An underpowered model is a disaster waiting to happen, here is a rough guide to choosing the electric powertrain needed for various model types. Bear in mind that overpowering is fine but the penalty is additional weight, and a good model is one that is balanced in terms of power, flying weight, and build quality.
This guide - as the title says - is a ROUGH guide and offers a basis from which to choose a power train for your model. It is not intended to be a definitive guide but will help get you into the air with performance that will make your introduction to electric RC flying enjoyable.
Motor Power Choice
(Based On Recommended All-weight up (AUW), Or Flying Weight Of Model Choice)
*Browse all HobbyKing’s Motors Here.
|Vintage types and many non-aerobatic indoor flyers||50w~70w per 1lb|
|Trainers, gliders, and high wing scale||70w~100w per 1lb|
|Sport flyer with general aerobatic performance||100w per 1lb|
|Warbirds||120w~150w per 1lb|
|Multi-engined models||100w per 1lb (thrust from Multiple props gives in effect, more than 100w per 1lb performance)|
|EDF Jets||150w~200w per 1lb|
|3D, F3A, and high-performance models||150w~200w per 1lb|
LiPo Voltage Choice
*Browse all HobbyKing’s LiPo Here.
Based on the above, we now need to work out what voltage (V) we are going to need to use. Generally speaking, to keep LiPos in good order, try to keep max amps (A) to around 50~60% of the capacity/C rating of the LiPo pack. For example, if you purchase a 2200mAh 20C pack, then it is rated for 44A constant discharge, so keep the max amps at around 20A~25A IF possible.
When unsure, you can always refer to the battery recommendations for the model by the manufacturer and in conjunction with the size/weight data published with all our advertised LiPo packs. For low-powered models, choose 20C packs; for general flying, choose 20C~25C packs; for high-performance models, 30C + packs.
|Up to 50w||1s~2s|
|Up to 100w||2s~3s|
|100w Up to 500w||3s (This is the practical upper limit for 3s LiPos, so basically, models of 5lb AUW)|
|500w up to 800w||4s (This is the 0.40~0.46 glow equivalent range favored by many club flyers)|
|800w up to 1000w||5s|
|900w up to 1500w||6s (this is the 0.60~0.90 ic equivalent range)|
|8s~10s packs are for very large and generally specialized models.|
Motor Choice - KV Or RPM Per Volt
*Browse all HobbyKing’s Motors Here.
Which actually means, what prop size? If you are used to internal combustion (IC), the simple analogy is to treat low kV motors as 4 stroke engine equivalents and mid-high kV motors as 2 stroke engine equivalent. If you are not used to IC then we can give you some examples of the approach to take, this is an important choice as you can literally choose how your model flies, however, there are practical considerations, the most obvious is ground clearance.
Please refer to motors such as the NTM range, which gives you prop data as well as power, dimension, and weight data.
|Example 1||Trainer/Sport Model, 1lb AUW, we want 100w motor (3s 20c LiPo) mid kV for general flying, probably around 1200kv~1400kv, so around 8" prop|
|Example 2||3D/F3A Model, 1lb AUW, we want 150w motor (3s 20c~30c LiPos) low kV, 1000kv or under, spinning 10~11" prop, highly efficient at low throttle openings giving lot's of prop wash over control surfaces at all times, high thrust for low rpm and low amps draw at higher throttle openings.|
|Example 3||Warbird/Scale Model, 1lb AUW 120w motor, kV choice, either of the above, it is a personal choice|
|Example 4||High-Speed Delta type model, 1lb AUW, 200w motor (3s 25c~30c LiPo) 2200kv~3200kv motor, 5"~6" Prop, high speed/low torque, low thrust at low throttle openings, high speed from high rpm at full throttle.|
Finally, ESC Choice
You have decided on your motor, so look at the MAX AMPS (A) figure given by the motor manufacturer in the data section and generally add 25% headroom. So, if a motor is rated at 15A, then choose at least an 18A ESC - better still a 20A and so on. Next make sure that the ESC voltage (V) is compatible, in other words, if you are using a 4s LiPo, that the ESC is rated for 4s voltage. Next, check if it has functions you desire. If you are flying a glider, for instance, you will want a brake facility so that the prop stops when soaring un-powered, allowing the prop to fold by not windmilling, we strongly advise purchasing a program card to make programming the ESC easier. Be advised, you need to get the specific card for the ESC of your choice.
Also, look at BEC rating, the BEC supplies radio receiver power for servos without the need for a separate receiver battery, however, they can be limited in the number of servos they are capable of powering. If the servo count is over 4, as it is on many models these days, then consider purchasing an ESC with a high AMP rated SBEC or a separate UBEC. OPTO type ESCs have no BEC, keeping the ESC separate from RX supply, and are recommended for large models that require a separate receiver power supply. They are also safer in high-powered, large models as they will not arm until the RX is switched on.
Note: We have blog articles that cover these areas in further detail. Check back regularly for updates.
|TURNIGY® Batteries Explained|
|RHINO||Great value for money. Average Cycle Life* (100+) and minimal voltage sag under load.|
|TURNIGY Standard||Excellent value, Longer Cycle life* (160+), and very low voltage sag under load.|
|TURNIGY Nano-Tech||Unbeatable performance, Longest Cycle Life* (250+), and almost 0 voltage sag under load.|
|TURNIGY Graphene||Premium performance, Continuous discharge offers lower internal resistance and minimal voltage sag.|
* Cycle Life results from discharging at full C rate to 3v. End of life when the battery has 80% capacity.
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