FPV Quadcopter Part Spotlight: Frames

FPV racing and freestyle quadcopters use a light and strong frame. You mount components to this platform. Each frame normally has a general layout which you will follow. This layout gives you an organized space and often special parts to mount the internals  of your build. The frame determines a good deal about your build and ultimately the flight characteristics of your copter.

This article is part of a series that covers the entire concept of quadcopter parts, how they work, and how they come together. For further reading, see the master article: Components & Anatomy of an FPV Quadcopter

There are two main parts to the frame - the base plate and the body. We cover the details of both of these main sections and their details below.

Construction of an FPV Quadcopter Frame

Base Plate

This is the main section of the air frame on which you mount the main components of your quad including the motors, ESCs and flight controller. This main section is designed for durability and is made using 3 to 4 mm thick carbon fiber.

In the center of the base plate you will find 4 holes drilled in a square pattern which is where the 'stack' lives. The stack consists of the main circuit boards for your quadcopter which includes a power distribution board, flight controller and often an on-screen display. Recently companies have been combining these components into a single board which shortens the height of the stack.

Size

The size of a frame is the diagonal measurement in millimeters from motor shaft to motor shaft. This size plays a big role in the flight characteristics, build, and propeller usage. Below we are going to cover common frame sizes for FPV racing/freestyle. There are much larger frames available than what we cover here, but they are not normally seen at race day.

• Small frames run 180mm and below. These frames normally use 4 inch propellers or smaller.
• Medium frames run between 180mm and 250mm. These frames normally use 5 inch propellers.
• Large frames run larger than 250mm. These frames normally use 6 inch propellers or larger. You won't commonly find frames for FPV racing much larger than this.
  • For reference the MultiGP FPV league allows no larger than a 305mm frame in all but the open class. See their classes and specifications page for more info.

When shopping for propellers for your frame, make sure and double check which size propeller is recommended. The diagonal measurement in millimeters doesn't directly translate into which size prop the frame supports. The most popular frames out will normally be running 5 inch propellers. This usually translates to between a 190mm to 220mm frame size. This size gives you a nice balance of performance, part compatibility, & build skill required.

Frame Shape

How the arms connect to the base plate determines the shape of the frame. The shape of the frame influences the body type and ultimately the flight characteristics. There are many variations out there, and we've covered the main ideas here. Beyond these 3 basic types you will find frames of all types of designs. Companies are constantly experimenting with different shapes and sizes.

H Frames

The front and rear arms on an H shaped frame connect at different points along the pitch axis of the base plate. The arms are 'spread out' along the This construction is known for more stable flight characteristics. Commonly the battery is mounted on top of the top plate of the body. This top-heavy design is supported by the more stable H shape.

True X Frames

All the arms on an X shaped frame pass through a single center point. You will find the arms set at different angles to each other depending on the frame. Arms set with 90 degrees between each is known as a 'True X' because it follows this pattern.

These frames are commonly found on smaller multi-rotors and are known for their snappy flight characteristics. This shape is commonly found on the race track. The battery on these frames is sometimes mounted below the base plate which encourages these flight characteristics even more.

Stretch X Frames

These frames are similar to X frames in that the arms connect to the center of the baseplate to form an 'X'. The main difference is that the arms don't meet in a true X pattern. They often meet in an elongated fashion along the pitch axis. This makes the frame longer than it is wide - stretched from front to back. This frame design carries benefits from a racing standpoint that provides stability in pitch (speed) while maintaining maneuverability in the roll axis.

Box Construction

These frames use an additional bar running between all (or some) of the arms of the frame. This type of construction allows for a stronger and more protected frame.

Body

Built up off the base plate, the body of the quadcopter surrounds the components allowing you to mount them to your build. As we mentioned at the beginning of the article, the body usually has a standard layout that you will follow when building.

Things like the flight camera, video antennas/transmitters, and battery often have pre-defined places they live in the body. This is important to mention because often this means there are some compatibility requirements to consider when purchasing parts.

Top Plate

The body space is created by using standoffs and a top plate. This spacer system allows for mounting of additional components as well as protecting the inner components during crashes. The top plate is thinner carbon fiber because it does not have main components mounted to it.

Length / Shape

Early FPV pilots used larger H shaped frames which encouraged a longer body layout. Smaller X shaped frames changed this practice. Now it is common to see small, square bodied frames.

• Longer bodied airframes allow for more build space because components can be mounted along the length of the body. You normally mount the battery on top of the body. This layout spreads the weight distribution out above and along the pitch axis of the frame.
• Shorter or square bodied airframes are generally tighter in build space and lay components out in more of a vertical fashion. Often you will find the battery mounted below the base plate. This layout keeps the weight distribution more centralized.

The popular ImpulseRC Alien frame is an X shaped frame with a long body.

Most square body frames are X shaped, but there are X frames that are long bodied. There are no hard and fast rules when it comes to frame design.

Find an FPV Frame

Hopefully this article helps give you a deeper understanding of frames for FPV mini quads. Please leave questions and comments below. Here at Controller Craft we catalog every drone product from around the industry. Visit the frames section to browse the options available industry wide.