FPV FRAME
In this GUIDE, we want to provide an overview of what to look for in order to get the best FPV drone frame that suits your needs and how the frame influences flight performance.
A well-chosen FPV racing frame can help give you an edge over the competition.
1. WHAT IS A FRAME?
A frame is like armor for all the sensitive electronic components that make up a racing drone.
It is essential for a frame to be as durable and robust as possible while still meeting the pilot’s needs without hindering the flight experience and the inevitable maintenance that will follow.
2. MATERIALS
A mini quad frame can be made from any imaginable material: wood, 3D-printed plastic, injection-molded plastic, fiberglass, aluminum, or even PVC pipes. However, carbon fiber remains the most popular material for mini quad frames due to its relatively low cost and excellent physical properties:
Lightweight: Lighter means higher speed, better agility, longer flight time, and less destructive inertia in case of a crash.
Strength: Carbon fiber is known to be relatively tough and durable.
Rigidity: Frame rigidity is crucial for stability and flight performance.
However, there are some downsides to using carbon fiber for frames:
Carbon fiber is electrically conductive. If there are wires under tension touching the frame, short circuits may occur, leading to component burnouts.
It also blocks radiofrequency signals (such as 2.4GHz and 5.8GHz), so make sure your antennas are not hidden inside the frame.
In the rest of this article, we will focus on carbon fiber mini quad frames.
3. HOW IS A FRAME MADE?
The frame is divided into 2 parts: the body and the arms.
The arms are where you install the motors and often the ESCs as well. The arms are designed to be durable and are usually made with carbon fiber sheets ranging from 3mm to 4mm. Nowadays, it’s becoming common to see frames with 5mm or even 6mm thickness used for the arms.
The body houses and protects electronic components, including the flight controller, PDB, FPV camera, VTX, etc. Typically, it consists of a bottom plate, a top plate, and some spacers in between to hold them securely together.
4. FRAME DIMENSIONS
The size of a frame, called the wheelbase, is calculated by measuring the diagonal from motor to motor in millimeters. The frame size has a significant influence on your drone, affecting:
1. Maximum propeller size
2. Motor dimensions
3. 4-in-1 ESC or individual ESCs
4. Compatibility with FPV and HD cameras
5. Moment of inertia
6. Air resistance
7. Total weight
The frame size determines the choice of most components you will use in building a drone. Therefore, when you consider starting to build a drone, make sure you have already selected a frame.
Motors are mounted at the ends of the arms, and the farther they are from the center, the greater the moment of inertia, introducing a tendency to resist angular acceleration and deceleration. All else being equal, a smaller frame makes the aircraft more agile.
Furthermore, the larger the frame, the greater the air resistance when flying forward. The weight of the frame also increases due to the additional material.
5. FRAME SHAPES
The shape of the frame or arm not only concerns aesthetics but also influences flight performance. While frame shapes may appear very similar and mostly rectangular, each type of frame has different performance characteristics. Currently, there are many types of frames available in the market, and below, we will mention the most common ones:
- H FRAME
H-style frames have unlimited space for components, making these frames very easy to build.
The arms connect at the front and back of the body on an “H” frame, creating a long and spacious body that can comfortably house your electronics. The HD camera and battery can both sit on the top plate, distributing the weight of the quad more evenly. For this reason, it may seem less agile than the newer X frames due to the higher moment of inertia on the pitch axis. However, some people prefer this behavior for a smoother freestyle flight.
- X FRAME
On an X-style frame, all arms converge at the center forming an “X,” with equal width and length (the motor layout is a square). The body is shortened as much as possible, and components are designed to be stacked in the middle for a more centralized mass. This results in a lower moment of inertia and ultimately more responsive flight characteristics compared to H frames, making them more suitable for FPV racing.
X-style frames are typically lighter due to reduced material usage, but due to the smaller body, it might be a bit more challenging to build. Everything is stacked in the center like a tower, including the HD camera and battery.
- HYBRID-X FRAME
The Hybrid-X has the arms of an X-style frame but the long body of an H-style frame. Some argue that this makes little to no difference compared to the H frame in terms of flight characteristics, as the mass distribution is the same. However, I believe there is a difference in how forces are applied to the frame (think of leverage). There may also be a change in how prop/motor vibrations are transferred to the FC in different directions through the arms.
- STRETCH X FRAME
Very similar in appearance to a “true-X” frame, the “stretched X” has arms configured closer together at the front and back. The idea is to improve cornering performance in races and high-speed flights. Moving the rear arms away from the front arms can minimize air turbulence, allowing the aircraft to remain more stable when flying at high speeds.
X-stretch frames require a slightly different touch when tuning PID and speed due to the change in frame geometry. X-stretch frames seem to be more sensitive/reactive on the roll axis compared to a standard X frame. Additionally, they tend to weigh slightly more due to the increased material used in the longer arms.
- BOX FRAME
A square frame could be based on an H or X frame, with additional material on the outside connecting the motor mounts. This essentially creates a sturdier structure that is less likely to have broken arms. However, the increased material blocks airflow, adds weight, and increases air resistance. It is not a good choice for high-performance aircraft unless you are new to this hobby and are concerned about breaking things.
- UNIBODY
Choosing between a unibody frame and a frame with replaceable arms can be challenging.
The advantages of a unibody frame include ease of use due to not needing to assemble a collection of carbon plates. Frames with separate arms are generally more budget-friendly as they do not require the larger sheet of carbon from which they are cut. The replaceable nature of the arms also allows for designing a lighter quad, as the arms can be reduced to a narrower width. If an arm breaks, it can be easily and quickly replaced at a lower cost. The replaceable nature of frames with separate arms promotes reliability, a crucial factor to consider, especially if the selected frame needs to be competitive.
Which frames are suitable for racing and which for freestyle? Whether a drone FPV frame should be suitable only for freestyle or racing is a decision left to the pilot.
For racing, the most important factors are weight and impact resistance. Having lightweight and easily replaceable arms is usually recommended. An X or stretched X configuration with a motor-to-motor distance of 180-220 mm and a weight of less than 80 g is more comfortable on the track. A true X or wide X can be suitable.
For freestyle, the most important factor is how easy it is to build/repair and how well it withstands crashes. It is recommended to choose a frame of approximately 220-250 mm with a preferable weight of 140 g or less, making it more favorable for freestyle flights.
6. CONCLUSIONS
You will have well understood that when choosing a new frame, there are many considerations to be made in design, aesthetics, features, ease of construction, component placement, and user experience. We have reached the end of this GUIDE, and we hope that it has helped you understand the basics of the mini quad frame!
