An FPV Drone Frame is like a suit of armour for all of the sensitive electrical components that constitute a quadcopter. It is essential that a frame is as durable and rugged as possible, while still accommodating to the needs of the pilot without hindering the flying experience and the inevitable maintenance that will ensue.
Each frame has a designated size class, based upon the longest distance from motor to motor measured in millimetres, typically taken by measuring diagonally across the frame. A frame measuring less than 150mm motor-to-motor is categorized as a micro. A frame larger than 150mm motor-to-motor is considered a mini. When measuring an unconventional multicopter frame, such as a hexacopter or tricopter, the size will always be given by the greatest motor-to-motor distance.
What’s in a FPV Drone Frame?
The majority of mini and micro frames are cut from carbon fiber sheet. Carbon fiber is a composite material, being made up of many layers of interwoven carbon fibers that have been rigidly cemented within a binding matrix of epoxy. The popularity of carbon fiber as a frame material is due to its low weight and high strength. It is important to note that carbon fiber is an electrically conductive material. The average 5” frame has arms milled from 4mm carbon fiber and other plates 1.5-2mm thick. Apart from carbon fiber, the next most popular frame material is high-density polyethylene, or HDPE. HDPE is not as strong as carbon fiber, therefore designs that incorporate HDPE are typically heftier. HDPE frames are more flexible and forgiving than carbon fiber which allows improvement of overall durability. There are many frames that use a combination of carbon fiber and another material such as aluminium or 3D printed TPU (a flexible polymer) in their construction. The use of these materials is a great way to improve the strength of a frame, better protect components or simply to add flair to a design.
The Naming System of an FPV Drone Frame
The quadcopter is the most popular design for several reasons, namely mechanical simplicity, quantity of motors and ESC’s required for flight and their compact size. There are other forms of multicopters that although unconventional are perfect for certain applications, or even simply the whimsy of their unique structure. Multicopters are simply named with a numeral prefix (e.g. Bi, Tri, Quad) followed by “copter”.
FPV Drone Frame Styles
There are many different styles of frame, all related to the stance of the arms and the size and shape of the electronics carriage. Below, each frame type is explained along with a graphical example.
The true X is shaped as it sounds, an X geometry to which a motor is mounted to each end of the arms. The perpendicular distance between the centre of each motor is equal, therefore giving the quadcopter the same level of stability on all axis.
A wide X has its arms splayed outward to the side. The wide X geometry is more common in freestyle frames, this is because more central space is often required to mount an action camera and battery on top of the frame.
The stretch X is a rotated wide X. The stretch X is typically favoured by racers who are seeking more stability on the pitch axis, which can improve control when the quadcopter is racing at high speed.
The dead cat style is typically favoured by larger quadcopter designs. Its purpose is to remove the propellers from the sight of the on-board HD camera, this is achieved by increasing the perpendicular distance between the two frontal motors. The popularity of the dead cat design has sagged along with the increasing interest in smaller miniquads. Although, there are some mini and micro quads that continue to utilize the dead cat design, typically as a means of accommodating uniquely shaped centre carriages. (The dead cat style was named after the pioneering design undertaken by Dutch artist Bart Jansen. Jansen used taxidermy to preserve his recently deceased cat before converting its body into an organic quadcopter. We wish we were joking.)
The H style is another archaic style of quadcopter design. In a H quad, the arms are positioned at the front of a long “bus” style carriage. Recently, the H quad has lost favour due to its bulky size and awkward configuration.
The HX is a newer variant of the H. Instead of placing the arms at the tip and tail of the carriage, a true X, wide X or stretch X configuration is applied, most often wide or true X.
A Z quad uses two similar base plates mounted on top of each other to produce a stepped geometry between the front and rear motors. Mounting the motors on different planes improves the prop wash handling of the quadcopter, as less turbulent air is directed towards the rear motors during forward flight.
A plus frame has the same footprint as a X frame that has been turned 45°. A plus frame can be seen as advantageous in that each motor is responsible for rotational movement in only one axis, theoretically meaning finer control is possible. Although, plus frames are more prone to breakage due to most impacts involving a forceful strike to the front arm only.
Vertical arms rotate the orientation of the arms to produce as small of a surface area as possible to minimize drag. Durability is not usually compromized as the arm may still maintain width, however, construction of the frame is often more complex than standard horizontal frames.
Unibody or Separate Arms?
Deciding between a unibody or a replaceable arm frame can be difficult. The advantages of a unibody frame are the ease of use due to not having the need to assemble a collection of carbon plates. Separate arm designs are typically favoured because of their cheaper cost and ease of repair. Separate arm designs are typically cheaper than unibody frames as they do not require as much of the carbon sheet they are cut from to be wasted. The replaceable nature of the arms also allows the quad to be designed lighter weight, because the arms may be made to a narrower width. If an arm breaks it can simply be quickly replaced for a low cost. The replaceable nature of separate arm frames promotes reliability, an important factor to consider especially if the selected frame is to be competitively raced.
Weights can vary wildly between differing frames. The typical weight of the average 5” FPV Drone Frame is approximately 100g including hardware. The average weight range in the 5” class is about 60g-140g, depending on certain factors such as whether or not the frame is unibody, X or XH and the hardware used in its construction. Micro frames have a huge amount of variation in terms of mass, most often weighing between 5g-50g dependant on size and a range of construction parameters.
Top or Bottom?
Top or bottom battery mounting is subjective, with different pilots usually preferring one method over the other. Most racing frames are suited only for an underslung battery, as it allows the frame to be designed as compact and lightweight as possible. Freestyle frames are typically designed with a top mounted battery in mind, sporting a long central carriage that can support a battery and action camera for recording HD footage.
A pod is a canopy that is attached to a frame as a means of protecting the sensitive internal electronics from damage. FPV Drone Frame pods are typically 3D printed in TPU (a flexible polymer) or sometimes even manufactured by moulding carbon fiber or polycarbonate. Some FPV pilots find pod frames to be more attractive than standard carbon plate frames because a pod provides better protection from dust, water and other factors that may damage the electrical components, for example, the flight controller. Pods are however, often more costly than standard plate frames and sometimes constrictive of maintenance, as some pod designs require many nuts and bolts to be loosened in order to access the internal electronics. A pod can also confine high power electronics, such as the video transmitter from airflow, possibly causing overheating issues.
A mounting pattern is the distance and distribution of holes that are milled into a FPV Drone Frame, the two that are to be considered are the motor and flight controller mounting geometry. The mounting patterns available on a frame are another factor that must be carefully investigated prior to frame purchase, as they will limit the compatibility of the frame with certain electronics and components. Concerning the flight controller, there are three different varieties of mounting patterns: 30.5×30.5, 20×20 and 16×16. 30.5 is the most common mounting arrangement, being more mature than the newer, smaller patterns. Most frames in the 5” range are designed solely for 30.5×30.5, although some have options for only 20×20 or both 20×20 and 30.5×30.5. Frames smaller than 5” most often accommodate 20×20 or 16×16, 16×16 being most common in micro frames smaller than 70mm motor-to-motor. In terms of motor mounting, there are four key configurations to consider. 16x19mm, found on 220X/230X motors, 16x12mm, for 180X motors, 12x12mm on 130x/140X motors and 9x9mm for tiny 110X motors.
Freestyle and Racing
There is no particular reason that a FPV Drone Frame must be appropriated for only freestyle or racing, that choice is solely for the pilot to decide. Usually, a true X or stretch X configuration 180-220mm motor-to-motor and weighing less than 80g is most at home on the race track. A true X XH or wide X XH, approximately 220-250mm motor-to-motor with a preferable weight of 140g or less is often more favourable for freestyle.
The purpose of the FPV Drone Frame is not only to simply protect the delicate electrical components from harm. A frame also provides individualism and character to a build. However, while aesthetics may be tempting, it is imperative that the size, durability and appropriateness of the frame are also considered.