RC Terminology Guide
Welcome to the Speed Sports glossary and terminology guide. This guide will help you to
understand and speak “RC” on a whole new level. If you have any questions, please email us at
speedsports@cox.net. Thanks!
A/C (Alternating Current)
A/C, or Alternating Current, is what most people consider “wall power” as found in your home. Battery
chargers are often A/C and D/C which allows standard household wall charging (A/C) or D/C operation from
your car or truck while you are out away from town.
AM
The term AM refers to amplitude modulation, which is just like AM radio in your car. Many RTR cars come
with AM transmitters/receivers which are not as powerful as FM systems and more prone to interruption. Just
as in your car, a FM radio station is stronger than an AM station.
Articulation
A term mostly aligned to rock crawlers, articulation refers to ability of the axle to move in varying directions,
independent of the chassis. Articulation allows the wheels to stay in contact with the ground on uneven
surfaces (such as walking up, and over rocks).
Battery Elimination Circuitry (BEC)
A BEC allows an electric vehicle’s main battery to also power the radio receiver along with the motor. This
eliminates the need for a separate receiver battery pack.
Blue Groove
This term refers to a dirt track that has been worn in with heavy use where the rubber from the tires adheres
to the dirt forming a line around the track that appears blueish from the rubber laid down. Blue groove tracks
can be so packed and sticky that slick tires, rather than dirt tires are sometimes used.
Body Reamer
This is a tool used to make holes in lexan bodies for the body posts of an RC car. Reamers are not
expensive and will save a lot of botched bodies from drilling and cutting errors.
Camber
Camber refers to the angle of the tires, relative to the ground as seen from the front or rear of the car. Heavy
camber makes the tires appear leaned in at the top and the tires slightly tilted away from the ground. This is
referred to as negative camber. A zero camber condition would have the tires completely flat, or
perpendicular to the ground. Camber is used to compensate for chassis roll in corners and keep the primary
contact patch of the tire flat to the ground while cornering.
Caster
Caster refers to the angle of the tires with respect to the chassis. Caster is sometimes called toe-in because
a car with heavy caster will appear to have its tires toed-in, or slightly pointing toward each other. Caster is
used as an adjustment to stabilize, or de-stabilize a cars handling. With zero caster, or the wheels perfectly in
line with the chassis, a car is prone to dart left and right under acceleration. Caster, or toe-in, will stabilize a
car with these characteristics.
Cell
Battery packs are mode from individual battery cells. For example, a six cell battery uses six cells soldered
together to form a single batter pack.
Center of Gravity (CG)
This refers to the balance point of a car or aircraft. If your chassis components reside above the axles of the
car, then your car would have a higher CG than a car with its components housed lower in the car. A high
center of gravity will cause a car to be more likely to roll over in a turn. Generally, the lower the CG of a
vehicle, the more stable it will be.
Chassis
This is the main plate that the car is built up from. Chassis plates can be made from plastic, carbon,
composites or metals.
Comm Lathe
A comm. Lathe is used to re-condition the commentator of an electric motor. Over time motor commentators
become worn and will reduce the motor’s performance. The comm. Lathe cuts thin layers of old material
away and can refurbish a motor to new condition.
Contact Patch
The part of the tires that comes in contact with the ground at any given moment. The contact patch of a tire
will vary as a car leans as it corners. Adjustments and acceleration will also affect the size and area of the
tires contact patch.
Crankshaft
This is the primary shaft of an engine that the rod and piston connect to and the shaft that the flywheel and
clutch bell mounts to.
Crystal
Crystals are small, changeable components that determine the channel, or frequency that the vehicle will
operate on. Just as a radio station, crystals are tuned to one frequency and function by use of a transmitter
and receiver crystal (marked TX and RX respectively). Two cars cannot operate on the same crystal (same
as channel, frequency) within a half mile radius or they will experience glitching and disruption.
Direct Current (D/C)
D/C is what you will get from a direct connection to a car battery, or other battery source. Battery chargers
are often A/C and D/C which allows standard household wall charging (A/C) or D/C operation from your car
or truck while you are out away from town.
Drafting
This is a term borrowed from stock car racing where a leading car pushes a hole in the air that creates a
slight vacuum behind it, allowing following cars to run faster due to less wind resistance.
Exponential Rate
Refers to the amount of servo travel that is not directly proportional to the degree of control input. A negative
exponential rate will have a milder response makes the control effect milder around the servos center point
but becomes increasingly stronger as the input approaches 100%.
Electronic Speed Controller (ESC)
The ESC is used in electric cars, replacing the older mechanical speed controllers, and is the “brains” of the
car’s electronics. ESCs have a limit on how powerful a motor they can handle without failing so it is important
to match you motor and ESC according to manufacturer specs. By “failing” we mean potentially burn up (i.e.
smoke).
Fail Safe Switch
A switch installed in-line on the cars throttle servo channel that will return the servo to a predetermined
position (hopefully applies the brakes!) if there is an interruption or loss of power from the car’s on-board
power source. This is a must for cars using alkaline batteries which can wear quickly and unevenly.
Linkage (Throttle & Brake)
Small steel rod or heavy gauge wire is used to connect the throttle and brake servos to their respective
controls on the car.
LiPo (Lithium Polymer) Batteries
These batteries which have been in cell phones and PC's for a while have made their way in to the RC sport.
LiPo batteries deliver more power and run time than standard batteries but are volatile and can catch on fire
or explode if mis-handled or over-discharged.
Locknut
A nut with nylon around its head that helps to secure the nut to a bolt and is more resistant to vibration.
Loaded Up
This is a condition where the engine has excess unburned fuel in the cylinder and the engine is either hard
to start or run sluggishly and is probably prone to stalling. To clear a loaded up engine, check the glow plug
and glow igniter to make sure they are up to the job. While the glow plug is out of the engine, turn the car on
its side and work the pull or roto starter to clear excess fuel from the cylinder. Sometimes a loaded up engine
just needs a good hard run to clear it out.
Needle Valve
A valve on the carburetor that controls the fine tuning points of a fuel burning engine. There can be up to
three needle valves that control air/fuel mixture and the idle stop point. On almost all engines, these are
used just like a valve on your garden hose; turning clockwise or to the right will reduce or stop flow – turning
counter clockwise, or to the left increases flow.
NiCad (NiCd)
This term refers to Nickel Cadmium batteries which are rechargeable. Nickel Cadmium can be used to power
a car, transmitter or receiver. Nickel Cadmium batteries can develop memory. These batteries degrade with
temperature, use and time.
Nickel Metal Hydride (NiMh)
Nickel Metal Hydride batteries are most commonly found in RC cars and electric aircraft. These batteries are
usually higher capacity than Nickel Cadmium batteries and do not memory. These batteries degrade with
temperature, use and time however.
Nitromethane (Nitro)
This is a fuel additive that is oxygenated for higher combustion. RC fuel is typically a mixture of alcohol, oil
and nitromethane. The nitro is measure by percentage marked on the fuel bottle and typically ranges from
10 to 30%.
Peak
The point at which a battery is fully charged and will not accept any more charge. Charging and dis-charging
batteries causes heat from the energy moving from charger to battery and battery to car.
+ Safety Tip: Excessive charging OR operation of a vehicle (rapid discharging) will cause heat that can
eventually melt the battery. Always monitor battery temperatures. Batteries should never be left unattended
while charging.
Pinion Gear
Pinion gears are used by electric cars and are attached directly to the motor shaft which then drives the
larger spur gear that is connected to the rest of the drive train.
+ Mechanical Tip: When upgrading or changing motor types in a RC vehicle, it is a good idea to monitor the
heat of the motor and ESC. If there is excessive heat, reduce the size of the pinion gear.
Piston & Sleeve
The piston is the part of a fuel burning engine that moves up and down within a cylinder (sleeve) helping to
create the combustion process of a fuel burning engine. A replacement piston and sleeve is necessary when
an engine becomes worn out.
+ Maintenance Tip : When a engine is “worn out”, it will have a tendency to start O.K., run until it heats up,
then dies and will not restart (due to low compression – see Pinch below). Replacing the piston and sleeve
should correct this symptom.
Pitch
Pitch refers to the size of the tooth on a gear, in teeth per inch. The higher the number, the more teeth on
the gear and the finer the gear itself. The most common pitch sizes are 32 and 48.
Pinch
The amount of pressure between the piston and the sleeve during an engine cycle, or rotation. If the engine
rotates from the flywheel through some cycles without giving some good resistance, the engine has weak
pinch. On the other hand, if an engine rotates through, giving a popping sound at the peak of resistance, the
engine has a strong pinch. New engines should always have a strong pinch and can be difficult during the
first tank of operation because of this which, on a new engine, will cause stalling.
Power Supply
A small enclosed device that converts A/C to D/C for charging batteries.
Preload Shocks
A shock body that is adjustable so that the car’s ride height can be modified for conditions. Adjusting the
preload on a shock absorber can change a vehicle’s ride height.
Pull Start
A coil spring mechanism used to start fuel engines, such as found on the common lawn mower. Unlike the
lawn mower however, an RC pull start should never be pulled excessively away from the engine or it will be
prone to failure.
Push / Under steer
A condition where the front wheels loose grip, causing a vehicle to slide straight ahead instead of turning into
a corner.
Receiver (RX)
A device that receives the radio signals transmitted from an RC controller/radio/transmitter and sends those
signals to the input channels of the servos. The servos are then plugged into the receiver and respond with
steering input, throttle & brake use, reverse gear changing and other functions.
Ride Height
The distance from the bottom of the chassis to the ground when the car is sitting naturally. Ride height is
also measured from the vehicle’s lowest point to the ground under the same conditions.
Roto Start
A hand held, battery operated, drill-like device that is used to spin start fuel burning engines.
Servo
The device that moves the steering, throttle and reverse functions of some RC vehicles. The servo consists
of a small motor and gears that respond to commands from the receiver.
Servo Saver
A device, typically spring loaded, that absorbs shock in the steering mechanism. Usually located on the
steering servo, they prevent the shock from a front end impact from transferring directly into the servo and
breaking the servo gears. Some servo savers have adjustable tension.
Shock
This is the shock absorber assembly which contains a main body, piston & rod and a spring around it. These
enable a car/truck to ride over bumps more smoothly than a direct connection to the axle. Many types of
shocks are adjustable for their degree of tension and can be filled with different oil weights and different
spring rates for chassis tuning.
Skid Plate
A plastic or metal cover / plate that protects the under-side of a vehicle.
Sleeve
See Piston
Slipper Clutch
An assembly that provides a small degree of slippage in the drive system to prevent all shock and energy
transfer from reaching critical components such as the transmission, differentials and axles. Slippers are
typically found on, or near the spur gear and can be rubber material, fiber, springs or a combination of these.
Stinger
A small tip on the end of a tuned pipe.
Sway Bar
A chassis tuning device, usually made of heavy wire that attachés both sides of a vehicle’s front, and or, rear
axle to reduce side to side rolling in corners. As a vehicle rolls to the right while cornering, the sway attachés
to the left side and helps to hold the unloaded side down for more stable handling.
Turn Marshall
These are the people that are responsible for helping to get crashed cars back into their race by flipping
them back over after a roll, or assisting a car nosed in to a wall (most RC tracks do not allow reverse gear
due to the wrecks it can cause). Turn marshals are essential for racing and are racers who have finished
their respective class of racing and return to the track to help the next race class.
Universal Dogbone
A drive shaft with a typical dogbone on one end and a universal, pivoting end on the other side. These allow
more flex in the drive lines.
Unloading
A condition where the gravity load is reduced, making the vehicle or component lighter and less resistant.
The term unloading is most commonly used when describing the characteristics of a chassis, shock absorber
or tire.
XYZ
Your stuff is all broken. Time to go home.
