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What motor to use?

#1
How do you figure out what motor to use in a plane? I have bought a few electric motors for profile jets and the motors were called out. I am building the swappables and would like to know what and how to figure out what motors to buy. The plans mention some motors but the number call outs do not match the motors that HK or RCtimer sell. Also, they build up the planes and show them to us flying but not necessarily with the suggested motors and they do not tell us the ones they are using. The numbers are different and I have asked several times about them without a complete answer. The 2628 in most cases it the measurement of the motor size. What does the number after that mean? 2628-10 I have seen the suggested watts per pounds mentioned before. What is the difference in the bell type verses the other out-runners type? How do you figure out the battery run time per pack? Some people say not to run the batteries below the storage voltage? How do you figure this out? I use the 2200 3s packs.
I need to buy motors for the slinger and the dusty and need suggestions for motors. What run time should I get with the 2200 packs and the suggested motors you come up with. I need to buy these motors soon and the planes are building up in the house and the wife wants them completed and in the garage!!!!!!!! Please help.
Thanks in advance for suggestions and any information supplied.

Don
 

tramsgar

Senior Member
#2
Wow that's at least seven questions... I've seen motor recommendations on all scratch builds here, but there isn't as you say a recommendation per store, so if you must buy from HK or RCT then find a motor with specs as close to the ones recommended and you'll be fine. Regarding motor numbers there's a video here where David explains them all - try the awesome search engine =).

What "some people" say seldom is what "other people" say, and when very few actually are specialized in electrical chemistry knowledge is replaced by opinion and we get a dozen micro-religions regarding the correct voltage to stop discharging at, among other things. Not being an expert myself, I have looked at what voltage my cell phone says "shut me off now!" at, and that's what I've chosen as my cut-off. Almost everyone agrees that 3V is or is below the absolute minimum. If in doubt, ask the manufacturer, they'd know for sure!

And make sure to quickly move your hobby to the garage (bring your wife's hobby there too while you're at it).
 

xuzme720

Dedicated foam bender
Mentor
#3
How do you figure out what motor to use in a plane? I have bought a few electric motors for profile jets and the motors were called out. I am building the swappables and would like to know what and how to figure out what motors to buy. The plans mention some motors but the number call outs do not match the motors that HK or RCtimer sell. Also, they build up the planes and show them to us flying but not necessarily with the suggested motors and they do not tell us the ones they are using. The numbers are different and I have asked several times about them without a complete answer. The 2628 in most cases it the measurement of the motor size. What does the number after that mean? 2628-10
That number is the number of turns or wraps the motor has and isn't important to you at this point in choosing a motor. What IS important is the size and the Kv number. The Kv is how fast the unloaded motor will spin per volt applied to it. Keep in mind that generally, the lower the Kv, the larger the prop it will be able to use efficiently.

I have seen the suggested watts per pounds mentioned before.
This is a recommended way to figure motor sizing and can be easier to use for someone new. How heavy is the model is considered along with the type of performance needed as different types of flying require differing watts per pound.

What is the difference in the bell type verses the other out-runners type?
Bell types are usually better at swinging a larger prop and rapid speed changes due to a longer moment arm. Fancy way of saying they have more torque.

How do you figure out the battery run time per pack?
Runtime is the usable capacity (it's usually agreed on around 80% of pack mAh) divided by amperage drawn during flight. Say you have a 2000mAh pack and fly using 6A, this will give you about 18 minutes, theoretically. Always better and safer to check voltage so as not to drop below 3V per cell and get a charger that can tell you the mAh it puts back in during charge.

Some people say not to run the batteries below the storage voltage?
Storage voltage is the voltage that the battery chemistry likes. It's a happy medium where the chemicals basically rest and very little transfer is taking place, most batteries are 3.7-3.9V per cell for storage and the storage voltage really only comes into play when you aren't flying for a few weeks.

How do you figure this out? I use the 2200 3s packs.
I need to buy motors for the slinger and the dusty and need suggestions for motors. What run time should I get with the 2200 packs and the suggested motors you come up with. I need to buy these motors soon and the planes are building up in the house and the wife wants them completed and in the garage!!!!!!!! Please help.
Thanks in advance for suggestions and any information supplied.

Don
Hopefully the info I gave can help you choose for yourself, but if you still have confusion, I'm sure we can make a more distinct recommendation.
 
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#4
Thanks for the responses. I went to HK site to look at motors. I looked at bell motors. Everyone mentions wattage for what would be the ability to supply thrust. I looked at a Turnigy L2210-1400 Bell Style Motor (210w) that supplies 880 grams of thrust with no prop mentioned. Then I looked at a Turnigy L2210-1650 Bell Style Motor (250w)-(more wattage should supply more thrust rignt?) and this motor only provides 520 grams of thrust! Again it does not menton the prop. The rpms are slightly different, but more wattage and less thrust. Can you add the explanation of this to my question!
Thanks
 

xuzme720

Dedicated foam bender
Mentor
#5
That's where the Kv comes into play here. It's more wattage but higher Kv which means smaller prop. This is a balancing act in matching all the variables for how you want it to fly or perform.
Best bet is to try to match size and Kv on the recommended motors and that will get you very close.