The Difference between Analog and Digital RC Servos

If you’ve had to ever purchase a servo or replacement servo for your application, you may have stumbled in to these terms. What is the difference between an analog servo and a digital servo?

Analog vs Digital Servos
Analog vs Digital Servos

If I were to grab a bunch of digital and analog servos, ripped the labels off and asked for you to hand me only the digital servo’s, it would be very challenging. The reason is, there really isn’t a difference between digital and analog servos on the outside. In fact, there really isn’t much of a difference on the inside either. Both types of servos contain the same gear train, same 3 wire lead to the Rx, motor, case, and even potentiometer to determine the servos position!

Where the real difference lies is within the circuit board found in the servo. In a servo the signal sent from the receiver to the servo gets process by the circuit board. From here the signal is converted in to power pulses that are sent to the motor inside the servo.

The Analog RC Servo

The circuit board in an analog servo receives the signal from the receiver and then outputs a power signal to the servo motor. The frequency at which the output occurs is 50hz. This means in one second an analog servo would only apply an output every 20 milliseconds. It may seem like a very short period of time, however, 20 milliseconds (0.02 seconds) is a long time in any control system.

In order to create movement of the servo arm, the controller would apply full voltage to the servo motor. If there is little servo arm motion required, the circuit would turn the motor on only for a split second within this 20 millisecond period. However, if the servo arm would have to rotate a significant amount based on control input from your transmitter, the servo would apply a longer duration on time to accomplish this. The on time during each cycle is what determines the amount of power that the servo may actually output. Below is a list of advantages and disadvantages for an analog servo.

Analog Servo AdvantagesAnalog Servo Disadvantages
InexpensiveSlow Response
Low Power ConsumptionLarge Deadband Zone
Low Frequency Audible NoiseWeak Holding Torque
Poor Resolution

The Digital RC Servo

A digital servo receives a signal from the receiver onboard the RC vehicle and translates this in to a pulse sent to the servo motor. The rate at which pulses of power are sent to the servo motor are much higher. You can expect that a digital servo would send a pulse to the servo motor at a rate of 500hz. This is equivalent to every 0.002 seconds. The delay in time before the next pulse of power is much better than an analog servo. It is this very reason that provides a digital servo with many advantages. Below is a list of advantages and disadvantages for a digital servo.

Digital Servo Advantages Digital Servo Disadvantages
Fast ResponseExpensive
Excellent Holding PowerHigher Power Consumption
Minimized Deadband ZoneHigh Frequency Audible Noise
Excellent Resolution

Why do Digital Servos Whine?

Is it ok if my digital servo makes noise when there is no control input or external forces acting on the servo? The quick answer to this question is yes. It is quite normal for a digital servo to sing to you. The reason for this is because of the high frequency pulses that get sent to the motor within the servo. You are in fact hearing these high frequency pulses that the motor is receiving.

In the next article, we will look at the application of digital vs analog servos. We will also make some interesting comparisons of specifications.

5 Reasons why the Spektrum iX12 is a Great Radio

iX12

I’ve owned the Spektrum iX12 now for well over a year. After tens of hours of ownership and the radio being bound to several models, there are many features and advantages of this radio that stands out. Just for the record, I bought this radio with my own money, and the thoughts shared here are of my own opinion.

#1 – First Air Radio from Spektrum to Include a Tablet

I’ve been waiting for this for quite some time. Many manufactures of a variety of products are beginning to utilize the Android operating system.  Not that I want to go on the internet or play mobile games on my transmitter. There’s more than enough devices that allow for that. What I was looking for is primarily an option to be able to do more with my radio. Options that were important to me at the time of purchase were programmable voice read outs and alerts, customization, more 3 position switches than I previously had, reliability and a decent amount of channels. This is exactly part of what the IX12 has to offer.

#2 – Highly Customizable Menus and Options

As mentioned above, one prime reason that I wanted to purchase the iX12 was due to the menu’s that are built in to the app installed on the tablet in the radio. All toggle switches, buttons and sliders built in to the iX12 are completely programmable. Any voice read outs that you need to be tied in with functionality on the radio such as RX voltage or model GPS speed can be pulled using macros. This allows you to customize the voice read outs / alerts to suit your requirements. 

You can have a pre-flight check list that the radio will force you to go through based on your own setup. The check list functionality is fully customizable. You may also setup the flight check list to be certain switches are in the correct position.

#3 – Spektrum IX12 has the same great feel as the DX18

Although the DX18 and the iX12 appear as different radios, they contain many of the same lines. The iX12 feels very comfortable in your hands. Even with the included Lithium battery pack and tablet, the radio does not feel heavy. Button and switch positioning on the iX12 feels natural, and buttons have great response. I have not owned a DX18 but I do know when you have both radios in your hand, they both feel great. 

#4 – Spektrum IX12 is built on a Reliable Platform

The very first question I had before purchasing the radio was, what happens if the tablet quits while flying? This would be a very common question coming from anyone who has used this technology before. Tablets are running quite a bit of software in order to function as they do. If you’ve owned a tablet, you know that they do crash from time to time. The tablet crashing should not allow your model to crash.

Obviously Spektrum has thought of this, and makes certain that you can operate your model without needing the tablet. You may lose your custom voice message when a switch is activating but you won’t lose your model aircraft.

Interference with the Spektrum iX12

Nope, none here. I am easily over 200 flights just on one airplane alone.  Not once have I experienced a glitch or interference where I could not correctly control the model.  This is true for the 10 years or so that I have owned Spektrum radios and not just on the iX12.

I do have one crash on this radio. I was fighting the aircraft for about a minute until my thought process ran out of CPU power and the plane went in. After walking up to the model, it was apparent that a control surface was stuck. After further investigation it has been determined that a Y servo extention was not providing a reliable connection between the rx and the 2 elevator surfaces. Not iX12 related.

#5 – Easy intuitive menus on the Tablet and App

This one is easy to explain. You have to keep in mind that there are so many more features on this radio when compared with any other Spektrum radio for air models.  Even with all the additional stuff crammed in to the iX12, the menus feel very intuitive. What probably helps me is I’ve owned an Android based operating system on my cell phone for many years prior to owning the iX12. If you can work your way around a tablet or cell phone, working the iX12 will be a breeze.

Coming from the typical Spektrum radios of the past with a roller button and no android experience, will be a change of pace for sure. Once you are inside the AirWare software app installed on the device, learning where to access all the key information and model data will be learnt fairly quickly.

You no longer have to use a scroll wheel to scroll through a bunch of options you don’t need just to get to the option that you are looking for. Simply open up a menu and select the option that you are looking for. Navigating through the menu options is accomplished by touch screen functionality only. 

RC Car Suspension Setup Basics – Caster, Camber, Toe, Oil, Springs

On an RC car there are many components that you can fine tune to see optimal performance for your application. Tuning the suspension setup is just one of those items that should be considered when going for optimal performance. The suspension consists of a handful of different areas that can be fine tuned. If on the track you are fast, a really good suspension tune will make you faster. It’s very similar in tone to differential tuning which was covered in a previous article. If you are just a basher, a specific tune will allow you to make higher jumps. Included in our list for setup basics is spring rate, shock oil, caster, camber and toe.

Tuning Camber

Camber is best defined as the angle that the tire makes as it contacts the ground. Negative camber will have the top of the wheel angled towards the RC car. Where as positive camber will have the top of the wheel angled away from the car.

Typical Camber Settings for all 4 corners is between -2.0 to 0 degrees. It’s recommended to use a negative camber when racing a circuit that involves more corners. For straight line racing or offroad rock crawlers, a zero degree camber is a good place to start. It is very uncommon to see positive camber on most RC applications. If you are driving an RC tractor, look at positive camber.

Negative CamberPositive Camber
– Increased traction on front/rear wheels
while entering a corner
– Increased braking in to a corner.
– Instability in a straight line
– Reduced traction for straight line acceleration.
– Reduced straight line braking
– Premature tire wear		– Increased stability
– Less steering effort to turn wheels
– Reduced traction when entering a corner
– Reduced traction for straight line acceleration
– Reduced straight line braking
– Premature tire wear

If your suspension setup is stiff, you will require less negative camber since there will be less body roll in to corners.

Tuning Caster

Caster is best defined as the angle that the suspension makes between the upper and lower steering pivot points when viewed from the side of the vehicle. A good practical example would the looking from the side of the front wheel of a bicycle. A bicycle is known to have positive castor. A good example of negative castor could be found on the front wheels of a shopping cart.

On a bicycle, it is not too difficult to ride one without using your hands to steer. This is because of caster. Positive caster allows the front wheel to try and get back to center.

In general you always want positive castor for RC specific setups.

More Negative CasterMore Positive Castor
– Decreased steering effort
– Weaker in straight line tracking
– Less stable at higher speeds
– Improved straight line tracking
– More stable at higher speeds
– Increased steering effort
– Produces negative camber when cornering

Toe in / Toe Out Settings

Toe in an RC car setup refers to the angle that the tires make relative to the direction that they point in. This can be viewed directly from the top of the RC car. Toe out refers to tires that are pointed away from the car where toe in represents tires that are pointed inward.

Keep in mind that excessive toe can result in wasted power and increased levels of drag. Typical Toe ranges from -2.0 to 2.0 degrees in the front

Toe Out [negative toe] (Front Wheels on a 4WD vehicle)Toe In [positive toe] (Front Wheels on a 4WD vehicle)
– Reduced under steer
– help free up the car during initial turn in when
entering a corner		– Reduced over steer
– Enhanced high speed stability
Toe Out [negative toe] (Rear Wheels on a 4WD vehicle)Toe In [positive toe] (Rear Wheels on a 4WD vehicle)
– No real benefit– Improved grip
– Enhanced high speed stability

Suspension Shock Oil

The weight of oil that is used inside of the shock also known as the strut changes the dampening rate. A thicker oil will slow the piston inside the shock. A thinner oil will allow the piston to travel quicker inside of the strut. If the shock oil does not allow the piston to travel quickly when an RC car goes over a bump, the car can lose traction. If the shock oil allows the piston inside the strut to travel too quickly, the car is at risk of bottoming out.

Suspension Spring Rate

The springs ultimate purpose is to support the weight of the vehicle. The spring rate goes hand in hand with the shock oil weight used. If you plan to use a tighter setup, you will want a heavier oil with heavier springs. If you use a heavy oil with light springs, when the spring compresses while going over a bump, the light spring will not be able to extend the strut quick enough before it hits another bump. This will caused weak performance. Instead use a spring rate that matches the oil weight you plan to use.

Thicker / Heavier Shock OilThinner / Lighter Shock Oil
– Reduced traction on an off road / bumpy surfaces
– Reduced body roll in high speed turns
– Improved energy absorption in higher jumps (bashing)
– Reducing the odds the vehicle can bottom out		– Increased traction on off road / bumpy surfaces
– More body roll in high speed turns

Brushless Motors the Truth About Waterproof – Sensorless Sensored

In many applications of radio controlled vehicles, the brushless motor may come in contact with water. This could be as significant as being even fully submerged. Some manufactures of radio controlled vehicles advertise right on the box that the RC inside is waterproof. What does this mean? Is the brushless motor in the vehicle really waterproof?

First let’s understand that there are 2 different types of brushless motors that are important for our topic today. The first type is sensorless motors and the last type are sensored motors. Click the link to learn more.

Waterproof Sensorless Motors

The short answer here is that the sensorless brushless motor will indeed operate while being fully submerged, however not without wear and tear. Electrically there will be no issue at the lower voltages we typically run. Here is an example from my own experience when racing fast electric boats. Below is a picture of what the hull looks like. You can see at the back of the boat, that the entire brushless motor is exposed. This is known as an outboard motor as the motor is external to the boat. In the second image, you can see what the hull looks like when the boat flips. In the image, if you look closely you can see the small trail of disturbed water behind the path of the boat.

Fast Electric race boat

Fast Electric race boat

Operating a Brushless Motor Submerged in Water

Operating a Brushless Motor Submerged in Water

I was operating the boat upside down in order to return it back to shore. The brushless motor was able to operate without any issue. However, mechanically wear and tear does occur within the brushless motor. Let’s look at how and where.

Water is very good at penetrating small openings. It’s only a matter of time before water can find its way in. The shaft found on a brushless motor is supported by using a minimum of 2 bearings found on either side of the motor. Typical RC bearings found in brushless motors are shielded against debris from entering the ball bearing. The truth is brushless motors are water resistant however they are not really waterproof. Water is never pure in a lake or puddle or even rain. Small particles will find there way in to the bearings on a brushless motor delivered right from the water itself.

Over time this is what can destroy the bearings. Worn bearings on the motor can cause the rotor of the motor to contact the stator causing near permanent damage to the motor if spun up.

Also, depending on how your rotor was manufactured, you may find bulging or bubbling of the rotor material. These areas can also scrape along the stator causing damage.

Waterproof Sensored Motors

It is not recommended to place sensored motors in to a wet environment. Sensored motors have these components known as sensors (who would have guessed that?) inside the brushless motor that are not waterproof. A brushless motor would have to be entirely sealed to prevent water from entering the motor destroying the sensors. If you are looking at turning a sensored motor into a sensorless motor, water may be a good way to get you there.

Waterproof Motor Conclusion

If you do plan on running a brushless motor in wet conditions, careful inspection is required to ensure optimal condition. Checking the condition of all the internal motor parts would be a good way to prevent complete destruction of your motor. Sensored motors are not fit for operation in water unless otherwise noted by the manufacture. The same precautions would then apply.

Can the E-Flite 2.1m Carbon Cub Take off from Water on 4s?

The carbon cub was designed to run 6s. After all, this thing has a 2.1m (84in) wingspan. However, the airplane is also designed to operate on 4s and as such is advertised as 4s-6s. With this said, does 4s have enough power to get the E-Flite 2.1m Carbon Cub off the water?

While on 6s the power system is able to generate enough power for about 130 watts per pound. However on only 4s LiPo, there is only enough power for approximately 50 watts per pound. The difference is huge.

Here’s the video:

Can the 2.1m Carbon Cub take off from water on 4s LiPo?