Choosing an FPV frame

The frame is the first component you choose in a build, and it is the one decision you cannot walk back without starting over. Motor mounting pattern, arm spacing and prop size all fall out of the frame you pick, and prop size in turn decides the motor class you need, the current your ESCs have to handle, and how the aircraft actually flies. Get the frame wrong and you are not swapping a part, you are buying a second frame.

The question worth asking is not which brand makes the best frame. It is which size and which arm geometry match what you actually want to fly: thread a 3" quad through a hallway, freestyle or race a 5", or cover distance on a 7" and up. This guide works through how frame size is measured, what the geometry families actually change, where frames break, and the unibody-versus-replaceable-arms decision that decides your repair bill.

How frame size is actually measured

Two different numbers get attached to every frame, and they are not the same measurement. The first is the motor-to-motor diagonal, in millimetres: the distance from one motor mount straight through the centre to the motor mount diagonally opposite it. The second is prop size, in inches, the propeller diameter the frame is built to swing. A "5 inch frame" does not mean the frame is 5 inches across in any direction; it means the frame is built to give a 5 inch propeller room to spin without its tip meeting the arm, the camera mount or the opposing prop.

Both numbers get quoted because they answer different questions. The diagonal tells you whether the frame physically fits the space you fly in, and whether the motor mounting pattern suits the stack you already own. The prop size tells you almost everything about how the aircraft will fly: lift, current draw, top speed, and how much of a hit it can survive. Two frames with very different diagonals can be built around the same prop size, and the reverse is also true.

The former Mode 2 FPV frames documented in this domain's archive give a clean before-and-after of that relationship. The Kilowatt, a 3" unibody frame, has a 145 mm motor-to-motor diagonal. The Shredder scales the same idea up: 220 mm for its 5" version, 280 mm for the 7" version. The diagonal grows with the prop it has to clear, but not in lockstep. Going from a 5" to a 7" prop added 60 mm to the Shredder's diagonal, not 2 inches' worth of frame.

• Kilowatt145 mm diagonal, 3" prop, 30 g
• Shredder 5"220 mm diagonal, 100 g
• Shredder 7"280 mm diagonal, 105 g

Geometry families: what an X actually looks like

Almost every FPV frame sold today is some version of an X: four arms, four motors, camera and stack in the middle. What changes between frames is how that X is drawn.

A true X, also sold as a symmetrical X, places all four motors the same distance from the centre, front and back identical. Yaw authority is even across all four motors because the geometry in front of the flight controller mirrors the geometry behind it. Both the Shredder and the Kilowatt are built this way; the archived documentation for both names them explicitly as symmetrical X. It is the more common layout because it is the more predictable one: nothing about the frame biases yaw response toward the front or the back.

A stretched X moves the front arms further out than the rear arms (occasionally the reverse), which pulls the front motors and props out of the camera's forward view. The payoff is a cleaner picture, with less prop visible at the edges of the frame; the trade is that front and rear arm lengths are no longer identical, so yaw response is no longer perfectly even between the front and rear motor pairs. The Ghost 2, also from the former Mode 2 FPV catalogue, is built this way. Its own product listing calls the layout a "Stretch X".

Neither family is simply better. A symmetrical X gives you even handling and is easier to reason about when tuning; a stretched X gives you a cleaner FPV feed at a small cost to that symmetry. Which one to buy depends on whether you care more about the picture or about handling that behaves identically in every direction.

Arm thickness, and where a frame actually breaks

An arm rarely snaps in the middle. The failure point is almost always at the mounting holes closest to the centre plate, where the arm is thinnest relative to the load and where every impact concentrates its stress. This is why arm thickness and the plate it bolts to matter more than the arm's total length.

The two former Mode 2 FPV frames with documented arm and plate thickness sit at opposite ends of the size range, and the numbers reflect it. The Kilowatt, a featherweight 3" unibody design, uses a 2 mm side cage, a 3 mm bottom plate and 2 mm locking tabs: thin, because the frame is small, light, and carries little momentum into a crash. The Ghost 2, which spans 4" to 7", uses 5 mm boomerang arms, roughly double the Kilowatt's material, because a 7" quad carries far more mass and momentum into the same kind of impact.

The practical takeaway: arm thickness should scale with the frame's size and your flying style, not be judged in isolation. A thin arm on a 3" frame is not undersized; the same thickness on a 7" freestyle rig would be.

Unibody versus replaceable arms: a repair-cost decision

Some frames are cut and built as one piece; others bolt the arms onto a separate centre plate so a single arm can be swapped without replacing the frame. The Kilowatt is unibody, documented as such in the former Mode 2 FPV shop listing, and it is a sensible choice at 3" and 30 g: the whole frame is light and cheap enough that replacing it after a hard crash is not a large cost, and a one-piece design saves weight and machining steps a bolted design cannot.

That calculation changes as the frame gets bigger. A 5" or 7" build represents motors, an FC stack, wiring and a battery mount already invested in the frame. On a bolt-on-arm design, a snapped arm costs one replacement part and twenty minutes with a hex driver. On a unibody design at that size, the same crash can mean desoldering and remounting everything onto a new frame. Neither approach is wrong; the question is whether you would rather save weight and cost up front, or save a rebuild later.

Matching size to what you actually fly

Size is where all of the above comes together, because it is the decision that sets prop size, and prop size sets almost everything downstream.

3" frames are for tight spaces: gaps between trees, hallways, anywhere a 5" prop swing will not fit. The Kilowatt is a concrete example of what a 3" build looks like: 145 mm diagonal, 30 g, a 20×20 mm FC mount, and 13xx/14xx class motors, all sized down together so the whole aircraft stays light enough to survive clipping something.

5" is the default for freestyle and racing, and most of the frame market is built around it. The Shredder's 5" version, at 220 mm and 100 g, sits squarely in that class: enough prop for real speed and punch, light enough to throw around without the aircraft fighting you.

7" and up is for long range. More prop diameter means more efficient lift per watt at cruise, which is what buys distance. The Shredder's 7" version weighs only 5 g more than its 5" sibling, 105 g against 100 g, despite the larger prop swing and the frame growing from 220 mm to 280 mm; Mode 2 FPV's own documentation credits it with having "helped to popularize the 7" long range frame segment". The Ghost 2 makes the same point from the other direction: built across 4" to 7" on one geometry, it scales from 60 g at 4" to 75 g at 7", about 15 g for the whole span from a tight-space frame to a long-range one.

What decides your next component

Once you have settled on frame size, you have effectively settled the prop, and the prop constrains everything that bolts to the frame next. Check that a given prop size actually clears the frame you are looking at with the prop clearance calculator, and check whether your intended motor and battery combination will actually lift the finished aircraft with the thrust-to-weight calculator before you buy anything. The next component decision, matching motor KV and stator size to the frame and prop you have chosen, is covered in the motors and ESCs guide.

For more on the frames used as examples throughout this guide, including construction detail this page did not have room for, see the archive pages for the Kilowatt, the Shredder and the Ghost 2. All three were designed by the former Mode 2 FPV and released as open-source frame files; this site has no connection to that business beyond sharing its domain. For the rest of the build sequence, go back to the components overview.