Why RC Car Servos Matter to Quality Performance

by Josh | Last Updated:   5 months ago
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If you’re an RC car enthusiast, the word servo is likely not new to you. However, newbies will not be as familiar with it, especially if they purchased a pre-built car. It is best to know about the car components, though, for upgrading models or building new ones, so what is an RC car servo?

All radio controlled cars are controlled by servo motors, these small motors are used to make the changes that allow you to steer and operate the throttle on a RC Car. They convert the radio signal sent from the RC controller into a specific motion on the RC vehicle to provide physical movements.

R/C servos are special little motors that guide the steering and the operation of the throttle embedded in your RC car by following instructions from the transmitter. This RC servo converts electrically transmitted commands from the receiver into the motor’s physical motion.

Not to mention, they do so to a tee ensuring precise motion control at all times. Do you want to know more about servos and how they control your car’s movement? If so, read on because this article will answer all your questions!

What Is The Purpose Of RC Servo?

RC servos’ purpose is to convert transmitted electrical commands from the receiver into the motor’s physical motion. You plug a servo into a designated gyro or receiver and then employ it to move specific parts of your model.

The movement produced by the servo is entirely proportional. That means it moves only as much as the receiver instructs it to or enough to match the signal width. These signals, called PWM signals, make mechanical movement possible.

How Does An RC Servo Work?

The degree to which a servo performs depends on the control signals that direct the motor where to go. The more appropriate name for these signals is pulsed signals.

Typically, you’ll find that a servo plug comes with three wires that each follow color codes. There are three types of cables in a servo:

  • Power supply
  • Ground
  • Control signal

Here’s a table to better understand them.

PIN NumberSignal NameColor Scheme 1Color Scheme 2Color Scheme 3
1GroundBlackBrownBlack
2PowerRedRedRed or Brown
3Control SignalWhiteOrangeYellow or White

The power supply’s responsibility is to provide the voltage while the control signal communicates the motor’s messages. These messages direct the movement of the engine through pulsed signals called Pulse Width Modulation or PWM.

These PWM signals typically have a frequency of 50 Hz per 20ms. Essentially, this means there is an improvement to the servo every 20 milliseconds.

The servo motor includes a rotating shaft and a potentiometer. The latter helps in detecting the servo’s position. The control signal sends out a pulse which in turn applies a current to the motor.

The result being, the shaft moves until its position is in line with the pulse width according to the potentiometer. These pulse widths can vary quite a bit.

So, the servo will continue to hold the shaft’s angular position after rotation as long as the pulse signal exists. However, if there are any changes to the signal pulse, the angular position will change too.

For this reason, the servo gets preference against competing actuators. Basically, with a servo, you can set signals and then forget about them. As the operation continues, the servo will adjust itself per the feedback with no interference needed on your part.

Types Of Servos

Initially, RC servos were available only in analog form, as was the case with most electronic devices. However, over time, there have been developments in digital ones as well.

Before we get more in-depth, here’s a table to understand the fundamental differences between the two.

FeatureAnalogDigital
TorqueLow to moderate; slow build-up to peak levelsModerate to high; very quick to reach peak values
Power ConsumptionLow to moderateModerate to high
CostLow to moderateModerate to high
ResponseSlowRapid
ResolutionLow to moderateModerate to high
Battery PowerLow to moderateModerate to high

Analog Servo

The receiver sends out a signal to the analog servo’s circuit board which becomes a power signal for the motor. The analog servo follows the standard servo frequency of 50 Hz per 20ms.

While this may not seem like an extended period, it is when concerning control systems. The voltage applied by the controller changes depending on the required movement.

For instance, if only a little motion is needed, the circuit will switch on the motor for a quick second within the 20ms window. On the other hand, if it requires more movement, the controller applies full voltage.

If the servo arms need to rotate significantly, it will require a longer duration. The running time of every cycle is what controls the output of power in this servo.

Advantages

Analog servos do have benefits, so here are a few of them:

  • Low power consumption
  • Relatively noiseless
  • Inexpensive

Disadvantages

They also come with certain drawbacks, including:

  • Slow response time
  • Insufficient holding torque
  • Poor resolution
  • Huge Deadband zone

Digital Servo

Typically, the RC vehicle will have an on-board receiver that gets signals from the digital servo. These signals then become pulses to control the movement of the motor.

However, the rate of sending the vibrations is much quicker than the former. A digital servo can send out signals as high as 500 Hz per 0.002 seconds! The time delay before a new pulse goes out is also superior to analog servos.

Advantages

Digital servos are far superior to analog ones, and here’s why:

  • Quick response time
  • Much better holding power
  • Reduced Deadband zone
  • Amazing resolution

Disadvantages

Of course, digital servos, too, have a few minor flaws:

  • Costly
  • More power consumption
  • Noisier

Types Of RC Servo Motors

RC Servos will usually have one of three motors. Here’s a quick overview of the different types.

Brushed Motors

These come with the standard three-conductor commutators and two brushes to send out positive and negative currents. 

These are the most prevalent among the DC motors.

Brushless Motors

In place of the previous motor’s commutators, this one uses an electric controller. 

They are superior to brushed motors and have benefits like more torque per weight, efficiency, reduced noise, and reliability.

Coreless Motors

These motors typically have a steel core with wires wrapped around them. On one end, they also have a commutator. 

The drawback here is that these motors tend to be quite heavy because of all the steel and magnets. They also take longer to start and work quicker.

How To Choose An RC Servo

The servo you should go for depends mostly on the model of your RC car. As per that, here are some factors you need to pay close attention to:

Size 

When choosing a servo size, you must consider the mountain dimensions. 

They are available in various measurements, including micro, mini, small, standard, or large. 

Some may even come in varying depths, which is a problem for models with restricted mounting areas.

Torque

If you have a bigger, heavier model, you will do better with a servo giving more torque.

Along with this, you want to consider the airplane control surface area and servo arm length.

Speed

The feel of your model depends on its speed. Of curse, it will feel smoother with a fast servo, but too much speed can make it twitchy. So try to maintain the right balance.

Voltage

Servo voltages need to be compatible with your model for optimum performance. 

Typically, they tend to run on six volts. However, for a 2S LiPO receiver battery minus the BEC, you’ll need a 7.4-volt servo for compatibility.

Gears

RC cars and trucks do better with metal gears. These gears will work well with any RC model that needs to be aggressive. 

Typically, such models have the potential of undergoing severe impacts, so they need to be healthier.

If, however, you’re sure your model will only be subject to low impacts, then you can work with plastic gears. 

If you’re uncertain, though, it is best to stick to metal ones. 

Also, consider throwing in a servo saver regardless of the gear material to protect your model from impacts.

Servo Case

You will usually find aluminum servo cases. These can help dissipate heat from the motor, but they tend to be on the heavier side. If you prefer a lightweight case, go for a plastic one.

That said, aluminum ones have the advantage of reducing flex and creating a more stable area. 

They also produce steadier platforms for mounting points on heavier models. They are also quite strong, albeit not indestructible.

Waterproof

Usually, servos come with an IP67 rating. That means they will work fine even after immersion in water up to 1 meter. 

So you can dunk your model in water, but any lower than that, and the underwater movement will damage it.

Motor

The motors discussed above also play a critical role in how your model performs. DC motors are best for low-impact applications and also cost the least. 

Coreless offers more power, stability, and control. However, brushless is top-tier in terms of performance.

Wrap Up

With this guide, you’re now well on your way to knowing how to upgrade your RC or build a new one entirely. 

Remember to take every factor from size to gear to motors into consideration before deciding on one servo. After all, the performance of your model mostly depends on it.

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Sources

Euro RC

PCB Heaven

Radio Control Info