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Old May 22, 2001, 07:59 AM
JP
Registered User
Portugal
Joined Mar 2001
59 Posts
What's wrong in electric flight world?

I'm currently trying to get the performance of the following setup:
Graupner 400 6V
Graupner 2,33:1 gearbox
8"x6" Graupner Slim Prop
10 cell 600AE

MotoCalc 6 gives me (no temperature effect):
11v motor
11Amps
9200 rpm (wow!!)

Well I don't get this kind of numbers (particularly rpm...). I get:
7500 rpm @ 10A, with less V than expected which could justify some loss in rpm but no way will justify 1700 rpm!

This setup is to be used with my Little Extra (E-Zone plans, Jim Young) and I must say that the numbers I get in paper seems pretty good. Motocalc numbers give me 30║ climbout, which should be good for this kind of plane.

My experiences were because:

*this weekend I've tried to fly the plane with a SP400 6V, 1,85:1, 8"x6" on 8 cells
*the plane crashed after my fear of not so good flying. I was expecting a much stronger climb.
*I believe top rpm (pack fresh out of charger) was 7500 and stablizing fast in 7000-6800 range
*Motocalc give me 8300 RPM in this conditions

1.Anyone was experience in this kind of setup (X-250 for instance)? What are your numbers?
2.Are the Speed 400 constants wrong or somewhat "inconstant"?
3.The 11V number (10 cells pack) is realistic? or it's the INITIAL value? (the same to RPM'S and VOLT's)


JP
Lisbon, PORTUGAL
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Old May 22, 2001, 09:05 AM
p471701
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jp:
i believe the x250 set up uses a 7.2v s400 motor on 10 cells.
i use the 6vs400 2.33 graupner setup with 8x600ae's (w9x6apc)on a 23oz,ferias and the performance is very good.............gregg

[This message has been edited by p471701 (edited 05-22-2001).]
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Old May 22, 2001, 09:28 AM
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stefanv's Avatar
Moorefield, Ontario, Canada
Joined Mar 2001
315 Posts
If you turn the temperature compensation on, you'll get a prediction of 9.8A and about 8700 RPM. The RPM is still a bit high, most likely because the motor is running _so_ hot, that the temperature compensation is losing accuracy.

Stefan
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Old May 22, 2001, 09:47 AM
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Rochester, NY, USA
Joined Aug 2000
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Typically, you use 8 cells on the geared 6v Speed 400 motor and 10 cells on the 7.2v motor.

With the 2.33:1 gearbox, use the Graupner SLIM 9x5 prop.

With the 1.85:1 gearbox, use the Graupner SLIM 8x4 prop.
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Old May 22, 2001, 06:01 PM
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Canada
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If you absolutely must play with Sim programs.. Try Maxis "The Sims" just as usefull and a lot more fun.
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Old May 23, 2001, 04:14 AM
JP
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Portugal
Joined Mar 2001
59 Posts
Quote:
Originally posted by stefanv:
If you turn the temperature compensation on, you'll get a prediction of 9.8A and about 8700 RPM. The RPM is still a bit high, most likely because the motor is running _so_ hot, that the temperature compensation is losing accuracy.

Stefan
Stefan, I believe the constants are wrong, not your calculations, but even so, is stange so many people have used your program and there aren't many saying SP400 constant are wrong... after all this must be one of the most used motors.

JP
Lisbon, PORTUGAL
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Old May 23, 2001, 04:52 AM
JP
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Portugal
Joined Mar 2001
59 Posts
Here is a copy of my message to E-Flight list:

Last night I take some data including Permax 480 and Speed400 6V, 2,33 and 1,85 gearbox.
(I haven't tried some combination explained here because I'm only reading them now, 10.00am in Portugal, - about 5pm in east US I think)
I prefer to take some "points" rather than one point (typically the maximum), because comparisons are more evident.

PERMAX 480
==========
2,33:1
10 cells

CAM SLIM PROP 8"x6"
7,5k@9,6A@10,88V
7,3K@9,3A@10,09V
7,1K@8,8A@9,81V
7,0k@8,7A@9,69V (after 55 seconds)

CAM SLIM PROP 9"x5"
7,7k@10,0A@11,21V
7,5K@9,9A@10,82V
7,4K@9,3A@10,25V
7,2K@9,0A@10,05V (after 54 seconds)

After all these tests the motor stays only slightly warm.

SPEED 400 6V
============
2,33:1
10 cells

CAM SLIM PROP 8"x6"
7,1K@9,8A@11,19V
7,0K29,8A@10,60V
6,9K@9,6A@10,53V
6,8K@9,3A@10,34V
6,7K@8,9A@10,03V
6,6K@8,6A@9,89V (after 32 seconds)

CAM SLIM PROP 9"x5"
7,1k@9,7A@???V
7,0K@9,3A@10,23V
6,9K@8,8A@9,87V
6,7K@8,5A@9,79V

After these tests the motor stays only warm ("more warm" than PERMAX480)


SPEED 400 6V
============
1,85:1
10 cells

CAM SLIM PROP 8"x6"
7,3k@13,7A@9,99V
7,1k@12,9A@9,33V

CAM SLIM PROP 9"x5"
7,1K@12,4A@9,49V
6,9K@11,7k@9,31V

Motor gets hot very fast, guess why?....

After all,

JP
Lisbon, PORTUGAL
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Old May 23, 2001, 07:21 AM
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Jim Ryan's Avatar
Cincinnati, OH USA
Joined Oct 2000
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Originally posted by JP:
Stefan, I believe the constants are wrong, not your calculations, but even so, is stange so many people have used your program and there aren't many saying SP400 constant are wrong... after all this must be one of the most used motors.

JP-
Motor constants are easily measured with basic instruments. I don't have a copy of MotoCalc with me, but I'm confident that they're accurate within acceptable tolerances.

MotoCalc and ElectriCalc are both very handy tools. But they are also pretty simple tools. They're meant to offer a reasonable estimate of performance based on a few input variables. It's unrealistic to expect them to accurately model the effects of extreme heating on cheap ferrite motors being operated far outside the manufacturer's specs.

Now, you ask why the observed RPMs would be so much lower than MotoCalc's forecast which estimates 11 volts from the 10 X 600AE pack. In the real world, these AE cells are subject to significant voltage depression owing to their internal resistance. For rule of thumb estimates (and to make the math easy), I assume I'll get 1 volt per cell.

You said: 7500 rpm @ 10A, with less V than expected which could justify some loss in rpm but no way will justify 1700 rpm!

The voltage constant of the 6V Speed 400 is 2672. You're using a 2.33:1 gearbox. Depending on the prop and other factors, you could certainly lose 1,000 RPM or more if input voltage dropped by a full volt (likely in this application). How much friction is your gearbox adding? The Slim prop has pretty wide chord blades; do you think you're capturing that added load?

*this weekend I've tried to fly the plane with a SP400 6V, 1,85:1, 8"x6" on 8 cells
*the plane crashed after my fear of not so good flying. I was expecting a much stronger climb.


I fly the Lavochkin La-5FN that I got from Guy Fawcett with this exact system except I'm only using an 8 X 4 prop. Even with an AUW of 21 ounces, the plane climbs away with authority and has acceptable vertical for its weight. I don't fly it often because it's a tip-stalling beast, but the power is more than adequate.

1.Anyone was experience in this kind of setup (X-250 for instance)? What are your numbers?

The X-250 uses a 7.2V motor, so it's not being operated under the extreme conditions your 6V motor is.

2.Are the Speed 400 constants wrong or somewhat "inconstant"?

In a word, no. Motor constants are tested on the bench in a "no-load" condition, and they make no attempt to capture what happens when the motor is subjected to high current and a heavy load.

3.The 11V number (10 cells pack) is realistic? or it's the INITIAL value? (the same to RPM'S and VOLT's)

You make a good point in asking whether the voltage is an initial value. After all, in the real world, voltage, current and RPM are going to change throughout the flight. There is simply no way a $50 computer program is going to model that. It shouldn't have to.

Jim
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Old Jun 06, 2001, 04:12 PM
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Santa Maria, CA USA
Joined Mar 2001
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I usually use my clipped Zagi to experiment with S400 power options. It crashes well, and I can fly it from 19oz to 30oz depending on cell size. As an airframe it may not be that helpful, but across power options it gives me a good relative base.

Regarding the 1.85 8x7... I think that pitch is way too aggressive for that motor or geaarbox. Take your pick.

With a standard 6v S400 or Dymond 480 (Permax 480) and 8 cells I've had decent results with 1:85 and an 8x4 (as Jim Ryan also reports). It's not terribly quick, but it thrusts well and is pretty efficient.

Moving to an APC 8x5 resulted in the amp draw and rpm going down. Thrust and efficiency OK at part throttle, but the setup doesn't seem to yield much useable above 75% throttle. Which leads me to believe those motors can't turn that aggressive a prop fast enough due to the diameter. I can only imagine the same with the 8x6 or 8x7. On a 1.85 they would just result in bad efficiency and comparatively huge amp draw. In essence, you're giving it up in heat.

Interestingly, at 1/2 throttle the 8x5 thrust more than the 8x4 and is more efficient to boot. But the 8x4 can spin faster at the top end. I must admit it's strange to see the 8x4 draw more at 100% than the 8x5, but it does with me.

I have had good results with a 7x7, on the other hand. RPM is higher than the 8x4 or 8x5. Amp draw is greater (I think around 13.5 static w/Dymond 480), and speed and thrust are up. Of course it's not as efficient as the 8x4, but it's also a hotter setup capable of good thrust and speed, considering the 1.85 ratio.

I measure draw with a Whattmeter, but unfortunately I ear the rpm. I need to get a tachometer, or build one.


Jeff
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Old Jun 06, 2001, 05:09 PM
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broddarn's Avatar
Gothenburg. Sweden
Joined Jan 2001
28 Posts
I was using 1.85 with a 6*7 prop. Worked well but the 600AE 8cell pack didn┤t give too much power I think.
Now with 500AR 8 cells it is much better.


Gunnar.
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Old Jun 07, 2001, 01:35 AM
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Novara ,ITALY
Joined Sep 1999
522 Posts
Maybe I'm off way... but have you tried to run the numbers with the 7.2V one? These motors are 99% Mabuchi re-labeled, maybe a wrong label... just an idea.
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