ELECTRIC
Determining Power Requirements Hidalgo move |
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1. Power can be measured in watts. For example: 1 horsepower = 746 watts 2. You determine watts by multiplying ‘volts’ times ‘amps’. Example: 10 volts x 10 amps = 100 watts Volts x Amps = Watts 3. You can determine the power requirements of a model based on the ‘Input Watts Per Pound’ guidelines found below, using the flying weight of the model (with battery):
NOTE: These guidelines were developed based upon the typical parameters of our E-flite motors. These guidelines may vary depending on other motors and factors such as efficiency and prop size. 4. Determine the Input Watts Per Pound required to achieve the desired level of performance:
2.1 lbs x 150 watts per pound = 315 Input Watts of total power (minimum) required to achieve the desired performance 5. Determine a suitable motor based on the model’s power requirements. The tips below can help you determine the power capabilities of a particular motor and if it can provide the power your model requires for the desired level of performance:
Average Voltage (depending on cell count) x Continuous Current = Continuous Input Watts Average Voltage (depending on cell count) x Max Burst Current = Burst Input Watts HINT: The typical average voltage under load of a Ni-Cd/Ni-MH cell is 1.0 volt. The typical average voltage under load of a Li-Po cell is 3.3 volts. This means the typical average voltage under load of a 10 cell Ni-MH pack is approximately 10 volts and a 3 cell Li-Po pack is approximately 9.9 volts. Due to variations in the performance of a given battery, the average voltage under load may be higher or lower. These however are good starting points for initial calculations.
Per this example, the Power 10 motor (when using a 3S Li-Po pack) can handle up to 376 watts of input power, readily capable of powering the Brio 10 ARF with the desired level of performance (requiring 315 watts minimum). You must however be sure that the battery chosen for power can adequately supply the current requirements of the system for the required performance. Examples of Airplane Setups NOTE: All data measured at full throttle. Actual performance may vary depending on battery and flight conditions. E-flite Brio 10 ARF Option 1:
Expect good speed and extreme vertical power for artistic aerobatics. Average duration is approximately 6-9 minutes depending on throttle management. Option 2:
Expect high speeds and strong vertical performance ideal for F3A precision and artistic aerobatics. Average duration is approximately 7-10 minutes depending on throttle management. |
Brushless Motor F.A.Q
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Frequently Asked Questions & Techinical InformationQ. What does “brushless” mean? A. Though inexpensive, traditional “brushed” electric motors offer short run times and limited power. Current passes into the heart of the motor through soft to semi-hard blocks of material called brushes which contact the spinning commutator. Friction from this contact reduces power and causes wear, eventually requiring brush replacement. “Brushless” motors avoid these inefficiencies. Current passing around the outside of the motor’s can causes magnets on the motor shaft to follow in a circle (imagine the passing current acting like one magnet, pulling the magnets on the motor shaft toward it). Brushless technology is more expensive, but also more efficient - and can be MUCH more powerful! Q. What advantages do brushless electronics have over glow engines? A. Previously, only glow engines could achieve the performance now available from brushless motors, ESCs and accessories. Brushless technology, however, has benefits that glow power can’t match.
Q. When I use a brushless motor, do I also have to use a brushless ESC? A. Yes. Brushless motors will not work with non-brushless ESCs - the two technologies are completely incompatible. A brushed ESC just pumps out current like a fire hose pumps out water. A brushless ESC spreads current in a precise pattern to different places in the motor with an AC current as compared with DC for brushed motors.. Q. How does motor choice affect my model’s performance? A. In electric motors, an increase in winds means an increase in top end speed. A decrease in winds means an increase in torque, or acceleration. Conversely, more turns means more torque/acceleration, while less turns means more top end speed. Pinions and spur gears work the same as turns—more teeth, more torque, less teeth, less torque but more speed. Q. How do I break in an electric motor? A. Ideally you’d like to run the motor at about 1/3-1/2 it’s rated voltage with no load (without prop) for an hour or two—long enough to wear the brushes down without arcing. R/C car modelers have special transformers for optimum breakin on high performance motors. If what you’re working with is a typical 05 can motor, you can make your own system that works fairly well. Start with 2 alkaline D cell batteries and some spare 12 gauge wire. Simply hook the batteries up in series so you have a 3 volt power source and hook the wires to the appropriate terminals on the motor. Let the motor run until the batteries are dead. |
What types of NiMH battery charger are available?
“fast” chargers and microprocessor controlled “ultra-fast” intelligent chargers (IC just stands for Integrated Circuit, meaning that the timing is done by a silicon chip).
Manual battery chargers gently charge your batteries with a small current. They are very slow (up to 36 hours for 2000mAh NiMH batteries) and the user has to manually cease charging by unplugging. This involves a bit of guesswork regarding charging times. Nevertheless, they are cheap and effective.
IC timer controlled
“fast” battery chargers charge rapidly for a fixed period and then automatically switch to trickle charge mode. They charge in less than half the time of manual chargers, and you don’t have to worry about unplugging them. However, a timer controlled battery charger can’t detect the initial state of your batteries - if they are already fully or partially charged it will still attempt to charge them for the full duration of its timer, so they are not suitable for top-up charging. Nevertheless, high quality IC timer controlled chargers incorporate sensors which cease fast charging if an overcharge state occurs (this is termed ‘overcharge protection’).
Microprocessor controlled “ultra fast” battery chargers are the latest type and are completely automated. They continuously monitor either the voltage or temperature of your batteries and are able to determine precisely when to cease fast charging. They then switch to trickle charge mode. Batteries in any charge state can be brought up to full charge in less then about 3 hours without risk of overcharging. The best battery chargers of this type independently monitor and charge each battery (this is termed ‘individual supervision’).
Which battery charger do I need?
A timer controlled fast charger provides some level of automation. But they are not suitable for top-up charging because the timer will attempt to run for its standard duration regardless of how much the batteries need charging. Nevertheless, many users are content to use their NiMH batteries until they fail and change to a new set whilst recharging the old set. Top-up charging is only necessary if you want to be assured that your NiMH batteries are always at peak capacity. So a high quality timer controlled charger with overcharge protection is suitable for most purposes - and they are excellent value for money.
If you want to be confident that your NiMH batteries are at maximum capacity a microprocessor controlled charger featuring delta V or delta T control is the solution. The process is completely automated and batteries can be topped up at will. This is the only charger type that ensures that the rechargeable batteries you are putting in your device are at their maximum energy level. Ultimately it all comes down to price!
I already own a manual NiMH battery charger - will it be OK for 2000mAh rechargeable batteries?
It will be OK, but you will need to adjust your charging times for 2000mAh NiMH rechargeable batteries by adding about 10% onto the usual charging time for 1800mAh batteries.
How long should I charge NiMH rechargeable batteries in my manual battery charger?
Note: unless your charger specifically permits it, don’t charge batteries of different capacities together in a basic charger as this can lead to overcharging of the smaller capacity batteries.
What is meant by “delta V” control?
What is meant by “delta T” control?
My NiMH batteries get warm in the charger - is this OK?
What is “trickle charging”?
My ‘intelligent battery charger’ tries to re-charge fully charged batteries - why is this?
No battery charger, even the most advanced, can immediately determine the charge state of batteries. Whenever batteries are placed in an intelligent charger it goes through a series of tests to determine how much they need to be charged. It may even conduct a partial discharge followed by a quick re-charge to ensure they are at maximum capacity. This always takes a minimum period of time. You should only be concerned with the functioning of your intelligent battery charger if it doesn’t complete these operations in a shorter time than it takes to charge your batteries from flat.
WARNING
Safety precautions for Lithium Polymer
cells/packs stocked by Model Flight
1. Never fast-charge any battery type unattended.
2. Never charge LiPo cells/packs at any rate unattended.
3. Only charge LiPo cells/packs with a charger designed specifically for lithium polymer chemistry. Example chargers include the Kokam LIPO 402, and Schulze chargers with lithium charging capability.
4. LiPo cells can ignite because of unmatched cell capacity or voltage, cell damage, charger failure, incorrect charger settings and other factors.
5. Always use the correct charging voltage. LiPo cells/packs may ignite if connected to a charger supplying more than 6 volts per cell.
6. Always assure the charger is working properly.
7. Always charge LiPo cells/packs where no harm can result, no matter what happens.
8. Never charge a cell/pack in a model. A hot pack may ignite wood, foam or plastic.
9. Never charge a cell/pack inside a motor vehicle, or in a vehicle’s engine compartment.
10. Never charge a cell/pack on a wooden workbench, or on any flammable material.
11. If a cell/pack is involved in a crash:
a. Remove the cell/pack from the model.
b. Carefully inspect the cell/pack for shorts in the wiring or connections. If in doubt, cut all wires from the cell/pack.
c. Disassemble the pack.
d. Inspect cells for dents, cracks and splits. Dispose of damaged cells (see below). Harry Potter and the Sorcerer’s Stone rip
12. Dispose of cells/packs as follows:
a. Discharge: with the cell/pack in a safe area, connect a moderate resistance across the terminals until the cell/pack is discharged. CAUTION: cell/pack may be hot!
b. Discard:
- NiMH: place in regular trash.
- NiCd: recycle (cadmium is toxic).
- LiPo: puncture plastic envelope, immerse in salt water for several hours, place in regular trash.
13. Handle all cells/packs with care, as they can deliver high currents if shorted. Shorting by a ring, for example, will remove a finger.
14. Always store cells/packs in a secure location where they cannot be shorted or handled by children.
15. When constructing a pack, use only cells of the same capacity (mAh).