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Dec 21, 2015, 07:18 PM
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Purchased wrong motor, could I still fly?


Hi,

I'm new to the forum, so I apologize in advanced if I have posted in the wrong place.

I am new to electric planes and decided to buy the Phoenix Spitfire MK2 and make it an electric plane. I purchased everything as suggested by the manufacturer for electric flying... except for the motor. The manufacturer recommended motor is a 480kv brushless. I accidentally purchased a 1050kv motor instead (probably because I had about 10 open tabs when I was shopping around), and just noticed today when I opened the package and saw the kv rating. The motors size and weight are similar as the 480kv counterpart, and are the same brand and series. I am wondering if it will be okay to use this motor instead (any significant performance issues etc?) or should I just order the 480kv to be on the safe side?

This is to be used with 2 x 2S LiPo 25C 4000mah batteries in series and a 60A ESC.

I appreciate any input on this.
Last edited by fusionrc; Dec 21, 2015 at 08:07 PM.
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Dec 21, 2015, 07:25 PM
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shonmac's Avatar
If it fits ; it will work , I think. Will be a faster plane .
Dec 21, 2015, 07:26 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Links to the motors?

Kv = 1050rpm/volt would give you a screamer at roughly 4 4 1050 = 17krpm, but not for long

Since you only mentioned Kv here: Kv says nothing about power a motor can handle (could be 10watt, could be 10megawatt), or torque.
Motorcurrent and -power are proportional to Kv cubed, they both want to increase by factor (1050/480) = 10! (a.k.a. ten!). Controller and motor would go up in smoke instantly, battery would take a severe beating.

Same weight means about the same power, so you'd have to prop down and/or use lower voltage to get current within bounds again. Motorcurrent is proportional to voltage cubed. Using half the pack would quarter you current, still 2.5 times higher than with Kv = 480rpm/volt.

Do you have flying experience?


Vriendelijke groeten Ron
Last edited by Ron van Sommeren; Dec 22, 2015 at 04:10 PM.
Dec 21, 2015, 07:44 PM
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Thread OP
Quote:
Originally Posted by Ron van Sommeren
You'd get a screamer at say 4 4 1050 = 17krpm, but not for long.

Since you only mentioned Kv here: Kv says nothing about power a motor can handle, or torque.
Motorcurrent and -power are proportional to Kv cubed, they both want to increase by factor (1050/480) = 10. Controller and motor would go up in smoke instantly, battery would take a severe beating.

Do you have flying experience?

Vriendelijke groeten Ron
Yes, I have experience flying, but no experience with electric planes as mentioned before, only glow. Here are the specs of the motor:

Net Weight (g) 223.1
Watts 1300
diameter (mm) 43.5
length(mm) 65
Stator(mm) 35*20
No of cells (lipo) 4
max efficiency (%) 89%
max efficiency current (A) 45-80A
no load current (A) 3
current capacity (A/s) 160A/60S
Internal Resistance (mohm) 10
Max Voltage 18.5V
Shaft Diameter (mm) 5
Shaft Length (mm) 65
KV (RPM/VOLT) 1050


The closest motor to a 480kv in stock has these specs:

Net Weight (g) 292.29
Watts 1600
diameter (mm) 49.5
length(mm) 65
Stator(mm) 40.6*20
No of cells (lipo) 5
max efficiency (%) 90%
max efficiency current (A) 30-60A
no load current (A) 1.6
current capacity (A/s) 140A/60S
Internal Resistance (mohm) 19.5
Max Voltage 22.2V
Shaft Diameter (mm) 6
Shaft Length (mm) 65
KV (RPM/VOLT) 465
Last edited by fusionrc; Dec 21, 2015 at 07:52 PM.
Dec 21, 2015, 10:08 PM
Registered User
scirocco's Avatar
Please always provide links to both models and motors. It means we can fill in the blanks if you leave anything out.

Let's take a wild guess and assume this is the model http://www.phoenixmodel.com/Product.aspx?ProductId=601

And this is the motor http://www.hobbypartz.com/86mc302-3520-1050kv.html

It's probably going to weigh at the top end of the range, 3.2kg/7lb

I just stopped flying (well actually the impact with the ground stopped it) a similar size and weight warbird. It had an OS 5020-490, Kv=490 rpm/volt 350g. To fly really nicely, that took a 6S 5000 and 13x8 prop. Or a 5S and 14x10 would have worked. 4S on Kv around 500 rpm/V is too low voltage to get enough rpm and thus pitch speed on readily available prop sizes, and 4S 4000 mAh is not much total energy for a 7lb warbird - let's face it you don't build a warbird to just putter around in.

So looking at the motor you have - a 223g motor is not a 1300W motor except in marketing speak. It might be the actual peak power point where the motor is at 50% efficiency, but that is absolutely no use in a model - it will be cooked inside 60 seconds. Think of holding a 100W lightbulb, then think of dissipating 650W through a 200g motor.
A better guide for realistic power levels is 3W/g, so @ 223g, call it 700W.
On 4S with a 10x6, ECalc predicts 720 Watts in, ~2900g static thrust and 77mph pitch speed. That will fly a 7lb spitfire OK, but practical flight time will be unlikely to exceed 5 minutes.
The other problem you're almost sure to face is that a 223g motor is going to need to be accompanied by a lot of lead to balance, given the design is for .46-.55 glow engines.

Even the larger motor you mentioned might be marginally small for both weight and power handling, but is likely a much better bet. But as I mentioned, it's not a 4S motor with any practical prop size, so no use without also buying new batteries.

So, given you have the choice of persisting with the little motor you have bought, or start over, I suggest you stay away from the buy button until you have the model assembled and can assess how much motor and battery weight is going to balance it, and critically, critically, what size prop will fit with ground clearance you are happy with. That way you can optimise the power system without being constrained by what you have or the vague and contradictory buying guidance on the manufacturers's website.
Dec 22, 2015, 01:11 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by fusionrc
... I'm new to the forum, so I apologize in advanced if I have posted in the wrong place. ...
The Power Systems subforum is the best place for questions like this.

Quote:
Originally Posted by fusionrc
... I am new to electric planes ...
Some reading for rainy/windy days. Will save you, and us , a lot of questions.
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer(s) and tools

Vriendelijke groeten Ron
Dec 22, 2015, 02:39 PM
Registered User
scottc39's Avatar
here is your ranger of specs and recommendations for setups, if it was me i would get the 480kv motor and run on 6 cells, i have looked at the plane to

Battery: 4-6S LiPo, 4000-5500mAh
Motor: 1000-1400 W, 480 kV Outrunner
ESC: 50 - 80 Amp
Prop: APC 14x7 2-Blade
Power WOT: 1200 Watts
Dec 22, 2015, 03:16 PM
Registered User
E-Challenged's Avatar
Motor you should be OK on 4S lipo pack. May need a somewhat smaller prop. Check max amp draw at full throttle with a wattmeter or clamp meter to be sure you are within safe max amp range with whatever prop diameter and pitch that you use.
Dec 25, 2015, 03:02 PM
Ronaldo Nogueira
ronaldopn's Avatar
Can't you simply return the motor and get a replacement according to manufacturer's recommendations? Much better to start electrics with a proven setup.
Oct 19, 2016, 08:19 AM
Registered User

similar question


I have a pheonix spitfire MK2 and am concerned about electric power I fitted min with an equivalent to the 0.46 nitro engine from turnigy

Designed to be a direct swap out for your .40 to .46 size glow engine. This brushless outrunner will provide more power and with it's high efficiency, long run times.
A quality motor, built specifically for planes designed to fly with a .40 ~ .46 glow engine.
Spec.
Battery: 4~5 Cell /14.4~18.5V
RPM: 670kv
Max current: 40A
No load current: 10V/3.9A
Current capacity: 55A/15sec
Internal resistance: 0.04 ohm
Weight: 303g (not including connectors)
Diameter of shaft: 6mm
Dimensions: 76x50mm

Required;
60A ESC
4S~5S Li-Po / 12 ~ 16-cell Ni-MH/Ni-Cd
12x8 ~ 14x10 prop
Suitable for sport and scale airplanes weighing 4 to 7 pounds (1.83.2 kg).
I have a 70 amp ESC and am running on 5 C lipo

The question is what PROP, I had a 14 x 8 x2 on her and was told the current draw was to high.

so now i have a 15 x 4 x2 Am interested in putting either a three or 4 blade prop but have no idea of size..

looking for any suggestions
Oct 19, 2016, 08:30 AM
Registered User
Basic rule of electric motors....if the spec. gives a range of batteries like 4S - 5S and a range of props like 12x8 - 14x8 the larger battery (5S) always goes with the smaller prop (12x8) and vice versa.

So guessing that when you say a "5 C lipo" you actually mean 5S...you should be on about 12 x 8. And you should have a wattmeter so you can MEASURE the current draw.

The rule of thumb for going from 2 -3 blade props is same pitch but reduce diameter by 10%. For 2 - 4 blades reduce diameter by 15%. So 12x8x2 = roughly 11x8x3 or 10.5x8x4 (or the nearest sizes you can find, there not being many 3 and 4 blade props to choose from).

Steve
Oct 19, 2016, 09:30 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Tony, are you still new to the hobby? In that case, a Spitfire is not a good choice to learn to fly with.
HI I am new to this Sport and the Spitfire is my...


Some well-structured reading and handy e-tools for rainy/windy days. Will save you, and us , a lot of questions. Notably the 'what went wrong?' kind of questions
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer and tools

And please, do your RC equipment, wallet, ego, battery, controller, motor, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding the best setup.
close out: Hyperion watt-meter II (optical tach, servo tester, remote logging)

Vriendelijke groeten Ron


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