Author Topic: motor size (Read 1222 times)

pete beddows · « **on:** February 03, 2008, 10:44:11 AM »

i have a air frame that has 800" and weighs 37 oz with out paint or motor i have a stalker 61 for this plane but would like to go electric ,

so how many cells and what size motor this air frame has 6 inch round cowl so will need a large prop .
thanking you pete beddows

.

Dean Pappas · « **Reply #1 on:** February 04, 2008, 08:01:00 AM »

Hi Pete,
What would you say the realistic flying weight would be with the Stalker?
Let's say 70 ounces, for now.
To actually fly the schedule "costs" you 0.71 Watt-Hours per ounce. That would mean 49.7 W-H.
You need 20 ~ 25% or the battery to ber l;eft after the flight for LiPOs, and maybe 10% or more for A123s.
Let's assume LiPOs.
That works out to 66 W-H.
With a 4-S pack ( 14.4V) that would be a 4.6 A-H pack. This will weigh 16 oz.
With a 5S pack, that would mean you need at least a 3.6 A-H pack. This will weigh almost exactly 16 oz!
We have good lightweight cells available in 5.3 A-H and 4.2 A-H from Thunder-Power, but they ain't cheap.
Most other brands involve a 10% weight penalty, so add two ounces for laughs.

I'm going to make an assumption here that we wish to turn something like a 6" pitch at close to 9,000 RPM.
Assuming about 10% of the voltage is lost in "copper losses" this means the 4S setup will need a Kv of between 800 and 900 RPM/Volt.
That's after assuming that the governor (more later) will keep the RPM to 80% of the max possible at full charge.
The 5S setup will need a motor with a Kv of 600 ~ 650 RPM/V.

Both packs above will have a little extra capacity, so you shouldn't be beating them up.
Assuming the 125 Watts per pound figure ( which is really the same as .7 W-H / oz for a 6 minute flight)
you'll be flying at about 550 Watts. i'm guessing that you'l be running a 12-1/2 X 6 to a 13 X 6 prop.
You may be able to run more diameter, depending on blade shape.

There is more to it, of course.

later,
Dean Pappas

Alan Hahn · « **Reply #2 on:** February 04, 2008, 11:36:29 AM »

Pete and Dean,
Both of you need to edit out the Zip Code/ Location information from your profile. Having this information there causes the software to try and load the weather at your location--but infortunately the weather site no longer seems to exist. This causes some people's web browsers to really slow down loading. Also note Sparky's request up at the top of the page under "news".

Otherwise an interesting topic. I am guessing that the motor size is something equivalent to the AXI 2826 (6.4 oz) or equivalent (such as the Scorpion 3026 (6.7oz) or 3032 (7.9oz). Nomenclature for each is Stator diameter (first two digits) and stator length (last two digits), both in mm.

Dean Pappas · « **Reply #3 on:** February 04, 2008, 02:05:16 PM »

Hi Alan,
Thanks for the reminder, I'll do it right now.
No, at 550W you are probably talking about an 8 or 9 ounce motor like a Hacker A40L or the Pletty that Kim and paul are running.

later,
Dean

pete beddows · « **Reply #4 on:** February 04, 2008, 03:17:51 PM »

Hi Alan and Dean
i have a 2826/10 900kv i have seen a turnigy 42 50a 700kv that weighs 195 grams a review states that at 9000rpm its pulling 42 amps setling down to 36 amp
would this suit also the esc would this need to be uped to 60amps
i have 4 cell packs 4100ma would buy 5 cell for the above motor,
thanking you for your time Pete Beddows.

Alan Hahn · « **Reply #5 on:** February 04, 2008, 03:56:17 PM »

Scorpion does have 40mm diameter motors too which they claim are equivalent to the Hacker 40L--I have no experience. Here is a link to their motor comparison chart

http://innov8tivedesigns.com/Scorpion/Motor%20Comparison%20Web.htm

Of course AXI also has the>40mm diameter motors.

Scorpion claims their 3032-10 (kV=823) can pull 80 A continuous--but again I have no experience with this motor, but also have no reason to doubt either--but it sure sounds like this is already more than enough to handle 500 watts. Even their smaller 3026-12 (kV=840) is claimed to handle 60A continuous. Here is a link to a prop chart for this motor.

http://innov8tivedesigns.com/Scorpion/Scorpion%203026-12%20Specs.htm

I will say that it isn't obvious to me that one needs to keep "supersizing" these motors. I also don't mean to be pushing Scorpion, but at least they have some data out there to compare things to.

And thanks for getting rid of the ZIP code stuff. This loads up quite fast now.

Dean Pappas · « **Reply #6 on:** February 05, 2008, 10:58:47 AM »

Hi Gang,
So what was your guess as to weight, Pete?
Assuming we are working with 70 oz. you have the choice described above. me? I would probably go 5S and about 4A-H, like the 4200 Pro-Lites.
Now, even if you utterly flattened a 4 A-H battery in 6 minutes, that would only be 40A, so there is no need to get an ESC bigger than maybe 45A. Everybody knows that I prefer the castle Phoenix because of its faster, tighter RPM governor control. All these ESCs will handle peaks that are above the rating, and ...

In real terms, with A 4 a-h battery, your average flying current will (actually must be) 30 A or less, so that you don't overuse the battery and hurt it. The peak currents during maneuvers will be about 1-1/2 times that. Hey! 45 A is sufficient.

So now you are looking for a motor that will handle 550 W with a Kv of somewhere between 600 and 700. ( a little looser range than I described previously)

I have a work meeting, Ill write later.

Dean

pete beddows · « **Reply #7 on:** February 05, 2008, 11:54:35 AM »

Hi Dean
70 oz is spot on air frame 37 power train 23 paint 10 one of the reasons for considering this conversion i can reduce the nose by a inch ,i would like to go with a
jetti and a prog box , thanks for your time
Pete Beddows

Dean Pappas · « **Reply #8 on:** February 05, 2008, 12:49:38 PM »

Hi again Pet,
Thanks Alan,
So your options look like a

Plettenberg Orbit 25-14 at a Kv of 670 and a weight of 8.8 oz. Expensive, well-built, and efficient.

Hacker A40-10S or 12S with kv of either 750 or 610 (but hacker specify an effective Kv (behaves like something maybe 10% higher) and a weight of 9.3 oz. This is moderately priced, well-built with the aft bell bearing, but it needs a front mount which I don't like.

Electrifly Rimfire 42-60-600 which is cheap, has no bell bearing but is surprisingly efficient with a 29 milli-Ohm winding resistance and weighs 9.5 oz.

The 8 oz. Scorpion S-3032-12 that Alan mentioned is light, but the relatively high winding resistance and moderately high no-load current tells me that the efficiency and heating will be poor. Efficiency under high current (near 45A) is the best indicator of how good a power "bump" you will get when the RPM governor gives the throttle, under maneuvering load.

Me, I'd go Hacker or Rimfire depending upon price. If they cost the same, then the bell bearing in the Hacker makes the difference for me.

Dean

pete beddows · « **Reply #9 on:** February 06, 2008, 11:08:21 AM »

Thank you Dean and Allan i think i will go with the hacker if i went with a123 cell would i still use 5 cell pack
thanking you Pete Beddows.

Dean Pappas · « **Reply #10 on:** February 08, 2008, 09:56:42 AM »

Hi Pete,
You mean 5S2P for 16 volts and 4.4 A-H? That's 24 oz of battery.
later,
Dean

pete beddows · « **Reply #11 on:** February 08, 2008, 11:11:43 AM »

Hi Dean
i have some cells for another project they are 2700 but have a lower c rating 20c if they can be discharged almost flat could i not use 5 cells
24 0z is too heavy ,16 oz of lipos is heavy enough i think i will go with the lipo at least i will now they work.
thanking you for your time Pete Beddows.

Dean Pappas · « **Reply #12 on:** February 08, 2008, 04:56:13 PM »

Hi Pete,
You can't run LiPOs nearly flat, because they will become useless in no time at all. Limit yourself to using 75% of the rated capacity, maybe 80% at worst. I agree that the A123s are too heavy, thouygh they can be used to 90% of rated capaicity with no harm. You need 3200's at a bare minimum.

let me know how you work it ouit,
Dean

Author Topic: motor size (Read 1222 times)

pete beddows

motor size

Dean Pappas

Re: motor size

Alan Hahn

Re: motor size

Dean Pappas

Re: motor size

pete beddows

Re: motor size

Alan Hahn

Re: motor size

Dean Pappas

Re: motor size

pete beddows

Re: motor size

Dean Pappas

Re: motor size

pete beddows

Re: motor size

Dean Pappas

Re: motor size

pete beddows

Re: motor size

Dean Pappas

Re: motor size