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Old Jul 18, 2015, 10:48 AM
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is this possible? 28A=450W

i did a search on HK motor finder to find a motor with the most power from the least amps. would this motor be worth the price.
http://www.hobbyking.com/hobbyking/s...er_1030KV.html
KD 30-25L Brushless Outrunner 1030KV

The KD 30-25L 1030KV motor is a smooth running, high quality brushless outrunner. The prop may be fitted directly to the motor shaft using the supplied adapter set to allow for front or rear mounting. A comprehensive accessory pack is supplied which includes a cross style mount, prop adaptor, prop saver complete with screws and a spare motor shaft. In testing this motor produced up to 450W of power making it perfect for all kinds of sports or scale aircraft.

Specs:
Kv: 1030 rpm/v
Max Current: 28A
Max Power: 450W
Cell Count: 3 ~ 4S LiPoly
Weight: 153g
Dimensions: 36 x 48mm
Shaft Size: Dia 5mm/ Length 20mm
Mounting Hole Dimensions: Rear 25 x 25mm / Front 16 x 16mm
PRODUCT ID: 244000030-0
Kv(rpm/v) 1030
Weight (g) 189.5
Max Current(A) 28
Resistance(mh) 0
Max Voltage(V) 15
Power(W) 450
Shaft A (mm) 5
Length B (mm) 48
Diameter C (mm) 36
Can Length (mm) 30
Total Length E (mm) 68
Update/Add my own data
Customer Data
Weight: 297g
Quantity:
International Warehouse
stock
9
Price $16.28
was $21.70
Wish List | Email Buddy | Issue | Price War

thanks
Ken
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Old Jul 18, 2015, 11:54 AM
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Watts = Amps x Volts or Volts = Watts / Amps

So 450w / 28a = 16v required.

So just about feasible with a full charged 4s, as long as it's a darn good 4s pack.

My only slight worry is there are no Discussions/Reviews shown on the HK page. So no recommendation on what prop to use or whether that 450w is really usable.

Personally I would work the other way round, knowing the model and how I would want it to fly, I would choose a prop and then look for a good motor, battery, combination that will turn it fast enough to do the job.

You probably could draw the 450watts with a flywheel or even a piece of wood with a hole in the middle, the question is, would it fly the model how you want. ?
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Old Jul 18, 2015, 12:21 PM
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Fore APCe 10x5 with 4slipo.

APCe 12x6, 13x4 with 3slipo.

It is noteworthy that in this brand, HK is very cautious when dialing only 450 watts of maximum power.
Which I think is correct.

If NTM, or Turnigy cheerfully Maximum blof with 750 watts.
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Old Jul 18, 2015, 12:28 PM
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Quote:
Originally Posted by eflightray View Post
My only slight worry is there are no Discussions/Reviews shown on the HK page. So no recommendation on what prop to use or whether that 450w is really usable.
Personally I wouldn't rely on HK reviews for anything. I've seen some pretty wild claims in them. Better is a good motor calculator like DriveCalc.

Here is a DriveCalc prediction for a KD A36-12L which has similar weight and Kv. Looks like 4s battery and a 9x4.5 APCe propeller.

Larry
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Old Jul 18, 2015, 12:56 PM
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I still prefer to read someones review of what they actually achieved, there is often some good information from real world tests.

But mainly as I said, choose a prop to suit the model, then the motor.
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Old Jul 18, 2015, 06:27 PM
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I was looking for something to swing a bunch of FMS Skytrainer 11x9x3 blade props i have left lying around. I'm also getting fairly good at scratchbuilt foamboard planes. I only have the Esc and servos left from the skytrainer after the foam ele hinge tore partway and sent her spinning in. So I thought this motor looked fairly efficient to run on a 30C 3s lipo with the 35 A esc. the original motor was 3536 850kv. I also have an NTM propdrive 3530 1100kv and an NTM4238 750kv The 4238 pulls a 55" 2kg scratchbuilt around with a 12x10 apc on 2 old 35c 4s in parallel which have lost some of their rating due to age and abuse, and are a bit puffed . after 7 min mixed flight they are really warm. The NTM4238 pulls 56A at WOT
The plane I'm designing for this motor or the NTM3530 has a 48" ws , symmetrical high wing with a flying weight around 1300gr. (3lb) I also have 9x7 and 9x8 2 blade apc props if the 3 blade ones are too much draw for my battery.
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Old Jul 19, 2015, 01:40 AM
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I think you're approaching this a bit backwards. Those Hobby King specs are only telling you what's going in to the motor and say nothing about its efficiency. In fact they say more about the power supply being used than the motor as the relationship between current and power is purely a function of the input voltage. And that might be the ability of the battery or power supply that was used for testing to hold a certain voltage, or sometimes simply multiplying a current limit by an arbitrary voltage like 14.8V (4x3.7V per cell nominal voltage for a LiPO) or 16.8V (fully charged 4S LiPo).

In this case the only relationship between 28A and 450W is that it happens to be 16V input, and as eflightray as already pointed out - that's just not realistic for any real world 4S battery you might use with this motor for more than about 3 seconds.

The only way to know motor efficiency is to know power out as well as power in. That's darned near impossible without a dynamometer; however prop rpm is a pretty good proxy for power out, especially for comparison purposes. For a well known prop the power to turn it at a given rpm can be estimated reasonably well - any motor calculator will do that. And companies like Aeronaut publish graphs of the power it take to turn their props.

So "pulling x A/W at WOT" is not a good measure of anything other than whether you are within the motor, ESC and battery current limits. If 40% of that power is going as waste heat, then pulling x A/W is a bad thing if a different motor can achieve the same or higher prop rpm for less current/power.

An alternative strategy to choose a motor works with some well established rules of thumb starting with the model and how you want to fly it, an intended prop size depending on physical limits and purpose, then sizes battery to deliver the power, then sets a motor size range by weight based on desired power and then chooses Kv to work with your battery and prop size, but seeing as you have a 3S battery and 35A ESC current limit and a motor in mind and some existing props ...

First, @ 88g the 3530 is too small for the 300w you'll likely want for good performance.
The KD 30-25L motor you are looking at is a fairly close clone of the Hacker A30-12L so using it in Ecalc will give ballpark figures. With your 11x9x3 on 3S say 2500, you could expect around 50A/480W/7800 prop rpm. That's fine for a 155g motor and would be more than ample for a 3lb model, but way over your ESC limit. Your 9x8 is likely too small for that motor and model, drawing only about 230W. But an 11x7 or 10x8 2 blade should be around 35A or 30A respectively, with decent efficincy and pitch speed.

ps - a 35A ESC implying max power on 3S of around 350W is fine for a 3lb model. But my next step would be to remove existing prop size constraints and set max prop size based on what will fit, and then choose a motor with Kv to run that sized prop within the ESC current limit, sticking with minimum motor size at 3W/g, but also considering whether model balance might be easier with a heavier motor (which should be more efficient).

Or if you're wedded to those 11x9x3 props, look for a motor at least 100g and Kv less than 1000, and apply a bit of trial and error in Ecalc to home in. For example, the 159g D3548-6 (Kv=790) should give about about 6800 rpm for 30A/310W in. The 102g 3536-9 (Kv-910) should do about the same rpm, but use nearer 34A/350W.

To further illustrate my earlier point about power in on it's own being a poor measure, the predicted power in for your existing 3530-1100 with the 11x9x3 is 410W, much "better" than 300W, but predicted prop rpm is still only 6800 and the motor is going to get mighty hot at that power.
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Last edited by scirocco; Jul 19, 2015 at 01:50 AM. Reason: added a ps
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Old Jul 19, 2015, 05:38 AM
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thanks for your input. I never realized how confusing some of this could get. i assumed that the more watts power out per amp current in meant more efficiency. the stock FMS motor was a 3536 850 kv and the FMS props are fairly thin. the motor is in propcalc, but the prop is not, so i used a MA 11x7 3 blade and got these specs: Motor @ Maximum
Current: 32.95 A
Voltage: 10.07 V
Revolutions*: 7054 rpm
electric Power: 331.9 W
mech. Power: 261.8 W
Efficiency: 78.9 %
est. Temperature: 56 °C
133 °F

heres the Hacker A30-12L
Motor @ Maximum
Current: 46.17 A
Voltage: 9.66 V
Revolutions*: 7824 rpm
electric Power: 446.0 W
mech. Power: 358.0 W
Efficiency: 80.3 %
est. Temperature: 66 °C
151 °F

I have a 60A ESC as well. I went ahead and ordered a watt meter,and the KD 30-25L motor as I had to order some receivers for my radio anyway. I could also use the NTM 4238 that I have on the other plane, but with only 3s, I might need more prop, I don't know. If i keep the weight under 1500gr.
here are some spec from HK on the 4238
Specs:
Model: NTM Prop Drive Series 42-38 750kv
Kv: 750rpm/v
Max current: 55A
Max Power: 403W @ 12v (3S) / 785W @ 15v (4S)
Shaft: 5mm
Weight: 169g
ESC: 60A
Cell count: 3s~4s Lipoly
Bolt holes: 25mm
Bolt thread: M3
Connection: 4.0mm Bullet-connector

Prop Tests:
13x10 - 11.1V - 344W - 31A - 1.79kg
13x10 - 14.8v - 740W - 50A - 2.8kg
14 x 6 - 11.1V - 403W - 36A - 2.23kg
14 x 6 - 14.8v - 785W - 53A - 3.05kg

Thanks
Ken
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Old Jul 19, 2015, 06:25 AM
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Quote:
Originally Posted by KennyMc View Post
thanks for your input. I never realized how confusing some of this could get. i assumed that the more watts power out per amp current in meant more efficiency.
It's worth realising that the figure quoted in motor specs is power(watts) IN not OUT. So more watts for a given current just means they're using a higher voltage.

As already said for power out you need to take efficiency into account. E.g. if the efficiency is 80% (which is more than many motors manage) then for 500W IN you're getting only 400W OUT....and perhaps just as important you're wasting 100W just heating the motor up.

Steve
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Old Aug 30, 2015, 12:42 AM
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update

the KD 3025L is a fairly good motor. I tested it with the HK-010 power analyzer, and on a fresh 35c 3200mah 3 cell, with a 60A ESC, it starts out well above 50 amps and 500 watts at WOT. when the battery came down to 12v, which was after 10 sec. or so, it was at 51 amp and 485 watts. this is spinning an APC 10x8E. I put it in a 48" high wing foam board scratch build that weighs 1400gr (3.08lbs) and i get 5-6 min flights as long as i keep the full throttle stuff under 5 sec. . and i must say that at WOT for 5 sec you can use up some airspace. at the end of a flight everything is mildly warm, coolest being the motor and warmest ,the battery.
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