This article was originally published in the RC Driver’s March 2016 issue.
Terminology in any hobby can be challenging to understand, especially to the newcomer. So this month, we’re going to take a walk through some of the buzzwords and terms used by various brands and RC gurus.
Battery packs have a language all their own. The various terms that refer to capacity, voltage, cells, the magical “C” rating, balancing and the whirlwind of safety warnings and care techniques are enough to scare anyone away. Let me be one of the many to say clearly and loudly, follow the safety guidelines of the battery manufacturer. Balance charge often, and check your battery leads, plugs or terminals frequently. If and when a problem does occur with a LiPo battery, it is never a simple problem. Even smaller, low power LiPos pack enough punch to cause serious injury and significant damage. Okay, now that we have that out of the way, let’s move on to the terminology.
LiPo or NiMH
Battery packs break down into two basic groups, nickel based battery packs and lithium based battery packs. Nickel packs are known as NiMH packs in the RC world and the more commonly used lithium polymer based packs are referred to as LiPos. While the technology behind the packs is drastically different, they share a few basic terms. The capacity or runtime of the battery pack is rated in Milliamp Hours, or “mAh”. More mAh means more runtime, and sometimes more grunt or oomph from the low end response.
NiMH and LiPo packs have different numbers of cells and voltages. This gets a bit tricky. A six-cell NiMH pack has a nominal voltage rating of 7.2 volts. Each cell is 1.2 volts. When you get into LiPo packs, the voltage ranges and cells are different. A two-cell LiPo has a nominal voltage rating of 7.4 volts. Each cell is rated at 3.7 volts. Three-cell LiPos are rated at 11.1 volts. This basic break in voltage scaling causes a bit of confusion. NiMH packs are rated by voltage and cells, while the LiPo packs get called out by the “S” value. This refers to the number of cells connected in ‘series’ in the battery. So a two-cell 7.4 volt LiPo is called a 2S pack. While a 7.2 volt rated NiMH is called a six-cell pack.
Here is where the ratings stop for NiMH packs. They are simply noted by capacity and number of cells. LiPo packs have a bit more information, in the form of the C rating. This C rating tells you how fast or easily the pack can give up the charge. The higher the C rating means the battery pack should perform better under higher loads. Higher C rated packs are touted to have better power and are better for racing.
Another common category with lots of confusing numbers, letters and coded words is the motor. With sizes and RPM ranges only a small portion of the information, the rest of the specifications can send the mind reeling.
The size, of course, matters since finding something that fits the vehicle correctly is crucial. Most often, the sizes are expressed as numbers and these numbers will tell you the simple street terms for the size and make it easy to know if it will fit. The 540 and 550 motors are common to 1/10-scale vehicles. The 550 motor is slightly longer than a 540, but shares the same mounting hole pattern. Often 550 motors have larger pinion gear shafts. However, some 540 motors have these larger sizes as well. A 1/8-inch pinion shaft is common on most 540-size motors and 5mm is the heavy duty shaft from the 550 style and some 540 motors. Some vehicles will fit either motor correctly, but the motor may not be suited for the size of the vehicle.
After the size classification we need to look at the “poles”. This terminology refers to the number of segments in the motor’s magnet. Motors generally fall into either the two-pole or four-pole category. Most of the 540 motors are two-pole motors, but there are several 540-sized four-pole motors as well. 550 motors can also be found in two-pole and four-pole varieties, but are typically four-pole. What’s the difference? Four- pole motors accelerate faster. Two-pole motors have slightly better high rpm characteristics.
Next we have the RPM, or the Kv, Kilovolt rating that some motors use and some do not. This Kv rating is the RPM per Volt that the motor will turn in theory of course. These numbers are sometimes not measured under loads that are happening in the vehicle, so the actual RPM of the motor in operation can vary. These Kv numbers do give a
basic range of RPM, however. Other motors are rated by the winds of wires used to make the coils of the motor, called “Turns”. This measurement also gives a basic idea of the RPM of the motor. Higher Kv means higher RPM and a smaller number of turns means the same higher RPM. Typically four- pole motors are rated by Kv and two- pole motors are rated by their number of turns.
Radio gear is another area that is often tricky to say the least. Radios these days are typically either over-the-top complex or simple ready-to-run radios with limited adjustability. All of them share a few basic features that can be checked. The Trim is the central feature. Steering and throttle center points can be adjusted as needed. These trim adjusters are the clicker tabs on the transmitter/controller. Most radios also have channel/servo reversing. This allows you to make the output of a given channel go in the opposite direction and is often needed when replacing a servo or changing out various electronics. Dual Rate adjusting is becoming more common with even RTR radios. This controls the end point travel of the steering. This can limit the steering to allow fine tuning or prevent wear and tear on the servo. Independent adjustability of the channels is also a great feature to shop for. This allows precise setting of the steering to allow the servo to work correctly, as well as equal left and right steering. End Point or Travel Adjustments let you reduce or increase travel in either direction. This works great for adjusting the brake feel or reducing power for new drivers. Steering can be set up to maximize steering travel without damaging the servo. “Curves” or “Expo” settings are fine tuning features that allow the numbing up or advancing the feel/ response of the channels. These are great for when conditions get tricky and some help is needed to de-sensitize the response.
It never hurts to ask a few questions at the hobby shop, too. Often your understanding of the complicated side of the hobby doesn’t match up with how it applies. The hobby shop support can do wonders for making it all click, and breaking down the scary topics.