What is a hummingbird rotation servo?

A hummingbird rotation servo is a small servo motor that is designed to provide precise rotational movements. Servos are used in radio-controlled vehicles like drones, planes, helicopters, and cars to control the steering or other movable parts. Hummingbird servos get their name from their small size – they are designed to be lightweight and compact.

What does a servo motor do?

A servo motor contains gears and a control circuit that allows it to rotate to specific positions. Inside a standard servo there is a DC motor, potentiometer, control circuitry, and gearing. When power is applied, the motor tries to turn, but the position is controlled by the servo mechanism using feedback from the potentiometer. The control circuitry compares the potentiometer position with the desired position from the control signal and moves the output shaft accordingly.

Servos are used when you need precise angular rotation and control. The motor will turn to the desired rotation angle based on the width of a control pulse. A 1ms pulse will make the motor turn to 0 degrees, 1.5ms to 90 degrees, and 2ms to 180 degrees. This allows servos to be controlled by a digital signal from a microcontroller or radio receiver.

What are the key components of a servo?

Here are the key components found inside a standard hobby servo:

• Motor – This is typically a small DC motor in the range of 3-7V with high torque and speed in a small form factor.
• Potentiometer – This acts as a feedback sensor to detect the current angle of the servo horn/output shaft.
• Gear train – A set of gears that provides speed reduction and torque amplification between the motor and output shaft.
• Control circuit – This circuitry reads the position of the potentiometer and controls power sent to the motor to drive it to the commanded position.
• Output shaft/horn – The rotational output that can be connected to other mechanical linkages.
• Case – The plastic and metal housing that contains all the components.

Within the servo, the motor is attached to a gear train which drives the output shaft. The potentiometer is connected to the output shaft to provide position feedback. The control circuit reads the angle feedback and adjusts the motor power until the output is at the desired angle.

How does a servo work?

Here is an overview of how a hobby servo functions:

1. The servo receives a control signal pulse with a specific width, usually from a radio receiver or microcontroller. Common widths are 1ms, 1.5ms, and 2ms.
2. The servo control circuitry reads the width of the pulse and determines the desired angle of rotation.
3. The controller checks the current angle position as read from the potentiometer.
4. If the current angle is different than the desired angle from the control signal, power is applied to the motor to rotate it. The gear train converts the high speed motor rotation to slower output shaft rotation with higher torque.
5. As the output shaft turns, the potentiometer rotates and provides new position feedback.
6. Once the output shaft reaches the desired angle, power to the motor is stopped. The servo holds this fixed position against resisting forces.
7. If a new control signal comes in, the process repeats to turn the output shaft to the new desired position.

This feedback control loop allows the servo to turn an output shaft to precise angles despite variations in motor speed and loading forces. The power delivered to the motor is proportional to the difference between the commanded position and actual position, so minor errors are automatically corrected.

What are the typical specifications for servos?

Here are some typical specifications for RC hobby servos:

• Torque – Torque ratings are given in kg/cm or ounce/in units. Torque ranges from around 1.5 kg/cm for small servos up to 20+ kg/cm for large digital servos. This determines how much force the servo can exert while holding a position.
• Speed – Speed is measured by how fast the servo can move to a new position, usually given in seconds for a 60 degree movement. Faster servos have higher speed ratings.
• Size – Common sizes range from micro servos (20x10mm) up to large servos (60x30mm). Standard sizes are 23mm wide x 12mm tall x 29mm long.
• Weight – Servos typically range from 9 grams for micro servos to over 100 grams for large digital servos.
• Rotation – Most servos rotate up to 180 degrees total range, sometimes up to 270 degrees.
• Operating voltage – 4.8-7.4V is typical for servo operation. Some can operate up to 8.4V.

The torque rating is usually the main specification to consider based on the required forces expected in the application. Speed and rotation range are other important factors for how the servo will be used.

What is pulse width modulation?

Servos are controlled using pulse width modulation (PWM). This means the length or duration of the pulse controls the servo position. Here’s how it works:

• A repeating pulse signal is sent to the servo, usually 50 times per second (50 Hz).
• The length of each pulse controls the rotation angle. Common lengths are 1ms, 1.5ms, and 2ms.
• A 1ms pulse signals the servo to rotate to 0deg, 1.5ms to 90deg, and 2ms for 180deg.
• The servo moves to the angle commanded by each pulse.
• Pulse lengths between the extremes result in corresponding intermediate angles.

This use of PWM allows precise control of the servo rotation with just a digital signal. No extra encoding or analog values are required. The PWM pulses can be generated from a microcontroller or transmitted from a radio control receiver.

What is the role of the potentiometer in a servo?

The potentiometer inside a servo acts as an angular position sensor to provide feedback of the output shaft angle. Here is how it works:

• The potentiometer is mechanically linked to the output shaft so it rotates as the shaft turns.
• It acts as a variable resistor, with the resistance value changing based on the angle.
• The servo circuitry reads the current angle from the resistance of the potentiometer.
• This angle is compared to the desired angle from the PWM signal.
• If the angles don’t match, the servo rotates until the potentiometer angle matches the commanded angle.

This closed-loop feedback control with the potentiometer enables the servo to precisely move to specified angles. Without feedback, effects like motor friction and inertial forces would cause errors in the output position.

What gear train is used in a servo?

Servos utilize a gear train to convert the high speed motor rotation into lower speed, higher torque rotation of the output shaft. The gear train typically consists of 3 gears:

• Pinion gear – Small gear attached to the motor shaft.
• Intermediate gear – Larger gear meshed with the pinion, rotates more slowly.
• Output gear – Final gear attached to output shaft, rotates slowest.

With each stage, the speed drops but torque is multiplied according to the gear ratio. This allows the motor to operate at high efficient speeds while the output has much higher torque capable of moving external loads.

Gear ratios usually range from around 300:1 up to 1000:1 from motor to output shaft, depending on the servo torque and speed requirements.

How do gear ratios affect servo performance?

The gear ratio used in a servo’s gear train affects its speed and torque performance. A higher gear ratio leads to:

• Higher torque – More torque amplification from the motor.
• Lower speed – Increased speed reduction.
• Lower resolution – Reduced ability to make small position changes.

Conversely, a lower gear ratio provides:

• Lower torque – Less torque amplification.
• Higher speed – Faster movement and response.
• Higher resolution – Ability to make finer position adjustments.

Selecting the right gear ratio depends on the speed and torque required for the servo application. Slow, high torque uses like radio-controlled vehicle drive trains need high gear ratios. Fast, responsive applications like robot joints can use lower ratios.

What are the different types of servos?

There are several varieties of servos designed for different uses:

• Standard – General purpose for RC vehicles and robotics. Offers good compromise of speed, torque, and size.
• High speed – Optimized for very fast response and acceleration.
• High torque – Slower but capable of high forces for large loads.
• Digital – Higher performance with embedded control circuits.
• Mini and micro – Very small servos for tight spaces.
• Specialty – Unique servos like waterproof models.

So there are many servo types tailored to applications ranging from heavy robot drive trains to tiny RC aircraft. Specialized servos are also made for sail winches, focus control in telescopes, engine throttles, and more.

What are common applications and uses for servos?

Here are some typical applications and uses for hobby servos:

• RC vehicles – Steering, throttle, elevators, rudders, and other control surfaces.
• Robots – Manipulator arms, grippers, sensor platforms.
• Drones and aircraft – Flight control surfaces and camera gimbals.
• Cars – Power steering assist, shift control, brake actuation.
• Industrial – Precision positioning stages, Pick and place machines.

Any application requiring accurate rotational motion control can benefit from servos. Their feedback control allows them to move to precise angles under varying load conditions.

What are the advantages of servos over regular motors?

Servos have several advantages compared to basic DC motors:

• Precise angular position control – Can rotate to specific angles on command.
• Feedback mechanism – Uses position sensing for precise control.
• Closed loop speed control – Speed can be regulated by the control electronics.
• High shock resistance – Durable, absorbs heavy impacts.
• Compact package – Motor, gears, and control in one unit.

The integrated position feedback allows much more accurate motion control than open loop DC motors. The gear train also provides servo motors with higher usable torque at lower speeds compared to similar sized basic DC motors.

What are the limitations of servos?

Some limitations and disadvantages of servos include:

• Limited rotation – Often less than 180 or 270 degrees total.
• Not designed for constant rotation like a basic DC motor.
• Lower top speed than an ungeared motor – Tradeoff for higher usable torque.
• Potentiometer may experience wear over time.
• More complex design means higher cost than plain motors.

Understanding the restricted motion range and torque/speed tradeoffs of servos is key. They are made for angular position control rather than constant high speed rotation. The potentiometer also has a finite lifetime as a mechanical component.

How are servos controlled from a microcontroller?

A microcontroller like an Arduino can be used to generate the PWM control signals to command a servo. Here is a typical servo control process:

1. The Arduino’s microcontroller is programmed to output PWM waveforms on a specific digital pin connected to the servo.
2. The Arduino PWM frequency is set to the required 50Hz servo signal rate.
3. The PWM duty cycle is varied from about 5-10% (1ms pulse) to 10-20% (2ms pulse) to sweep the servo angle from 0 to 180 degrees.
4. Transistor buffers are often used between the Arduino and servo to boost the current driving capability.
5. The Arduino code can control the servo angle based on inputs like sensor readings, preset sequences, remote control, etc.

This is a simple way to add motion control to an Arduino project with just a digital pin and a few lines of code to generate the servo pulses.

What are 360 degree continuous rotation servos?

Standard servos only rotate back and forth about 180 degrees. Continuous rotation servos are a modified version that spin fully around 360 degrees, like a standard DC motor. They are often used in robot drive systems.

These servos work by converting the control signal pulse width into a motor speed:

• 1ms pulse = Full speed clockwise
• 1.5ms pulse = Stopped
• 2ms pulse = Full speed counter-clockwise

Varying the pulse width between 1ms and 2ms smoothly controls the speed and direction from full forward to full reverse RPM.

This allows continuous rotation servos to be controlled like standard servos from a PWM signal but with the ability to turn continuously. The built-in control circuit still allows for precise speed regulation.

How are servo angles and pulse widths matched?

For a typical hobby servo, the angle of rotation is matched to pulse width durations as follows:

• 1ms pulse = 0 degrees rotation
• 1.5ms pulse = 90 degrees rotation
• 2ms pulse = 180 degrees rotation

So the servo angle is directly proportional to the length of the input PWM pulse. A 1.25ms pulse would command a 45 degree rotation. The PWM signals are usually sent to the servo about 50 times per second.

Some servos can accept an expanded range of pulses for angles beyond 180 degrees. For example, a 1ms to 2.5ms range might cover 0 to 270 degrees rotation.

The servo control circuit interpolates between these pulse extremes to reach any intermediate position. This linear mapping allows any angle to be commanded with just the width of a repetitive digital pulse signal.

How do you control the speed of a servo?

There are a couple ways to control the rotational speed of a servo:

• Vary PWM frequency – Increasing PWM frequency speeds up servo movement, decreasing slows it down.
• Control acceleration in code – Accelerate servo over time toward target position in firmware.
• Add external control – Use a dedicated servo speed controller device.

The most straightforward method is to increase the PWM control signal frequency above the standard 50Hz. For example, increasing to 100Hz or more will make the servo rotate faster.

For smoother speed control, code can be written to gradually ramp the servo position toward a target angle over time. This allows custom acceleration profile tuning.

External speed controllers are also available that handle acceleration and allow changing speed on the fly with an analog input signal.

Conclusion

In summary, a hummingbird rotation servo is a compact, self-contained actuator that allows for precise angular position control. Key components include a geared DC motor, potentiometer, and control circuitry. Servo motors find wide use in radio-controlled vehicles and robotics wherever accurate, repeatable rotational motion is needed. Understanding servo specs like torque rating, speed, size, and operating voltage allows matching these smart actuators to the requirements of a project.