[AKM-47]

Hey guys,

I could use some help here. I am trying to figure out if the motor that I have is powerful enough for my airplane.

I ordered a World Models' Katana EP (flying weight is 780 grams) and was going to use a Turnigy motor (Turnigy 2217 16turn 1050kv 23A Outrunner) which has the following specs:

Kv: 1050rpm/v
Operating Current: 6A ~ 18A
Peak Current: 18A
Suggested prop: 10x6.0 E-prop
Suggested Battery: 1700~2200mAh 3S1P
Weight: 71g
Dimensions: 27.6 x 36mm
Shaft Size: 3.175mm

Ideally, I would like to be able to fly 3D with this setup. I know that I need approximately 350W of power to be able to do that but I don't know how to figure out how powerful this motor is. I guess one way of doing this is try and see if this works but I don't have my airplane yet.
I don't want to wait, and if this setup is not powerful enough I would like to order a new motor but again the HobbyKing site (where I get my stuff from) does not always lists how much power their motors can put out.

So, my question is:
Is it possible to calculate wattage of the motor from the specs I listed above, and if the answer is Yes, could you please post HOW to do that?

Any help/advice would be greatly appreciated.

Thank you,

AKM-47

[rusty33]

voltage x Amperage=Watts

Operating current is 6A-18A. Multiply 18amps x the voltage of your battery (3s=11.1) and you have watts (199.. The description of that motor says '23A' and then the specs says '6a-18a'. My gut tells me that you will not have quite the thrust you want for your application.

[AKM-47]

Originally Posted by rusty33

voltage x Amperage=Watts

Operating current is 6A-18A. Multiply 18amps x the voltage of your battery (3s=11.1) and you have watts (199.. The description of that motor says '23A' and then the specs says '6a-18a'. My gut tells me that you will not have quite the thrust you want for your application.

Thanks, Rusty,

I guess I'm gonna have to get another motor...

[Hughes500E]

Keep in mind that if you do the math with high voltage (freshly charged pack) you won't get a very realistic number; use a nominal voltage such as 10 volts for a 3 cell, 6 volts for a 2cell etc. This way you will basically get an average of watts delivered throughout your entire flight!

[moo]

A bigger beefier motor is only a small increase in weight, as long as you keep the same Kv you can always put bigger batteries in later.

[Tyler P]

My packs generally finish at over 11 volts after a 10 minute flight for 3s. And that's with a lot of 3Ding. Granted, they might drop down to 10 on a hard climbs, but 11.1 is the nominal voltage on a 3s pack. They peak at 12.6.

Originally Posted by Hughes500E

Keep in mind that if you do the math with high voltage (freshly charged pack) you won't get a very realistic number; use a nominal voltage such as 10 volts for a 3 cell, 6 volts for a 2cell etc. This way you will basically get an average of watts delivered throughout your entire flight!

[AKM-47]

Thanks everyone for your input.

I got another question... or two:

- Will it damage my ESC and /or motor (now I have a 30A - 40A peak ESC) if I use a battery with a higher "C" rating. Let's say I use a battery with a 30 or 40C discharge rate?

- Is there a way to boost motor's output without actually burning it out?

Thanks,
AKM

[Hughes500E]

Originally Posted by Tyler P

My packs generally finish at over 11 volts after a 10 minute flight for 3s. And that's with a lot of 3Ding. Granted, they might drop down to 10 on a hard climbs, but 11.1 is the nominal voltage on a 3s pack. They peak at 12.6.

Check under load! When your batteries are not under a load you are correct; when under a load, this is is your power output benchmark!

Many times under a load you'll see 10 volts, it's a much more acurate rating!

I am by no means a pro though, just sharing what I have experienced playing with my Eagle Tree

[Tyler P]

I'll have to check again with my Watts Up meter. My system puts out around 500 watts static, (going by memory from the last test) which is about as heavy a load as you'll see on a system. If you divide watts by 45A (which is the power handling capability of my ESC) that puts volts at exactly 11.1.

You may be right, though, as when the pack discharges it will drop more voltage under load as the capacity disappears.

I forgot to watch the volts last time I tested, and again it was on a fresh pack, so the numbers will be higher as you stated. Next time I take it to the field I'll do a test on the pack after a 10 minute flight and see what it can do, just for my own curiosity's sake!

Originally Posted by Hughes500E

Check under load! When your batteries are not under a load you are correct; when under a load, this is is your power output benchmark!

Many times under a load you'll see 10 volts, it's a much more acurate rating!

I am by no means a pro though, just sharing what I have experienced playing with my Eagle Tree

[Tyler P]

You can use as high a "C" rating as you like on your packs as long as you're not pushing the actual amp draw higher than what your ESC is rated for.

As for boosting a motor, most motors will take a bit more than is actually stated. So you can use a slightly bigger prop to draw more amps so long as your ESC and batteries are up to the task. However, it will be harder on the motor, and in turn could be harder on your ESC and battery. I wouldn't recommend over doing it to much on a Turnigy motor unless it is the better SK version, which have bigger bearings and are generally more efficient.

Personally, I would just recommend going with a slightly bigger motor like this one: http://www.hobbycity.com/hobbycity/s...6_910Kv_/_310w.

It is only rated at 310w, but I used to run one in my Acro Master, which is heavier than what you're looking at. On a 13x6.5 prop it was very capable of 3D. I was running closer to 400w on it and it never gave me an issue.

I'm currently running the 35-42 version of it in my Stevens Aero Edge, which weighs around 40 ounces all up weight.

Originally Posted by AKM-47

Thanks everyone for your input.

I got another question... or two:

- Will it damage my ESC and /or motor (now I have a 30A - 40A peak ESC) if I use a battery with a higher "C" rating. Let's say I use a battery with a 30 or 40C discharge rate?

- Is there a way to boost motor's output without actually burning it out?

Thanks,
AKM