This is the piece that holds the entire quadcopter together. The one I have used is the X525 frame. 

 

For every frame, you’re going to need four essential pieces. The first is the center holding plate, where most of your vital electronics (“the brains of the operation”) will be placed and protected. Throughout the build you might need to make modifications to the frame in order to attach certain components. The next piece is the motor arms. These are usually long pieces that extend out from the center holding plate to where the motors and the propellers will be attached. Lastly, you need motor brackets which is just a certain type of plate that allows motors of most sizes to be screwed and secured into. 

 

Something that is important to keep in mind with the frame is the material. You need the frame to be light but also very sturdy. Most frames are made of aluminum, fiber glass, or carbon fiber, although they can made of other materials such as duct tape or wood. Just a note to keep in mind. Some materials make more “noise” than others meaning that  they don’t absorb as much of the vibrations from the motors. Noise can impact the readings of the gyroscope which will effect the calculations of your flight controller. Another thing to be aware of is that if your quadcopter is metal, it might interfere with the receiver/ transmitter connection. Although unlikely that the receiver and transmitter will disconnect due to inference from the frame, if it does disconnect there are two things that might happen. Unless accounted for in the code, the quadcopter will probably just plummet to the ground, which in most cases that probably the best scenario. The other scenario is that (once again, this could be accounted for in your flight controller code) is something called flyaway in which the signals being sent to the electronic speed controllers (the device that controls the speed of the motors) are retained and not reset. When this happens the motors will just continue to run at whatever last speed they received from the transmitter which will ultimately lead to them gaining altitude or flying in a sideways direction until it a) hits something or b) runs out of battery. Now this isn’t to say that you shouldn’t buy a metal frame because a receiver and transmitter can disconnect for many other reasons.

 

Some vocabulary that you might not be familiar with:

Wheelbase - the distance from the center of one motor to the center of the motor diagonal from the original. 

Noise - Vibrations that are caused by motors and propellers that have the potential of affecting the gyroscope readings. 

 

 

Notes on the X525 frame:

 

It comes with a pretty unclear instruction manual. Note that this frame comes with extra screws so don’t get worried that you forgot to screw something.  You want to start with each of what I like to call landing gears and then attach it to the arms. Use the long thicker set of black screws for screwing the frame to the arms (you should do this part last). Use the thinner yet still longer screws for screwing the two side pieces of the landing gears together. The smaller screws are used for the part of the landing gears that is attached with a metal tube. You screw two screws into both sides of the metal tube. Remember, you don’t want to screw it too tightly or else the landing gear will not be able to absorb the weight if you do crash. So after you’re done assembling, ensure that the landing gears can move freely.