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伺服是一個帶有齒輪箱和控制電子元件的小馬達。你可以告訴它將軸旋轉到什麼位置。

在類似iDryer的設備中，伺服可以打開阻尼器、移動小插銷、按下機械開關或重新定向氣流。

The main mistake with servos: thinking it is a "small thing" and you can power it from any 5V pin on the controller. A servo can draw significant current, especially at startup, sudden movement, or when the mechanism binds.

Three wires

A typical hobby servo has three wires:

  • power: usually 5V or 6V;
  • ground: GND;
  • signal: control pulses from the controller.

Common colors:

  • red - power;
  • black or brown - ground;
  • yellow, orange, or white - signal.

But you cannot blindly trust colors. Different manufacturers may use different color schemes. Before connecting, check the marking, product page, or datasheet.

Power separate, signal separate

The signal wire does not power the servo. It only tells the servo where to turn.

The servo draws energy from the power wire.

The correct logic is:

  • the controller provides only the control signal;
  • the servo is powered by a 5V/6V source that can handle its current;
  • the controller ground and servo power ground are connected together.

Servo wire color code

Source: SparkFun Electronics, CC BY-SA 4.0

Why you cannot power from weak 5V

Many boards have a 5V pin. This does not mean a servo can be safely powered from it.

When moving, a servo may draw much more current than its size suggests. If power is insufficient, typical symptoms appear:

  • controller reboots;
  • screen flickers;
  • USB connection drops;
  • servo jerks;
  • Wi-Fi on ESP32 drops;
  • servo hums but does not move;
  • power sags at movement start.

For one small servo, board-supplied power sometimes works if the board and source are explicitly rated for that current. But for a real device with a damper, latch, or mechanism, it is better to use a separate 5V/6V DC-DC or power supply with a margin.

Common ground

If the servo is powered by a separate source, a common ground is needed.

Without a common ground, the controller and servo have no common signal level. The servo may not respond, may jerk, or may behave randomly.

Simple connection:

  1. +5V or +6V from the power source goes to the servo power.
  2. GND from the power source goes to the servo ground.
  3. The controller's GND is connected to the same ground.
  4. The controller PWM/GPIO pin goes to the servo signal wire.

Servo power and controller power may be different, but the ground must be common.

What signal is needed

A typical positional hobby servo is controlled by pulses.

Typical signal:

  • pulse roughly every 20 ms;
  • about 1 ms - one extreme of the range;
  • about 1.5 ms - middle;
  • about 2 ms - other extreme of the range.

This is not typical PWM for LED brightness or fan speed. Here, pulse width in microseconds matters.

The actual limits of a specific servo may differ. Some safely operate not from 0 to 180 degrees but less. So extreme positions need careful testing.

Do not jam a servo against the mechanism

A servo tries to hold the commanded position.

If a damper hits the housing, an arm binds, or the mechanism reaches a physical stop before the command ends, the servo keeps pushing. At that point, current rises, the motor heats, the gearbox wears out.

This is especially critical for dampers and latches.

Before permanent operation, verify:

  • the mechanism moves freely across the entire range;
  • no misalignment;
  • no binding of linkages;
  • the servo does not hum in the end position;
  • extreme angles in firmware do not force the mechanism into a stop;
  • with power off, the device stays safe or returns via spring, as intended.

If a servo hums at rest, it often signals load, a stop, or wrong lever geometry.

Starting and stall current

A servo has normal running current and current when the shaft is blocked. The latter is often called stall current.

Stall current appears when the servo tries to move but the shaft is blocked or the mechanism is too heavy.

This mode often causes:

  • power sag;
  • controller reboot;
  • wire heating;
  • DC-DC overheating;
  • gearbox breakage.

If the datasheet lists stall current, choose the power source accounting for this value and safety margin. If there is no datasheet, you cannot assume a servo is safe to run "by sight".

Capacitor next to the servo

Sometimes an electrolytic capacitor between +5V and GND next to the servo helps.

It does not replace a proper power supply, but can smooth a brief sag at movement start.

For a small servo: hundreds of microfarads, like 470 uF or more, with voltage rating above the supply voltage.

Electrolytic capacitor polarity matters:

  • capacitor plus to +5V;
  • capacitor minus to GND.

If the device needs to be reliable, first choose proper power and wiring, then use a capacitor as an extra measure.

Example Klipper configuration

In Klipper, a servo is described with a [servo] section.

Example:

[servo chamber_damper]
pin: PA8
maximum_servo_angle: 180
minimum_pulse_width: 0.001
maximum_pulse_width: 0.002
initial_angle: 90

Commands:

SET_SERVO SERVO=chamber_damper ANGLE=0
SET_SERVO SERVO=chamber_damper ANGLE=90
SET_SERVO SERVO=chamber_damper ANGLE=180

Pin names here are typical. In a real device, check your board's pinout.

For mechanics, do not start with 0 and 180 right away. First test a safe range like 60, 90, 120, then expand the angles.

Example Arduino/ESP32 logic

Arduino approach typically uses the Servo library:

#include <Servo.h>

Servo damper;

void setup() {
  damper.attach(9);
  damper.write(90);
}

void loop() {
}

This is just an example of signal logic. Servo power still needs to be designed separately. Even if the signal wire is connected to Arduino or ESP32, the servo motor must not overload the controller power.

What to check after connecting

Before mounting in the housing:

  • servo receives the correct voltage;
  • power source can handle servo current;
  • controller ground and servo ground are common;
  • signal wire is connected to the right pin;
  • servo moves in the right direction;
  • extreme angles do not break the mechanism;
  • mechanism does not bind;
  • servo does not hum continuously;
  • wires do not catch on the lever or gears;
  • power does not sag after movement;
  • controller does not reboot.

Test mechanics unloaded and under real load. A damper that moves easily by hand may bind after mounting in the housing.

Common mistakes

  • powering servo from GPIO;
  • powering servo from a weak 5V board pin;
  • forgetting common ground;
  • trusting wire colors without checking;
  • connecting power backwards;
  • using too-thin wires;
  • not accounting for starting and stalling current;
  • forcing servo to push against a mechanical stop;
  • using angle 0 or 180 when the real mechanism safely runs only in a smaller range;
  • mounting servo near heat without checking operating temperature;
  • treating a continuous rotation servo as a regular positional servo.

Key points

  • A servo has three lines: power, ground, and signal.
  • Signal does not power the servo.
  • Real devices often need a separate 5V/6V power source.
  • Servo ground and controller ground must be common.
  • The most dangerous load is jamming or mechanical binding.
  • Extreme angles need careful selection, not immediate 0 and 180.
  • If the controller reboots when the servo moves, first check power and common ground.