It should be tough to endure crashes that are inevitable.
Carbon fiber frames have really good stiffness and can result in really smooth and stable flights. But one disadvantage of carbon fiber frames is they can block your radio signals. Carbon fiber is used as a shield to block radio frequencies, so this should hardly be surprising. If you are going to be using a carbon fiber frame, you would always want to ensure line of sight between your antenna and the radio. You could also use dual antenna receivers in V shape.
If you are going to be using a CF frame and don't give much thought to your antenna placement, your drone can lose the signal mid flight - because the carbon fiber frame blocks the signals from your radio - and it could fall out of the air. This is a fairly common problem with 3D printed carbon fiber frames.
Fiberglass is another material that's used very commonly in building multi rotor frames. The main advantage of fiberglass is it's radiolucent - it does not block the signals from your radio. But on other parameters like stiffness, weight and rigidity it is inferior to carbon fiber. Fiberglass tends to bend and warp - so this is something you definitely do not want to use if you want smooth and stable flight characteristics.
You could use aluminum as well, but it's a lot heavier than either carbon fiber or fiberglass. But then it is also a lot stiffer. If you are prepared to use powerful motors, you should be able to use aluminum without much hassle. The main disadvantage with aluminum frames is the vibration - there is hardly any damping and vibration is a problem you will have to live with if you choose to use a aluminum frame.
Depending on the number of motors used, there are several possible configurations...
This is the cheapest multicopter to build, but it is also highly unstable. With two servos and two motors, achieving stable flight can be a challenge. But of late, better, more stable designs have been introduced.
3 motors are mounted on either a Y shaped frame or on a T shaped frame. Even this is not quite as stable as multi copters with a higher motor count. Achieving yaw can at times be hard with either the Y or the T shaped designs and you might want to use a servo to execute yaw.
With the bi copter and tri copter, there's really no redundancy. If a motor fails, the drone will crash. While redundancy can be said to be lacking with quadcopters as well, there are now algorithms than can keep a quadcopter in flight even after one of the onboard motors fails.
These have 4 motors. The most popular quadcopter frame is the X4 where the arms are 90 degrees apart. Two of the motors turn clockwise while the other two turn anti clockwise. This is necessary for stable flight. If all of the motors turn clockwise or anti clockwise, the quadcopter will have a tendency to turn clockwise or anti clockwise.
The H configuration is popular mostly with those interested primarily in aerial photography.
The Y4 and VTail are other possible frame configurations, but these are not very popular.
The main advantage of quadcopters is they do not need servos and are so very easy to set up. And their huge popularity has made replacement parts easily available and there's a lot of help available on online forums in case you need it.
Hardly anyone seems to have any interest in pentacopters. One possible reason could be that it's hard to turn these - or yaw - because you have an odd number of motors. With quadcopters, you could simply slow down two motors and speed up the other two motors to execute a yaw - but it can be a lot harder with a pentacopter. You will have to slow down two motors and speed up three - which is not very convenient. Another reason could be redundancy - or lack of it. If one of the motors were to fail, it might be impossible to keep a pentacopter from crashing.
These have 6 motors - 3 that turn clockwise and 3 that turn counter clockwise. They have more lifting power than similarly sized quadcopters because of the additional motors. And landing the craft will not be something you will have to worry about in the event of a motor failure - redundancy is built it.
It's also possible to mount the 6 motors on a Y shaped frame (Y6) in what is termed the Y6 configuration. Clockwise and counter clock wise propellers are mounted on the same arm - which means you do not need a servo to yaw. While the Y6 design is more powerful and reliable compared to a quadcopter, it does not have as much lifting power as the traditional hexacopter design.
Hexacopters have more power compared to quadcopters and yaw control is better. And then there's the added redundancy - they have 6 motors.
As the name suggests, these have 8 motors - 4 clockwise and 4 anti clockwise. Octocopters are most stable of multirotors and are the best suited for aerial photography and videography. Another advantage is the redundancy. The raft can stay in air easily even if a motor fails midflight.
X8 is another octocopter frame design that's fairly popular. This one has clockwise and counter clockwise motors mounted coaxially. This has more lifting power than any hexacopter while also being more reliable.
The real advantage of octocopters compared to other types is the reliability - they are very reliable and very stable. An excellent choice if you are going to be mounting very expensive electronics like high end FPV cameras.
The main disadvantage is octocopters require a lot more battery power.
These are directly attached to the frame and you would want to minimize the vibrations here as well. If the material of the arms is not stiff enough, they can start shaking in flight and these vibrations are transmitted all over the multi rotor, which is not desirable. But if they are too stiff, they will not dampen any of the vibrations that reach them and pass the vibrational energy - which is not good either.
Your best would be to buy pre built arms as these have better flight characteristics than what most amateurs can manage to achieve with their homemade quadcopter arms.
There is no such thing as 'the best quadcopter or multi-rotor frame'. Different people expect different things from their drone, and there's no way to satisfy them all with a single frame design. The frame design you would want to choose depends on your application.
If you are going to be doing a lot of aerial photography and will be mounting expensive electronics on your drone, your best choice would be a octocopter. That would give the smoothest video as this is the most stable platform and also very reliable. And it should be able to carry a good amount of payload. You are not looking for something that's fast and very responsive but a model that can provide super smooth video, is reliable and can carry one or more FPV cameras.
If you are going to be racing, you want your drone to be very lightweight, fast and very responsive. You are not looking at payload here.
On the other hand if you are into sport FPV, you will need a much more powerful model that can carry heavier payloads while being very responsive and able to fly fast.
Vibration in multi rotors can be a real nasty problem, more so if you are hoping to capture professional grade video using your drone. Not taking care to reduce or eliminate vibration will lead to wobbly video, even if you are using top end cameras. And vibration is not a easy problem to solve. In some cases, it may require you to do a lot of experimentation to isolate all sources of vibration and eliminate the causes.
You would want to note that the frame - like any other structure, has a particular resonance frequency at which the amplitude will be at its highest. The real key to eliminating vibration due to the frame is to make the frame stiff and light - and make the vibration mode of the frame much higher so that it is much higher than the excitation frequencies that are induced by the motors. That way, there is no resonance and the amplitudes will never be at the highest possible.
It may seem a bit counterintuitive, but wooden frames have a lot more damping than either carbon fiber or aluminum. Balsa wood frames are lighter than similarly sized CF or aluminum - and they do not transmit as much vibration. And using multiple layers of balsa wood can make the frame very strong and rigid. Wooden frames have one other advantage - in the event of a crash, they absorb all of the impact and break, saving your motors and other electronics. But CF and aluminum transmit almost all of the impact to the motors and the motors may get damaged.
In addition to choosing the right material for the frame, it is also important that you dampen the vibrations by absorbing as much of the vibrational energy as possible.
You would also want to ensure your propellers are balanced, and you use the right frame type and use a vibration damping mount for your flight controller.
If the mount your flight controller rests on is not damping vibrations coming from the motors and other sources, the accelerometers on the flight controller will not receive the right information - and the flight controller may issue erroneous signals to the ESCs that control the motors. So the performance suffers. Which is why you would want to use the right kind of mount for the flight controller and ensure it is not subject to vibrations.
Balancing your propellers: This is essential. You would want to balance your propellers using a propeller balancer that you can buy online. You could sand down the sides and the hub if needed until the propeller is perfectly balanced.
Unbalanced propellers can cause a lot of vibration and these vibrations get passed on to the motors, reducing their life. Vibrations from unbalanced propellers can sometimes loosen the screws and even make your drone crash.
You would also want to use vibration damping mounts for your motors and your camera too for stabilizing the images. But even with all of this, each quadcopter is different and you might have to experiment a bit before you can reduce the vibrations to acceptable levels.