Q. I am new to the Radio Controlled cars (R/C) hobby. What do I need to know to get started?

A. R/C cars come in a variety of shapes and sizes. The first thing you need to decide is where you will be running your vehicle. Terrain and space are important factors in choosing a vehicle that is right for you. The other factor is size of the vehicle. 1:10 scale (ten times smaller than the real thing) is the most common. 1:8 and 1:5 scale are larger vehicles while 1:18 and 1:25 scale are smaller. Some of the most common R/C cars are listed below:

Monster Trucks	Monster trucks are  great vehicles for backyard bashers and people who just like large vehicles that can run fast and go most anywhere
Buggies	This is a hybrid - half car and half truck. Buggies can generally go faster than a truck on a smooth surface and can handle some off-road better than a car
Truggies	Another hybrid that is half buggy and half truck. Faster than a truck and able to handle smoother surfaces well. Not as fast as a road car.
On-Road Cars	Designed specifically for running on hard surfaces (sidewalks, streets, tracks), these vehicles will not perform well off-road.

 

Q. Should I get an electric vehicle or a nitro one?

A. Each type of vehicle has its pros and cons. Let's start with nitro vehicles. Nitro vehicles run on nitromethane fuel. They require a spark to ignite the fuel. These vehicles come with a glow plug that must be heated to a high temperature before the motor will start. Glow igniters are used to heat the glow plug to the required temperature. The majority of glow igniters are battery-powered using a "D" or "C" battery cell. Then the motors are started using either a pull string, or an electric starter system. Nitro powered vehicles will run for as long as you have fuel on hand. They are considered 3 season cars (spring, summer, fall). They should not be run through water as they are carbureted and water must be kept out of the motor. They should not be run when outside temperatures drop below freezing as they can become difficult to start and rapid cooling of a hot motor could cause cracks in the housing. They do have a satisfying sound when running and some people enjoy the constant tuning they require due to changing weather conditions. Electric vehicles are as simple as plugging a charged battery into the car or truck. The typical run time of a brushed motor powered by a nickel metal (NiMh) battery is around 10 minutes. Most people will have 2-3 batteries on hand to reduce downtime while recharging. Electric vehicles can be run year 'round and have no issues with water or snow.

 

Q. What is nitromethane fuel and what kind should I use?

A. Nitromethane is the fuel used to power nitro vehicles. Nitromethane is made up of methanol, nitromethane, and lubricants. Methanol is the largest component of nitro fuel and is the component that burns. 

Nitromethane is flammable on its own, even without oxygen, but it has a very high burning point—well over 4,000 degrees Fahrenheit. When mixed with methanol, nitromethane acts as a catalyst, increasing the burn rate of the fuel blend to produce more power. The more nitromethane that is used in the fuel blend, the faster the fuel can burn, letting the engine run at higher rpm. The big percentage number you see on a bottle of fuel is its nitro content, which generally ranges from 10-40%. For all-around use, 20% nitro is the most popular choice. 

Lubricants are an integral part of nitro fuel recipes, since our 2-stroke engines don’t have oil-filled crankcases and instead rely on lubricants mixed into the fuel to keep the internals running smoothly. 

The percentage of lubricant in the blend depends on the purpose of the fuel; premium race fuels have less lubricant, typically in the 8-12% range, than fuels designed for engine longevity, which can consist of upwards of 20% lubricant. The reason for this is that with less lubricant in the blend, there can be more methanol, which makes for a more powerful combustion process, but with increased engine wear. Racers will gladly sacrifice piston and sleeve life for greater performance, but if you want your engine to last longer between rebuilds, choose a blend with a higher percentage of lubricant.

Q. What kind of electric motor should I get? Brushed or brushless? 

A. Electric R/C motors come in two flavors - brushed and brushless. What's the difference? 

Well, the brushes of course.

Yeah, but what does that mean?

The principle behind the internal working of both a brushless DC motor and a brushed DC motor are essentially the same.  When the motor windings become energized, a temporary magnetic field is created that repels (and/or attracts) against permanent magnets.  This force is converted into shaft rotation, which allows the motor to do work.  As the shaft rotates, electric current is routed to different sets of windings, maintaining electromotive repulsion/attraction, forcing the rotor to continually turn.

Construction differences

Brushes inside electric motors are used to deliver current to the motor windings through commutator contacts. Brushless motors have none of these current carrying commutators.  The field inside a brushless motor is switched via an amplifier triggered by a commutating device, such as an optical encoder.

Windings are on the rotor (Rotating part of motor) for brush motors and on the stator (stationary part of motor) for brushless motors. By positioning the windings on the outside stationary portion of the Electric motor the need for brushes can be eliminated.

Brushed motor Advantages:

Simplified  wiring:  Brush motors can be wired directly to DC power and control can be a simple as a switch.

Low cost:

Brushed Motor Disadvantages:

Less efficient

Electrically noisy: The switching action of the commutators constantly creating and breaking inductive circuits creates a great deal of electrical and electromagnetic noise.

Lifespan:  As they are in perpetual physical contact with the shaft,  brushes and commutators wear out.

Brushless Motor Advantages:

Long lifespan: No brushes to wear out
low maintenance: No brushes to replace
High efficiency

Brushless Motor disadvantages:

High initial cost: Need for commutating device like an encoder and a drive or controller.

Brushless motor vs brush motor efficiency:

Brushless motors are typically 85-90% efficient whereas brushed DC motors are around 75-80% efficient.

This difference in efficiency means that more of the total power used by the motor is being turned into rotational force and less is being lost as heat.

Q. So what kind of battery should I use?

A. This is a little trickier to answer. The old school thinking was stick with nickel metal hydride (NiMh) batteries for brushed motors, and lithium polymer (LiPo) batteries for brushless motors. However, it is not quite as simple as that. 

Lithium polymer batteries require a LiPo battery charger, and a speed control with a LiPo cutoff, or an external LiPo cutoff. The reason for this is that LiPo batteries will be damaged if the cell voltage drops below 2.7V or goes above 4.2V or 4.3V.  Additionally, the nominal voltage of a 2 cell LiPo is 0.2V higher than a 6 cell NiMH pack. The capacity is generally much higher than a typical NiMH battery pack. LiPos are lighter, more powerful, and last longer than NiMh, but you MUST charge them properly and NEVER over discharge them or they will be ruined, and possibly even catch on fire. You should only use them in vehicles that have an ESC (electronic speed controler) that can be configured for LiPo and has an adjustable cutoff voltage to prevent over discharging.

NiMh are cheaper, more durable, and have a longer life span than LiPo. They are also safer to charge as they have a minimal risk of fire. However, they do not deliver their current as efficiently as a LiPo battery does. You should see better performance from a LiPo capable vehicle with a LiPo battery installed than you would with a NiMh battery.

Bottom line - Use LiPo batteries when your ESC is capable of handling the higher voltage and has a LiPo cutoff mode, and your budget allows it. LiPo's can be significantly more expensive than NiMh. Use NiMh when your ESC cannot accept the higher current or does not have a LiPo cutoff mode.