Electronic Speed Controllers (ESCs for short) bridge the gap between your battery, motor, and receiver. The ESC takes input from your receiver (while often supplying power to your receiver) to drive your motor with power supplied from the battery. So, ESCs have three connection points – two wires for your battery, a set of wires for your motor, and a set of wires for your receiver.

This article and video will explain how ESCs typically work, looking at an ESC from a power standpoint, and a little bit on programming. Nothing too low level for this round – we’re really looking at points to consider for the power requirements of your circuit and the ESC that best fits your needs.

Types of Electronic Speed Controls

There are two primary types of ESCs, and they MUST match the type of Motor you’re using. It’s quite simple – Brushed motors require brushed speed controls, and brushless motors require a brushless speed control. The big difference here relates to the motor. Not to get to deep into the making of motors, let’s just say that since brushed motors rotate through ‘mechanical commutation’ – where there’s a commutator and brushes that drive your motor to turn, a brushless motor’s commutation is done via electronic signals from your ESC, which allows the motor to be just that – brushless.

This is why brushed ESCs have two wires for the brushed motor, and brushless ESCs have three wires for the brushless motors.

Battery Eliminator Circuits

Either way, if you have a brushed Motor/ESC pair or brushless Motor/ESC pair, you can use the same receiver and battery for either setup. However, there is one thing to keep in mind when you’re choosing a speed control. Whether or not there’s a BEC – Battery Eliminator Circuit – embedded in your speed control or if you need to purchase one separately.

So what’s a BEC? Well, receivers need power too, but they typically need somewhere in the range of 3 to 9 volts (depending on your receiver) to get power. If you’re using a 3S battery (11.1 volts) – you’ll easily fry your receiver if you plugged the battery directly into it. We’re talking the release of that magic blue smoke. That’s bad. Crossing the streams bad.

One option is to simply have a separate battery pack that powers the receiver and servos (which typically get power from the receiver). But… who wants to carry another battery pack around? Receivers and servos don’t take a lot of power for your smaller park flyers, carrying around a second battery pack to power your receiver and servos is cumbersome and only to be used when necessary.

A Battery Eliminator Circuit drops down voltage for your RX!

Enter the BEC. BEC’s are basically voltage regulators. They take a high input voltage and output a lesser voltage. This is what lets you plug in a 11.1 volt lipo and only let 5 volts out to your receiver and servos. Even then, there are two types of voltage regulators that BECs typically employ – linear and switching. Voltage regulators need to drop the voltage somehow. Linear regulators do this by dissipating heat. That means it will get warm, even hot, as it steps the voltage down to a level the receiver can handle. A switching regulator, on the other hand, rapidly cycles the power on and off, which makes it generally more efficient, as it doesn’t have to dump power in the form of heat.

You could dive more into that detail, but just know that those are your two types of regulators – which means two common types of BECs. Where you use one over the other often comes down to some gritty electronic details, so mostly… just make sure you have one IN your ESC or you get one to wire TO your BEC-less ESC.

A lot of ESCs you’ll find have a linear BEC embedded inside the shrink wrapped package. This works well, it’s all together and you have less wiring to worry about. However, let’s think about what we just discussed about heat. If I have a speed control that supports 6S batteries, that’s 22 volts that the linear regulator has to step down to 6 volts. That’s a lot of power a linear regulator has to dissipate as heat compared to say a two or three cell battery (7 – 11 volts).

In or Out?

This is why you’ll typically see higher capacity ESCs have a switch mode BEC or nointernal BEC at all. When you don’t have a BEC embedded with your ESC, you’ll need to supply one yourself and wire it in your circuit. What typically happens here is that your battery connects to both your ESC and external BEC, and your BEC outputs to your receiver for power, and your ESC outputs to your receiver for throttle signalONLY. (When you have a BEC embedded in an ESC, your throttle control and power to your receiver are combined into one set of wires)

Once again, this is typically necessary for larger RC circuits, but it’s not uncommon to see an external BEC in smaller circuits as well. A lot of your park flyers or 200-400 size helicopters are using 2 or three cell lipos, so it’s not often a consideration. Regardless, there it is for the time you decide to step up your circuits to larger voltage and amperage needs.

So now we’ve covered the two types of ESCs – brushed and brushless, and BECs – external and internal, and also switching vs linear.

Choosing the right speed control (for you) from a power standpoint

In your entire RC circuit shown here, you have a constantly changing equation you must balance to make sure you don’t over tax one part of your system. However, since the ESC is typically taking all of the current from the battery, it needs to have the highest amperage rating over any other part. You can always go higher in amperage on an ESC to be safe, but you can never go lower. But what is ‘lower’? Lower than what?

Lower than the maximum amperage you’ll be pulling through your circuit. This is defined by the load on your circuit – which means everything that uses power – your receiver, servos, and motor. The combined amperage pull from those components combined MUST be less than your ESC’s rating.

So look at this example here, if you have a motor that is rated at 18 amps maximum current allowed, and say the servos and receivers will take no more than 1 amp, you could get away with a 20 amp speed control. However, I like to play it a little safe for a few reasons, and would go with a 25 amp speed control. Remember, the ESC rating can always be higher than you need, at that point it comes down to an issue of weight (higher amp ESCs weigh more, of course). One thing I generally keep in mind is that if you crash and your throttle is up, this can cause an amp spike through your circuit – so a 25 amp ESC would have a chance to handle that better than a 20 amp ESC given the power requirements of this circuit. (We also keep that in mind with plane-on-plane combat, where your prop is a weapon.)

Of course, we need to make sure the battery can safely discharge that many amps, and in our case, it can. 20 amps continuous, 24 amps burst, so we’ll be safe here. That’s why the general rule of thumb is ESC Amp Rating must be greater than safe battery discharge, which must in turn be greater than load on the circuit – RX, servos, and motor amp pull combined.Once again, this time with feeeeeeeling. Make sure the total load of your circuit – all amps from servo, rx, motor, etc. are LESS than the rated amps on your ESC!

Now you can see why a watt meter is so nice when you’re calibrating your circuit – you can rev up the motor, move all the servos, and use the watt meter to see how many amps you’re really pulling through your circuit.

If you change any parts of this circuit out, you need to make sure the rest of the circuit can handle it. Say I put a bigger motor that can pull 30 amps. Well, now I need upgrade my ESC and battery to handle the extra load. Always keep that in mind. Change one part of the equation, and you need to balance it out.

Speed Control Programming Methods

ESCs often have different programming options that allow you to customize how theESC works. There are simply way too many brands of ESCs out there to cover in this article, but we’ll look at a few of the most common methods and options for programming an ESC.

ESCs can typically be programmed through three different methods:

• USB programming kits (Castle Creation’s Castle Link is a good example of this)
• Programming Cards – Small cards or hand-held devices that you plug a 6-7 Volt battery pack and ESC into, pushing buttons to change LED options on the device.
• Throttle Stick Programming – Using your ESC and receiver, you can use the throttle stick on your transmitter to choose options through a set of audible beeps.

Also, keep in mind, that different brands of ESCs can’t all be programmed the same way – you’ll need to read your ESC’s instructions and learn how to program it and which programming methods it supports. Each ESC maker is different.

Speed Control Programming Options

Clearly, programming an ESC is going to be another video and topic, and you can see from this list that some options are more tedious and error prone than others. Now that we’ve looked at how an ESC could be programmed, let’s look at some of the most common programming options. Once again, since ESCs are so different from factory to factory, some ESCs have spiffy auto detection for things like how many Li-Po cells are connected, while others require you to manually set the options.

This list of options is not necessarily related to a specific ESC, it’s a sample of some options your ESC may support. ESCs often also have ‘default’ settings for these options.

• Battery Types – Often defaulting to Li-Po, but can be changed to support NiMH or NiCd batteries.
• Low Voltage Cutoff – Extremely useful for Li-po batteries – this determines when your ESC will cut power to your motor, and whether or not it does this soft or hard.
• Low Voltage Cutoff Level – Protect your Li-pos by telling your ESC to power off your motor if your Li-Po pack goes down to 3 volts per cell, 3.2 volts per cell, etc.
• Brake Setting – Enabled or Disabled – This means if you reduce your throttle, does the ESC tell your motor to spin freely until it stops or to stop turning immediately.
• Start Up mode – Soft or Hard – Hard is often used for airplanes, Soft is often used for helicopters. It all comes down what you’re flying – this deals with how fast the ESC lets your motor accelerate.
• Timing – Low/Medium/High – an advanced setting for brushless motors, related to the signals sent from the ESC to the motor. You can generally use the default, but research your motor and ESC preferences together to know how they should fit.
• Throttle Range – Auto or fixed – This often depends heavily on the model – helicopter or airplane, and deals with how the transmitter throttle stick corresponds to the output of your ESC to your motor.

That’s a taste of your most common ESC programming options, which we may cover some day in a more dedicated article to ESCs. In the end, though, we’ve covered the high level basics but most importantly – the power considerations in choosing the right ESC for the job. Keep it’s amp rating higher than any load you’ll have on your circuit and you’ll be all set!

Note: HoverAndSmile.com is no more.  The content has been migrated into krystof.io.

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This video/article and the next few will go into a little more detail about the primary players in our examination of RC circuits, those being your Li-Po Batteries, Electronic Speed Controls and Electric Motors. After that we’ll put them all together to look at circuits as a whole, and together we’ll make sense of kV ratings, C ratings, Amp Draw, mAh, series and parallel batteries, thrust to weight ratios, prop sizes, and so on and so forth. We’ll still keep this at a high to medium level, we want to arm you with the basics, and perhaps in the future we’ll dive into extreme detail.

We hope you’ll find this information useful not only if you’re a scratch or kit builder, but also if you’ve bought a ready to fly model and want to understand how the circuits work. Remember that not all pieces of your model will last forever, and if you need to replace a battery or motor, you’ll have a better understanding of what will and what won’t work for your specific craft.

Li-Po Batteries

Li-Po (Lithium Polymer) batteries have been our greatest advancement yet towards everyday electronic RC flight. They weigh less than Nickel Metal Hydride (NiMH) and Nickel Cadmium (NiCad) batteries but supply the same power, so that’s what we’ll focus on here. Li-Po battery packs start at a basic component called a cell, which has a nominal voltage of 3.7 volts. Fully charged, the cell delivers 4.2 volts, and this drops off as the battery is drained. I typically discharge mine to around 3.6 volts, but often you’ll feel a noticeable decrease in power while flying near the end of your pack’s charge – when this happens – land immediately. Discharging a Li-Po battery too far damages the battery’s life span and can potentially be a heat issue. NEVER let a Li-Po pack go under 3 volts per cell. These are the rules of Li-Po batteries to live by if you want a long battery life and want to reduce the risk of overheating or explosion.

How do you know when the battery is drained enough while flying? You’ll notice either by power loss, or you can program some electronic speed controls that have a low-voltage cutoff capability, battery alarm, or use a LVC – Low Voltage Cutoff switch in your circuit. You can also just land occasionally, measure the voltages of your cells, and keep track of how long you were flying. Once you learn the ‘point of no return’ with your battery, you can time your flight and use that as a marker in the future as when you should end the flight and replace the battery.

Larger Li-Po packs are just multiple 3.7v cells wired together to get more capacity and voltage. Let’s break down the most common characteristics of any Li-Po battery you’ll see online with the following ‘fill in the blank’:

(w) S (x) P (y) mAh (z) C

w Cells wired in series,
x Groups of w in parallel,
y Milli-amp hours of capacity,
z Discharge rate.

Total number of cells = w multiplied by x
Maximum amperage discharge: (y multiplied by z) milliamps, divide by 1000 to get amps.

For example, the stock battery that comes with my Blade 400 helicopter has characteristics that matches the following:

3S1P 1800 mAh 20C

Let’s break down the pieces into three parts, cell wiring, capacity, and discharge rate.

Cell Wiring

The S and P stand for series and parallel, respectively. Your most basic battery packs are 1 or more Li-Po cells wired in series, and have no batteries wired in parallel, which is why the 1P is often dropped from descriptions – it’s assumed. Look at this diagram of the same battery in terms of individual cells:

Your smaller helicopters like the Blade mSR and ParkZone Vapor use one single Li-Po cell.

Every time you add a battery in series it increases the voltage by 3.7 volts. So, a Blade CX3 coaxial helicopter, which takes a 2 cell (that is, 2S1P) Li-Po pack, uses 7.4 volts, while the Blade 400, which takes a 3 cell (3S1P) pack – yields 11.1 volts.

Wiring cells in parallel doesn’t increase the amount of voltage, but it does increase the capacity of the battery pack. A 3S2P Li-Po pack actually contains 6 cells, 2 pairs of 3 cells wired in series, and each group of three wired in parallel.

So now you know what the S and occasional P mean when describing a battery.

Capacity

This example battery pack has 1800 mAh hours of capacity available. Think of capacity as your fuel tank – the larger the capacity, the longer you can fly – but also the more weight a battery will have, so it’s another ‘give and take’ example. Since wiring in series like this battery pack doesn’t increase our capacity but it does increase our voltage, each individual cell has a capacity of 1800 mAh.

The term milliamp hour describes how many amps would fully discharge the battery in one hour. Our 1800 mAh pack would be fully discharged in one hour if we pulled exactly 1.8 Amps (1800 milliamps) through the pack (i.e. the ‘load’ on the circuit).

Now, 1.8 amps isn’t enough to really drive a helicopter, so say a helicopter needs 14 amps (14,000 milliamps) to fly properly. This means we’d have only 7 minutes worth of time until the pack is discharged (although you don’t fly to complete and total discharge). You arrive at that value through this equation:

( (Capacity * (0.8)) / Load ) X 60 = Time in minutes until full discharge. Wait… why the 0.8 here? Where did that come from?

Just remember that changing a battery for one with higher capacity gives longer flight time, but also adds weight, which in turn increases your load on the circuit – since the motor has to work harder!

Discharge Rate

The magical “C” rating is defined as how fast you can discharge your battery safely. A higher C rating means you can pull more amps through your circuit before the battery starts taking damage.

You’ll often see a ‘Burst’ rating as well, which of course means maximum power output for say around 10 seconds or so. You definitely don’t want to run your craft continuously at this level of power output.

So what does the C itself mean? If 20 C is our discharge rate, we need to know the ©apacity of our battery to determine the true amp discharge. Take your Capacity and multiply it by your C rating – that is the maximum amperage discharge you’ll want to have during your flight. So, our 1800 mAh 20C battery supports no more than 36 Amps being pulled through the battery safely (Capacity multiplied by ‘C’ rating, then divide by 1000 for Amps) 36 Amps continuously would drain a battery right quick, but you definitely don’t want to go over that amount (especially if that’s your burst rating). Most of the time, you’re not drawing full C rated amperage through the circuit, and if you are, then definitely take heed of the possibility of reducing your battery pack’s lifespan and inherent risks.

However, C rating is often seen as a marketing gimmick, because of course – the higher C rating the better the battery, right?

With that in mind, don’t necessary trust your life with C rating alone. If you have a spiffy enough battery charger you can actually graph and track discharge rates and determine the proper rate for your battery. That’s more than we want to cover here – so let’s generalize by saying take the C rating with a grain of salt, it all comes down to whether your battery manufacturer is honest or not. Always consider a Google search of your battery’s make and model – someone may have already done tests on that specific battery for you.

A great tool for measuring your voltage and amp draw is a Watt meter. This takes the marketing out of the picture. We’ll cover these more in the later RC Circuit articles, but nevertheless they are extremely valuable in determining how much current you’re really pulling through your circuit.

Taking all three of these pieces together, the number of cells in your pack, it’s capacity, and it’s C rating, we hope we’ve armed you with some food for thought when it comes to Li-Po batteries, from what the numbers mean to how much you should safely pull through a circuit.

Note: HoverAndSmile.com is no more.  The content has been migrated into krystof.io.

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So, here we have the basic components to our current work in progress, a flying wing design combat airplane. Our cast, in no particular order, consists of:

A power source – in this case a Lithium Polymner (Li-po) battery

An electronic speed control (often abbreviated as an ESC)

A receiver – in this case a Spektrum 6100

Servos – in this case two Tower Pros weighing in at 9 grams.

A motor – in this case a brushless outrunner with propeller attached.

Last but not least, our transmitter, a Spektrum DX-7.

Keep in mind that this is a very high level introduction to the components as a whole, there is always more detail that we’ll cover in later segments in regards to each piece individually.

Li-Po Batteries

Li-Po is the common abbreviation for Lithium Polymer. A huge advancement in battery technology for RC enthusiasts, Li-Po batteries allow for more power with less weight than other battery types.

Li-Po batteries have a single common denominator of voltage called a cell. When fully charged, a li-po cell stores 4.2 volts. More power is obtained by adding more cells to the circuit. Therefore, a 2S (2-cell) lipo would have up to 8.4 volts fully charged. 3S would have 12.6 volts, and so on. Typically, a cell is referred by it’s nominal voltage of 3.7 volts per cell, not its peak voltage. The other two major factors in li-po batteries are discharge rate and milliamp hours (mAh). Discharge rate, measured in charge value C, determines how much amperage (current) can be pulled from the battery at one time. This helps determine how much of a ‘punch’ your battery packs.

The capacity of the battery is measured in milliamp hours, which determines how long your battery can supply power until it needs recharging. The more mAh, the longer your battery can supply juice.

Li-Po batteries don’t have the exact same memory issues you may find in a Nickel Cadmium battery, but they do have some limitations. They must not be charged over 4.2 volts per cell, and discharging them too low can result in a battery that can no longer charge properly. Charging or discharging a li-po battery too fast can lead to overheating, puffing, and explosion. Suffice it to say, if you read the instructions and treat the batteries with respect, you’ll have no problems. Given that they are more volatile than regular household rechargeable batteries, enthusiasts often use metal boxes or li-po bags to store the batteries while charging or for long-term storage.

ESC–Electronic Speed Controller

The ESC Component of an RC circuit is used to connect your batteries power to both your motor as well as your receiver and servos through a BEC – Battery Eliminator Circuit – typically contained within the ESC itself. The ESC supplies the different signals and power requirements of both the true electronic components and the motor.

The ESC input connection is from the battery itself. The outputs are directly to the motor and receiver. The throttle channel on your receiver, in our case channel 3, takes the output connection from the ESC. This will then supply power to the servos through the other receiver connections and other electronic components (such as lights or gyros).

An electronic speed control is rated in amount of Amps that it’s circuitry can withstand. The proper ESC for one circuit may not be enough for another, and typically power needs and motor capability often drive which ESC is right for which circuit. A good rule of thumb is to go 5 to 10 amps higher on the ESC rating than the motor itself, allowing for the other electronics in a circuit to receive power as well as any ‘bursts’ which may occur when pushing your model to the limit.

Another feature of ESCs is that many of them are programmable in some way, via your transmitter or data cables. A typical programming example is LVC – Low voltage cutoff – if the power supply runs below a certain voltage you’ve programmed for, theESC will stop supplying power to the motor so your li-po doesn’t discharge too far. The cutoff can often be set to a ‘hard’ or ‘soft’ value – where the motor can shut down fast, or gradually lose power. Soft cutoff is preferred when powering helicopters, as airplanes can typically glide in for a landing.

Receivers

The receiver is the component which lets you fly your craft without having a long line of wires connecting it to you. Receivers and their other half, transmitters, often run at government regulated radio frequencies such as 72 MHz or 2.4 GHz. Not only does your receiver and your transmitter have to properly match in radio spectrum, but they also must match in technology. Companies such as Futaba, Spektrum, Esky, and more supply their own pairs of receivers and transmitters. One companies transmitter is never guaranteed to work on a different companies receiver.

The receiver takes inputs from the transmitter (be it from stick movement, switches, or dials) and relays that to the appropriate component in your circuit. Pushing your throttle up on your transmitter sends a signal to your throttle channel on the receiver, out to your ESC, and then out to your motor, changing the speed accordingly. The same goes for your servos and other electronics. Pulling back on your transmitter cyclic would send signals to your helicopter to change the angle of your swash plate via a servo, causing the helicopter to move back towards you.

Receivers often have a specific number of channels associated with them. A channel is simply mapped to one specific element of your circuit, be it a motor or a certain servo. The more channels that a circuit is using, the higher caliber transmitter and receiver pair you’ll need. Simple two or three channel helicopters for example only control motor speed, yaw, and limited forward flight. Complex helicopters, capable of inverted flight and loops, will require at least six channels.

Some receivers are actually combined with an electronic component called a mixer, which, like a soundboard, takes incoming transmissions to your receiver and mixes them into multiple channel outputs. This is often the case with ’4-in-1’ units, which combine receiver, gyro, speed control, and mixing into one physical component. Without an on-board mixer, you’d need a programmable transmitter to handle any mixing. Regardless of being on-board or handled by a programmable transmitter, mixing is a complex topic in its own right, but often handled for you in beginner level stock configurations.

Servos

Servos are small motors controlled via signals sent from your receiver. These little guys, with the attached ‘servo horns’ – the white plastic connectors in our example picture, manipulate the various control surfaces on your aircraft or helicopter. For airplanes, a servo may pull or push an elevator, aileron, or rudder control surface back or forth, affecting the flight dynamics of your aircraft. For helicopters, servos can control the angle of your swash plate, which changes the angle which the blades rotate, affecting movement. They can also control tail rotor blades and pitch of your helicopter blades, not only affecting lift, but also allowing for 3D maneuvers such as inverted flight, loops, and rolls.

In general, the size and weight of a servo are chosen based on the type of aircraft you’re flying. Large scale helicopters and airplanes will require larger servos with plenty of torque to handle movement of your control surfaces. As with anything in our example circuit, there are many different types of servos to choose from. RTF – Ready to Fly kits have servos already attached and configured for beginning flyers.

Servos are often designated as digital or analog. The primary difference is related to how both servos work with pulses sent from the receiver. Digital servos are meant to handle more pulses per second from a receiver than an analog servo, allowing for faster and more precise movement. Often times digital servos are required for advanced acrobatic techniques, whereas analog servos are typically well-suited for beginner level craft.

Motors

The motor is the essential moving part that either spins a helicopter blade or aircraft propeller. Once again, as we have many different types of circuits and craft available, the choice of which motor to use is a necessary consideration.

Without going too deep into the actual inner workings of motors themselves, RC motors are often characterized with the terms outrunner vs. inrunner and brushed vs. brushless.

Outrunner motors generally have a lower Kv rating than inrunner motors. The Kv rating, known as RPM per volt, relates directly to how fast the motor will rotate given a specific power supply input. The higher the Kv rating, the faster a motor will spin. Even though outrunner motors may have a lower Kv rating, they supply more torque. The choice between one lies in a deeper understanding of the specific craft at hand, or by asking your fellow enthusiasts and going with the flow.

Brushed vs. Brushless – Brushed motors, like the name says, use metal contacts internally called brushes. Brushless motors obviously don’t use brushes, and work by instead powering up internal coils in sequence, causing a magnet attached to the outer shaft to rotate. Technicalities aside, brushless motors generally have more power and last longer than brushed motors, and are therefore preferred. However, for very small craft or cheaper ready to fly kits, brushed motors are an economic alternative.

Transmitters

Directly talking to the receiver in our circuit, transmitters are all about you becoming one with your aircraft. With sticks, switches and dials, transmitters allow your hand inputs to send signals to the receiver, causing the servos in your circuits to move, your motor to turn faster, or even turn lights on or off.

Many RTF kits come with transmitters along with the craft itself, and are often only suited for that specific type of craft. Low-end Ready to Fly Kits often include transmitters that are only somewhat flexible in terms of programmatic capabilities to control a different aircraft.

As you become more engrossed in the hobby, you’ll find yourself purchasing a programmable transmitter, which allows you to control multiple aircraft without the need for one transmitter for each airplane or helicopter you own.

We here at Hover and Smile hope this brief introduction helps shed some light on the most basic components of RC electronic circuits.

Note: HoverAndSmile.com is no more.  The content has been migrated into krystof.io.

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