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RC Glossary

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New to the RC Hobbies? What does buggy, bulkhead, nitro mean in radio control car hobbies? Check out the glossary for remote control cars below.

D

  • Damping --
  • Damping is a highly variable part of car tuning. It's affected by the strength of the shock spring (length and thickness of the wire, plus the number of coils), the size and number of holes in the shock piston, and the viscosity, or weight, of the oil in the shocks. The spring controls how hard the shock compresses, and both the piston and the oil control how quickly the spring pushes the shock to its full length (which can be limited by shock spacers), and so affect the quickness of the shock's return. Stiffer springs need heavier oil and/or smaller-hole pistons to control the speed of the rebound, and bumpy tracks need lighter oil so the shocks, or dampers, can compress and rebound quickly. Softer damping gives more 'stick' on a particular wheel, but makes the car less responsive because the chassis takes longer to reset after a turn, and is also more forgiving to drive. Softer damping also reduces weight transfer at that wheel. Stiffer damping makes handling more responsive, but reduces traction to a particular wheel which can make the car slippery as the chassis snaps back into place after a turn. Stiffer damping also increases weight transfer at that wheel.

  • Dead Band ( 1 ) Neutral Width (ESC & SERVO) --
  • The point in a servo's travel when no movement is actually transferred. This is caused by a slight lag when transitioning across the servo's center point from one direction to the other (such as when transitioning from left to right steering). Digital servos tend to have a narrower dead band due to faster initial reaction. ESC dead band is the distance between minimum drive and minimum brake, with neutral at the center. Most ESCs are programed with a small amount of dead band - usually 2% to 5% of maximum, to prevent 'instabrake syndrome'. Pro drivers may be able to detect dead band, but for the rest of us mortals, it remains a theory.

  • Dead Band ( 2 ) Linkage --
  • A small gap between the servo horn and the collar on a linkage system that relieves pressure on the servo at the neutral (center point) position. The goal of linkage dead band is to give the servo some 'breathing room' without creating excessive slop.

  • Dead Short --
  • Dead shorting is electrically shorting out a battery pack after it has been fully discharged. Basically, this is done by connecting the negative and positive leads together. This eliminates any residual voltage left in the pack, allowing the pack to retain the maximum possible charge. Occasionally dead shorting a pack may increase voltage, but reduces run time. Do not attempt to dead short a pack unless you know what you are doing and have the proper tools (some high end dischargers have dead short capability). If something goes wrong, you can easily destroy the cells (best case scenario), or cause a cell to vent (a.k.a. explode).

  • Decals --
  • A.K.A. stickers. Most RC decals are printed on vinyl. For larger decals, wet the body with window cleaner or mild soapy water first - this allows you to slide the decal into position, then squeegee out the excess liquid.

  • Delrin --
  • A durable plastic composite material used in the construction of many high abuse RC parts, especially gears.

  • Denatured Alcohol --
  • A common thinner (such as SLX) that is great for cleaning the oils and grime off nitro models. Just put some in a spray bottle and use it like nitro cleaner.

  • Detonation (Pinging) --
  • On nitro engines, detonation is usually caused by using a glow plug that is too hot or by too much engine compression. This causes the fuel to explode rather than burn properly, resulting in a distinctive hollow 'ping' sound. Detonation can cause serious damage to your mill, so try using a cooler glow plug or adding a head shim to decrease compression if you experience detonation.

  • Dialed (in) --
  • Refers to a ride that has the perfect tune and settings for the running condition.

  • Diff Action --
  • Refers to how loose or tight a diff setting is. A diff setting that allows the opposing tires to spin freely is said to have a loose or light action, while a diff setting that provides more resistance to the opposing tires is said to have a tight or heavy action. A locked diff would have no action. Diff action can be tuned with the use of thinner or thicker diff fluid or grease. The action of a ball diff is adjusted by loosening or tightening the adjustment nut.

  • Diff Angle --
  • This is an adjustment that may be available on some belt drive models, and refers to the height of the diff compared to the lay shaft. The diff is usually raised or lowered using cams, spacers, or specially shaped diff housings that allow the diff to be rotated to the desired height.

  • Diff Balls (Ball Differentials) --
  • A differential that uses a series of steel or carbide-steel ball bearings in a circle, pressed between two metal rings, to provide the differential action, allowing one wheel to rotate more than another in a turn. Ball diffs are easier to adjust than gear diffs but are harder to maintain, as they need checking every day of running and are not recommended for Nitro racers. Normally a screw on one side controls the tension between the metal rings, which controls how much the outside wheel in a corner can turn. The looser (to a point) a diff is, the more traction there is at that end of the car. To start tuning your car, set the ball diffs to the same tension at each end, and use the diffs only to fine-tune the car. Do not change the settings of your diffs first. The most common sizes of diff balls are 5/64 and 3/32.

  • Diff Collar --
  • A plastic or alloy collar used on many diff cases that reinforces the area where the input or output shafts enter or exit. This collar slides onto the outside of the diff case, and may be keyed to the bulkhead on some models.

  • Diff Cup --
  • A housing inside the case of bevel gear diffs that holds the spider gears and input / output gears. The ring gear is screwed to the cup, capping off the grease or oil (if the diff is sealed) inside.

  • Diff Fluid --
  • See DIFF OIL

  • Diff Oil - Diff Fluid --
  • A silicone based fluid used in sealed diffs to tune the diff action. Diff oil is rated by weight (wt.), such as 1000 wt. (thinner) or 5000 wt. (thicker). Thicker oil creates more resistance to the diff action, while thinner oil allows the opposing tires to spin more freely. Using diff oil in a diff that isn't sealed almost always results in a mess. A good starting point for the diff oil in 1:8 buggies is 7000 / 5000 / 2000 (center / front / rear), while the bigger tires of truggies would require something closer to 2000 / 7000 / 3000 (center / front / rear).

  • Diff Rings - D Rings --
  • The large steel discs that are keyed to the pressure plates of a ball diff. The diff rings ride against the diff balls. The inside of the rings are cut in a 'D' shape to key to the pressure plates.

  • Diff Screw --
  • A long screw used to hold some ball diffs together.

  • Diff Unloading --
  • This happens when one tire driven by a diff completely loses traction, eliminating any load on the diff. This causes the diff to send all available power to that tire, which leaves the tire still in contact with the ground powerless. A tell tell sign of a diff unloading is that the tire will balloon. Diff unloading is commonly caused by the inside tires lifting during cornering.

  • Differential --
  • A system that transfers power equally from a shaft input to shaft outputs. A differential (or ""diff"") allows the outside wheel of a car going through a corner to travel farther than the inside wheel, preserving corner speed and efficiency. There are two main types used in radio control cars: Ball Differentials or Gear Differentials. Ball differentials should be initially set to the kit specifications: with HPI kits, the diff should be set so that the pulley is not be able to be turned with two flat head screwdrivers or Allen wrenches slid through the outdrive. A different type of differential is the One-Way Diff, which uses expensive one-way bearings to control wheelspin.

  • Dig - Burn (Front# Rear# Locked# Unlocked) --
  • Used exclusively on rock crawlers, dig refers to the ability to selectively power only one axle (i.e. the front tires or the rear tires). If only the front tires are powered it's called a front dig (the most common), and if only the rear tires are powered it's called a rear dig. A dig may either be an unlocked dig or a locked dig. With an unlocked dig, the unpowered tires freewheel - this is usually used to help with side hilling and steep ascents. With a locked dig, the unpowered tires are locked - this is usually used to help with tight turns and steep descents. For dual motor rigs that don't use a driveshaft (i.e. super crawlers), a dual ESC set up is usually used to enable dig - this is known as an electrical dig. A servo actuated system (mechanical dig) is used on rigs that use driveshafts (i.e. 2.2 crawlers), such as a sliding axle system. All digs require at least a 3 channel radio system, with the 3rd channel operating the dig.

  • Digital Servo --
  • A servo that uses a high frequency motor controller that allows it to have a faster (and smoother) operation, hold its position under load, and center perfectly. Digital servos constantly use current to alter and hold their position - this means it may not last as long as an analog servo on throttle applications, since it is constantly under use even at idle (which also explains why it may drain your batteries faster than analog servos). Digital servos can operate at up to 300 pulses per second, compared to the 50 pulses a second of analog servos.

  • Disc Damper --
  • A type of rear damper system used on some pan cars, especially micro scale cars. 2 spring loaded discs (think of a sandwich with a spring or rubber O Ring between 2 discs) are mounted between the main chassis and rear pod, providing suspension damping.

  • Disc ˇV Discharge Rate (Battery Label) --
  • Refers to the number of amps used by the factory when discharging the cell for matching, and also stands as a guide for the amount of amps the cell can be safely discharged at. A higher discharge rate lowers the SEC (run time) rating of the cell, but more accurately simulates actual running conditions.. A 35 amp discharge rate is the industry standard used when matching cells. Note that a discharge rate of 30 to 35 amps is good for use with all motors, while a rate of less than 30 is best used for stock motors.

  • Discharger --
  • A device used to lower a battery packs voltage for conditioning or storage.

  • Discharger Tray --
  • A device used to lower the voltage of each cell in a battery pack individually. This is done for conditioning or storage.

  • Dish Rim (Wheel) --
  • A light weight, flat faced racing rim.

  • Displacement (Engine) --
  • Refers to the total cubic centimeters (c.c.) or cubic inches (c.i.) of volume available in a piston sleeve with the piston at full stroke (TDC), such as 4.59 c.c. or .28 c.i. (both engines have the same displacement). More displacement usually means more horsepower at the expense of fuel economy. The full formula for finding a nitro engine's displacement is : pi / 4 x bore squared x stroke. Multiply this by the number of cylinders if you are running an exotic multicylindered powerplant.

  • Dive (Anti DiveˇVNeutral Dive - Pro Dive) --
  • Dive affects the steering response, weight transfer, and CG of a model during braking or deceleration, and is adjusted by altering the angle of the front hingepins in relation to the chassis (this is commonly done by placing spacers under the front pivot blocks). Anti dive is achieved by raising the front of the hingepin higher than the rear - this is the most common dive setting, which helps to prevent the front of the model from dropping (diving) during braking. Neutral dive means the hingepin is level to the chassis, and pro dive means the rear of the hingepin is lower than the front - neutral and pro dive settings are virtually never used in RC.

  • Dogbone --
  • A part of the drivetrain that connects the outdrive to the axle. This allows the differential to get its power to the axle and tires of the car.

  • Double Wishbone --
  • A type of suspension design that uses two wishbone arms (parallel to the ground and each other - one for the main suspension arm and one for the upper arm) to help maintain a constant tire camber as the suspension is compressed. Most RC cars have this type of suspension design, because, although it is expensive to have on a full-size car because of cost and space issues, on a miniature car where there is no concern over the space needed for a driver, it is much easier to make. Older RC cars used different suspension technologies that are no longer in use today (at least in RC), including swing-arm and trailing arm suspensions.

  • Downforce --
  • The effect of air contacting the car body's sloped surfaces. Downforce is created by the air dam, hood, windshield, roof, spoiler(s) and wing(s) of the car. More downforce increases drag and slows the car, but raises the tire temperature, making the car easier to drive. Less downforce raises the top speed by reducing drag. The car should be set up so that it can drive with minimal downforce.

  • Draft --
  • In racing terms, draft is the area directly behind a car where the air is disturbed and there is very little wind. A real-world example would be putting your hand outside the window of your car, and moving it behind the side mirror, then out from behind the mirror. Behind the mirror is the draft.

  • Drafting --
  • In racing terms, this is the act of following the car in front of you close enough that your car does not have to fight drag. This lessens the load on your engine or motor, and on a long straight section of the track your car and the car in front of you can go faster than another car on its own. In RC racing, this is very rarely able to be used because of the size of the cars and the maneuverability of the cars, even on an oval track.

  • Drag (1) Race --
  • A type of race run between 2 competitors on a straight track. The object is to be the first across the finish line from a dead stop - its all about reaction time, acceleration, and pure speed. A drag race is usually used to settle the 'my car is faster than your car' argument. The scale length for a 1:10 scale 1/4 mile drag strip is 132 feet.

  • Drag (2) Resistance --
  • Refers to resistance caused by air or friction. Wind (air) resistance is caused by a models body shape - more aerodynamic bodies offer less drag, allowing the model to 'slice' through the air. Drag caused by friction can be caused by many factors, such as; dirty bearings, wheel nuts too tight, worn parts, improper mesh or belt tension, ect. In either case, unnecessary drag slows the model down.

  • Drag --
  • In car design, drag is the force of air that slows down the car. The lower the drag of the car (in other words, the more aerodynamically efficient it is), the faster the car can go while using the same amount of power.

  • Drag Brake --
  • This is an adjustment that gives the model a small amount of brake while the throttle is at neutral, eliminating the dead band between throttle and brake. Drag brake is commonly adjusted via the brake linkage, radio, or ESC.

  • Drive Frequency --
  • Refers to the number of times an ESC cycles the motor on and off while accelerating or at full throttle. This frequency is measured in Hz (hertz). A higher drive frequency (more cycles) equals smoother operation and better efficiency, but may provide slightly slower acceleration. Higher frequencies are best for modified motors. A lower drive frequency may seem to accelerate better, due to fewer steps, but is less efficient and may cause the motor to heat up faster or the batteries to drain quicker. Some high end ESCs allow the user to change the drive frequency or even map out the throttle curve with different frequencies. The term 'drive frequency' usually includes both the acceleration and braking frequencies, however, these usually differ, with the braking frequency being less than the acceleration frequency.

  • Drive Pin --
  • See AXLE PIN

  • Drive Profile (ESC) - Profile --
  • An option available on many ESC's that allows the user to choose between preset limits for options such as: throttle response, throttle curve, braking limits, and reverse enable.

  • DriveCup - Outdrive Cup --
  • A slotted cup that attaches to the outdrive shaft on a tranny or diff. The dogbone end is keyed to the slots, which allows the end to move in and out as the suspension compresses and rebounds. A drive cup may have an integrated pressure plate if used with ball diffs, and may include a silicone spacer or spring to help hold the dogbones in place.

  • DriveDog - Finger - PAWL --
  • This is a spring loaded lever on a gear that opens to engage a gear tooth when a specific RPM is reached. Drive dogs are commonly used in the gears of reversing or multispeed transmissions to change gears.

  • Drivers Stand --
  • An elevated platform the drivers stand on during a race. The drivers stand allows all racers to view the entire track.

  • Droop --
  • The measure of shock droop is the amount of uptravel the chassis will have if you weigh the car with its full running gear (servo, batteries, motor, etc.), settle the chassis (press down and release on the chassis), then lift each end until the tires lift off the ground. The total upward movement of the chassis at each end is measured as droop.

  • Droop Screw - Downstop --
  • A screw that can be adjusted to limit the amount of down travel a suspension arm has by stopping it before its full available motion is reached. The droop screw is commonly used to adjust ride height.

  • Droop Suspension --
  • Traditional RC shocks use outer springs that keep the shock extended. A droop suspension does the opposite - the shocks use internal springs below the shock piston to keep the shock compressed. This is used with rock crawlers, and allows the model to sit lower (with a lower CG) while still retaining the same amount of suspension travel as traditional shocks. Some crawlers run a partial droop, which uses springs above and below the shock piston. As an added bonus, droop shocks have a more scale appearance than traditional RC shocks.

  • DSC --
  • Direct Servo Control

  • Dual Chamber (Tuned Pipe) --
  • A tuned pipe that utilizes a separate internal convergent cone. This separates the pipe into 2 chambers, with the end of the pipe acting as a sound suppressor (muffler). Dual chamber pipes are easily recognizable by their 2 piece design, which allows the pipe to be separated to gain access to the convergent cone.

  • Dual Conversion (RX) --
  • A receiver that filters the signal twice to help reduce interference.

  • Dual One Way (DIFF) --
  • A diff system commonly used on dual belt on road models with rubber tires. This is a front one way diff with a one way bearing on the pulley layshaft. This setup helps the front belt spin freely while off power.

  • Dual Rate (Shock) Spring - Progressive Rate (Shock) Spring --
  • A shock spring that increases in stiffness as the spring compresses. Dual rate springs will have the coils spaced closer together at the top of the spring and farther apart at the bottom, or may be barrel shaped.

  • Dual Rate --
  • A feature available on most radios that allows the user to adjust the total movement of a servo from 0% to 100%, then change between two different settings with the flick of a switch.

  • Dual Start --
  • A starting system for nitro engines that includes a pull start and shaft start in one convenient package. This allows the engine to be pull started if you leave your shaft starter at home.

  • Dump (Battery) --
  • Refers to a cell or battery pack being drained through use to the point where it no longer has any usable energy. Once the batteries in a model are drained enough for the model to slow (if electric powered), or the control slows, it is said that the batteries have 'dumped'. If you're using rechargeable batteries, it's time to let them cool, then recharge them. If you're using alkalines, its time to break out your wallet.

  • DynoˇVDynamometer --
  • An expensive piece of computerized equipment that measures the efficiency of a motor. Can be used to select the right gearing, but the dyno in this function is normally only used by pan car or oval racers.

  • Gear Differential (Gear Diff) --
  • A differential that uses a series of gears to provide the differential action, allowing one wheel to rotate more than another in a turn. Gear diffs are harder to adjust than gear diffs but are much easier to maintain, because they must be sealed to keep the grease inside from coming off the gears. Tuning a gear diff can only be accomplished by changing the weight (viscosity) of the grease inside the gear diff case. The looser (to a point) a diff is, the more traction there is at that end of the car. To start tuning your car, set the ball diffs to the same tension at each end, and use the diffs only to fine-tune the car. Do not change the settings of your diffs first.

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