In this article we are going to become familiar with the basics of the electric powered systems that drive R/C vehicles.  Now, when we talk about hobby-grade electrics, forget everything you know about Toy-R-Us and Wal-Mart toys.  Hobby-grade electric vehicles can be extremely fast and dependable.  In fact, many pro R/C drivers/flyers are running electrics.  Some of the advantages to electrics are they are quieter than nitro powered vehicles, less messy, and they can run indoors as well.  First we’ll start off by looking at how the whole system is connected to provide power to your vehicle.  We will then review the different qualities of motors, speed controls, batteries and chargers available.  This will help you choose the right system or repair the system you already have in you car, truck, plane, helicopter or boat.  Last we’ll look at how varying each individual component will affect the rest of the system.

            Look under the hood of any R/C electric powered vehicle and you should see the same basic setup shown here in Figure 1.0 below.  You have one or more motors that power the drive train.  The motor is connected to a speed control (manual or electric).  Battery power is connected directly to the speed control as well, which is plugged into your radio receiver. Power from here is provided to the servo or servos that are also plugged into the other channels of the receiver.  That’s about it.  No big mysteries here. 

                                Figure 1.0

            The most expensive and complicated part of the system is the speed control.  In the vast majority of all R/C vehicles today, this is an electronic speed control or ESC.  It’s a small box with circuitry inside that provides variable power to the motor so you can have variable speed instead of just on or off.  This is the one component in the system that is usually covered by a manufacturer’s limited warranty (not in helicopters though). 

            ESCs are rated in terms of how much power they can handle.  How much power gets applied to the ESC depends upon the electric load, which is your motor.  The more current your load draws from the battery, meaning the more current it needs to operate, the tougher your ESC needs to be to handle that power.  If you have too small of an ESC for your motor it is likely to burn up and may even catch fire if it gets too hot.  Look in the instructions of your ESC and they will tell you how many turns in a motor that the ESC can handle.  Motors are rated in number of turns, 10T or ten turns, 20T or twenty turns, etc.  The fewer the number of turns, the faster the motor and the more power it will draw.  We’ll talk more about what that means later, but know that if you have a motor rated at 19T your ESC needs to be able to handle at least 19T and above, meaning anything more than nineteen turns.  When choosing an ESC, also be aware that some ESCs are designed to handle more than one motor at a time.  So, if you need an ESC for a truck like the Traxxas E-Maxx which has two motors and operates with two batteries at over 14VDC, you need an ESC that can handle both the number of turns on the motors, and the voltage you’ll be putting through it.  Finally, ESCs are available in either forward only or forward with reverse.  So make sure you’ll be able to go backwards if needed.

Now let’s look at the motor you’ve got.  Chances are when you buy an electric car, truck or plane that’s RTF or RTR it comes with an electric motor that’s considered to be very basic.  It’s a cheap 540 motor with maybe 20 turns or more.  This is adequate to drive/fly with and have fun, but there’s so much more fun to be had with faster speeds.  How do you get faster motors?  Well look to the number of turns the motor has in it.  This number represents the number of windings of wire around each of the iron cores inside the motor.  For instance a 19T Double motor has two wires wrapped around each iron core nineteen times.  A 10T Single motor has one wire wrapped around each iron core ten times.  The fewer the number of windings, the faster the motor is going to be.  Now I’m not sure why the cheaper motor comes with more wire inside.  That really doesn’t make a whole lot of sense, but that’s the way it is.  A 540 size motor refers to the physical size of the motor itself.  This is the standard for most 1/10 scale electric cars, trucks, and even planes.  Smaller motors like the 380 size are suited for the smaller vehicles, usually around 1/18 scale on-road vehicles and micro helicopters.  Companies like LRP, Trinity, Orion, and Novak make and sell these types of electric motors.

There are newer electric motors now readily available that provide more speed than conventional electric motors, and these are called brushless motors.  Brushed or Brushless refers to the way in which electricity is introduced into the motor itself.  Most all conventional motors you will see are brushed type.  The Brush is a small rod of silver held against the commutator of the motor.  See Figure 2.0 below.

                                       Figure 2.0

Electricity is passed from the ESC through the brushes (there are two of them on opposite sides) to the commutator and down through the windings around the iron cores.  These brushes are held in constant friction against the commutator by springs and will eventually wear down.  They can be bought separately and replaced very easily when needed.  Because of the friction against the drive shaft, they do slow the motor down to some small degree as any friction would do.  The whole assembly for the brushes also adds more weight to the top of the motor.  In a brushless motor, the use of the brushes is bypassed by sending electricity directly to the windings.  The physical design of the motor is much different, but the result is higher speed and efficiency.  Because the brushless motor is wired differently, it will require an ESC capable of powering brushless motors.  With the exception of a few very expensive ESCs you cannot mix a brushless motor with an ESC for Brushed motors and vice versa.  It simply will not work.  Brushless motors come in the same physical sizes as their counterparts.  Companies like Novak, E-Flite and Castle Creations are popular manufacturers of these motors and ESCs.

Now that we’ve covered the parts supplying power to the drive train, let’s talk about the item supplying power to those parts – your battery.  I think everyone in the free world has used batteries of some kind for something.  Here however, we’ll dive a little deeper to look at the different types of batteries and how they are rated and charged. 

Batteries come in two basic types based on the electrolytic material inside: Nickel batteries, (whether Nickel Cadmium (Ni-Cd) or Nickel Metal Hydroxide (Ni-MH)) and Lithium Polymer (Li-Po) batteries.  Ni-Cd batteries are common and very heavy in weight.  Ni-MH are also heavy but they can hold more of a charge than Ni-Cd ones.  Li-Po batteries are very thin, are the lightest in weight and can often have much longer run times then their Nickel counterparts.  Individual Nickel battery cells usually hold about 1.2VDC whereas a Li-Po cell can hold around 3.7VDC.  Typical R/C applications use either a 7.2V Nickel battery (6 cells) or a 7.4V Li-Po (2 cells).  When you do a weight comparison, you will see that there is just no contest, the Li-Po is about half the size and weight of the other.  In terms of run times, Ni-MH batteries now come as high as 4200MAH.  You can get Li-Pos as high at 8000MAH but those are harder to find.  They usually peak around 5000MAH.

Because of their different makeup inside, the two kinds of batteries will require different type of chargers.  Again, with the exception of the very expensive ones, most chargers will do one or the other, not both.  If you have Nickel batteries, most chargers will be able to charge either the Ni-Cd or Ni-MH.  You want to find a charger that’s versatile so make sure that it is capable of charging a wide range of voltages.  Here’s what you should consider when buying a charger:

•       Is it AC or DC powered?  If it’s DC powered you will need a 12V battery

•       What size battery packs can it handle?  It should be able to handle battery packs between three and eight cells (3.6VDC and 8.4VDC)

•       Does it have peak detection?  This feature allows the charger to sense when the battery pack is full and will then to stop charging. 

•       Can you adjust the charge rate?

•       What type of connectors do you need?

Everyone asks for quick chargers – they want to charge their batteries fast.  That’s fine in a pinch but chargers of this nature will only wear down the life of your battery.  These quick chargers are like fire hoses.  They come in two settings – on and off.  Imagine trying to fill an ice cube tray with the faucet on at full blast.  Gonna be kind of hard, isn’t it?  Your battery will overheat very quickly and is likely to leak electrolyte to keep from exploding.  When this happens, your battery loses energy capacity.  With quality chargers that charge at reasonable rates, the battery will stay cool, and the each of the cells will get an even charge.  Often times you can control the rate of electricity into the battery on the charger. 

            People often ask, how long will it take to charge a battery?  Well, this is where a little math comes into play.  Let’s say for example you have a 7.2V battery pack at 3000MAH.  Using a charger with an output rate of 3.0Amps you get…

3000 MAH = 3Amp Hours  /  3.0 Amps  =  1 Hour

Charging the same battery at a rate of 1.5Amps you get…

3000 MAH = 3Amp Hours  /  1.5 Amps  =  2 Hours

After your battery is done charging, you should make sure it cools down enough before you run it in your R/C vehicle.  The opposite is also true.  Before you throw it on the charger, make sure the battery has cooled down enough after running it.

            Finally, a word on discharging your battery.  When you buy a new battery, most likely it will have a few volts in it, but not a full charge.  For Nickel batteries you are going to want to run the battery down to dead then put it on the charger.  You can do this by putting the battery in the vehicle and hit the throttle while holding it in place.  This will ensure you get an accurate full charge.  Lithium batteries on the other hand will encounter problems if they drop below a certain voltage.  If a Li-Po runs too low, simple chargers may not be able to power them back up.  Your best bet is to monitor the battery level by simply watching your R/C vehicle’s performance.  When it starts to get too sluggish, as in if you can’t get the heli off the ground but the rotors are still moving, it’s time for a recharge.

            Well now you are ready to go tearing into your electric R/C vehicle.  With this information you should be able to go out and price out the customized system that you want in order to get the maximum speed and efficiency out of your vehicle.   Just be aware of heat conditions so as to not burn anything up too badly.  That pertains mainly to your ESC, battery and connections.  Keep it cool and running smooth.  Next time, we’ll look at gear ratios and how to select the right gears to get even more speed!  Until then, go out, have fun and please support your local hobby shop.

Abbreviations:

BL – Brushless Motor

ESC – Electronic Speed Control

Li-Po - Lithium Polymer

MAH – Milli Amp Hours

Ni-Cd - Nickel Cadmium

Ni-MH - Nickel Metal Hydroxide

RX – Receiver

SX – Servo

TX – Transmitter

VDC – Volts Direct Current