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Choosing a Power System

Old 05-05-2006, 04:33 PM
  #1  
omba
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Default Choosing a Power System

Hi again, folks.
I am considering two different power systems for a direct drive glider. I have NO IDEA how to tell the differences from the data. I have been told that the HIMAXX system works. I am trying to figure out if the MEGA system would "work" just as well. I realize that I am not comparing apples and apples, but I have no idea how to predict the results.

When trying to gather data on the two motors from the manufacturers, I learned that they don't even measure the same things! Here is what I was able to find ...

Motor > HC2812-0650 (this one works!)
Wt gms > 43
ESC Rating > 1-12 A
KV > 650
Rm > 0.285
IO > .36
Efficient Operating Current (Amps) > 2-8
Max Amps (15 sec.) > 11
Max Power Rating > 130W
Max RPM > 20,000
- - - - - - - - - - - - - - - -
Motor > MEGA 16/25/6
Wt gms > 110
Max Amps (15 sec.) > 18
Max Power Rating > 130W
Max RPM > 20,000
M(omega?) > 65
NO LOAD RPM/VOLT > 900

CELLS PROP RPM AMPS CONTROLLER
6 11X7 4780 12.6 Thunderbird 18
7 11X7 5240 15.1 Thunderbird 18
8 11X7 5600 17.6 Phoenix 25
9 11X7 5940 19.6 Phoenix 25
10 10X5 8780 16 Phoenix 25

Make any sense for me?
My goal is to get rid of the gearbox on the Easy Glider. I have no luck with gearboxes. I own the MEGA, but I don't know if it's a mistake to put into the EZG. Any help is greatly appreciated. And if you could take it a step further, what do you think the ESC and battery requirements would be?

Thanks,
Peter

Last edited by omba; 05-05-2006 at 05:04 PM.
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Old 05-05-2006, 08:36 PM
  #2  
slipstick
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Just to get you started
"KV" is the same thing as "No load RPM/volt"
Rm is measuring the same thing as M(omega?) but you need to multiply Rm by 1000 to get the same units i.e. Rm - 0.235 = M(omega?) of 235.

BTW the omega sign means Ohms.

But unless you want to spend all your time doing math(s) get a copy of Motocalc (www.motocalc.com) and use that to compare the motors.

Steve
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Old 05-05-2006, 10:30 PM
  #3  
Jeremy Z
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As you probably read elsewhere, the Himax 2812-0650 is what I'm running in my EasyGlider Electric. I did have to cut out some of the foam in the nose to make sure the motor can didn't rub. The reasons I went this route instead of the gearbox route were:
  1. to eliminate weight.
  2. to save money.
  3. to keep it very quiet.
  4. I love my other Himax outrunner, a 2812-0850.
  • My battery is a PolyQuest narrow 3S 2200 mAh
  • My ESC is a Thunderbird 18
  • My Receiver is a Hitec 05S Micro
With the above setup, I get about 30 climbs. Twice as good as stock, and good enough for me. Some (OK, lots of people) like to have stronger climbs than this. I'm under no illustions that this is a hotliner, and I'm not in that much of a hurry to get to altitude, so this was fine by me. Your mileage may vary. As a result of not trying to cram too much power into it, it stayed light and has a very low sink rate.

Under no thermal condtions, I can fly over 50 minutes on a charge. I left the huge ball bearing weight out of the tail of my EGE when I built it, knowing that I would have a lighter motor thant stock soon enough. Even with the stock motor/gearbox, it didn't need tail weight to balance.

You didn't mention whether you got the Electric version or if you're adapting the un-powered version.

Now, back to your question. The Mega is probably a higher quality motor than the Himax. It's a high-class inrunner, so it is likely more efficient too.

Look at this data page ---> http://www.megamotorusa.com/BrushlessNew/ACn16-25-6.htm

Here's a free online calculator, though it has less data in its database than MotoCalc: http://brantuas.com/ezcalc/dma1.asp

According to that, the maximum current is 18 A, and their efficient operating range is usually a bit below that, so 15 A might be a good target current.

In a sailplane, speed in the motor system is not really important; thrust is. The Mega you mention gives about 34 oz. of thrust on a good 3S LiPo. That will be enough to go nearly vertical, if not vertical with the 10x5 folding prop.

According to EZCalc, you could probably do well with the same 12x6.5 folding prop I'm using on mine. It shows 16.3 A @ 79% efficiency, and 29.3 oz. of thrust.

A bit better efficiency-wise is the 11x8, which comes out to 14.9 A @ 79.5% efficiency.

Hobby-Lobby has both of the props on this page: http://www.hobby-lobby.com/freuden.htm

Match them up with the appropriate Turbo spinner from this page: http://www.hobby-lobby.com/propadap.htm (You'll need item DKT4031)

Do you have a battery pack yet? If so, you might want to base your motor decision on your battery parameters. The go to EZCalc and start trying things.

Assuming you don't have a battery pack yet, I'd stick with your Mega, then buy the biggest 2S LiPo that will fit in the EGE's battery cavity. A Thunderbird 18 speed control will be fine. Then a Freudenthanler 11x8 folding prop and the Turbo Spinner, and you're all set.

Good tip Steve. I liked MotoCalc when I had it, but couldn't justify spending the $40-50 on it when the demo expired.
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Old 05-06-2006, 01:40 AM
  #4  
slipstick
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Originally Posted by Jeremy Z View Post
Good tip Steve. I liked MotoCalc when I had it, but couldn't justify spending the $40-50 on it when the demo expired.
I don't think it's gone up, it's still only $39 for a lifetime (updates have always been free to registered users). That's less than one wrong motor choice .

Still the free online calc is not bad and a lot cheaper. Experience is of course better than all the Calc programs but there is so much equipment around now that it's often difficult to find anyone using the exact combination that you are interested in.

Steve
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Old 05-07-2006, 12:40 AM
  #5  
watt_the?!
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im with steve.....i ALWAYS revert to motocalc when asked or considering choices. It's not limited to just doing these calcs...

it can be used to explore pitch speed, airfoils, stall speeds, load v diam v pitch relationships and more...

the trick is to use it as a reference tool- not an absolute tool.

for instance i use it to get a feel for the expected wattmeter results.

then when i do test, i adjust the values accordingly as the reference has been determined.

many times though ive found it within less than 5% so that's great when that happens.

Tim
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Old 05-13-2006, 04:39 PM
  #6  
omba
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Originally Posted by watt_the?! View Post
im with steve.....i ALWAYS revert to motocalc when asked or considering choices. It's not limited to just doing these calcs...

it can be used to explore pitch speed, airfoils, stall speeds, load v diam v pitch relationships and more...

the trick is to use it as a reference tool- not an absolute tool.

for instance i use it to get a feel for the expected wattmeter results.

then when i do test, i adjust the values accordingly as the reference has been determined.

many times though ive found it within less than 5% so that's great when that happens.

Tim
Well ...
First of all I thnk you all for your advice. So, just for fun I have purchased MotoCalc. Nightmare time for me again!

I used the Wizard. I did NOT know what to input for battery or prop. This is what I got as an opinion:

MotOpinion - Untitled
2ft above Sea Level, 29.92inHg, 59F
Motor: Mega ACn 16-25-6; 900rpm/V; 0.95A no-load; 0.065 Ohms.
Battery: Kokam 910SHD (15C); 2 series x 3 parallel cells; 910mAh @ 3.7V; 0.0275 Ohms/cell.
Speed Control: Generic Brushless ESC; 0.006 Ohms; High rate.
Drive System: Generic 14x7in Prop; 14x7 (Pconst=1.25; Tconst=0.956) direct drive.
Airframe: Multiplex Easyglider electric; 645sq.in; 31.6oz RTF; 7oz/sq.ft; Cd=0.047; Cl=0.54; Clopt=0.68; Clmax=1.26.
Stats: 85 W/lb in; 60 W/lb out; 12mph stall; 16mph opt @ 58% (75:15, 65F); 19mph level @ 64% (70:20, 66F); 1058ft/min @ 46.9; -118ft/min @ -4.7.
Power System Notes:
The full-throttle motor current at the best lift-to-drag ratio airspeed (21.2A) falls approximately between the motor's maximum efficiency current (10A) and its current at theoretical maximum output (53.4A), thus making effective use of the motor.
Aerodynamic Notes:
The static pitch speed (30mph) is within the range of approximately 2.5 to 3 times the model's stall speed (12mph), which is considered ideal for good performance.
With a wing loading of 7oz/sq.ft, a model of this size will have very sedate flying characteristics. It will be suitable for relaxed flying, in calm or very light wind conditions.
The static thrust (38.3oz) to weight (31.6oz) ratio is 1.21:1, which will result in extremely short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and vertical climb-outs. This model will probably be able to perform a hover or torque roll.
At the best lift-to-drag ratio airspeed, the excess-thrust (21.8oz) to weight (31.6oz) ratio is 0.69:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.
General Notes:
This analysis is based on calculations that take motor heating effects into account.
These calculations are based on mathematical models that may not account for all limitations of the components used. Always consult the power system component manufacturers to ensure that no limits (current, rpm, etc.) are being exceeded.


Now I'm really lost!

Any advice?

Thanks again ,
Peter
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Old 05-13-2006, 04:43 PM
  #7  
omba
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Default Thanks Jeremy

Jeremy,
Thanks again for your advice here:
According to that, the maximum current is 18 A, and their efficient operating range is usually a bit below that, so 15 A might be a good target current.

In a sailplane, speed in the motor system is not really important; thrust is. The Mega you mention gives about 34 oz. of thrust on a good 3S LiPo. That will be enough to go nearly vertical, if not vertical with the 10x5 folding prop.

According to EZCalc, you could probably do well with the same 12x6.5 folding prop I'm using on mine. It shows 16.3 A @ 79% efficiency, and 29.3 oz. of thrust.

A bit better efficiency-wise is the 11x8, which comes out to 14.9 A @ 79.5% efficiency.


I wonder if I should just install the MEGA, slap in a 3sLipo, and find any 11" or 12" folder. See that post above? MotoCalc just confuses me.

What you say out there?

TIA,
Peter
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Old 05-13-2006, 09:23 PM
  #8  
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Heh, the latter is my approach most times. Sure, I own Motocalc, and it's fun to get in the general range, but nothing beats taking your chosen motor and experimenting with props and power until you find the one that suits your flying style well.
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Old 05-15-2006, 01:53 AM
  #9  
Dr Kiwi
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If you think you need to limit yourself to ~15A, here's what Motocalc says for 3s with an 11x4 [the 11x8 mentioned above draws 23.2A, and the 12x6.5, 23.9A, according to Motocalc!]

Motor: Mega ACn 16-25-6; 900rpm/V; 0.95A no-load; 0.065 Ohms.
Battery: Thunder Power TP2100 (ProLite); 3 cells; 2100mAh @ 3.7V; 0.018 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: Direct; 11x4 (Pconst=1.06; Tconst=0.995) direct drive.
Airframe: Anything you want.
Motor Amps = 15.4
Motor Volts = 10.2
Input (W) = 156.8
Prop RPM = 8195
Thrust (oz) = 34.2
PSpd (mph) = 31.0
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Old 05-16-2006, 12:49 AM
  #10  
omba
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Default Motocalc Madness

Originally Posted by Dr Kiwi View Post
If you think you need to limit yourself to ~15A, here's what Motocalc says for 3s with an 11x4 [the 11x8 mentioned above draws 23.2A, and the 12x6.5, 23.9A, according to Motocalc!]

Motor: Mega ACn 16-25-6; 900rpm/V; 0.95A no-load; 0.065 Ohms.
Battery: Thunder Power TP2100 (ProLite); 3 cells; 2100mAh @ 3.7V; 0.018 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: Direct; 11x4 (Pconst=1.06; Tconst=0.995) direct drive.
Airframe: Anything you want.
Motor Amps = 15.4
Motor Volts = 10.2
Input (W) = 156.8
Prop RPM = 8195
Thrust (oz) = 34.2
PSpd (mph) = 31.0
Well ...
I just want to get my EZG built!
Not exactly ... see? I want to understand why I'm doing what I'm doing as well. :o

When I launch and update my MotoCalc and look through the Graupner Folding props, I can't find 11" or 12" or whatever. Any ideas what I've done wrong? I've even loaded up my MotoCalc screen.

Thanks for your patience,
Peter

PS > BTW ... I am DEFINITELY using the MEGA 16/25/6 unless someone tells me otherwise. I'll did up a 3s Lipo in the 1800-2200 range. Should work, right?
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