Servo arm (indoor)

About the servo horn

What it is for

This servo horn sits on top of the servo's stock horn and gives the arm the exact length the linkage needs.

The servo is most precise when it uses its full travel to give the throw you want: the small play in the servo and the linkage counts for little against a large travel. A servo horn that is too long forces you to reduce the travel in the radio, and the control loses precision. Too short, it does not give the throw you want. The “Control surface linkage” calculator gives the right length, and its “3D model” link opens this servo horn already set up.

Several shapes cover the usual setups: one arm for one pushrod, two opposite arms for two pushrods or cables. A straight arm gives the same movement both ways. An angled arm gives a larger movement on one side (differential, often used on ailerons). Two arms of different lengths have the same effect.

Fixing to the servo

The stock servo horn stays on the servo, and the servo screw goes through both parts. The servo horn is fixed onto it in one of two ways:

Tied on, without fixing holes.
Screwed into the holes of the stock servo horn, with fixing holes.

On the single arm, the back arm also holds the other side of the stock servo horn: the grip is wider, whether tied on or screwed.

Assembly

Set the servo to neutral.
Place the servo horn on the stock servo horn, centre hole on the servo shaft.
Tie it on, or screw it into the holes of the stock servo horn.
Tighten the servo screw.
Attach the linkage to the hole at the end of the arm: bent piano wire, or a ball link (more precise).
Check the throw on each side with the radio, and that there is no binding over the full travel.

Making it

3D printing (STL): PLA, 0.16 mm layers, 3 perimeters (walls), flat, no supports.
CNC or laser cutting (DXF): 1 mm carbon plate.

Related calculators and parts

Control surface linkage ›Servo arm or control horn length for the throw you want: four setups, differential, radio setup, 1:1 plan and 3D model.Control horn (indoor) ›Control horn that fits into a slot in the control surface: one arm on one side for a pushrod, or two arms on either side for a cable linkage (pull-pull). Solid base or tabs, adjustable linkage hole to put it in line with the hinge.

AArm length

Size it ›

KArm angle

Size it ›

EArm width

FLinkage hole

CHub diameter

DServo screw hole

Mounting holes

BThickness

Servo arm (indoor)

1ShapeSingleOne arm or two opposite arms, and shape options.

2ArmsA 25 mmK 0 °E 7 mmF 2 mmLength to the linkage hole, angle, width.

3Servo mountingC 10 mmD 5 mmNo mounting holesHub, servo screw and mounting holes onto the stock servo horn.

4ThicknessB 1,5 mmPart thickness.