This tutorial provides an overview of mini quad frame, what to look out for to get the best frame, and how the frame affects flight performance. There are many considerations go into choosing an ideal frame for your very personal requirement and style.
Index of Content
- What is a mini quad frame
- Frame size
- Frame shape
- Unibody design
- Freestyle or Racing?
- Other considerations
- Evolution of Frame Design & Style
What is a mini quad frame?
The mini quad frame is the main structure that contains the components of a mini quad, or quadcopter.
As you can see, there are different parts of a quadcopter frame or chassis. Some frames have all 4 arms cut from a single piece of carbon fiber, this is often referred to as a monobody or unibody. Some have protection for the FPV camera at the front and this is often called the camera “cage”
The Ideal Mini Quad Frame
The perfect mini quad frame should be lightweight and strong. But just like so many things with mini quads, it requires sacrifice and balance.
The design and material of a frame determine how crash-resilient it is. Generally stronger frames are heavier and tend to be more stable in the air. And lighter frames are more efficient and nimble.
Strong and resilient
Miniquads are designed for FPV racing, speed is top priority thus crash is inevitable. For hobbyists with a limited budget, this is especially important IMO. If you break an arm or top plate every session it’s definitely going to ruin the fun.
Light-weight and aeroydynamics
A lighter frame will require lower throttle to hover and therefore gives you longer flight time. It can also react more quickly to stick inputs and accelerate faster.
However some lightweight frames might use thinner material which has a tendency to flex and vibrate during flight. This can affect the FC and PID controllers and make tuning a real hassle.
Furthermore, ultralight frames often sacrifice protection for components in the quest to lose a few grams.
Quadcopter frames have significant impact on your flight performance: aerodynamics, weight distribution, rigidity, etc, all play a part in flight characteristics.
Further Reading: How a light weight racing drone is different from a heavier one?
Aesthetics and well thought out design
A mini quad frame is more than just some sheets of carbon fibre. The design determines how easy it is to install components and put together. More and more frame designers incorporate different materials and shapes into the frame to make them look cooler, weigh lighter and provide better protection.
As an interesting fact, we usually call our quads by the name of the frame (like, “let me show you the Blackout I just built!”). Maybe not as deciding as other factors, but indeed the name matters too :D
There are a lot of factors to think about frames, we will try to cover as much as we can in this article.
Materials For Mini Quad Frame
A mini quad frame can be made from any material you can possibly think of: Wood, 3D printed plastic, injection molded plastic, fibre glass, aluminium, or even PVC pipes. However carbon fibre remains the most popular material for mini quad frames thanks to its relatively low cost and excellent physical properties:
- Light weight – a lighter racing drone means faster speed, better agility, longer flight time, and less destructive inertia in a crash
- Strength – carbon fiber is known to be relatively tough and durable
- Rigidity – CF has high stiffness to weight ratio. Frame rigidity is important for stability and flight performance
However there are some downsides to using carbon fiber for frames:
- Carbon fiber is electrically conductive. If you have live wires touching the frame it could cause a short circuit and burn out components
- It also blocks radio frequency 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 fibre mini quad frames.
Construction of a Mini Quad Frame
A mini quad frame can be simply divided into 2 parts, the body, and the arms.
The body houses and protects your electronic components including flight controller, PDB, FPV camera, VTX etc. Typically it consists of a bottom plate, top plate and some standoffs in between to hold them together.
The arms are where to install your motors, and very often your ESC’s as well. The arms are designed for durability and they are usually made from 3mm to 4 mm carbon fiber (CF) sheets, these days it’s becoming common to see 5mm and even 6mm CF used for the arms.
The size of a quadcopter frame, a.k.a. wheelbase, is the diagonal motor to motor distance in millimeters.
A mini quad is usually designed for a specific propeller size, and therefore a frame may be referred to based on the size of propeller too. So when you hear people describing “a five-inch frame,” it means the frame is sized for 5″ props.
The size of a mini quad frame determines the choice of most of the components you will use in the build. A more powerful drone requires a larger frame for longer props and larger motors, while a smaller frame will use shorter props and smaller, less powerful motors.
Frames tend to be made as small as possible to keep the weight down, and motors as close to the centre as possible.
Motors are mounted on the very end of the arms. The further away they are from the centre, the larger the moment of inertia, which introduces a tendency to resist angular acceleration and deceleration. With all other things being equal, the smaller the frame, the more nimble the craft becomes.
Furthermore, the bigger the frame, the more air resistance when flying forward. The frame weight also goes up due to the increase in material.
To make things easier, here is a simplified table with mini quad frame sizes and maximum propeller size they can use:
|Frame Size||Prop Size|
Please be aware this table only aims to give you an idea.
Pro Tip: Regardless what the size of the frame is in “mm”, always check what prop sizes it supports. For example an 5″ frame might be larger or smaller than 210mm. Sometimes a 250mm frame might only accept 5″ but not 6″ props. It all depends on the actual design.
Although you can run smaller propellers on a frame, always try to avoid doing so for optimal performance. A quad performs best when using the largest possible props it is capable of swinging.
Frame Shape and Arm Layout
The frame shape, or arm layout is determined by how the arms are connected to the body. It does not only affect appearance but also impacts flight performance on a number of levels. Currently, the popular frame styles are:
- Hybrid X
- Stretch X
- Square (Box)
It might look like the motor layouts are very similar and are all rectangular, but each of these frame type performs differently in some way. Whether or not the different arm layouts provide any real benefit, has always been a controversial subject. But based on my own personal experience they do feel differently in the air.
Early mini quads started with H style frames. They have seemingly unlimited space for components, making these frames very easy to build.
The arms connect at the front and rear of the body on a “H” frame. It creates a long and roomy body that can house your electronics comfortably.
HD camera and battery can both sit on the top plate, and the weight of the quad is more spread-out. For this reason, it might feel less agile than the newer X frames due to higher moment of inertia on the pitch axis. However some people prefer this behavior for smoother freestyle flying.
On an X frame all the arms meet at the centre forming an “X” shape, with equal width and length. The body is shortened as much as possible to achieve a more centralized mass. This results in less moment of inertia and ultimately more snappy flight characteristics compared to H frames, more ideal for FPV racing.
X style frames are also lighter too because of the reduction in material. However your components have to be stacked up in the middle due to the smaller body, and it could be a little bit more challenging to build.
People sometimes call it the “true X frame” to differentiate from the other types of X frames.
The Hybrid-X has the X frame arms, but H frame’s long body. Some argue this has little to no difference to an H frame in terms of flight characteristics, since the mass distribution is the same. But I think there is a difference to how the thrusts are applied on the frame (think about leverage). There may also be a change in the way prop/motor vibration is transferred to the FC in different directions through the arms.
Stretch X Frames
Similar to a “true-X” frame in appearance, the “stretch X” has the front and rear arms configured further apart. The idea is to reduce air disturbance and improve cornering performance in racing and high speed flying.
Moving the rear props away from the front props can minimize air turbulence, this allows the copter to remain more stable when flying fast.
I find stretch X frames require a slightly different touch when tuning PID and rates, because of the change of frame geometry. Stretch X frames seem to be more precise on pitch, and more sensitive/responsive on the roll axis than a standard X frame.
They also tend to weigh slightly more because of the increased material used in the longer arms.
Square (Box) Frames
A square or box frame could be based on a H or X frame, with extra material on the outside that connects the motor mounts. This basically creates a tougher frame that is less likely to have broken arms. However the increase in material blocks prop airflow, increases weight and air resistance. Not a good choice for performance aircraft, unless you are new to this hobby and worry about breaking stuff.
Instead of flying forward like an “X”, a Plus Frame flies forward like a “+” sign. It’s a special type of frame because it’s not very popular. There may be some benefits with regards to motor turbulence though, because the side motors on a plus frame will always be spinning in clean air. One of the downsides is the front motor and propeller can easily get in the view of the camera.
To solve the problem with the motor being in the view of the camera, frame designers stretched the front and rear motors away from the centre. But it’s still not a popular frame design apart from the fact that it looks pretty unique and eye-catching.
Other Frame Configurations
There are some other different frame designs out there, such as the deadcat, V-tail etc. These configurations are not as popular because they often require custom motor mixing and they are harder to tune.
A frame can be designed to have replaceable arms, but that means extra hardware such as screws, bolts and extra bottom plate. That could mean a lot of extra weight!
You can avoid the extra weight by having an unibody design (aka monobody), where the arms and the bottom plate are a single piece of CF. It’s not only lighter but also makes assembling your quad much easier. However if you break an arm, you would have to replace the whole bottom plate. Obviously it’s cheaper to replace a single arm, and moving all the electronics and motors over to the new chassis is more time consuming.
When racing, you are going to crash often, meaning a greater chance to break the arms. Therefore it makes good sense for racers to have replaceable arms.
Modern frame design has brought us very durable unibody frame designs too, but I would probably only consider those for a freestyle quad, and only one that uses minimum 4mm thick CF (on a 5″ – 6″ frame).
As for rigidity, I generally find frames with replaceable arms stiffer than a unibody. The stiffness of unibody depends on how wide and thick the arms and plates are, and how big the cut-outs are. I have had some bad experience with 3mm unibody design, It was so bendy and I had oscillations that were difficult to eliminate. I replaced the 3mm with 4mm CF and it was much better.
Carbon Fibre Thickness
Thicker carbon fiber results in better rigidity and sturdiness, but it also gets heavier.
Durability matters most on the arms, as they take most of the strain in a crash. This makes it common to see top, center and bottom plates cut from thinner 2mm, even 1mm CF
5″ frames commonly used 3mm or 4mm CF, but advancements in racing motors have made 5mm and 6mm more common, to withstand the greater forces of higher speed impacts. For 5″+ frame sizes you should be looking for at least 4mm thick arms, for 3″ – 4″ you can go down to 3mm and for 2″ just 2.5mm. Any thinner than this will break too easy.
Serious ultralight racing quads often use 3mm arms to save weight, with the idea that “racers crash, they break arms! Make the arms light and practically disposable”. Less weight on the arms means less rotational inertia and improved flight performance, ittop’s a good business strategy too!
Filing Carbon Fibre Edges
When you receive a new frame it is a good idea to handle it carefully and wipe it down with a damp cloth to remove any residual.
If your frame comes with a rough finish and sharp edges, I recommend you chamfer the edges not only for the better look and feel, but also the following practical reasons:
- Sharp edges can cut through wires, LiPo straps, etc
- Chamfered the edges, and then applying Cyanoacrylate glue (CA) can prevent the carbon fibre from delamination in a hard crash
In this tutorial I will show you how to prepare a carbon fibre frame by filing the edges. It’s best to do this under running water to avoid breathing in CF dust, the ultra fine particles are harmful to your lungs.
Freestyle or Racing
For racing, I would say the most important factor is weight and crash-resistance. Having light and easy-to-replace arms are going to be really helpful.
For freestyle, the most important factor for me has to be how easy it is to build/repair, and how well it withstands crashes.
FC standoff spacing – Make sure the frame supports the FC and PDB you are planning to use, most commonly FC’s have a mounting pattern of 30.5mm x 30.5mm, or 20x20mm. Although there are 3D-printed adapters you can easily obtain, these are not always supported.
FPV Camera Mounting – There are now 3 main sizes in FPV camera, standard, mini and micro. Make sure to find a frame that supports the camera you are planning to use. You will also need to find out what kind of camera tilt you can achieve, and how easy it is to adjust. A tilt angle that is too low or too high can hugely affect your FPV experience
Rigidity – We have mentioned the importance of frame stiffness more than a dozen times . A well designed frame should be strong, crash resistant, yet rigid. If there is bending or warping in the arms during flight, your quad will be prone to problematic vibrations. As a result the quad can be hard to tune, and you might get jello in your FPV feed as well as the HD flight footage. If your quad suffers from vibration, the flight controller must work harder to stabilize the copter, and in extreme cases vibrations can even cause your motors to overheat.
Weight is an extremely important factor to your quad’s performance. Good quality carbon fibre is all generally similar in weight. The main difference comes down to how the frame is designed, how much material is used, what sort of screws and standoffs are used etc.
Durability – It’s very difficult to predict how durable a frame is just by looking at pictures and spec. The best thing to do is to look at reviews and comments. Pay attention to how well the components are protected by the frame and make sure nothing is exposed to crash damage. Countersunk screws look nice, but they can introduce weakness in the frame, watch out for screw holes too close to the edge of the material.
HD Camera Mounting – If you plan to fly with an HD camera such as a GoPro or Runcam 3, make sure to check whether or not the frame can support it! You might have to spend extra to get a 3D printed mount, or it might be included in the kit.
Spare Parts and Warranty – No spare parts available means buying a new frame when you break an arm or top plate. The availability of spares is extremely important. Some manufacturers even offer a “lifetime” warranty which allows you can get replacement parts whenever you break them. These frames normally cost a bit more to begin with, but it’s comforting to see designers show such faith in their own product.
Protection for the motors – Extra material around the motor mount could potentially protect your motors from damage in crash. but this does increase weight.
Chamfered carbon fibre edges – It is a time consuming job filing those sharp edges. Therefore some manufacturers are now shipping their frames with chamfered edges, giving you one less job before you can build, fly, and crash!
Battery Location – Top Mounted or Underslung?
Should we put LiPo battery on top of or underneath the frame?
Here is a more in-depth discussion whether it’s better to mount your battery on top or bottom.
I personally prefer to have the battery mounted on top for 2 reasons:
- Center of mass is closer to the level (or plane) of the propellers, where the force is generated. This reduces the moment of inertia when rotating, it also makes the quad handle corners better in my experience
- Landing on the battery repeatedly can damage it (crashing is a different matter, you never know which side will will take the blunt of the impact)
- Mounting the battery on the bottom can introduce a pendulum effect, which makes control a little less precise when doing extreme maneuvers
Anyway, on some really compact frames I have no choice but mount the battery underneath due to space limitation, and I am happy to do it.
Evolution of Mini Quad Frame
The world of racing drones evolves extremely quickly, products can often become redundant in just a few months. In this section I will feature some of the interesting frame designs throughout the history of mini quad, they all have some unique features to offer. Please note that this is not a comparison. :)
If you think I should cover other frames, please comment down below!
The Blackout frames were the beginning of mini quad, released back in 2014. It was expensive and hardly available back then due to popularity. Shortly after the ZMR250 made it more affordable and accessible for hobbyists world wide (many consider it as a clone of the blackout). Most frames at this time were 250 sizes and running 5″ and 6″ props.
The Lumenier QAV frames were made popular by Charpu (he was sponsored by Lumenier after all). And then there was this cool looking, but heavy Atas Defiance 265 and Robocat.
The Alien by ImpulseRC was an iconic frame, as it was one of the first hybrid-X frames and endorsed by many top pilots at the time. The Armattan F series frames were also very popular back then.
The most popular size of mini quad settled at 5″, because most people believed 5″ is the best balance between power and agility. And we began to see more and more “True-X” frames.
Later we have X frames with different camera pod designs, and 3D printing started to play a bigger part in mini quad frames.
Different materials are used in mini quad frames, such as the Ragg-E that uses super durable HDPE. On the other extreme, some frames tried to shave as much weight as possible by making skinny arms, such as the X-foot or the QAV-ULX.
In the 2nd half of 2016, we started to see vertical standoffs replaced with side plates structures. The Armattan Armadillo and DemonRC Fury are great examples of that.
The beginning of 2017 saw the introduction of aluminium (and other metals) into frame design. These materials are often used to provide additional protection to the FPV camera and other components, they can also be anodized to add a flash of color. The new designs create a strong structure yet it looks awesome! Both of these frames, the DQuad Obsession and Armattan Chameleon have been featured in our top 5 best frames in 2017.
Buy clone frames to save money… ?
There are a lot of overpriced frames out there, you should consider carefully how much a frame kit is really worth. And frame cloning is a very common problem in this hobby because how cheap and easy it is to copy a frame design.
If you are considering a clone, then you must really like the design. I don’t encourage people to buy clones, but if that’s what you can afford, I don’t blame you. Anyway, try to avoid clones whenever possible, not just for the quality, it’s more about sustainability.
It takes a company months to design, test and release a frame, it doesn’t cost the cloners anything. Especially so for mini quad frames, after all they are just pieces of carbon fibre, anyone with a CNC machine can do it. Therefore frame manufacturers inevitably suffer from copying and cloning. Cloners can sell their frames at half of the price or even lower, because they didn’t invest in R&D, and they often use cheaper material.
You can measure the performance of a motor or ESC pretty easily and fairly objectively, but it’s a little bit more complicated than that with a frame. There are a lot considerations in the design, aesthetics, features, ease to build, placing of the components and user experience.
Anyway I hope this guide has helped you understand the basics of mini quad frame!
- Mar 2017 – Article created
- Feb 2018 – Added plus configuration description and image, updated frame size image, added anatomy image, fixed various grammar errors