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Rudderless
11-03-2005, 02:06 AM
I want to use a li-po battery in a Giles G-202. It has a Cobalt 400 direct drive motor already installed. First, can I do it? Second, how?

Dr Kiwi
11-03-2005, 02:39 AM
This seems reasonable - but I've never run one of these Cobalt 400's so take what i say under advisement!: most charts seem to indicate 7-8 cells max, so 3s might be too much - but it is said to be a 200W+ motor and I would have thought 20A-25A might be okay.

Motor: Wattage super cobalt 400; 2395rpm/V; 3A no-load; 0.1 Ohms.
Battery: Thunder Power Pro Lite 2000; 3 cells; 2000mAh @ 3.7V; 0.007 Ohms/cell.
Speed Control: Castle Creations Pegasus 35; 0.0015 Ohms; High rate.
Drive System: Direct; 7x4 (Pconst=1.11; Tconst=1) direct drive.
Airframe: Anything you want.
Motor Amps = 21.9
Motor Volts = 10.6
Input (W) = 232.0
Prop RPM = 13844
Thrust (oz) = 19.3
PSpd (mph) = 52.4

Please wait for others to chime in - I don't want to tell you the wrong thing.

If you drop down to 2s you could increase prop size considerably.

Cheers, Phil

Matt Kirsch
11-04-2005, 02:12 PM
Yeah, a 3S will definitely shred the Wattage Cobalt 400. It has enough problems on 7-8 cells, unfortunately. Unfortunate, because it's a real screamer of a motor...

I was running 8 Sub C cells on mine and it was drawing 16 Amps with a 5x5 prop. With a 7x4, I would expect the draw to be in the mid 20's. I would plan for at least 30A worth of capability in the pack, so that's around 3000mAh for your typical 10C pack these days.

For sure, a nice robust pack like a 2S Kokam 3200 (20C) would easily handle anything the motor could throw at it. It's a little pricey, but if you price out the other options, you won't see much difference.

Dr Kiwi
11-04-2005, 04:28 PM
Here is what Motocalc says: Motocalc was several amps low with Matts 5x5 scenario (14A rather than the 16A he measured) - so perhaps just under 25A here???

Motor: Wattage Super Cobalt 400; 2520rpm/V; 3A no-load; 0.1 Ohms.
Battery: Thunder Power Pro Lite 2000; 2 cells; 2000mAh @ 3.7V; 0.007 Ohms/cell.
Speed Control: Castle Creations Pegasus 35P; 0.0015 Ohms; High rate.
Drive System: Direct; 8x6 APC SF (Pconst=1.29; Tconst=1.29) direct drive.
Airframe: Anything you want.
Motor Amps = 21.6
Motor Volts = 7.1
Input (W) = 152.9
Prop RPM = 7779
Thrust (oz) = 16.2
PSpd (mph) = 44.2

Only thing to do is try it and measure what it REALLY does.

Cheers, Phil