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Know your Helicopter If your new to model helicopter flying and need to learn more about
your machine we have pages of information and links to great help
sites for set and flying your T Rex , Walkera or 3DX 450 helicopter.

Whats the Ideal Pinion Size for 3DX450 helicopters

The general rule of thumb is this using a pinion with fewer teeth will allow the motor
to spin bigger rotor dia's or apply more collective pitch without bogging down the
motor and keeps it running cooler, this usually leads to longer flight times longer
motor life and lower rotor speed.

Using a pinion with more teeth will spin the main rotor faster but the motor can
will usually run hotter, this can lead to high performance and shorter flight times
and potentially shorter motor life if the motor is pushed to it's limits.
This is equivalent to driving a car in high gears all of the time.

For beginners and average pilots if you are suing a 3400kv motor then an 11T pinion is ideal with a 2,200 rotor speed is perfect for the 3dx 450 and t rex models. If you have a 3400 to 3600Kv motor and try a 15T pinion your helicopter will feel like it's on steroids at 2900 rpm and should only be flown by experienced pilots only!!

110 to 120'c is considered normal after 3D flights and if your getting up to 140'c Plus for your brush less motor your pushing it too hard.

You should consider buying an infrared temperature gun (maplins) to measure after flight motor and battery temps.

Also do not repeatedly fly again and again battery after battery on your heli motor without a full cool down period as this will lead to failure of the motor even fire!

Do you know how the Tail Rotor Works ?

The tail rotor system of a helicopter is essential for stable flight. If you didn't have a tail rotor your helicopter would spin violently in the opposite direction to the main rotors with disastrous results!

Fortunately for us we have the tail rotor to counteract this happening.
How it Works
The tail rotor works by spinning at high speed and generating side thrust that counteracts the torque produced by spinning the main rotor. By changing the amount of side thrust produced by the tail rotor (via changing the pitch of the blades) the pilot can control the rate at which the helicopter pirouettes. Now we have a controllable helicopter.

Recently Found a fantastic web site dedicated to knowing your Helicopter worth a quick look

Check out Swash Pate for help on getting going in RC Helicopters right through to that first flight etc Swash Pate Fantastic tips and tricks

Setting up a CCPm Helicopter

Cyclic Collective Pitch Mixing, or CCPM for short, is one of the two popular methods for controlling the swash of a RC heli. CCPM has been around and available for numerous years, but has really taken a foothold in the hobby recently. Modern radios make CCPM easier and more problem free than earlier hobbyists could have ever dreamed. With a little understanding and some simple tips, any heli pilot can be a CCPM expert.

Explanation of CCPM
CCPM can simply be defined in a helicopter as multiple servos working together, interdependently, to execute all the control movements (collective, aileron, and elevator) of the swashplate. There are 4 servo and 3 servo CCPM setups, this discussion will focus on what the majority of the CCPM helicopters use, a 3 servo 120° setup. The other method of swash control, non-CCPM, is often called Single Servo Mechanical. What is the difference one may ask? In simple terms, Single Servo Mechanical control uses a single servo for each control movement, and these servos are completely independent of each other--each has a duty that is distinct on the swashplate.

On the other hand, CCPM mixes a combination of the three servos together to complete the control movements. For example, when the collective stick on a radio is moved all three servos will flow in unison to raise or lower the entire swashplate accordingly. In CCPM no swash movement occurs without at least two servos doing the job.

Image 2

Set Up 1

The mechanical setup of a CCPM heli is extremely important, just as on non-CCPM machines. Doing proper setup in the beginning saves time and prevents troubles later on. It is important to follow the manufacturer directions as closely as possible from the manual. The crucial thing to remember with a CCPM setup is symmetry and right angles. The radio setup is also included in this section as they are intertwined.

1. Build the helicopter per the instructions, setting all linkages (and bellcranks if applicable) to the correct lengths. Install the servos and plug them into the proper channels. Many pilots get stuck at this stage, deciding which servo plugs in where. This can be confusing but there is a simple way to do it. Plug the servo that controls the ball that is inline with the frame of the heli (the ball that sits directly behind or in front of the mainshaft) into the elevator channel of the receiver (channel 3 on a JR system, channel 2 for Futaba and Hitec, for other makes check the radio manual). Then plug the other two swash servos into the aileron and pitch channels (channels 2 and 6 on JR radios). Do not worry about which of these two servos ends up in which channel, they will be taken care of in the radio setup.


REc set up

2. Turn on the transmitter and set it to 120° CCPM in the swash type menu (or 140° if the heli is a 140° machine). Center all the trims, get rid of any sub-trim, and make sure all endpoints are at 100% for the 3 swash servos. It is also crucial at this point to set a linear pitch curve (0, 50,100) for the initial setup.

3.Make sure the throttle stick is at the halfway point (for electrics, make sure the motor is disabled). With the servos centered, try attaching control arms to the servos so each arm is perfectly lined up, either parallel with the servo, or exactly 90° to it depending on the heli. It is important that it be as close as possible to perfect, try various servo wheels and arms until one is found that fits the bill. If necessary, use a small amount of subtrim to center the arm, but only as a last resort. It is best to do as much mechanically with the arms and links. Once the three "perfect" arms have been found, install the ball links to them at the distances instructed in the heli manual then install the arms on the servos.

Servo set up

tech tip

Notice that eCCPM or mCCPM is not mentioned. Since all CCPM is done electronically (in the radio), there really is no mCCPM. What we have is "CCPM" or "Single Servo Mechanical" (can be shortened to just "mechanical" if preferred). No electronic mixing happens in a single servo setup, each servo is completely independent. When one servo fails in single servo machines, the radio still has control of the other two functions. This is not the case in a CCPM setup, where each servo relies on the others to complete their tasks. The terms eCCPM and mCCPM can cause quite a bit of confusion as the terms imply a similarity between the two, which is not the case. If one sticks to the historically more accurate terms of "CCPM" and "Single Servo Mechanical" it will help differentiate the two systems better. In other words, heli kits advertised as CCPM will be eCCPM, since that is the only type of CCPM available.

There is much debate on what the true advantages and disadvantages are for using CCPM over Single Servo. We will stick to the basics here and leave the debate for another time.

Some of the advantages of CCPM include:
• Easy mechanical setup, usually less linkages and hardware.
• Less slop due to less links.
• CCPM helicopters often weigh less, also due to the lower parts count.
• More torque is applied on the swash movements, multiple servos sharing the load compared to one in Single Servo.

Some disadvantages of CCPM may include:
• Interaction--this is evidenced by the "dance" a CCPM swashplate does on occasion, especially when it is moved quickly. Its cause lies in the basic geometry of the system (one servo has to travel a little more than the others to move the swash the same distance for elevator) and in the inherent, minute speed/wear differences between one servo and the next. The slower the servo, the worse the interaction. Modern radios do a pretty good job at taking this into account and rectifying the situation, but some interaction usually remains.
• CCPM helicopters that use direct links from the servos to the swashplate leave the servos more susceptible to damage in a crash.
• In a CCPM heli, when one servo dies inflight, all basic swash control is lost; slightly lowering the chances to save the heli.
• CCPM requires the use of high quality servos that are the same make and model (and preferably age), mixing servos or penny pinching here will cause some headaches in setup and in flight.QQ

4.Next, get the 3 servos moving in the right direction. This can be a difficult and trying task but there are some well known tricks that make it easy. Remember the following detail and things will be simple; servo reversing in CCPM is used to set the relation between the servos. Meaning they move together when they should, and in opposite directions when they should. Servo reversing is not used to reverse a function's direction, such as pitch or cyclic--for this, adjustments in the swash mixing menu will be made.



5.Before connecting the swashplate to the servos, make sure the servos are moving properly in relation to each other. Use the servo reversing menu to do this. The two side servos (the pitch and aileron channels) are setup first using the reversing menu. Set them so that the two servo arms move in opposite directions when a left/right cyclic command is given (one arm moves up and the other moves down). Set the servo plugged into the elevator channel so that its arm moves in the opposite direction as the other two servos when a fore/aft cyclic input is given (the other two servos will move together with fore/aft swash movement). Only reverse the elevator servo to fix the fore/aft direction, leave the aileron and pitch servos at the settings set in the left/right setup above.

image 4


6. Now move on to getting the servos moving in the right direction in relation to the helicopter. Center the controls and connect the swashplate, making sure it is level and in the EXACT center of its travel range by adjusting the linkages. Move the throttle/pitch stick up, if the swash is moving in the right direction (inducing positive pitch) then this function is working properly. If the swash is giving negative pitch when positive is expected, use the swash mix menu to reverse it by changing the value for Pitch in the menu from a positive to a negative (retaining the same number value). For example, if the number next to Pitch in the radio was +70, setting it to -70 will reverse the pitch function and make the swash move in the opposite direction. Do the same thing with the Aileron function (left/right cyclic) and the Elevator function (fore/aft cyclic)--using the mix numbers to reverse the direction if necessary.



7.Once the swashplate is moving in all the right directions in respect to the control stick, it is time to set the travels and prepare for flight!! Please note that most radios have a default expo amount for the swash mixes in CCPM. These expo settings help counteract interaction and it is generally recommended that expo is used for a smooth swashplate. Use the values found in the swash mix menu (the same ones used earlier to change the pitch, aileron, or elevator function direction) to increase or decrease the travel for each movement (check for binding as well). If more pitch is needed simply increase the Pitch value to add more travel. Do not change the "+/-" found in front of the value, only the number itself. For example, if more pitch is needed and the Pitch value in the Swash Mix menu is initially -60, changing the number to -70 would add more travel, and likewise, if the Pitch value was initially +60, changing it to +70 would also add more travel. Clear as mud? Don't worry, some time spent using the radio and seeing the effects of each change will help CCPM make more sense.


With the mechanical setup done properly, the helicopter should end up with equal positive and negative pitch and equal cyclic throws. Finish by setting the pitch curves and getting everything else ready to go on the heli. If small adjustments are needed to get a "hands free hover" during flight testing, it is ok to use the radio trim. But if too much trim is being used, change the linkages instead to center things up. CCPM helis work best when the mechanical setup is near perfect and the less trim used the better for the mixing.[10}

140° Versus 120° CCPM
There are a small number of helis out there that are offered in a 140° CCPM version. The huge advantage a 140° system has over a 120° is that the geometry is more evened out between the two side servos and the front servo. This gives a more equal cyclic rate all the way around, where on a 120° setup the left/right cyclic is slightly faster than the fore/aft. The drawback is that there are still only a handful of radios with 140° mixing available (though a radio with a 120° program can be made to work with a 140° setup with some simple mixing). Also, only a handful of kits with 140° CCPM are currently available.



The End!
Though it may appear complicated on paper, and in theory, setting up a CCPM heli is really no more difficult than setting up a Single Servo Mechanical heli. The trick is to be exact in the mechanical setup and to read the radio and helicopter manuals thoroughly. Follow the steps just outlined and that CCPM heli will no longer be a mystery.

Belt Tension ? do you know how to do this ?

Topics like getting a proper gear mesh and good belt tension can be very confusing for new helicopter junkies. The term "feel" is used a lot when an experienced pilot is attempting to explain either of these procedures, and the problem is that a new heli pilot has nothing to base this "feel" on. Not to worry; with a little understanding and practice, setting gear mesh and belt tension can be made easy.
Gear Mesh. What is it?
Gear mesh is the relation between two or more gears where their teeth engage. The point where these gears join together is very crucial, as that point is where all power is transferred from one to the other. Basically, gear mesh measures how tightly two gears are pressed together as they operate.

Where would I worry about mesh in a helicopter?
There are numerous types of gears and locations in a model helicopter. Here is a short list of the most common:

• Pinion Gear: The gear that is attached to the motor shaft in an electric helicopter and the gear attached to the clutch assembly in a nitro one.
• Main Gear: This is the large gear found below the main shaft, receiving power from the pinion gear and driving the main rotor head.
• Tail Drive Gear: This gear is found underneath or on top of the main gear, and is driven by the main gear or by the main shaft via a one-way bearing. This gear can be of numerous types: a standard gear, a crown gear, or a belt pulley, depending on the helicopter it is in.
• Secondary Tail Gear: This gear is not found in all helicopters, but is present in many. When a helicopter's tail drive gear is a crown gear or a belt pulley, this gear is omitted. This gear meshes with the tail drive gear. This is usually done in one of two ways: In belt-driven tails, this gear shares a shaft with a belt pulley which will run the tail belt. Or, in shaft- driven tails, this gear shares the shaft with a bevel gear which will mesh with the bevel gear at the end of the tail shaft.
• Tailbox gears: In shaft-driven tail systems, the tailbox will have two bevel gears (one at the end of the drive shaft and one on the tail shaft) that mesh together to run the tail rotor.

Please note that in many modern helicopters, the mesh has already been set for some of these gears and the factory mounting holes are already set for them. In these cases, just bolt and fly!

Why is proper mesh important?
When any set of gears in a helicopter is not meshed properly, performance can greatly suffer. When gears are meshed too tightly, drag is induced in the system, which will rob power from the system, wear out the gears prematurely, and will put extra strain on the components that the gears are attached to (especially in electric systems, where the added strain on the motor can burn it or the power system out in a hurry). When gears are set too far apart, the teeth can strip in flight, there will be play between components, and the teeth will wear off quickly.

How to Spot & Avoid Gear Wear
There are a few clues that a heli will give you when a gear is wearing poorly. Look around a gear for large amounts of dust that is colored the same as the gear material, which would be actual material coming off the gear during flight. A little gear dust is normal during break in, but large amounts may point to a gear mesh that is far too tight. Also, look in between the gear teeth for marks and material which may indicate that the gears are meshed tight enough to bottom out on each other. When a gear is running too loose, the wear is generally indicated by the gear teeth rounding off. When a gear's teeth have lost their sharp edges you can be sure that the mesh is loose. Also, a loose mesh can often be indicated by missing teeth and slop between the components. All these types of wear can be avoided by setting the mesh properly and by regular checking of the gears to make sure they are still lined up.

How to Set Proper Mesh
So here it goes, there are a number of ways to set a good gear mesh. Car and truck drivers may have heard of the "paper method," in which a piece of notebook, printer, or even cigarette paper is cut into a small strip and placed between the two gears being pushed together. With the paper strip pressed tightly between the two gears, tighten the adjusting screws down and remove the paper. The paper should be pressed into a zigzag shape from the teeth, but not be cut through. If the paper is cut through, the mesh may be too tight. This method works for many applications and has been proven as a tried and true system. But it is important to check the gears regardless of the method used. To check gear mesh, hold the smaller gear of the two and move the other gear back and forth. A small amount of movement--very small--should be present. This movement is called backlash, the movement of the teeth of one gear inside the gaps of the other. This movement should, in most cases, be very small and just perceptible; anything more will be too loose. If no movement is present, the gears are too tight. This is where "feel" comes in. With time and practice, a pilot will know what the proper amount of backlash feels like. It is very helpful to have an experienced pilot set it the first time so that you can get a "feel" for it by moving the gears. Using the paper method will get very good results until this "feel" can be obtained.
It is also important to note that since most gears are not perfectly round, the mesh needs to be checked at various points around the gears. If there is a high point in a gear where the mesh is tighter than the rest of the circumference, it may work best to set the mesh tighter than normal at that point, so that mesh will be right around the rest of the gear, the high point should wear in over a short time.
All gears should be set with a small mesh, with as little backlash as possible (but with no drag or tightness). Another way to check if things are too tight is to just spin the gears and listen; they should spin freely with little noise. If there is a grinding noise when the gears are spun, the mesh may be too tight. Use shims or spacers wherever necessary to get gears nicely meshed together.


Belt Tension

Belt Tension
Belts, where are they used?
Belts can be used in helicopters in two places: the tail drive and the main drive. Using a belt as a main drive (in place of a pinion and main gear) is pretty rare in a modern helicopter, but can still be found. Belt drives being used to run the tail rotor are more common, and in fact are becoming more popular than their shaft drive counterparts due to their ease of installation, lower parts count, and inexpensive repair costs. The belts in a helicopter have teeth in them as do the pulleys that drive them.


Belt Wear

How to Spot & Avoid BELT Wear
Belts can wear just as gears do. Some telltale signs of a belt that is wearing out are a fine dust or powder coming from the belt, missing teeth on the belt, strands of the reinforcement bands coming out of the belt or stringing off of it, or teeth that are rounded on one side or the other. While it is difficult to avoid belt wear, as they do wear out quicker than gears usually do, it is possible to prolong their life by doing some of the following actions. Make sure that the belt is neither overly tight, nor overly loose. One way to check for a belt that is too loose is to grab the head block and tail hub at the same time, and while holding the tail hub tightly, turn the head block. The tail belt should not skip, even with considerable force. If it skips, tighten it up. Also, make sure the boom is straight and that the belt does nut rub against anything in its run. Once a belt has started rounding off at the teeth, it needs to be replaced.

belt set up

Belt tension, how to set it?
Setting belt tension is fairly straightforward. The manual for the helicopter should have a general recommended tightness, usually measured by how far the belt can be pushed, or deflected, in before it stops. Start with the recommended setting. Setting this tension is simple; with a main drive belt, simply loosen the motor mounts and move the motor back and forth until the desired tightness is found (main drive belts like to be pretty tight to prevent skipping during use). With a tail belt, loosen the boom and pull it from the frame until the belt is at the desired tightness. Too tight of a setting will stretch the belt, rob power, and wear out quickly. Too loose of a setting can cause the belt to skip while running, strip teeth, rattle in the boom, and run off the pulley.

best set up2

belt tension

Why would I run the tail belt loose?
The tail belt can be run tight and loose, and unlike gear mesh, can be run either way and work fine (within limits). The main reason a pilot would want to run a relatively loose belt is to maintain power during autorotations. A tight tail belt will rob a bunch of head speed in a driven auto, making the auto more difficult to perform. A looser belt will use less power to run and creates less wear on the shaft bearings that support the pulleys.

Why Would I Run The Tail Belt Tight?
3D pilots generally run a tighter belt than sport pilots. The reason to run a tight belt is for greater tail authority. A tight belt has very little play and will not skip or flex during hard maneuvers.

Learning to set proper gear mesh and belt tension will help you throughout your time in this hobby. When the gears and belts are set correctly in a helicopter, the machine runs smoothly and efficiently, not to mention that the gears and belts will last a very long time as well. And who doesn't like that?

Avoiding a crash

Li Poly Batterys everything you need to know

Data - Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports

Lithium batteries are the preferred power sources for most electric modelers today. They offer high discharge rates and a high energy storage/weight ratio. However, using them properly and charging them correctly is no trivial task. There are many things to consider before using lithium cells for e-flight. But none is more important than safety.

1. Charging/Saftey IMPORTANT!
Until you are willing to follow all saftey precautions, DO NOT use lithium batteries. If your a type of person that prefers to push the limits of products, or be haphazard about following saftey requirements. Lithium technology is not for you. Read on to find out why.

Lithium cells must be charged very differently than NiCad or NiMH. They require a special charger specifically designed to charge lithium cells. In general any charger that can charge lithium ion can charge lithium polymer, assuming that the cell count is correct. You must NEVER charge lithium cells with a NiCad or NiMH only battery charger. This is dangerous. Charging cells is the most hazardous part of using lithium batteries. EXTREME care must be taken when charging them. It is important to set your charger to the correct voltage or cell count. Failure to do this can cause the battery to spew violent flames. There have been many fires directly caused by lithium batteries. PLEASE BE RESPONSIBLE when charging lithium batteries.

Here are a few MANDATORY guidelines for charging/using LiPos (Lithium Polymer Batteries).

1. Use only a charger approved for lithium batteries. The charger may be designed for Li-Ion or Li-Poly. Both batteries are charged in exactly the same. Some older cell phone chargers may charge the batteries .1 volt to low (4.1 vs 4.2), but that will not harm the battery. However, inexpensive lithium chargers are widely available and the use of cellphone chargers is highly discouraged.
2. Make certain that the correct cell count is set on your charger. Watch the charger very closely for the first few minutes to ensure that the correct cell count continues to be displayed. If you don't know how to do that, get a charger that you do know how or don't charge the batteries.
3. Use the Taps. Before you charge a new Lithium pack, check the voltage of each cell individually. Then do this after every tenth cycle there after. This is absolutely critical in that an unbalanced pack can explode while charging even if the correct cell count is chosen. If the cells are not within 0.1 volts of each other then charge each cell individually to 4.2 volts so that they are all equal. If after every discharge the pack is unbalanced you have a faulty cell and that pack must be replaced.
Taps are provided on most new lithium packs. Taps give you the ability to check individual cell voltages and charge one cell at a time. Make sure and get the appropriate connector to go into your taps. Don't try to stick you volt meter probes in the taps to measure voltage. They could slip and short your cells. Don't try to charge more than one cell at a time from the taps. Unless you have an isolated ground charging system, you'll short your batteries out. Refer to your individual cell maker for tap pin-outs.
4. NEVER charge the batteries unattended. This is the number one reason for houses and cars being burned to a crisp by lithium fires.
5. Use a safe surface to charge your batteries on so that if they burst into flame no damage will occur. Vented fire safes, pyrex dishes with sand in the bottom, fireplaces, plant pots, are all good options.
6. DO NOT CHARGE AT MORE THAN 1C unless specifically authorized by the pack vendor. I have personally had a fire in my home because of violating this rule. Todays highest discharge batteries can supposedly be safely charged at greater than 1C, however so far in all cases doing so shortens the life of the pack. Better to buy 3 packs than to try to charge 1 pack 3 times quickly. This may change in the future but as of Winter 2005 1C is still the recommended charge rate.
7. DO NOT puncture the cell, ever. If a cell balloons quickly place it in a fire safe place, especially if you were charging it when it ballooned. After you have let the cell sit in the fire safe place for at least 2 hours. Discharge the cell/pack slowly. This can be done by wiring a flashlight bulb of appropriate voltage (higher is voltage is ok, lower voltage is no) up to your batteries connector type and attaching the bulb to the battery. Wait until the light is completely off, then throw the battery away.
8. If you crash with your lithium cells they may be damaged such that they are shorted inside. The cells may look just fine. If you crash in ANY way carefully remove the battery pack from the aircraft and watch it carefully for at least the next 20 min. Several fires have been caused by damaged cells being thrown in the car and then the cells catch fire later and destroys the car completely.
9. Charge your batteries in a open ventilated area. If a battery does rupture or explode hazardous fumes and material will spew from the battery.
10. Keep a bucket of sand nearby when you are flying or charging batteries. This is a cost effective way to extinguish fires. This is very cheap and absolutly necessary.
11. It can happen to you, do not think to yourself that “it won't happen to me” as soon as you do that it you'll be trying to rescue your kids from your burning house or car. I'm very serious about this.

Now that we have covered that important topic let's move on to lighter matters:

2. Lithium What?
Lithium Polymer batteries are used in many electronic devices. Cell Phone, Laptops, PDA's, Hearing Aids just to name a few. Most, if not all, lithium polymer batteries are not designed for RC use, we use them in different applications than they were designed for. They are similar to Lithium Ion batteries in that they each have a nominal voltage of 3.6 volts, but dissimilar in that they do not have a hard metal casing but rather a flexible material encloses the chemicals inside. The "normal" lithium polymer batteries are thin rectangle shapes with two tabs on the top one positive one negative. The reason we use Lithium cells is that they are significantly lighter than comparable NiCad or NiMH batteries, which makes our planes fly longer and better.

3. Voltage and Cell Count:
LiPolys act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. It is important not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can harm the battery.
The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.
If your ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.
If you have previously been flying with NiCad or NiMH batteries, switching over to lithium polymer will result in a different number of cells being used. If you had 6 to 7 round cells then 2 lithium polymer cells will correctly duplicate the voltage of those cells. If you had 10-11 cells then 3 lithium polymer cells would be right for you. There are a lot of 8 cell flyer's out there that are stuck between 2 and 3 cells. In my experience the best option is to determine how many watts you were using before and duplicate that with your LiPos, Motor, and Prop. For example. If you were running 8 cells (9.6volts) at 10 amps on a speed 400 airplane, then you have 9.6 x10, 96 watts. So if you went with 2 lithium polymer cells (7.2 volts nominal) then you'd need to change your prop such that you used 13 amps. If you went to 3 LiPoly's (10.8 volts nominal) then you'd need to reduce the amperage to 8.9 amps. These estimates are approximate, and some experimentation is required for best results but conserving Watts is a good way to start.

4.10C from 3S4P? Naming conventions explained.
How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in ½ or half an hour. All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).
All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.
The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).

5. Which battery should you buy?
With so many choices out there it is difficult to decipher what is marketing hype, what is brand
loyalty, and what is outright lies. Battery manufacturers are constantly trying to one up one another. While capitalism can drive prices down, it also can give cause to false claims about products.
One great way to find out what the best battery is, is to look at graphs of the batteries performance. Looking at how low the voltage of the cell drops at various amperages will give you a metric to compare that battery to similar size/weight batteries.
If graphs aren't your thing then simply look at what other people are using in successful setups that are similar to your application. If a lot of people are reporting long flight times and lots of power from airplane X, with power system Y, and battery Z and you do the same, then if your setup is similar the same battery will probably work well for you.
It pays to learn something about Watts, Volts, and Amps. Understanding these concepts is beyond the scope of this document, but can serve you well in not only figuring out what battery is best but also in your electric aircraft hobby.
I'm not convinced that a 30C battery is really any better than a 10 or 20C battery. Sure a higher C rating means it can discharge faster. But at the same time a battery discharged at 20C continuously will be empty in 3 minutes. Do you really only want to use the battery for 3 minutes? I love having burst power in helicopters and boats, but in almost all other applications actually running a battery at or above 20C is useless to me. I prefer to run batteries at 8-10 C and have a little headroom if I need it.
A final note on choosing a battery. Don't cheap out. Confirm that your batteries are capable of running that the amperage level you plan to use them at. Running a cell at a higher C rating than the battery can handle can not only damage your batteries, but it can also damage your speed control. Castle Creations has an excellent article on how using a weak battery can destroy a perfectly good speed control of any brand. Better to buy a bit better battery than you need than to destroy your electronics.

6. Dealing with temperature.
Lithium batteries like heat, but not too much. In the winter time, try to keep your batteries from the cold as much as possible. Leave them in the car while your flying, or keep them in your cargo pants... etc. At the same time don't let them heat up too much. Try to keep your batteries from reaching 160F after use. This will prolong the life of the cells. A good way to measure temperature is a handheld IR meter, they can be found for around $50.00 at most hobby shops.

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