Kyosho Inferno MP9 TKI4 Competition 1/8 Nitro Buggy Kit

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Radio-controlled (or R/C) cars are usually categorized as either "toy" or "hobby" grade. Remote control vehicles are usually of one of two types: control of a vehicle by radio transmission or by a wire connecting between the transmitter and car. This article focuses on the radio-controlled vehicle category, both toy and hobby grades.

Cars are powered by various sources. Electric cars are powered by small but powerful electric motors and rechargeable nickel-cadmium, nickel metal hydride, or lithium polymer cells. There are also brushed or brushless electric motors. Most fuel-powered models use glow plug engines, small internal combustion engines fueled by a special mixture of nitromethane, methanol, and oil (in most cases a blend of castor oil and synthetic oil). These are referred to as "nitro" cars. Recently, exceptionally large models have been introduced that are powered by small gasoline engines, similar to string trimmer motors, which use a mix of oil and gasoline. Electric cars are generally considered easier for the novice to work with compared to fuel-driven models, but can be equally as complex at the higher budget and skill levels.

In both of these categories, both on-road and off-road vehicles are available. Off-road models, which are built with fully-functional off-road suspensions, can be used on various types of terrain. In comparison, on-road cars, which generally have a limited or non-existent suspension, are strictly limited to smooth, paved surfaces.
Toy-grade radio control
This Nikko-produced Subaru Impreza WRX STi is a toy grade radio controlled vehicle

The term "toy" or "toy-grade" in regards to radio control cars is used to describe vehicles of the pre-assembled type generally found in discount stores and consumer electronics stores. Sometimes they are colloquially referred to as "Radio Shack cars". Some toy-grade R/C models may also be found in hobby shops in an attempt to gain some market share from discount stores and appeal to younger users.
[edit] Advantages

Cost is one of the main advantages of toy R/C vehicles. The average medium-scale toy R/C car is around $50–$100 cheaper than an entry-level electric hobby class vehicle. Toy class vehicles are easy to operate, have a relatively low danger level (top speeds are typically under 20 mph (32 km/h) (with most capable of only about 10 mph (16 km/h) ), and are even easier to set up than the simplest hobby class ready-to-run vehicles (RTR's). Toy class vehicles are usually modeled after real cars, and often feature details that hobby class vehicles lack, like working lights, sounds, windows, opening doors and hoods, and realistic interiors at the expense of weight and durability. Some vehicles also feature working sound systems with radios or MP3 player inputs. There is also an almost endless array of toy R/C vehicle designs, ranging from common cars and trucks, to tanks, bulldozers, and motor cycles, to increasingly odd vehicles with unorthodox designs.
[edit] Disadvantages

Toy-grade R/C cars are typically manufactured with a focus on design coupled with reducing production costs. Whereas a hobby-grade car has a standardized motor and separate electronic components that are individually replaceable if they fail, toy grade cars are typically made with a non-standard motor, non-replaceable chassis components and a single electronic circuit board integrated into the design of the vehicle. This makes them difficult, if not impossible to repair, with exceptions being Nikko models and some Radio Shack models. Usually when one component on the vehicle fails, the entire vehicle must be thrown away. Performance is poor as well. Most are equipped with small, weak motors and are powered by cheap alkaline or NiCad batteries which means their top speed is usually only 5-15 mph, and they have short run times before new batteries are required. Most lack any form of a suspension and the ones that do feature a suspension have very primitive or rudimentary designs. Steering is typically not proportional (with only three positions: straight, full left, and full right) and there is typically no proportional "throttle" either, with stopped and full power usually being the only options.
[edit] Hobby-grade radio control

In recent years, hobby-grade "ready-to-run" (or "RTR") models have become available from every major manufacturer of radio-controlled cars, attracting many hobbyists who would otherwise have purchased a pre-assembled car (ARTR or Race-Roller). Vehicles of this type need little or no final assembly and in most cases, the bodies are shipped painted and trimmed, requiring little or no work from the owner before they can be used (other than purchasing and installing batteries). A number of cars and trucks are presently available only in ready-to-run form. The growing popularity of the RTR vehicle has prompted many manufacturers to discontinue production of kit vehicles. High-spec racing vehicles are generally still available or sold only as kits, and companies like HPI and Tamiya sell kit and RTR versions with the benefits of a kit version being in upgraded parts or lower costs, respectively.
[edit] Electric models

Electrically powered models utilize mechanical or electronic speed control units to adjust the amount of power delivered to the electric motor. The power delivered is proportional to the amount of throttle called for by the transmitter - the more you pull the trigger, the faster it goes. The voltage is "pulsed" using transistors to produce varying output with smooth transitions and greater efficiency. Electronic speed controllers use solid state components to regulate duty cycle, adjusting the power delivered to the electrical motor. In addition, most electronic speed controllers can use the electric motor as a magnetic brake, offering better control of the model than is possible with a mechanical speed control. Mechanical speed controllers use a network of resistors and switch between them by rotating a head with an electrode around a plate that has electrical contacts. Mechanical speed controllers are prone to being slow to react because they are actuated by servos, waste energy in the form of heat from the resistors, commonly become dirty and perform intermittently, and lack a dedicated braking ability. They are less expensive than high performance electronic speed controls and usually ship in older hobby-grade models. They are gradually being phased out. Most electric cars up to recently used brushed motors but now many people are turning to brushless motors for their much higher power and because they require much less maintenance. They are rated either in relative turns or Kv. The Kv number tells how many RPM the motor will turn per volt, assuming no load and maximum efficiency. However, the ability of the system to put out power is dependent on the quality of the batteries used, wires and connectors supplying power. A well wired brushed system can outperform a poorly wired brushless system in many cases. Due to their power, brushless motors are also used in bigger monster trucks and 1/8 nitro-powered buggies that have been converted to electric. Some 1/5 scale gas to electric conversions are in production but are uncommon due to high price.
[edit] Fuel models
A Traxxas T-Maxx nitro powered off-road monster truck with no body.

Nitromethane fuel powered models utilize a single servo for throttle and braking control; rotation of the servo in one direction will cause the throttle on the carburetor to open, providing more air and fuel mixture to the internal combustion engine. Rotation of the servo in the other direction causes torque to be applied to a linkage and cam which causes friction with the braking material. The brake is commonly located on the driveshaft or spur gear in some cases and applies stopping power only to the driven wheels. Some models will also use an additional servo to control a transmission box, enabling the vehicle to drive in reverse.

Fuel engine sizes most often range between .12-.35 cubic inches. This is due to restrictions by the main sanctioning bodies for radio-controlled racing. Many "outlaw" engines are manufactured larger than these, mainly intended for vehicles which will not be used in sanctioned races and therefore do not need to comply with these regulations. Engine size is related to the class of car; 1/10th scale on and off road vehicles usually are equipped with .12-.18 cubic inch engines, with 1/8th scale vehicles using .21-.32 cubic inch engines. There are exceptions, with many Schumacher and Thunder Tiger/Team Associated RC models being good examples of unusually large engines coming as standard equipment on certain models.
An Ofna Hyper 8 Pro 1:8-scale nitro-powered racing buggy.

Fuel-powered engines allow model cars to reach moderate speeds unmodified. Maximum power is generally achieved at medium to high speeds, and a slightly slower throttle response than electrically powered vehicles is to be expected due to clutching and lack of torque. Electric motors effectively produce instantaneous torque, whereas nitro engines, like full-sized gasoline engines, take time for the engine to spool up and for the clutch to engage. Nitro- (and fuel) powered cars may be refueled and returned to action in a few seconds, as opposed to electrics needing to remove the body shell and battery fasteners to replace a discharged battery. Nitro cars are cooled some by air, some by the oil mixed in with the fuel and may be run continuously with no need to take breaks for cooling down assuming they are properly tuned.

Nitro-powered cars operate like full-sized fuel vehicles more than their electric counterparts do, making use of a two stroke engine rather than an electric motor. The sound of the engine and generally higher stock top speeds are main selling points to nitro enthusiasts. However, their exhaust contains unburned oil, which usually ends up coating the chassis. This, in turn, requires more cleaning than an electric-powered equivalent. Cleaning is usually achieved by the use of compressed air nozzles and solvents (such as denatured alcohol). Tuning a fuel-powered vehicle requires learning to maintain optimum performance and fuel economy, and to minimize engine wear and overheating, even in ready-to-run vehicles. Running a nitro-fuel motor without tuning or tuning improperly can hurt performance in rich conditions, and cause severe damage in lean conditions.

Because of higher stock performance and their ability to be driven for longer periods of time, mechanical wear in nitro vehicles is generally greater than in electric vehicles. In addition, the increased speed and weight of fuel-powered vehicles generally lead to higher speed collisions, causing greater damage to the collided vehicles, and a greater degree of safety concerns needs to be taken into account. Maintenance such as cleaning of the air filter and general chassis cleaning, replacement of worn clutch parts, proper after-run lubrication (necessary for storage) and maintenance of other motor-related items such as glow plug replacement makes for a more frustrating experience for first time RC users. In addition, nitro motors typically require rebuilding or replacement after 2-8 gallons of fuel run through them, due to loss of compression, which can be accelerated by poor tuning and overheating. It is also possible to seriously damage the engines by over-revving them with no load or ingestion of dirt into the carburetor. As such, nitro-powered vehicles are by nature expensive to maintain.
[edit] Gas-powered models

Gasoline powered vehicles, also known as "fuelies" or "gassers", run on premixed gasoline and oil. They cost much more (usually $800–$3000 RTR) than nitro and electric cars. They are also much bigger and therefore require much more space to run. They don't usually have as high top end speeds (compared to nitro and some electrics) but have lots of power and don't take a lot of fuel to run. Over time the cost of a gas-powered car can be less than some nitro-powered vehicles, because of the high cost of nitro fuel and buying new nitro engines to replace worn-out ones. In addition, gas-powered motors rarely if ever require tuning and have a very long lifespan. These large scale models have been popular in Europe for over a decade and have recently become very popular in the US thanks to companies like HPI Racing producing affordable high quality models locally.