Lithium Polymer Battery FAQ(2)

Q3.) How fast can I charge my batteries?

Different cells can withstand different charging rates. Check with the manufacturer to make certain you don't damage your pack.
For fast charging, most packs can be safely charged in 15 minutes, which requires a charging current of 4 times the capacity of the pack.
Trickle charging is usually done at a rate of 1/10th the capacity, or C/10. Cell manufacturers list this as the charge rate in which the cells will not vent (release gases that build up from overcharging). However, even this charge rate can reduce the life expectancy of a cell if left on after the cell is fully charged.

Q4.) What is Cell reversal?
In a battery, not all cells are created equal. One will be weaker than the others. So, as the battery is discharged, the weakest cell will use up all its active material. Now, as discharge continues, the current through the dead cell becomes a charging current, except that it is reversed. So, now reduction is occurring at the positive terminal. As there is no more nickelic hydroxide, it reduces the water, and produces hydrogen. Cell pressure builds, and it vents. The cell has lost water and the life of the cell has been shortened
This is the big danger of battery cycling to prevent memory. Invariably, unless one is very careful, one ends up reversing a cell. It does much more harm than the cycling does good. Also, keep in mind that cells do have a finite life. Each cycle is a bit of life.

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Lithium Polymer Battery FAQ(1)

Q1.) Does Temperature Affect Lithium Polymer Batteries?

Yes, lithium polymer batteries are affected by temperature. All batteries use a chemical reaction to provide electricity, and a low temperature slows this reaction down significantly. You cannot harm a lithium battery by running it at a low temperature, but you will notice a significant decrease in performance. Allowing lithium polymer batteries to freeze is generally not recommended, so be sure to store the lithium battery in a cool, dry location over the winter months.

Q2.) How can I calculate theoretical flight time?

In order to calculate the maximum theoretical flight time of your models, you will need to know some information about your battery and motor equipment:
#Motor Amperage
#Pack capacity in Mah (milliamp hours)

After you have that information, you can use the following formula to compute the maximum theoretical flight time of your model:
Time (hours) = (battery capacity (amps) / (motor current (amps)

Notice how the battery capacity must be given in amps. To find your battery capacity in amps, divide the capacity in milliamps by 1000. You will probably want the result expressed in minutes. so multiply the time you just calculated by 60.

By this formula, a 33.5 amp motor powered by a 5000 Mah battery would have a run time of a run time of 8.96 minutes. This is a theoretical maximum, if you actually ran the above set up for the calculated maximum time you would destroy the battery. Most lipo batteries shouldn’t be discharged below 80%, so multiply the calculated time by .8 to account for this.

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How To Safely Use, Charge, and Discharge Lithium Polymer (Lipo) Batteries

Lithium polymer batteries are great for RC aircraft, but they have an explosive chemistry that must be treated with caution.

Prevent this from happening to your batteries by following these tips:

1. Store lithium polymer batteries in a flame proof LipoSack while charging. - Charging your lithium polymer batteries in a flame proof LipoSack can contain a fire should it occur. It could mean the difference between a minor clean up and the loss of your house or car. Also make sure that the storage area is well ventilated.
   
2. Read the manual – The importance of reading your battery and chargers manual cannot be emphasized enough. The battery manual will state the proper charging rates and times.
   
3. Use common sense – Don’t charge batteries unsupervised. Even when you do everything right, incidents can occur. Also, do not charge lithium polymer batteries in your car. A flame out can be disasterous if it occurs inside a vehicle.
   
4. Use the right battery charger – Charging a lipo battery with a charger designed for other batteries will cause problems, and will probably result in a fire.
   
5. Charge lithium polymer batteries on a fire proof surface – It’s really important to charge lithium polymer batteries on a flame proof surface such as concrete. In the event of a fire, a fire proof charging surface will stop it from spreading, or at least slow it down significantly.
   
6. Keep a fire extinguisher, or bucket of sand near the charging area – If a fire does occur, you don’t want to be running around looking for something to put it out with. Water will not help put out a lipo fire. Being a conductor, it will cause a short circuit and could even make the fire worse.
   
7. Don’t charge lithium polymer batteries near flammable substances – lithium polymer batteries are flammable enough as it is. Don’t make the problem worse by storing flammable substances near charging batteries.
   
8. Check lithium polymer batteries for swelling prior to charging and each use – A puffed battery is unstable, and can be in danger of exploding. If you see a puffed battery, immediately disconnect it from the charger or aircraft and put it in a bucket of water. Dissolve a few tablespoons of salt in the water to aid conductivity, and leave the battery in the bucked for about 4 days. The salt water depletes any power remaining in the battery by creating a short, and it can’t catch fire while underwater. After the four days are up, take the battery out and cut off the connectors (which may come in handy for other projects). You can then dispose of the battery in the trash. The battery no longer contains toxic metals, won’t harm the environment, and by using the salt water you’ve guaranteed that it won’t catch fire. This should be done as soon as you see a puffed battery. You can’t salvage a puffed battery, the best you can do is to dispose of it safely.
   
9. Never charge a lithium polymer battery in a model – If you charge a lipo battery in your RC airplane or helicopter, you are risking the total loss of your model. Only charge lithium polymer batteries on a flame proof surface, in a LipoSack.
   
10. Make sure the charging leads are connected properly – Connecting positive to negative and negative to positive can cause a major fire.
    
11. Don’t overcharge batteries – By their very chemistry, lithium polymer batteries cannot be discharged to a potential of less than 3 volts without damage. For the same reason, don’t charge them to over 4.2 volts. This means that you have to land your rc aircraft before the motors stop turning. Some aircraft come equipped with a voltage cut-off, others do not. If you don’t have a voltage cut-off, then land as soon as you sense the propeller or rotors slowing down.
    
12. Double check that the charger settings are correct – Lithium polymer battery chargers require you to set the battery configuration. Ensure that this configuration matches the battery you’re charging, or else your lipo could get overcharged and explode. Some chargers automatically sense the battery configuration, but make sure that the setting is correct regardless. They have been known to be wrong on occasion.
    
13. Balance lipo batteries – Lithium polymer batteries have balance connectors, designed to make sure that each cell in the pack has the same charge. If this isn’t the case, some cells can become overcharged and explode.
    
14. Never let the battery leads touch – If the battery terminals touch each other, the battery will short circuit and, in most cases, be destroyed. If this happens and you get a puffed battery, dispose of it by following tip 9 above.
    
15. Don’t ever store / charge lithium polymer batteries in your car – Unless you hate your car. Batteries can and do explode, and if this happens inside a vehicle the result is usually catastrophic. On a hot day, temperatures can rise inside the car and cause stored packs to rupture.
    
16. In the event of a crash, remove the battery and supervise it for at least 4 hours – A crashed plane’s battery can appear fine, but can have an internal short circuit. This short circuit can cause an explosion, even hours after the crash occurred. A LipoSack is a great place to keep a battery that’s been in a crash. If enough time elapses and nothing happens, then your battery is probably fine. If you see puffing, dispose of it immediately following the instructions in tip 9 above.

Always use common sense, read the manual, and know the risks associated with lithium polymer batteries. Handled properly, the risk of a fire is relatively small. Store lithium polymer batteries in a LipoSack for additional saftey.

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The difference between Ni-Cd, Ni-MH, and LiPo

As you know ,there are three main types of batteries currently in use for electric airplane motors. These are Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPo).

Dou know the difference between Ni-Cd, Ni-MH, and LiPo this three type of batteries?


Li-polymer Battery
LiPo (Lithium Polymer). This is one of the newest cell types available. It is also the lightest battery type currently available on a commercial basis and can provide more power than the other main cell types. There are no known problems of memory effect with this battery type and it is the easiest battery type to care for. The downside of this battery is that it has the highest engineering costs and therefore the price is usually considerably higher than other cell types.


Ni-MH Battery
Ni-MH (Nickel Metal Hydride). This cell type is the most common cell type currently available for laptop computers, (although Li-ion is rapidly becoming the most popular) This battery type is relatively cheap to manufacture and therefore tends to be cheaper than Li-ion. This cell type is prone to 'memory effect' so it is important to take good care of your Ni-MH battery to ensure that you obtain the best runtimes.


Ni-Cd Battery
Ni-Cd (Nickel Cadmium). This is one of the oldest cell types and is generally only found in older laptops. The main pro for this cell type is its ability to handle higher loads, and therefore is more commonly found in portable power tools or devices that need a lot of power to work efficiently. The main downside of this cell type is that it is notorious for suffering with memory effect so good care must be taken with this battery to ensure most effective use of battery.

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Definetly recommended Motor

RC Smart 893 RPM/V Outrunner Brushless Motor is one great small motor that I have had on gliders and park models.I have had the motor for two years with no problems.Definetly recommended.

RC Smart 893 RPM/V Outrunner Brushless Motor

Specifications

• Rotational Speed: 893 RPM/V
  
  
• Continuous Current: 42A
  
  
• Max. Current: 50A
  
  
• Input Voltage: 8 - 23V
  
  
• Max. Efficiency: 98%
  
  
• No Load Current: 0.9
  
  
• Internal Resistance: 74m ohm
  
  
• Motor Dimensions (Diameter x Length): 37.1mm x 41.1mm
  
  
• Shaft Diameter: 3.93mm (Front and Back)
  
  
• Shaft Length: 12mm (Front) 8.7mm (Back)
  
  
• Input Battery Types: NiCd/ Nimh/ Li-po Battery
  
  
• Recommend Model: Airplane
  

Package Included

• 1 x 893 Outrunner Burshless Motor (with accessories & English Manual)

I brought this motor the internet(http://www.rcmodelland.com/)

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My recommend Battery Charger (2)

In last few day, I recommend two battery chargers to my friend. Today, I will introduce the last one battery charger to you~

G.T.POWER A6 Digital LiPo Li-polymer Balance Charger

The A6 balance charger is a rapid charge / discharger with built in balancer, computerised with micro-oprocessor and specialised operating software.

Specifications

• Operating Voltage Range: DC 10 - 18V
• Circuit Power: Max. 50W for charging, Max. 5W for discharging
• Charge Current Range: 0.1 - 5A
• Discharge Current Range: 0.1 - 1A
• NiCd/NiMH battery cell count: 1 - 15 Cells
• Li-ion/Polymer Cell Count: 1 - 6 Series
• Pb Battery Voltage: 2 - 20V
• Dimensions: 135mm x 100mm x 40mm
• Packet Includes: Multifuctional Connector

Features
Optimized operating software
When charging or discharging, It has an 'AUTO' function that sets the feeding current automatically. Especially for Lithium batteries, it can prevent the over-charging can lead to an explosion by users fault. Every program in the unit is controlled with mutual links and communication for every possible error so it introduces a maximum safety. These can be set at users option.

Special recharge plugsport for receiver, transmitter and igniter charger. And for frequently used charger port such as multi purpose crocodile pin etc.

It provides most convenient balance charge port for Lithium batteries, with separated 3,4,5,6 charge port, and external reverse connector.

High-power and high-performance circuit
It employs the circuit that has maximum output power of 50W. As a result it can charge or discharge up to 15 cells of NiCd/NiMH and 6 series of Lithium batteries with maximum current of 5.0A. Furthermore the cooling system is so efficient that can hold such a power without any trouble of running the CUP or the operating program.

Individual voltage balancer for Lithium batteries inside
It has an individual-cell-voltage balancer inside. This does not require any extra balancer separately when charging Lithium batteries (Lilo/LiPO/LiFe) for cell voltage balancing.

Balance individual cells on discharge
It also can monitor and balance individual cells of the Lithium battery pack during the discharge process. If the voltage of any one cell varies abnormally, the process will be stopped with the error message.

Accept various types of Lithium battery
It can accept three types of Lithium batteries - Lilo, LiPo and LiFe. They have different characteristics by their chemistry. You can select any one of them that you are going to process before the job. For their specifications, refer 'Warnings and safety notes' section.

Lithium battery 'Fast' and 'Storage' mode
You can charge Lithium battery for special purposes. 'Fast' charge reduces the charging time of Lithium battery and 'storage' mode controls the final voltage of the battery to be suit for long time storage.

Maximum safety
Delta-peak sensitivity: The automatic charge termination program works on the principle of the Delta-peak voltage detection. (NiCd/NiMH)

Auto-charge current limit: When charging NiCd or NiMH at 'AUTO' current mode, you can set the upper limit of change current to avoid from high current charging. This is very useful when charging the low impedance and small capacity NiMH battery in 'AUTO' mode.

Capacity limit: The changing capacity always calculated by multiple of the charging current and time. If the charging capacity exceeds the limit the process will be terminated automatically when you set the maximum value.

Processing time limit: you can also restrain the maximum process time to prevent form any possible defect.

Input power monitor: To protect the car battery using as input power from being damaged the voltage of it always monitored. If it drops below the lower limit the process will be ended automatically.

Automatic cooling fan: The electric cooling fan comes into action automatically only when the internal temperature of the unit is raised.

Data store / load
For users convenience it can store maximum 5 data of different batteries. You can establish the data contains program setting of the battery to charge or discharge continually. These data can be called out at any time you need and the process can be executed without program setting.

Cyclic charging / discharging
Perform 1 to 5 cycles of charge>discharge or discharge>charge continually for battery refreshing and balancing.

PC based analysis using USB communication
For technical expert, it offers PC based program can analyze the characteristic of the battery by USB port. It shows a graph of voltage, current, capacity and temperature curves. It also shows the individual voltage of each cell in the Lithium battery pack.

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My recommend Battery Charger (1)

In yesterday, I recommend two battery chargers to my friend. Today, I will introduce one of it to you~
iMAX B5 Intelligent Digital Li-polymer Balance Charger

This charger is computerized with a high performance microprocessor and specialized operating software. It can maintain your battery at its best condition and also control them safely. Please read this entire operating manual completely and attentively as it contains a wide of information you need to keep the manual in a safe place and be sure to pass it on to the new owner if you ever dispose of yours imax B5.

Specifications

• Operating Voltage Range: 11 - 18V
• Circuit Power: max. 50W
• Charge Current Range: 0.1 - 5A
• Current drain for balancing Li-po: 200mAh/cell
• NiCd/NiMH battery cell count: 1 - 14 Cells
• Li-ion/Polymer Cell Count: 1 - 5 Cells
• Battery Voltage: 2V, 6V, 12V
• Dimensions: 130mm x 80mm x 23mm
• Packet Includes: Multifuctional Connector
  

Features
Cell Balance and Charger in 1
The iMAX B5 Balance Charger has an individual-cell-voltage balancer built in so it does not need a separate balancer when charging Lipo batteries.

Maximum Safety
The automatic charge termination program works on the principle of the Delta-peak voltage detection.

Capacity Limit
The charging capacity is calculated by multiple of the charging current and time. If the charging capacity exceeds the limit the process will be terminated automatically when you set the maximum value.

Charge Time Limit
You can also set a maximum charge time to prevent any possible over charge.

Input Power Monitor
This function monitors the input voltage from your battery supply and will automatically stop the charge program if your battery falls below the required level.

High Power and High Performance Circuit
The iMax B5 Balance Charger has a maximun output power of 50W. As a result it can charge up to 14 cells of Nicd/NiMh and 5 series of Li-polymer batteries with maximum current of 5A.

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Recommend battery chargers

My friend is planning to buy a Li-polymer Battery balance charger. But he does not know choose which one is better. His intention is to get a reasonably good charger with sufficient function to take good care of the Li-polymer Battery.

He ask me what is my suggestion. I recommend two Battery balance chargers for him to choose.

- iMAX B5 Intelligent Digital Li-polymer Balance Charger

- G.T.POWER A6 Digital LiPo Li-polymer Balance Charger

I will discuss this two Battery balance chargers in next time ~bye

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knowledge of Li-polymer Battery (2/2)

Storage temperature and charge of Li-polymer Battery

Storing a Li-Po battery at the correct temperature and charge makes all the difference in maintaining its storage capacity. The following table shows the amount of permanent capacity loss that will occur after storage at a given charge level and temperature.

It is significantly beneficial to avoid storing a Li-Po battery at full charge. A Li-Po battery stored at 40% charge will last many times longer than one stored at 100% charge, particularly at higher temperatures.

If a Li-Po battery is stored with too low a charge, there is a risk of allowing the charge to drop below the battery's low-voltage threshold, resulting in an unrecoverably dead battery. Once the charge has dropped to this level, recharging it can be dangerous. An internal safety circuit will therefore open to prevent charging, and the battery will be for all practical purposes dead.

In circumstances where a second Li-Po battery is available for a given device, it is recommended that the unused battery be discharged to 40% and placed in the refrigerator or freezer to prolong its shelf life. Batteries should be allowed to completely warm to room temperature over up to 24 hours before any discharge or charge.

Permanent Capacity Loss versus Storage Conditions

Storage Temperature	40% Charge	100% Charge
0 °C (32 °F)	2% loss after 1 year	6% loss after 1 year
25 °C (77 °F)	4% loss after 1 year	20% loss after 1 year
40 °C (104 °F)	15% loss after 1 year	35% loss after 1 year
60 °C (140 °F)	25% loss after 1 year	40% loss after 3 months

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knowledge of Li-polymer Battery (1/2)

Serious Safety Issues of Li-polymer Battery

If LiPo batteries are improperly charged they can cause an explosive fireball. We cannot over-emphasize the importance of using a charger specifically designed to charge LiPo batteries, and to be positive that the manual cell count (if the charger has one) is correctly set for the specific battery being charged. If you use a good quality LiPo charger, these batteries are totally safe.

LiPo Do's and Don'ts
Do: Only use a charger that is specifically designed to charge LiPo batteries. Using other types of chargers can cause an extreme fire hazard!

Do: LiPos don't develop memory or voltage depression characteristics like Ni-Cds. Do charge them without the worry of cycling or discharging them.

Do: Store LiPos at least partially charged. LiPos will maintain their performance levels over time, even during non-use, much better than Ni-Cds and there's no need to cycle them.

------------------------------------------------------------------------------------

Don't: Use any type of charger that is not specifically designed to charge LiPo batteries. Using non-LiPo-specific chargers can cause an extreme fire hazard!

Don't: Fully discharge your LiPo battery pack. Most speed controller have a voltage cut off that will prevent over-discharging the battery. Discharging a LiPo beyond it's critical minimum voltage will cause damage to the battery.

Don't: If you have a crash and the battery is damaged, don't put the battery in your car or house immediately after a crash. It's possible that a chemical reaction can take place in the damaged battery that could cause a fire. Put the battery in a safe place for a least one hour.

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Review on AXI Motor (Gold Line 2217/9D )

I shared some information of axi motor before.

Today, i want to discuss AXI Gold Line 2217/9D Outrunner Brushless Motor .

I brought this motor on rcecho.com last weekend.




The high quality and performance of AXI 22xx GOLD LINE motors meant that they were a perfect base for development of the new AXI 2217/xx GOLD LINE. New small and powerfull motor AXI 2217/9D GOLD LINE with rotating case is suitable for aerobatic models up to 800g and for microhelicopters up to 700g. Hardened steel Shaft have 3,17mm diameter and is supported by two large ball bearings wich ensure very good mechanical stability. Thanks to using newest materials this motors achieve in their weight category extremely high efficiency and high load possibility. The optional Radial Mount Sets can be use also with AXI 2217/xx series motors.

Motor Nomenclature
Electric motors manufactured by Modelmotors are marked with name and numbers with slash. Name means type of motor (eg.: AXI - brushless 14-pole outrunner, MiniAC - brushless two-pole inrunner). First two numbers mean diameter of stator and next two numbers lenght of stator in mm. Simplified the bigger diameter and lenght the bigger power of motor. The number behind the slash is winding number. The lower winding number the higher RPM and current capacity.

Motor Specifications

No. of cells: 2 - 3 Li-Poly

RPM/V: 1880

Max. efficiency: 84%

Max. efficiency current: 17 - 30A (>75%)

Current capacity: 34A / 30s

No load current: 1.9A

Internal Resistance: 39m ohm

Dimensions (Diameter x Length): 27.7 x 35mm

Shaft diameter: 3.17mm

Weight with cables: 69.5g

This motor has high quality . It is suitable for my helicopter.^^

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What Battery should I use?

What Battery should I use?



When in doubt, use your airplane manufacturer’s recommended battery. This is generally a good starting point, although with experience you will probably have your own ideas about the best battery to use. Here is some basic info about battery types.

There are three main types of batteries currently (no pun intended) in use for electric airplane motors. These are Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPo).

NiCads are the oldest generation of these batteries. They pack more power but are heavier than the NiMH. The NiMH voltage (power) tends to fall off fairly fast during the flight. The wonder batteries LiPos have great power for little weight and hold that power well throughout the flight. However, LiPos tend to be much more expensive than NiCad or NiMH. Again, go with the recommended battery, you will have time to experiment after you learn to fly.

Note that more cells in the battery means more voltage, which means more power.

Power (Watts) = Current (Amps) x Voltage (Volts)

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RC Lithium-ion Polymer batteries

Let you can learn more about RC Lithium-ion Polymer batteries

LiPo batteries are very different from previous generation batteries and understanding how they work, and especially how to charge them, is the key to getting the best performance.

Series
Individual Lithium Polymer cells have a nominal voltage of 3.7 volts (vs. 1.2volts per cell for Ni-Cds or NiMHs). Cells are wired in series to give the following pack voltages:
1 cell = 3.7 volts
2 cells in series = 7.4 volts
3 cells in series = 11.1 volts

Parallel
Unlike Ni-Cd and Ni-MH batteries that self-discharge when wired in parallel, LiPo cells can be hooked up, charged and discharged in parallel with no detrimental effect. Wiring two LiPo cells in parallel doubles the capacity (more run time), plus an important advantage of wiring in parallel is that each cell only sees half the total current.

3S 2P
A battery pack that has three cells in series (giving 11.1 volts) and 2 of these 3-cell packs are wired in parallel is commonly referred to as a 3S, 2P (3 series, 2 parallel).

C Rating
LiPo cells are also commonly given a C or current rating. This is the maximum average recommended discharge current for the cell. For example, the VP2150/20C packs have a 20C rating. To determine the maximum recommended discharge rate multiply the capacity times the C rating. 2150mAh x 20C = 43,000. So the maximum recommended discharge rate would be 43,000mA or 43 amps. If your application has a higher amp draw, remember that LiPo cells can be wired in parallel, and with 2 cells in parallel each cell sees half the total current. With 3 cells in parallel, each cell see one third the current.
By wiring packs in a combination of series to get the voltage and parallel to achieve the capacity and individual cell current to an acceptable level, LiPo cells can be used to power nearly every type and size of model.

Charging
Charging LiPo batteries requires a very different charge method than other types of cells. It's imperative to use a battery charger designed specifically for LiPo batteries, and with most LiPo-specific chargers it's necessary to correctly select the cell count (1, 2 or 3 cells) manually.

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Understanding Motor Specifications

Haha~

Do you know different motor specifications's mean?

Today, i will tell you the motor specifications's mean.

Most electric airplanes either come with a motor or the manual will tell you exactly what size motor it needs. If you're converting from a brushed motor or glow engine to a brushless RC motor, understanding what these designations mean will be important.

1.)Voltage Constant
Kv is the "Voltage Constant". This is how many RPM's the motor turns for each volt applied. Actually, it's a tad less because even brushless motors aren't 100% efficient.
For example, if you apply 12volts to a 200Kv motor, it will turn at just under (12 x 200) 2400 RPM's.

2.)Torque Constant
Kt is the "Torque Constant". For all motors, Kt= 1355/Kv. You'll have to ask someone smarter than me where the 1355 comes from, cause I don't have a clue! Just accept it for what it is.
In a nut shell, this means the faster the motor spins for a given voltage (Kv), the lower the output torque will be (Kv).

Outrunners generally have a lower Kv, which in turn produces more torque at a slower speed for spinning those larger props. The opposite is true with inrunners.

3.)No Load Current
Io is the "No Load Current". This is the amount of current it takes to spin the motor with no prop.

For example, if your motor is pulling 25Amps, and the Io is 2Amps, then you really only have 23Amps turning the prop.

4.)Terminal Resistance
Rm is the "Terminal Resistance". This is the internal resistance of the motor measured in Ohms. The higher the Rm, the less efficient the motor is.

5.)Current and Power
The maximum current and power is what determines how large of a prop and what size plane can be used with the motor. Simply multiply the current by the battery voltage to get power.

The larger the propeller's diameter and pitch, the more current the motor will draw for a given RPM. For example, the 200Kv motor will run at 2400 RPM's regardless of whether it has a 10x6 prop or a 11x5 prop. But, the 11x5 prop will cause the motor to draw more current. Drawing too much current will destroy the motor.

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How does Timing effect the power of an electric motor?

In general terms this describes motor action:-) But (bet you knew that was coming) more specifically you need to first visualize that the permanent magnets create a fixed field in magnitude and position (for this discussion). This field has a shape with a maximum intensity exactly between the magnets (in a 2 pole motor - most DC motors - directly opposite each other). To generate the maximum torque from the motor, the electric field generated by applying current to the windings must be located 90 ELECTRICAL degrees from the center of the magnet field (90 physical deg. in a 2 pole motor). This is defined as the max. Kt (torque constant - oz.in./A)


What happens in a real motor under load is that the electric field lags the magnet field due to inductance effects in the windings and possibly some saturation effects in the steel parts (magnetic iron). The amount of lag varies with load (and rpm), so is a complex variable.


We try to preset the motor timing (brush position) so that at a selected load current, the fields are at the 90 E deg point for max. Kt., and max. magnetic power conversion efficiency. At no-load (without a prop) this will be an advanced position and since it is ahead of the 90 E Deg. point, will have a reduced Kt (take the SIN of the angle x KT90, eg SIN108 x 1 = .951 x Kt), which requires more current to turn the shaft (at no-load. The current will pull into phase at the selected load current. This will actually look like the current decreasing as the load increases, up to a point.


In a brushless motor the same thing is happening, but we advance the hall sensors for this effect. The big difference is that we have to visualize the analogy while sitting on the rotor (stationary frame of reference) and look at the stator field.


This is explained in most texts of ac and dc electric machines. It's a lot more complex than this, so I hope I've given you some insight as to the goings on in that little bundle of wire and magnets.

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brushless motors

In general, we will use brushless motors more than brushed motor. It is because brushless motor have much higher power to weight ratio.

There are some advantages of Brushless Motors:

l No brushes or commentator wear out

l Don't have to worry about cleaning the brushes or commutator.

l There's no Friction from brushes to slow the motor down.

l Longer flight times and extended battery life due to the absence of friction from brushes.

l Much higher power to weight ratio!

How brushless motors work

Brushless RC motors work on the same principle as brushed motors, except the electromagnets(poles) are stationary and the permanent magnets are on the spinning portion of the motor.

Since the electromagnets are stationary, there is no need for brushes! The electronic speed controller(ESC) takes care of switching the voltage of the electromagnets.

It's important to know that a brushless speed controller and a brushed speed controller can not be used interchangeably. They perform completely different tasks.

The quickest way to tell the difference between a canned motor and a brushless motor is to count the number of wire leads. All brushless RC motors have 3 wires. Canned motors have 2 wires. The third wire is used for feedback. Switching any two of these wires will change the rotation of the motor.

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Inrunner motor & Outrunner motor

There are two types of brushless RC motors for RC Helicopter, Inrunner motor and Outrunner motor .The permanent magnets of inrunner brushless motors are positioned on the inside of the electromagnets.

Inrunner brushless motors are set up very similar to the canned motor explained above, except the permanent magnets and electromagnets are in opposite positions.

An outrunner brushless motor has the permanent magnets on the outside of the electromagnets. You can see in the picture to the right that the outer hub holding the permanent magnets has the output shaft attached in the center.

Inrunner Brushless Model Aircraft Motors
The faster a motor spins, the more efficient it is. Inrunner motors turn very fast and are much more efficient than outrunner motors. Inrunner brushless RC motors require a reducing gearbox between the motor and propeller of your RC airplane. For this reason, the output speed and torque of the propeller can easily be "tweaked" to facilitate different flying characteristics by using different size gears.

The downside is added parts that can and do fail. The gears get stripped, and the gearbox shafts are easily bent. It can also be an obstacle when mounting the gearbox motor combination for your RC airplane neatly, especially under a cowling.

Inrunner vs Outrunner

Outrunners motor
# Low RPM's, high torque
# Less efficient than inrunners
# No gearbox required
# Narrow prop selection
# Silent

Inrunners motor

# High RPM's, low torque
# More efficient than outrunners
# Require a gearbox
# Wide prop selection
# Noisy

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Difference between brushed and brushless motors .

Today, i am going to talk about motor.
RC motor can be divide into two classifications, brushed motor and brushless motor.
Today, i will tell you the difference between brushed and brushless motors .


Brushed vs. Brushless
RC MotorsTo fully appreciate the advantages of a brushless RC motor, you need to have a basic understand of how motors work.

"How Stuff Works” has an in depth explanation of how motors work, and the graphics in the section were taken from that article. Below is a quick summary of how a canned motor works.

Standard "canned" Motor
A standard brushed motor is often referred as a canned motor. Every canned motor consists of the following parts:

Armature
The rotating portion of the motor. It consists of the poles, terminals, and the commutator.

Poles
Copper wires wound around a piece of metal forming an electromagnet. The poles are attached to the armature. Most motors have 3 or more poles

Terminal
Point at which the copper wire of a poll attaches.

Commutator
A switch on the armature that reverses the current to the poles every 1/2 rotation so that the magnetic fields of each will always maintain rotation.

Brushes
Tabs in the motor cap that are wired to the battery and make contact with the plates on the commutator as the armature rotates.

Magnets
The outer shell (or can) of the motor is lined with two permanent magnets, of opposite polarity. This non-rotating portion of the motor is also referred as the motor stator.

The battery is wired directly to the brushes. The brushes make contact with the plates of the commutator as the motor turns. There are the same number of plates on the commutator as there are poles on the armature.

When the brushes come in contact with the appropriate plates of the commutator, a particular pole (electromagnet) is charged. When a pole is charged, it is attracted to one of the magnets in the can and repelled by the other.

The commutator acts as a switch by switching the polarity of each pole every time the pole passes a magnet. When the polarity is switched, the pole is attracted to the next magnet in the can while being repelled by the one it just passed. This process repeats as long as power is supplied to the motor.





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Li-polymer Battery

When we play RC Model , we will use different type of battery, for example,Li-polymer Battery ,Receiver Battery, Transmitter Battery, etc.

Do you understand their use?
Today i want to share some knowledge of Lithium Polymer Battery to you~~

About Lithium Polymer Batteries
In a nutshell, a battery consists of two metals immersed in an electrolyte solution. A chemical reaction takes place that causes electrons to flow from one metal to the other. This produces a voltage difference between the positive and negative poles. When a load (such as a motor) is placed between the two poles, electrons will flow through the circuit until the metals are chemically neutralized (battery dead).

The voltage produced between the two metals is called the electrochemical potential. This energy is directly related to the types of metal used in the battery.

Lithium is the lightest metal in the universe and has the highest electrochemical potential. Lithium would be perfect for making lightweight powerful batteries right?

Well, almost... Because lithium metal is very unstable, battery manufacturers began using non-metallic lithium-ions.

Using Lithium Polymer Batteries
Lithium ion polymer batteries harness an enormous amount of energy in a very small space. These batteries will explode if used improperly. I don't say this to scare you. When proper LiPo battery safety precautions are followed, these batteries are completely safe. Lithium polymer battery care can be broke down into three categories, which are discharging, charging and storage.

Storing LiPo Battery Packs
LiPo batteries should always be stored in a cool environment. In other words, don't leave them in your car with the windows up on a hot summer's day. Keep the battery in a cool location out of the direct sunlight. It is highly recommended that Lipo batteries be kept in a charging bag while be charged and while not in used. A charging bag is a very cheap form of insurance!

Advantages of LiPo Batteries
#1
Have nearly double the capacity with half the weight of NiCad or NiMH battery packs
#2
Retain charge significantly longer than NiCad or NiMH batteries when not being used
#3
Do not develop a "memory" as NiCad batteries do
#4
With LiPo cells in combination of series and parallel, LiPo packs can be built to power most all RC aircraft

Disadvantages of LiPo Batteries
#1
Have very short shelf life of two to three years
#2
Very sensitive to high temperatures
#3
Very sensitive to high and low voltages. Exceeding either will damage the battery
#4
Prone to explode if exposed to heat, or charged/discharged improperly


LiPo Battery Safety
LiPo Battery Packs are safe as long as they are used properly. The video below is an example of what will happen when a LiPo battery is used improperly.

#1
Always let your LiPo batteries cool to ambient temperature before charging
#2
Make sure your charger is designed specifically for Lipo battery packs
#3
Double check that your charger has counted the cells correctly and is charging at or below 1C charge rate
#4
Always charge your batteries on a solid non-flammable surface in a well ventilated area
#5
Always check your LiPo batteries for any damage after a crash. If the LiPo back is punctured or damaged in any way, don't use it.
#6
Always charge and store your LiPo batteries in a charging bag! Charging bags are relatively inexpensive and could potentially prevent your housing from burning down.
#7
Never, under any circumstances, leave your batteries charging unattended
#8
Never leave your batteries inside RC aircraft while charging

Hope u have a greating and safe memory with playing Rc Model.

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Do you know AXI this band?

Today, I received my AXI Gold Line 4120/14 Outrunner Brushless Motor which I buy from www.rcecho.com in last week~HAHA ~~^^

Do you know Axi this band? If you don’t know what is AXI motor, there are some information about AXI motor.Axi have high quality.

AXI RC motors are a special brand of RC motors that have been designed by Model Motors Ltd. A company that specializes in building motors and their parts for all types of RC models. AXI RC motors are high quality motors that produce a large amount of output despite their tiny sizes. If you are looking to build your RC model from scratch and are looking for a reliable and powerful power station, then you definitely need to consider an AXI RC motor for your project.

AXI motors were first developed in 2001. The first model, The AXI 2820/10, was a brushless motor with an outer rotating case. The outer case became known as the ?Outrunner?, a word derived from the German word ?Aussenlaeufer?. The motor soon became one of the topmost selling models in the world and was considered to be one of the best performance motors in the market. Today, the company produces motors for all types of RC airplanes, boats and cars.
If you are looking for the best RC motor for your model, then you need to look for one made with the latest materials and technology. The ideal motor offers you high efficiency despite varying loads that need to be propelled. AXI RC motors are renowned for their ability to pull even heavy RC models at high speeds without compromising on the efficiency.

Due to the high torque generation of the Outrunner, the brushless AXI RC motor can generate a great amount of thrust despite its smaller size. While on direct drive, AXI RC motors can drive large diameter propellers as well as high pitch propellers with extremely high levels of efficiency, something that ensures that you do not lose out on power or performance due to your RC model's large size or weight.

If you are looking to run your RC model at higher than normal current levels, while extracting a high weight-to-power ratio, then you need to look at the line of products offered in the AXI RC motor range. These motors are manufactured with pin-point precision and are extremely reliable for all RC models.

Whether you are a first-time builder or an experienced hobbyist, you should look at the prospect of harnessing a strong and powerful motor that offers you the latest technology and the highest levels of performance and AXI RC motors fit the bill.

I will test my new motor in next few days. When I tried it, I will share my option to u~~

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