A servo is an electronic device that is used to operate RC cars, robots, electronic toys, and electrical appliances by determining the motion direction.
In this article, we will put our attention on two different types of servos – analog and digital. Stay tuned while we compare the similarities and differences between an analog vs digital servo.
And while this article is mainly focused on the analog vs digital servos used in RC cars, this knowledge can be applied to other uses like in an arduino board.
But first, watch this video to learn the basics.
What is a Servo Motor?
Before we go ahead and compare the two servos in depth, we first need to learn the technical aspects of a servo and how it works.
In general, a servo contains a DC motor, circuit, gear train, output shaft, and potentiometer.
The potentiometer is a position sensor that is connected to the output shaft. The shaft is attached to the control wheels by gears. The movement and its direction are controlled by an electrical signal.
Servo motors function based on the waves of pulses sent by a command, like from a transmitter, to create a mechanical motion.
For example, we use a servo to control steering by adjusting the levers back and forth. We also use a servo to control the speed of a radio control car by connecting it to the engine throttle.
The specification of a servo is normally being set by the turning angle per time at 60 degrees (speed) and the load carrying capacities (torque). There are also weight and dimension in the specifications.
So, how does the servo work?
Servos have three wires that extend from the casing (See photo on the left).
Each of these wires serves a specific purpose. These three wires are for the control, power, and ground.
The control wire is responsible for supplying the electrical pulses. The motor turns to the appropriate direction as commanded by the pulses.
When the motor rotates, it changes the resistance of the potentiometer and ultimately allows the control circuit to regulate the amount of movement and direction. When the shaft is at the desired position, the supply power shuts off.
The power wire provides the servo with the power needed to operate, and the ground wire provides a connecting path separate from the main current. This keeps you from getting shocked but is not needed to run the servo.
Analog RC Servos Explained
An analog RC servo motor is the standard type of servo.
It regulates the speed of the motor by simply sending on and off pulses.
Normally, the pulse voltage is at a range between 4.8 to 6.0 volts and constant while at that. The analog receives 50 pulses for every second and when at rest, there is no voltage sent to it.
The longer the “On” pulse is being sent to the servo, the faster the motor spins and the higher the produced torque. One of the major drawbacks of the analog servo is its delay in reacting to small commands.
It does not get the motor spinning quickly enough. Plus, it also produces a sluggish torque. This situation is called “deadband”.
Digital RC Servos Explained
A Digital RC Servo has a different way of sending pulse signals to the servo motor.
If the analog servo is designed to send a constant 50 pulse voltage per second, the digital RC servo is capable of sending up to 300 pulses per second!
With this rapid pulse signals, the speed of the motor will increase significantly, and the torque will be more constant; it decreases the amount of deadband.
As a result, when the digital servo is used, it provides quicker response and faster acceleration to the RC component.
Also, with fewer deadband, the torque also provides a better holding capability. When you operate using a digital servo, you can experience the immediate feel of the control.
Let me provide you with a case scenario. Let say you are to link a digital and analog servo to a receiver.
When you turn the analog servo wheel off-center, you will notice it responds and resists after a while – the delay is noticeable.
However, when you turn the wheel of the digital servo off-center, you will feel like the wheel and shaft responds and holds to the position that you set very quickly and smoothly.
Analog vs. Digital – The Two Servos Compared!
When it comes to choosing the type of servo for your RC cars, RC trucks, and RC helicopters, there are multiple options available out there.
If you are comparing them just based on their looks, then there is not much of a difference.
Both use a three-wire connection system and contain similar inner parts.
The only difference is that the digital has a microprocessor that automatically regulates the frequency of the pulses.
When we compare the two RC servo motors, the difference is more obvious from the operational perspective.
Upon comparison, we have learned that the digital version has several advantages over the analog.
- Digital servos produce higher speeds and acceleration than analog servos
- Digital servos have a higher torque and consequently better-holding capability
As you can see from above, the digital type has a quicker and smoother output compared to analog.
However, there is a little bit of disadvantage that comes with this type of servo – high power consumption.
It makes sense because the signals of on/off are being sent more frequently compared to analog. A digital servo has much greater accuracy, but this comes with the cost of power.
If you want to switch from an analog to a digital servo in your RC cars, I highly advise you to use a capable battery or switch to BEC circuit to power the servo. Once you adjust the battery or circuit to suit the powerful digital servo, the power consumption is no longer an issue.
Plus, the digital RC servo also comes with a little bit of noise when it is in a neutral mode or not being commanded to move. This is due to the rapid voltage adjustment made inside the motor.
In addition to that, the hundreds of voltage pulses sent to the motor can also drain the battery pretty quickly.
Regarding the prices, digital servos are also more expensive than the analog models.
You should also know that not all digital servos are better than the analog ones. When you compare between the low-spec digital and high-spec analog, the latter might provide better speed and torque.
Digital servos are much more efficient in doing their job. However, this does not mean that you should always choose them over analog servos for your cars. If you are shopping for a new steering or throttle servo, try to think about the speed and torque that you need and whether or not it is necessary.
Depending on the type of radio controlled vehicle, an analog might function just fine. Plus, a bashing RC truck may need a different servo than a regular RC racing car. You should also consider the extra expenses (e.g. higher price tag, additional upgrades) that come with a digital servo.
Choose wisely, and you will definitely enjoy a better steering and speed performance on your car!