Choosing an electric power system for your model

[kyleservicetech]

Originally Posted by GFH

I'm no dummy but it seems to me everyone has two different names for everything and one uses apples for measurement and the other oranges.

I've been a gas guy and decided electric for the next

SO I'm confused .............what do I need.

The model is 10 pounds a Jerry Bates Interstate Cadet (similar to a J3). Recommended power is a 60-90 2 stroke or 90-120 4 stroke or 23cc Gas.

What do I put on it for power? I might also use it to tow gliders up bt what is suggested with and without the towing option?

Cheers and thanks

G

Lets see, you need a minimum of 100 watts per pound of airplane, so that is 100X10 or 1000 watts. Since your model calls for up to a 120 4 stroke engine, that would be on the order of perhaps 150 watts per pound or a little more.

That is getting into serious electric motor horsepower. A wide variety of electric motors from a lot of different suppliers are available for this purpose. The question is which one to use?

One program that will help a lot is www.motocalc.com, free for 30 Days, then $39. You can enter in your models wingspan, area, weight without motor and battery, and it will give you an idea on how well the model will fly.

I'm an admitted Hacker nut, and would look at a Hacker A60-6SX. This motor would be an expensive, but very good power unit that will definitely pull your model around. Running this motor on an 8S1P (8 series, 1 parallel) LiPo pack with about 5000 Mah will allow this motor to turn a 16X8 APC-E (Electric) prop at around 9000 RPM. Motocalc indicates this motor will be running around 91% efficiency, a pretty good value. Again, per Motocalc, this motor will be pulling around 1900 Watts at full power, which turns out to be around 2.5 Horsepower. That comes out to about 190 Watts per pound, which will give plenty of power to haul up a sailplane in tow. I'm guessing on the wingspan, wing area and bare weight of your model as 66 inch span, 950 square inches, and 120 ounces bare weight with everything but the motor and battery.

Nice thing about the Hacker motors, they will do what their specifications say they will, and will do it year after year.

9000 RPM on a 16 inch diameter Electric prop might be pushing the maximum RPM limits on an APC-E prop, you might have to go to a glow engine type of prop on this setup.

As for speed controls check out the Castle Creations 75 Amp Phoenix ICE ESCs. The CC units work, and work well. (Looks like CC is out of stock on most everything, but perhaps other on line hobby stores will have one.)

[GFH]

Thanks Kyle

I should have added it has a 107 inch wingspan, 1550 sq inches. Not a high performer just large

I tried motocalc link a couple of times and it was a dead end.

Ill try again..

[GFH]

AXIs website comes up with an AXI 5320/28 but I have no idea how to easily compare that with other manufacturers.

[kyleservicetech]

Originally Posted by GFH

Thanks Kyle

I should have added it has a 107 inch wingspan, 1550 sq inches. Not a high performer just large

I tried motocalc link a couple of times and it was a dead end.

Ill try again..

No problem.
Check out the attached screen dumps for Motocalc on your proposed model and power setup. Bates # 1 and 2 are for a 17x6 prop, Bates # 3 and 4 are for a 16X8 Prop.

Looks like either a 16x8 or 17X6 prop would be good with a good quality 8S LiPo pack. IMHO, it would be a good idea to stuff in as big a 8s LiPo pack as you can afford, since with the huge wingspan of this model, overall weight wound not be an issue. This model will obviously be a little overpowered with that Hacker motor, but if you're planning on towing sailplanes, being way overpowered is a good thing.

Problem with some of those off brand higher powered motors, they've been known to have bearing problems, or have magnets come loose and so on. Not a good thing to have a power failure if you're towing a sailplane.

This is for a smaller model, but a lot of the stuff covered in the PDF file will apply to your setup.
Thread on 70 size glow engine conversion to electric
http://www.wattflyer.com/forums/showthread.php?t=45222

One big problem with the larger electric model airplanes, is their cost skyrockets, something apparent when you look at the Hacker motor, the CC ESC, the LiPo battery, and the charger for the LiPo battery. On the other hand, you don't have vibration issues shaking your model and its servos apart, you don't have fuel getting all over everything, and fuel dripping on your auto carpet, or carpet in your home. I've got models that are on their 9th flying season with well over a thousand flights on one of them, that looks brand new.

DennyV

[CT4]

I have been flying for 40 years I am an instructor and I am authorized to issue permits to fly for oversize aircraft (anything over 12 Kg but under 25Kg in Australia). I am however a total newbi to electric flight with aircraft. I have been reading endless threads on line but I am having trouble understanding prop size to motor to amp draw. In order to try and understand this I have started using either the CC ICE data logger or the Eagle Tree logger.
The results I am getting are so far from those published by the manufacturer of the motor I am really confused and would appreciate some help.
Example
Scorpion SII-3020-1110Kv (V2) motor CC ICE 75 ESC 3 cell and 4 cell 25c battery

Scorpion says with a ACP 10x5E prop on 3s I should pull 29A and with 4s should be 48A
I get 37A and 56A respectively. If I change to a SP 10x3.7 prop the current draw jumps to 71A

I have tried similar other setups with different motors and in every case the current draw has been a lot more than the figures published.

If anything what am I doing to get such a different result to the manufactures published results. I have tried Motorcalc but could not get it to work due to the data base not having ICE ESC or any of the current Hyperion batteries in its data base. Any help would be appreciated.

[kyleservicetech]

Originally Posted by CT4

I have been flying for 40 years I am an instructor and I am authorized to issue permits to fly for oversize aircraft (anything over 12 Kg but under 25Kg in Australia). I am however a total newbi to electric flight with aircraft. I have been reading endless threads on line but I am having trouble understanding prop size to motor to amp draw. In order to try and understand this I have started using either the CC ICE data logger or the Eagle Tree logger.
The results I am getting are so far from those published by the manufacturer of the motor I am really confused and would appreciate some help.
Example
Scorpion SII-3020-1110Kv (V2) motor CC ICE 75 ESC 3 cell and 4 cell 25c battery

Scorpion says with a ACP 10x5E prop on 3s I should pull 29A and with 4s should be 48A
I get 37A and 56A respectively. If I change to a SP 10x3.7 prop the current draw jumps to 71A

I have tried similar other setups with different motors and in every case the current draw has been a lot more than the figures published.

If anything what am I doing to get such a different result to the manufactures published results. I have tried Motorcalc but could not get it to work due to the data base not having ICE ESC or any of the current Hyperion batteries in its data base. Any help would be appreciated.

I've not used the Scorpion motors, but have found that the various $$$$ Hacker motors are fairly close to their published value.

The CC ICE ESC will have little effect on the actual current pulled by the motor/battery/prop combination. By far, with a given motor, the propeller and cell count in the battery will have the greatest effect.

So, rather than using a Hyperion battery, find another battery with similar capabilities in the motocalc battery database.

Now, for the Scorpion motor. What I've done is take a current/voltage/rpm reading off of the motor with a given propeller. Then compare that reading to the measured values that you've taken.

Then, go to the Scorpion motor specifications, save it as a different name, such as Scorpion my tests. Then tweek the KV numbers of the motor to match your actual tests. Now you've got a baseline on your Scorpion motor to try different props and so on in motocalc.

You will find it doesn't take much of a change in the KV numbers to really make a big difference in how much current that motor/prop/battery pulls. And, just a few percent more in battery voltage under load (with a higher quality battery) can also make a big difference in the current pulled by the motor.

Take a look:
Thread on 70 size glow engine conversion to electric
http://www.wattflyer.com/forums/showthread.php?t=45222

Also:
http://www.wattflyer.com/forums/showthread.php?t=44686

And, if you decide to go for real high powered electric models, you will find that the cost skyrockets! And, you've got to find a way to field charge the motor battery. It takes either an AC source, or a PAIR of 120 Ampere Hour deep cycle batteries. And those deep cycle batteries won't last much more than a year or two. Personal experience.
http://www.wattflyer.com/forums/showthread.php?t=59273

[archd7]

amazing!! Just what I have been looking for thanks!

[kyleservicetech]

Originally Posted by archd7

amazing!! Just what I have been looking for thanks!

Are you after larger giant scale models? If so, I've got a few threads on those.

[Barrymartin]

I was looking for this kind of tutorial on internet for few days. Actually i am interesting in buying electric power system for your model. I have found your tutorial very helpful. Thanks for sharing....

[kyleservicetech]

Originally Posted by Barrymartin

I was looking for this kind of tutorial on internet for few days. Actually i am interesting in buying electric power system for your model. I have found your tutorial very helpful. Thanks for sharing....

What size model?

One of these threads should cover just about any size model with electric power.

Giant Scale Power System:
Battery Backup System
http://www.wattflyer.com/forums/showthread.php?t=63794

Giant Scale electric motors vs Gasoline Engines
http://www.wattflyer.com/forums/showthread.php?t=58035

Harbor Freight Gasoline/Alternator Setup
http://www.wattflyer.com/forums/showthread.php?t=66066,

Great Planes Giant Big Stick Electric Conversion
http://www.wattflyer.com/forums/showthread.php?t=65052

Giant Scale Cessna Model
http://www.wattflyer.com/forums/showthread.php?t=66414

Thread on 70 size glow engine conversion to electric
http://www.wattflyer.com/forums/showthread.php?t=45222

Hacker 6S2P A123 powered Models
http://www.wattflyer.com/forums/showthread.php?t=44686

Hangar 9 Kantana Model (Still waiting for flying weather on this model. Right now, its snowing outside. Again.)
http://www.wattflyer.com/forums/showthread.php?t=68844

AEAJR's Site on Electric Power
http://www.wattflyer.com/forums/showthread.php?t=18521

BEC Linear Current Rating
http://www.wattflyer.com/forums/showthread.php?t=63497