Chapter 02 · Components
The drone’s skeleton
The frame holds and protects all the electronics, takes every hit and largely decides how the drone flies. It’s the first part to choose, because it sets the size of everything else.
Size
Frames are classified by the largest prop they can fit. Another common measurement is the diagonal distance between motor shafts (wheelbase): on a 5" it’s usually around 220–230 mm.
First choose the size for the kind of flying you want to do (see Which drone and what to buy), then look for a frame of that size that fits the rest of your parts.
Geometries
| Shape | What it looks like | What it’s for |
|---|---|---|
| True-X | Motors in a perfect square | Freestyle: responds the same on roll and pitch. |
| Squashed-X | Slightly wider than it is long | Freestyle and racing: more stable going forward and more room for the electronics. |
| Stretched-X | Longer than it is wide | Racing: less turbulence between the front and rear props. |
| Deadcat | Front arms spread wider | Cinematic: the props stay out of the shot. |
Materials and construction
Carbon fibre
Stiff and light, but conductive: no bare wire should ever touch it. Edges well finished or filed.
Arm thickness
5–6 mm for freestyle, so they survive crashes; 4 mm or less for light racing builds.
Separate arms
If one breaks, you replace just that one. On a unibody you have to replace the whole bottom plate.
Top or bottom battery
Top mount is the most common for freestyle. Bottom mount lowers the centre of gravity; common in racing and on some 7" builds.
Before you buy, check
- That the stack fits (30.5 × 30.5, 20 × 20 or 25.5 × 25.5 mm mounting holes).
- That the camera mount is the right size (micro 19 mm, nano 14 mm or the one for your digital system) and lets you adjust the angle.
- That there’s room and protection for the VTX and the antennas.
- That the camera is protected in a head-on impact.
- That spares are available: arms, plates and 3D-printed parts.
- The weight: a heavier frame is tougher, but the drone will be less agile.
After a hard crash, check the arms against the light: a small crack can snap mid-flight.
Open-source frames
Some frames are published by their designers under an open licence: the drawings for the carbon plates (in DXF) and the models for the printed parts (in STEP or STL). You can have them cut by a CNC machining shop, modify them or print the spares yourself.
5" freestyle
The Source family (One, Two and V) is the best known: tough, cheap to make and with spares from the many manufacturers who sell their own version.
Small quads and cinewhoops
There are micro versions from 2.5 to 3.5" and whoop-style designs for flying near people and indoors.
Racing
Light, narrow frames built for speed, like the PodRacer, with printed parts to protect the camera and the receiver.
Long range
7" designs with room for GPS and big batteries, for long, relaxed flights.
- Getting it cut: send the DXF and ask for 3K carbon in the thickness the design specifies (usually 5 or 6 mm for the arms). Ask for rounded edges: sharp edges cut wires.
- Printing the parts: in TPU, which is flexible and soaks up impacts. PLA breaks on the first crash.
- Check the licence: every design has its own. Some let you sell it, others allow personal use only or ask you to credit the author.
If you modify an open design, publish your changes under the same licence: that’s how these frames have improved year after year. More projects like this in Open-source FPV.