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-   -   Selecting Electric Power Systems - (https://www.wattflyer.com/forums/showthread.php?t=18521)

peterboshoff 05-20-2008 12:25 PM

If you have a 5lb plane and are using a motor with 5lb of thrust, you are way over powered for some planes and under powered for others. Ed[/quote]
*************************************************
I am designing my own plane for a 145gm 450Watt motor, a high wing with dihedral. I am using 6 mm depron on the fuselage.
The wings is asymetrical NASA airfoil with 18% thickness ratio, 3.8% camber, with balsa skin, to cover whole wing. I am aiming at 20 oz/ft² with 4.5 ft². 62" WS.
The minimum weight will be 2.5 Lb but it will have to be heavier to get a 20 Oz/ft² wing loading to fly in moderate wind of 10 to 15 mph.
The motor is a Himodel Max2820-07 with 919 KV on a 256gm 4cell 20C15.8V 2100mAh Lipo. Prop is 9 x 5
I need to know how heavy the plane can be and still take off from long grass with a short take-off distance. ( I belong to a manage by crisis club and the grass don't get cut very often.) I can still change some of the parameters as only the fuselage has been partly built.
Should I make the wings smaller or load the weight, taking in consideration the motor size.?
Thanks for your help in anticipation.

AEAJR 05-20-2008 01:11 PM


Originally Posted by mossman (Post 408893)
Ive got a n E max motor 2215/25 brushless with a dualsky 2200mah Battery motor is new after crash replaced it at 3/4 throttle to max runs real rough then cuts out like power surging.

coul hgis be the ESC. Battery is new dualsky 2200 mah 3 cell 16 C E Shy ballance charger for 3 to 4 cells charging off car battery takes a few hours to charge.

Ive had two supercubs which i loved flying then went to glow scanner & boomerang flew ok but messy & after a couple of flights crashed Ive gone back to electric.

frustrated

I am having a little problem with your post. The lack of puncuation makes it hard to read.

When you ask for help about motors you need to provide a link to info about that motor and the ESC you are using or you will get answers that are about some motor that someone thinks is similar. We also need information about the propeller.

Just a tip to avoid confusion.

Is this your motor?
http://www.truenorthernhobbies.com/m...r/BLSERIES.pdf


Originally Posted by mossman (Post 408893)
Ive got a n E max motor 2215/25 brushless with a dualsky 2200mah Battery motor is new after crash replaced it at 3/4 throttle to max runs real rough then cuts out like power surging.

So, you crashed your plane and replaced the motor? Now it runs rough at 3/4 throttle?

By rough I presume you mean it vibrates. That would be caused by an out of balance or bent motor shaft, a bent propeller or a loose motor mount. I assume this new motor does not have a bent shaft.


Originally Posted by mossman (Post 408893)
coul hgis be the ESC. Battery is new dualsky 2200 mah 3 cell 16 C E Shy ballance charger for 3 to 4 cells charging off car battery takes a few hours to charge.

If the motor shaft is bent, if the prop is bent, this will cause the motor to draw excessive power which could exceed the capacity of the ESC causing it to overheat and shut down.

You do not say what propeller you are using. You also don't provide any information about the ESC that you suspect. As you can see from the motor specs, the power draw depends on the propeller you use.

So, there is a lot of information missing. Tell us more.

mred 05-20-2008 01:53 PM

The easiest way to get the weight you want is to build a box to put weight in at the CG inside the fuse and then you can play around with the weight all you want. There are still a lot of things we need to know about this plane to help you more though. Take care and give us some more information. By the way, 20oz wing loading is asking for problems if you are not used to flying a heavy plane. Work up to it slowly.
Ed

PS. That can't be his motor. It only puts out around 168W with 2.25lb thrust. He says 450W motor at 5lb thrust. If this is the motor, you have a smaller motor then you are leading us to believe or you are running it way over the max on the spec sheet.

JGMM_BC 08-17-2008 03:30 PM

Weight and multiple motors...
 

Originally Posted by AEAJR (Post 190103)
This is not an extremely exact science. +/- 10% in weight is not going to matter. Even 20% if you are not tyring to size it too close. When in doubt go for a little higer power to weight ratio unless you are trying to go very light, like an indoor flyer.

So taking all this into account, what happens when you have 2 motors? Do you divide the AUW by 2 and have the load shared by both motors or do you plan it so that the motors are over powered so you have a higher thrust to weight ratio?

Did I explain this right?

AEAJR 08-18-2008 12:21 AM


Originally Posted by JGMM_BC (Post 458515)
So taking all this into account, what happens when you have 2 motors? Do you divide the AUW by 2 and have the load shared by both motors or do you plan it so that the motors are over powered so you have a higher thrust to weight ratio?

Did I explain this right?

That is up to you.

I would take the total power of both motors as my total watts and compare that to the weight of the plane.

So,

Let's say you have a 6 pound plane with two motors. At 75W/lb, that would be aroudn 450 watts you want. so you could use two motors of about 225-250 watts to hit that number.

or, you could use a pair of 300 watt motors to hit 100 watts/pound. This way if a motor failed, you would still be at 50 watts/pound which is adequate to fly most planes so you can limp home on one motor.

Of course that does not address that the plane will be unevenly powered and all that goes with that, but that is not what we are discussing.


I have not tried this, but this is the approach I would probably take and I would go for a pair of 300-350 watt motors, if the weight target allowed it.

JGMM_BC 08-18-2008 11:09 AM


Originally Posted by AEAJR (Post 458746)
That is up to you.

I would take the total power of both motors as my total watts and compare that to the weight of the plane.

So,

Let's say you have a 6 pound plane with two motors. At 75W/lb, that would be around 450 watts you want. so you could use two motors of about 225-250 watts to hit that number.

or, you could use a pair of 300 watt motors to hit 100 watts/pound. This way if a motor failed, you would still be at 50 watts/pound which is adequate to fly most planes so you can limp home on one motor.

Of course that does not address that the plane will be unevenly powered and all that goes with that, but that is not what we are discussing.


I have not tried this, but this is the approach I would probably take and I would go for a pair of 300-350 watt motors, if the weight target allowed it.

Thanks for your advice.

Maybe you can help shed some light on this for me. The plane I have is just shy of 6lbs and I have a setup with 2 E-Flight Park 400 brushless motors (4200 KV) with 6:1 gear box and two 2000mah 3Cell lipos. With this setup how would I figure the max weight of a plan for 100W/Lb flying?

AEAJR 08-18-2008 11:44 AM

How many cells in your lipos? 3? Use about 3.3V/lipo Cell as your working voltage. =9.9V for a 3 cell pack. 10V is fine for estimating purposes.

How many amps? That will depend on the prop. Either measure it with a watt meter or read it off the MFG chart for estimating purposes.

V X A = Watts

Watts/pounds = watts per pound.

mred 08-18-2008 04:22 PM

I don't know where you got the idea you had to have 20oz per square foot of wing area. I fly a Super Sportster E and am no where near that kind of weight and it flies great in the wind. I also have a Miss Stick and it is very lite and I fly it in 10 to 15mph winds without much trouble. If I were to weight them up to 20oz per square foot, I think they would be a little on the heavy side. As for a twin, you need enough power from one motor to fly the plane in for a landing or you are in big trouble. I normally go 100W per pound on one motor just so I have enough to fly on. Anything less and you are asking for trouble unless you are a very good pilot. Unless you really know what you are doing, I would say cut the remaining motor and glide in where ever you are. At least that way you cut down on the damage somewhat. We still need to know some more about your system though.
Ed

ron_van_sommeren 08-30-2008 12:52 PM

Compilation of e-flight calculators:
http://www.rcgroups.com/forums/showthread.php?t=606703

Prettig weekend ;) Ron

watt_the?! 10-12-2008 10:43 PM

hey Ron, one of the myths in RC is the high V versus low V application of power setups.

given the same respective equipment overheads- i.e. battery discharge, ESC overhead, motor stress- power losses should be the same and it makes no difference in eihter setup...in fact numerous pole motors under high V present new challenges for ESCs...

does your calculator suite support this?

could it be used to provide evidence so we can communicate this to the RC community?

i still find myself coming across many posts where people are making "efficiency claims about high V- but of course not changing any other variables...

tim

Crash Serum 12-28-2008 03:46 AM

Hi I am a beginner with electric. I am building a Bird of Time and have selected a "Cyclon" outrunner its a 30 size that I bought from Horizon. I bought it because it is suppose to put out 300watts at 25 amps and a 3 cell lipo. The most I can get on an online calculator is 204 watts and that with a 12/6 folding prop and that will have been at about 24 amps. Should I get a different motor?

Thanks in advance
Crash Serum

AEAJR 12-28-2008 12:20 PM


Originally Posted by Crash Serum (Post 532257)
Hi I am a beginner with electric. I am building a Bird of Time and have selected a "Cyclon" outrunner its a 30 size that I bought from Horizon. I bought it because it is suppose to put out 300watts at 25 amps and a 3 cell lipo. The most I can get on an online calculator is 204 watts and that with a 12/6 folding prop and that will have been at about 24 amps. Should I get a different motor?

Thanks in advance
Crash Serum

I can tell you nothing about the motor because you have not provide a link to the specs. See several posts up where this is discussed. If you have questions about a motor, post a link to the specs.

300 watts at 25 amps? That means you would have to be running a 4S pack. 12X25=300. 12 Volts would have to be a 4S pack or a 10S NiXX pack. Can't get that out of a 3S pack at 25 amps.

Sounds like you need a higher voltage battery or a larger prop in order to get 300 watts out of that motor. I would plug in a 14X6 or a 13X7 prop into your calculator and see what you get.

Crash Serum 01-09-2009 04:30 AM

motor selection
 
Sorry I did not give you the link. I will know better next time! Thanks again! It seems I must post three links before I can send a link??? Any way i will post this one then post a third with the link

Crash Syrum

Crash Serum 01-09-2009 04:32 AM

link for cyclon motor
 
This is my third post so I hope it goes

Crash Syrum

http://www.horizonhobby.com/Products...ProdID=CYLOR30:cool::cool:

mred 01-09-2009 05:24 AM

Sounds like you need to prop up a bit. If you are getting 25A with a 12X6, then try a 13X6 or 13X7. Horizon says it uses an 11X6 to 13X7, but that depends on the glider and how much power you need to pull. A Bird of Time should be able to fly fine with a 12X6 or 13X6or7. Anywhere in that range should pull the glider fine. You don't always have to prop for the max, but you do need to prop for the climb you want out of it. If you are real new to gliders, I would start with something smaller like the 12X6 , or even an 11X6 and go from there. A 13X7 prop on that glider is going to give you a pretty fast climb and for a beginner, you may want something a little slower at first. After you fly it a little while, you can start proping it up for a faster climb.

Ed

Crash Serum 01-09-2009 02:00 PM

motor for BOT
 
thanks for your time and sharing of know how!

Crash Serum;)

mred 01-09-2009 04:08 PM

By the way, I did forget one thing. If you don't want to spend a lot of money for different props, you can get something like a 13X7 and control the climb with the left stick. That's what it's there for and you can control the climb with it so it's not going crazy on you on the first few flights. After you get it trimmed out and flying the way you want it to, you can start giving it more until you get to full throttle. Al least then you get a chance to see what it is going to do on the first few flights without killing it right away and either crashing it, or ripping the wings off and yes, you can do that if you get it going to fast.

Ed

Crash Serum 01-12-2009 07:59 PM

BATTERY
 
hI Hi I was wondering about balancing plugs. My E flight charger has a 6 pin balancing port but some of the Lipos have JST connectors on their balancing connectors. Will I always be limited to e-flight batteries?

Thanks
Crash

mred 01-13-2009 04:04 AM

Hi Crash;

It would seem that everyone and their brother has their own type of connector on the balance plug. It's to bad they don't all agree on a standard, but I don't think they ever will. In the mean time, you can buy just about any kind of changer you want and then get an adapter for the type of battery you are using. Who ever makes your changer normally sells an adapter for different types of batteries. If you don't see what you need, just ask them. A few of them you have to get from someone else, but they are out there and are not to hard to find. I have three different balance plugs on mine, but have decided to go with JST for now on the new batteries I buy.

Ed :)

run 02-11-2009 04:12 AM

Great. Learn a lot. Thank you.

AEAJR 02-11-2009 11:42 AM


Originally Posted by Crash Serum (Post 532257)
Hi I am a beginner with electric. I am building a Bird of Time and have selected a "Cyclon" outrunner its a 30 size that I bought from Horizon. I bought it because it is suppose to put out 300watts at 25 amps and a 3 cell lipo. The most I can get on an online calculator is 204 watts and that with a 12/6 folding prop and that will have been at about 24 amps. Should I get a different motor?

Thanks in advance
Crash Serum

Crash Serum,

Being a glider pilot myself, I was wondering how your BOT came out? What did you finally use and how did it work?

stiknrudder 02-17-2009 01:57 AM

Hi Y'all from WINDY and too cold to fly Virginia. All this electrical stuff is new to me, soooo. I am converting a HZ Supercub from brushed and geared to brushless. Inline wattmeter shows about 175 watts wide open. Why can I fly on 9.6v and about 20A draw, but when I look at conversion tables I get engine recommendations that are 33- 40A draw? I thought the brushless was more efficient.


THanks for the help.

Rick

mred 02-17-2009 02:05 PM


Originally Posted by stiknrudder (Post 566160)
Hi Y'all from WINDY and too cold to fly Virginia. All this electrical stuff is new to me, soooo. I am converting a HZ Supercub from brushed and geared to brushless. Inline wattmeter shows about 175 watts wide open. Why can I fly on 9.6v and about 20A draw, but when I look at conversion tables I get engine recommendations that are 33- 40A draw? I thought the brushless was more efficient.


THanks for the help.

Rick


They are more efficient, but it depends on the size of the prop that you want to turn that is giving you the amps. A 200W motor can turn a 10X6 at 20A or there abouts depending on the motor you are talking about. It also depend on the size battery you are planning to use. Are you talking about using the 9.6V battery, or installing a new battery? Using a 11.1V LiPo battery you can turn a fair size prop and at 14.8V a little smaller. Just depends on what you are trying to turn for prop size and the voltage you are using. You could give us a little more information on the set-up you are looking at and maybe we can come up with something for you. It would also be nice to know how much money you are talking about spending in this set-up.

Ed

stiknrudder 02-18-2009 12:42 AM


Originally Posted by mred (Post 566463)
They are more efficient, but it depends on the size of the prop that you want to turn that is giving you the amps. A 200W motor can turn a 10X6 at 20A or there abouts depending on the motor you are talking about. It also depend on the size battery you are planning to use. Are you talking about using the 9.6V battery, or installing a new battery? Using a 11.1V LiPo battery you can turn a fair size prop and at 14.8V a little smaller. Just depends on what you are trying to turn for prop size and the voltage you are using. You could give us a little more information on the set-up you are looking at and maybe we can come up with something for you. It would also be nice to know how much money you are talking about spending in this set-up.

Ed

THanks for the info. got a SC mount for a park 480 from Ebay

But I think the park 480 is too much what about e-flite park 450, it claims 175 watts. with 1250 or 1500 mAh 3s lipo 15c.

You got any input?

thanks..
Rick

PS already converted it to 6eax 2.4 futaba and 3114 servos.

Rick

mred 02-18-2009 01:00 AM


Originally Posted by stiknrudder (Post 566725)
THanks for the info. got a SC mount for a park 480 from Ebay

But I think the park 480 is too much what about e-flite park 450, it claims 175 watts. with 1250 or 1500 mAh 3s lipo 15c.

You got any input?

thanks..
Rick

PS already converted it to 6eax 2.4 futaba and 3114 servos.

Rick

I am using a KD A20 22L motor in mine running a 10X6 around 200W and I love it. You can power down if you like, 175 watts will still give you a good flying glider and it will still climb pretty good too. I am using a 2200mah 3cell battery in mine also and it climbs about 10 times if I really want to. Normally I go 6 climbs and bring it in for a new battery and go again. If I'm having a good day and there is good lift, I fly until my neck gets tired and then land and then fly again a little later. 175 watts will get you up there pretty fast, so you will have plenty of time to find lift. I just depends on what you are looking for. Some want a little more power and some are happy with less. Fly it and see how you like it and if it doesn't go up fast enough for you, go for the 480. Limit your first flight to 2 climbs and it bring down and see how much battery you have left. That should tell you how long you can fly on your battery after that.

Ed


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