Differences in Lithium Ion (Li-Ion) Lithium Polymer (LiPo) batteries

Most battery packs are of the LiPo type. Li-Ion and LiPo batteries have essentially the same chemical make-up, they both rely on lithium ion exchange between the lithium carbon cathode & anode, and are cared for in the same way; the primary differences are in how the cells are packaged and the type of electrolyte that is used.

Li-Ion

Li-Ion batteries use a flammable solvent based organic liquid as the electrolyte. This electrolyte is responsible for the lithium ion exchange between the electrodes (anode and cathode) just like any type of battery. Li-Ion batteries are usually encased in a hard metal can (again like a more conventional battery) to keep the electrodes wound up tight against the separator sheet adding weight and not allowing many different options as far as shape and size.

LiPo

A true LiPo battery doesn’t use a liquid electrolyte but instead uses a dry electrolyte polymer separator sheet that resembles a thin plastic film. This separator is sandwiched (actually laminated) between the anode and cathode of the battery (lithium carbon coated aluminum & copper plates) allowing for the lithium ion exchange – thus the name lithium polymer. This method allows for a very thin and wide range of shapes and sizes of cells.

The problem with true LiPo cell construction is the lithium ion exchange through the dry electrolyte polymer is slow and thus greatly reduces the discharge and charging rates. This problem can be somewhat overcome by heating up the battery to allow for a faster lithium ion exchange through the polymer between anode and cathode, but is not practical for most applications.

If they could crack this problem, the safety risk of lithium batteries would be greatly reduced. With the big push towards electric cars and energy storage, there is no doubt some pretty huge developments will be made in ultra light weight dry and safe LiPo’s in the coming years. Seeing that theoretically this type of battery could be made flexible, almost like a fabric, just think of the possibilities.

How RC Heli Servos Work

A servo’s job is to convert the angular movement of a servo arm to the linear movement of a control surface. This is done by attaching linkages, called control rods to the servo arm and the associated control surface. When the servo head rotates, it pushes the control rod back and forth. The rod is linked to a control surface, and can move it up or down as the servo rotates.

Three wires control a RC helicopter servos: two to provide the DC electricity that the motor needs, and one that sends the signal, controlling the servo. The signal wire works by sending the servo a series of pulses, which are interpreted by it’s internal circuitry. By varying the timing of each pulse, the servo knows exactly which position to move to.

Main Shaft Repair

Main shaft may crack or break. A loose strand of hair may also be wound up in the main shaft. This causes the main rotor to slow down, and may even stop the rotor from spinning entirely, if serious enough. Do not fly with a cracked main shaft. If this happens, the best thing to do is remove the shaft from its holder and replace it (or just remove the hair, if that is all). Usually, this entails removing the main gear and any securing screws, so make sure you remove all that hold the shaft in place and place them in a secure location! These are the most important screws on your RC helicopter.

Take care to avoid removing any extra grease, as this will make the shaft a bit less efficient in rotation. For a coaxial, in order to remove the outer shaft you must first take out the inner shaft. In the picture to the right, the main gears are in the bottom white box, and the inner shaft is denoted by the top white box. The inner shaft always connects to the lower gear, and the outer shaft to the higher gear. So to remove the inner shaft, be sure to remove the lower gear. If you must remove the outer shaft as well, you will likely have to remove some extra screws. For a general idea of how to remove the inner shaft, view the first bit of the lower blade swap video on Volitation Mods and Upgrades.

For a CP / FP Heli and 4 channel coaxials (and some 3 channel ones), you will have to disconnect the swashplate from the servos. Simply pop off the pushrods (or rods with circular openings at the top) from the swashplate. Then remove the main gear and any necessary screws (which there may not be any). You will be able to tell when the shaft can come out because it will slide out of the frame with just a push. It should not require much effort, otherwise there is still something holding the shaft to the frame.

RC Servo Motors

The motor which drive the RC Servos can classified into several different types:

  • Coreless – Conventional electric motors use copper wires wrapped around metal cores to form electromagnets. In a coreless motor, there is a metal mesh that rotates around the permanent magnets. Coreless motors respond more quickly than conventional motors, because they don’t have to overcome the momentum associated with heavy metal cores.
  • Brushless – RC helicopter Servos can be powered by brushless motors, giving them longer life, faster response time, and more torque.
  • 3 Pole and 5 Pole – DC Electric motors have permanent magnets, called poles, that electromagnets are attracted to. Servo motors can have either 3 or 5 poles, with more poles providing better torque. If you’re new to RC or have a regular sport model, you probably won’t notice the difference between 3 pole and 5 pole servos.

Digital Servo VS Standard Servo

RC Servos can be rated two types: digital and standard. Both digital and standard servos can be used with a normal receiver, the real difference is performance.

All servos use a series of short pulses as signals that determine what angular position they should maintain. The series of signals is usually very fast, somewhere around 50 pulses per second at maximum. On a standard RC helicopter servo, the rate is so fast that very small movements of the control sticks may not have an affect. This means that there is a “deadband” on the control sticks, in which no servo movement takes place. Although it’s not a problem on trainers and most sport class models, the deadband becomes a significant issue with 3D aircraft. Even a small delay with a 3D aircraft could cause a severe crash.

Digital servos remove the deadband by speeding up the rate at which it receives pulses. Usually, this is increased from around 50 to 300 pulses per second. This increase in resolution allows the servo to operate much more precisely.

Blade Grips replaced

The blade grips / holders are black clevis like objects which clamp down on the root of each blade and hold it to the main shaft. If one of these becomes damaged, use this procedure to replace it:

  1. Remove the both of the rotor blades that the blade grips are holding by following the instructions above.
  2. Lay the RC helicopter on its side and observe the two screws that hold the blade grips together and on the main shaft. This picture shows one screw removed, viewed from the bottom of the helicopter.
  3. Unscrew the blade grips and keep the screws in a safe place where they can’t roll away.
  4. Replace the broken blade grip and install the screws.

blade-holders

How To Select The Right Servos For Your RC Helicopters

Servos In Brief:

A servo is a device rotates a shaft to a position set by the user, and holds this position until further input is given. Servos usually consist of a small DC (direct current) electric motor, several gears, and a head where an arm or wheel can be attached. When the user tells the servo what angular position to move to, the servo rotates and holds position until further input is specified. Servos are designed to hold position because external forces are always interacting with the aircraft, and would set control surfaces to undesired positions unless stopped. Servos exert a torque on external forces, that prevents them from changing the position of any control surface.

How RC Helicopter Servos Work

A servo’s job is to convert the angular movement of a servo arm to the linear movement of a control surface. This is done by attaching linkages, called control rods to the servo arm and the associated control surface. When the servo head rotates, it pushes the control rod back and forth. The rod is linked to a control surface, and can move it up or down as the servo rotates.

Three wires control a RC helicopter servo: two to provide the DC electricity that the motor needs, and one that sends the signal, controlling the servo. The signal wire works by sending the servo a series of pulses, which are interpreted by it’s internal circuitry. By varying the timing of each pulse, the servo knows exactly which position to move to.

Selecting the Right RC Helicopter Servo

Servos have a number of qualities that make them suitable for different applications:

  • Torque – This is a measure of the servos “strength”, or how much “push” it has. Torque is the product of force and the radius at which it acts, or the . This is shown graphically in the figure on the right. Bigger planes need high torque servos to move their large control surfaces. In general, servo size goes up with rated torque.
  • Speed – Speed measures how fast the servo can move from one position to another. Different RC airplanes and helicopters will need servos with different speeds. For example: a trainer doesn’t need to change control surface positions rapidly, but a 3D helicopter or plane does. High speed servos are many times more expensive than standard ones.
  • Dimensions – As stated previously, the dimensions of a servo increase with the torque that it provides.
  • Weight – The weight of a servo depends on several variables. Most often recorded in grams, the weight of a servo is always reported on the package.
  • Bearings – There are two ways to support the output shaft of a servo – bearings and brushes. Brushes are cheaper, but bearings last longer and operate more smoothly. Very small and very cheap servos tend to be brushed, while high end and very large servos generally have bearings. It’s possible to upgrade a brushed servo to bearings, with several upgrade kits being available on the internet.
  • Gears – Most hobby grade servos use nylon gears, while higher end servos use metal gears. Metal gears add more weight, but their advantage is that they can’t “strip”, causing an RC helicopter or airplane to crash. Metal gears wear over time, which can cause “slop” in their rotation, but the gears can be replaced somewhat economically. In general, nylon servos are adequate for sport flying. If you’re particularly worried about losing a model in a crash, or are flying intense aerobatics, a metal geared servo could be the right choice.

 

Introducing of Flight Simulators

Flying your rc helicopter in the first time can be risky, especially if you have not had prior experience. Using a simulator is a good way to see what the hobby is all about and to practice without risking a crash.

There are many simulators available, both commercial products and free software. Any of them can provide a realistic way to try flying an rc helicopter. There are several benefits of using a flight simulator, the most important being you cannot damage a model while learning how to fly. Simulators can provide a good way to improve your flying skills. Many simulators support using your actual rc helicopter transmitter to control the simulated model, further enhancing the realism, while others require the use of a controller specifically designed to connect to your computer and simulate an rc transmitter. RC helicopter simulators will allow you to fly a variety of models, under different conditions. Most simulators will allow you to adjust various flight parameters. This means that you can simulate your own rc helicopter, and even simulate equipment failures. Unlike real flying, the simulator is not dependent on weather or time of day. Some simulators have training systems that will let you control different axis of motion, while the simulator controls the rest. This makes learning easy for the beginner.