Which carbon fiber tube size should I use for drone arms and booms?

Go as large in diameter as the motor mount and frame allow, and keep the wall thin. Bending stiffness grows with the fourth power of diameter, but weight only with the area. A 14/12 mm tube weighs about 65 g per meter and is slightly stiffer than a 12/8 mm tube at about 100 g per meter.

65 g/m14/12 mm tube

100 g/m12/8 mm tube, slightly less stiff

×9stiffness from 10/8 to 20/18 mm

×2.1weight from 10/8 to 20/18 mm

Multirotor drone frame with carbon fiber tube arms — Arm stiffness keeps motors aligned and reduces vibration reaching the flight controller and camera.

Weight and stiffness of the standard sizes

Calculated for our standard round tube sizes^[1], with a laminate density of 1.6 g/cm³^[2]. Stiffness is shown relative to the 10/8 mm tube, for the same material and layup.

Tube (OD/ID, mm)	Wall (mm)	Weight (g/m)	Relative bending stiffness	Stiffness per gram (relative)
6/4	1	25	0.18	0.32
8/6	1	35	0.47	0.61
10/8	1	45	1.00	1.00
10/6	2	80	1.47	0.83
12/8	2	101	2.82	1.27
14/12	1	65	2.99	2.07
16/14	1	75	4.59	2.76
16/12	2	141	7.59	2.44
18/16	1	85	6.68	3.54
20/18	1	95	9.32	4.41

Formulas: area = π(D² − d²)/4, weight per meter = area × density, bending inertia I = π(D⁴ − d⁴)/64.

Bending stiffness per gram (10/8 mm = 1.00)

10/8 mm1.00

12/8 mm1.27

14/12 mm2.07

16/14 mm2.76

18/16 mm3.54

20/18 mm4.41

Why not always use the biggest tube?

Motor mounts and clamps are made for set diameters. Check what your motor mount and arm clamp accept.
Thin walls crush. A 1 mm wall can crush under a tight clamp or a crash. Use a longer clamp, an inner sleeve or plug at clamp points, or a 2 mm wall at the root.
Drag and prop wash. A bigger tube under the propeller blocks more air. On small quads that matters more than the weight.

Roll-wrapped or pultruded for arms?

Roll-wrapped tubes have plies at several angles, so they resist twisting, crushing and crash loads better, and take a glossy or matte 3K finish^[3]. Pultruded tubes have all fibers along the length: very stiff in bending, consistent and economical, but weaker across the tube^[4]. For arms that carry motors and see crashes, roll-wrapped is the usual choice; for long straight booms, antenna masts and landing gear struts, pultruded is often enough.

Roll-wrapped carbon fiber tubes — Roll-wrapped: resists twisting and crash loads.

Bundle of pultruded carbon fiber tubes held in a hand — Pultruded: stiff, straight and economical in volume.

TipTest arm stiffness the simple way: clamp the arm, hang a weight equal to the motor's maximum thrust at the motor position and measure the tip deflection. Compare two tube sizes before you fix the frame design.

What to send for drone tubes

OD, ID and length, or the arm length and motor mount diameter.
Roll-wrapped or pultruded; glossy or matte; plain or twill.
Cutting, drilling or slotting needed, with a drawing.
Quantity per order and per year.

Send it through the quote form. Frame plates are covered in ordering CNC carbon sheet parts. Use the weight calculator for other sizes.