C-47 Building tips. - Page 2 - RC Groups
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Aug 11, 2004, 08:34 AM
MINE!
Mick Molloy's Avatar
Quote:
Originally Posted by Ben_E
Slow scale roll????

That's one c-47 manouver I haven't heard of before! lol what did the paratroopes say??

Ben_E
Good point

Here is a pic of the second take off.
It was a very short ROG before the C47 get airborne.
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Aug 11, 2004, 10:09 AM
Alphabandaid
FYI, my dc3 amped aout at 19-20 amps using a vario 3 blade adjustable prop setup with minimum pitch! Havent flow it yet, wind rain big time.
HOvertime, did you use the stock blades in your measurements? If so the vario 3 blade minimum pitch pulls the same load. Wonder how it'll perform?
Aug 11, 2004, 11:08 AM
Registered User
Quote:
Originally Posted by Hovertime
I have Pixie 20P for esc, and motors have some RPM fluctuation, Anybody else has noticed this?
My friends Slow Stick had same problem, was cured by installing diode across motor terminals, I think I'll do it for C-47 motors too.
Great tips guys!!!
I noticed you have a question in the CC forum about the motor fluctuation problem. I'm curious about this too.

Did you do any break-in on these motors before using them?

For instance, I ran both 300H motors in parrallel, no load on 3V alkaline cells for 30 minutes as a way of seating the brushes.

I'm wondering if your motor, or motors may just need to be run - no load for a while.
Aug 11, 2004, 03:02 PM
Always right
Hovertime's Avatar
My motors are broken in for a few hours with one cell.
They are new, and I have no others to test.
Amp draws were tested connecting wattmeter between esc and different batteries, with different cell counts and different states of charge, thats how I got different voltages, measurements taken at WOT.
At full throttle brushed esc acts as a piece of wire.
These motors had stock 5x3 prop. they are real amp guzzlers
And small round cell loose A LOT of voltage under those loads....
Aug 11, 2004, 03:05 PM
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Hovertime's Avatar
Oh, and forget motocalc
Aug 11, 2004, 03:44 PM
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Hovertime's Avatar
BTW motors run at constant speed with no fluctuations when connected directly to a battery.
Aug 11, 2004, 04:08 PM
Registered User
Quote:
Originally Posted by Hovertime
BTW motors run at constant speed with no fluctuations when connected directly to a battery.
Now that's a point the folks at CC should know as part of your question.

Could it be that your programed LVC is set to high?

I had first set my Pixie-20 to 6V LVC, (using 2S lipo) but I noticed while using the Astro Whattmeter, the soft motor cut-off would start cutting off at almost 7 volts. I reset to 5V and now soft cut off starts at 6.1V.

Suppose I'll have get one of the USB thingies one day.
Aug 11, 2004, 04:47 PM
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Hovertime's Avatar
Few more numbers-
CBP 650 8 cell nimh 2/3 AA pack - when 200 mAh were used - Voltage -6.6, Amps 15.
CBP 1400 8 cell nimh AA pack when 200 mAh were used - Voltage 7.7V Amps 17.8
Radioshack 1600 8cell AA nimh after 200 mAh were used - 6.5V 14.2A.
Aug 11, 2004, 05:25 PM
Registered User
I have been folowing this and another thread on the C-47.

Mine is almost ready for maiden, but the current figures scare me.

Does anyone have tests done on a series wired setup with 2 and 3 cell lipos?

No way can you pull 17 amps from a Kokam 1500 3s1p without puffing it. Right?
Maybe a TP2100......
Aug 11, 2004, 06:13 PM
Registered User
Quote:
Originally Posted by Hovertime
Few more numbers-
CBP 650 8 cell nimh 2/3 AA pack - when 200 mAh were used - Voltage -6.6, Amps 15.
CBP 1400 8 cell nimh AA pack when 200 mAh were used - Voltage 7.7V Amps 17.8
Radioshack 1600 8cell AA nimh after 200 mAh were used - 6.5V 14.2A.
I wish I knew how you are getting those high amp numbers. Somethings draging on those motors

I just now hooked up my DC-3 through my Astro Whattmeter to my 2S2P 2400mAh Lipo and got a reading of just over 12A @ 6.5V at full power. It's been running that way since I started flying it. The highest reading I ever had was when I first connected both motors, with stock props, directly through the Wattmeter to a freshly charged 2S 2400mAh Lipo: Just over 14A.

I know you need adequate amps from the battery, or the voltage drops so quick that the ESC cuts out. I had to program the Pixie-20P to soft cut off so I could use the Kokam 2S 1200mAh just for test runs.

When I set 1/2 power/stick at the transmitter and the wattmeter hooked up I have a reading of 6.5A. I normally fly 3, 5 minute flights , mostly at half power on 2S2P 2400 Kokam Lipos.

Also noted that my Kokam Lipos perform best after the third charge cycle.
Aug 11, 2004, 07:13 PM
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Hovertime's Avatar
Quote:
Originally Posted by VBSuperMaxx
No way can you pull 17 amps from a Kokam 1500 3s1p without puffing it.
According to my amp draw measurements I estimate 3S lipo amp draw way above 20A. (with capable cells of course)

Please also note that my motors got very hot with 8 cell AA pack, after it consumed only 200 mAh at WOT and voltage under load of 7.7-8V and amp draw 17-18A.
Aug 11, 2004, 07:16 PM
know it all
that sounds better David, ecalc predicts 11.4Amps at that voltage setting..how does the airplane perform at that power level?

Herm

Quote:
Originally Posted by David A Ramsey
I wish I knew how you are getting those high amp numbers. Somethings draging on those motors

I just now hooked up my DC-3 through my Astro Whattmeter to my 2S2P 2400mAh Lipo and got a reading of just over 12A @ 6.5V at full power. .
Last edited by hermperez; Aug 11, 2004 at 07:23 PM.
Aug 11, 2004, 07:23 PM
Always right
Hovertime's Avatar
Quote:
Originally Posted by David A Ramsey
I wish I knew how you are getting those high amp numbers. Somethings dragging on those motors
I just checked props, and yes they are 5x3 (GWS EP50x30)
Motor turn very freely, no binding.
Wattmeters are not very precise instruments at low loads like these....
Also another explanation is that your lipos are pulsing voltage at a very high rate, (ripple current) and are outputting effective voltage lover than the average that watt meter shows. Round cells voltage is stable. Also-you may be not getting full throttle? Or high resistance wires/plugs? Whats your field elevation? temperature?
Anyways our results are not that far from each other , and still far from GWS charts.
Aug 11, 2004, 07:43 PM
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Hovertime's Avatar
Another thought-maybe I got wrong motors?
More numbers 7.2V 16.8A 15800rpm.
(motocalc prediction: 7.3V 12.9A 14000 RPM) What motor do you use in ecalc?
Aug 11, 2004, 09:13 PM
Registered User
I just completed my Skytrain.

Series wired motors....

Castle Creations 25 Sprite ESC

Thunder Power 2100 3s1p

Full throttle.........6.9 amps max.

Plenty 'o thrust ....maiden set for the next calm day. (please let it be tomorrow.)

I live near the Windy City.....Chicago...but it was called Windy because of braggarts not Mother Nature.

I forgot what the watt reading was on the Astro meter. but it was under 100w .

Harromeo in the other threads was right.....series and 3s1p is the ticket.

Of course after the maiden I will report flight times and capacity taken from the battery. Fingers crossed.

I did mine in the D-Day paint scheme...painted Olive Drab over the silver on top. The decals make it look cheesy.....I will paint it completely if it is still in one piece after the maiden. 10 feet away it looks cool. I guess that is all you can ask for.


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