mackey1

My Feedback: (24)

Hi,

I'm a fuel/gas pilot trying to go to some electric. I have 4 brushless motors but couldn't tell you which has the most or least power. How does one know "which" motor to use in a given A/C? In fuel, you put a .40-.46 in a 6 lb A/C, etc.

I have a Hacker A20-20L, Himax HA2015-4100,HC2812-0850 (2). I've read about all I can find and I'm totally confused. In the current Model Aviation (AMA) magazine there is an article about homemade motors. The two charts appear to show almost identical specs for both motors although one has a "stacked stator" (2 together) and the article says it is more powerful. How can this be based on the numbers?

HELP!

Bill

Matt Kirsch

My Feedback: (21)

The main issue with people going from glow to electric is this tendency to believe the thing bolted to the nose of the plane is where the power comes from. It's true for an internal combustion engine, but not with an electric. The first rule of electrics: Motor does not equal Engine

If you want to get to the nitty-gritty core of the issue, the motor is generally the LAST thing you select when powering an electric aircraft from scratch. The motor is essentially just the crankshaft in the electric "engine" which includes the battery (combustion chamber and fuel tank), and ESC (connecting rod and carburetor). When you build a race engine from scratch, you select the crankshaft based on how much power it needs to handle, and that's the same thing we do here with electrics. Depending on how big and heavy the plane is, and how you want it to fly, you determine how much power, how many Watts, it needs. From there, you size a battery to produce those Watts (so many Volts at so many Amps). After that, you pick a speed control to handle the Volts and Amps. Finally, you pick a motor based on the same, generally looking to swing the largest-diameter prop that's practical for the plane.

Nowadays, there are many known good combinations of motor, battery, and prop. When people say, "Use XXX motor," they're also implying a particular narrow range of batteries and props that will give the plane the power it needs to fly as desired. To the untrained eye, it looks like the motor is being chosen first, but in reality, all the legwork to size the rest of the power system has already been done. You're just seeing the end result, and it can be very misleading.

Gryphon

mackey1

What plane are you trying to power, wing area, weight? What is your budget? HOw fast do you want to go? How hard do you need it climb, or what size prop do you want to spin how fast? Would you like to use one of the motors you already own? Do you have a speed control already/which one?

May be one/some of us on this site can help point you in the right direction. But first answer as many of the above questions as possible.

Gryphon

mackey1

My Feedback: (24)

Good Morning,

Thanks for the input. My real interest is in how one can determine, without testing, the relative power of different motors. Like we all agree, glow/gas motors are pretty easy to rank. Why can't electrics be that way? I see people adding batteries in series to increase watts. How much voltage can a specific motor take? There probably isn't an easy way to figure all this out. If it was simpler, more people would get involved.

Gryphon

Download a free copy of motocalc simulation software. It will be good for 1 month before it stop working and you have to pay for it if you want to keep using it.
It has many motors in it, if there is a motor that you are interested in and it does not have in it, get the main 3 specs from the manufacturers web site.
KV, Io, resistance
weight too
It will give you an idea, but it is by no means exact, it can point you in the right direction, a very usefull tool.

I've been told that you need to double the resistance for MEGA motors, but not for himaxx.

Gryphon

CAhardhat

My Feedback: (14)

Now I'm really confused.....I'm another gas guy that's trying to fly an electric or two. I just purchased a 25 size GeeBee about 4 pounds that I'm trying to figure out what to power it with in electric size..... I'm researching every article that I can find....trying to look for prop size etc....and I really am getting confused by everything I'm reading. I tried to use the motor calk but alas became confused there too. Guess what us old guys need is some young guys to point us in the right direction

mackey1

My Feedback: (24)

Barney, I'm with you! I did see a club member with a 4lb trainer type flying at the field this week. I flew the plane and it flew very well. It had an AXI 2814/12 motor with 2-3s1p 4400 Mah batteries. I think it would actually fly better with one battery and less weight. Just not as long.

Bill

Gryphon

Hi guys,
Depending on his combination of electric motor and Prop, he might need more AMPs that one of those two batteries can provide alone.
So it is not just for flying longer, he might need to split the current requirement between the two so it wouldn't damage one of them if used alone.

Gryphon

Flypaper 2

Guys:
I've been electrics for a while and still get confused On the maxx-prod website, under the Himax configurations , they show the equivalent glow motor and application. I've found it very helpfull in picking a motor for a heli conversion.

ghost123uk

Bill ( O.P.) hope this isn't considered a "HiJack" - just trying to help us all learn about your subject posted.

I know very little about E-Power.

I own 2 x Herr Little Extra as seen at =

http://www2.towerhobbies.com/cgi-bin...&I=LXFWM2&P=RF

basically =
Low wing aerobatic sportster
Wingspan: 36.5
Weight: 18 - 22 oz
Wing Area: 344 sq in
Designed with the Novell 074 in mind

I fly one with a Thunder Tiger 10 installed and it is very nice to fly, but a bit more power would be nicer.

The other one is yet to be assembled, and I would like to fit Electric Power

I am looking for help in deciding what setup I be looking for to get similar, or slightly more, performance ?

From info I have learned elsewhere on here it seems a quality 30A ESC is first thing to buy, but what LiPo packs and what Motors should I be looking for ?

Price is a fairly important consideration I am afraid - with this in mind are any of the motor offerings from the far east, on eBay any use, or to be avoided.

Matt Kirsch

My Feedback: (21)

When all else fails, look for a similar airplane with similar weight, size, and flying qualities that someone else has already successfully converted. Use the same power system.

JB, I'm not sure where you're getting your information from, but the ESC is NOT the first thing to buy. The battery would be, if you were starting from scratch. The ESC needs to be able to handle the Volts and Amps from the battery, and buying before you know how many Volts and Amps you're going to be using may well lead to wasted money, wasted time, and/or a smoked ESC...

There are plenty of airplanes similar in size, weight, and flying characteristics to your little Herr Extra. The Eflite MiniFuntana and MiniEdge 540 are prime examples. Also, the Wattage series of "400" size scale aerobatic planes, including the Giles, CAP 232, Extra... I've seen these quite successfully powered with a ThunderPower 2100mAh 3S LiPoly, an AXi 2808/24 motor, 10x3.8 prop, and ~25 Amp ESC. I guess in this case the 30A ESC was a good choice, and probably is for airplanes this size with similar flying characteristics.

ghost123uk

Thanks Matt, that helps.

What voltage is 1 x LiPo cell ?

I ask because so far I had "earmarked" a 2200 MAh / 11.1 Volt / 10C pack at about $40 ( on eBay !! ) and I am not sure if 11.1 Volt = a 3S pack ?

EDIT = I have found the answer on the NSP website - 11.1 Volt does = 3S

Gryphon

each lipoly cell is 3.7 volts.
1S means 1 in series 1X3.7V=3.7V
3S means 3 in series 3X3.7V=11.1V

if each cell is 2100 and for example Thunder Power has 15C continous, 24C max burst
then 3S1P means 1 in parralel would be 15X2.1=31.5 AMP cont, 24X2.1=50A max burst

But 3S2P 4200, means 2 parallel(packs of 3S 2100 each). 11.1V, 2X31.5AMP=63A cont, 2X50A=100A max burst

5S4P 5300 is made of 5X4=20 of 1325 cells, 5 in series 5X3.7=18.5V, 4X13C=4X13X1.325=69A cont

ghost123uk

Thanks for that, I think I am getting close to a viable setup now !

So the pack I have earmarked as =2200 MAh / 11.1 Volt / 10C can provide a max current of ~22 Amps at 11.1 Volts -Yes ?

So that equals 244 Watts

So the 30 Amp ESC is suitable - ( with 3 cheap mini servos tho I could fit an external BEC or RX batt if ness ) Yes ?

and an outrunner that takes up to say ~250 Watts is good, Yes ?

and lastly I take it I can "tune" the current consumption by going down on the prop pitch, Yes ?

Sorry about all the questions, and Bill ( O.P. ) hope you don't mind the hijack

Gryphon

Under load the voltage of the battery drops so it will not stay at 11.1 even if you start higher, depending on the current draw.

YOu might be right about 10 Volts under load, when you turn off the motor then voltage spikes back up. So 11.1V is just a nominal value.
Also the battery voltage is always gradually dropping till it gets to the cut-off voltage.

22AX10V=220W input, then there are some losses in heat/friction, so output is less(take of at least 35W). All that if you don't drop below 10V.

In general batteries with higher capcity and/or higher C (current flow) rating will drop less voltage under load compared to other one's.