Will this power system blow up? - RC Groups
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Sep 29, 2005, 02:51 PM
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Will this power system blow up?

Here is my planned setup:

Mountain Models Magpie
* Weight 20 to 35 ounces depending on whether flying light or with AP gear

HiMaxx 2025-4200
* Kv: 4200, Io: 0.75 A, Rm: .075 Ohms

Castle Creations Thunderbird - 18
* Cells Lithium: 2 - 3
* Continuous Amps: 18
* BEC: 5V

Apogee 2170 mAh 10.5C 3S1P 11.1V
* Continuous Discharge: 10.5C / 22.8 Amps
* Burst (5-10 seconds): 14C / 30 Amps

6.6 : 1 (will have optional choices 5.3:1 and 4.4:1)

12 X 8 (will have optional 11 X 7)

I have heard that a similar setup has worked well for others. The primary difference is that I am going to use a CC Thunderbird 18 rather than the CC Phoenix 25. Is this difference going to create a big problem for me or will it be OK? Thanks for any comments or suggestions.

Oh, I will be flying mostly slow and sedately, but might like to do the odd near vertical climb.

Last edited by johnhay73; Sep 29, 2005 at 03:10 PM.
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Sep 29, 2005, 04:46 PM
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Dr Kiwi's Avatar
If one believes Motocalc, with the 12x8 on 6.6:1, it looks to be in line with the 20A max 175W limit for that motor:

Motor: HiMaxx HA2025-4200; 4200rpm/V; 0.75A no-load; 0.075 Ohms.
Battery: Thunder Power 1900 (G2); 3 cells; 1900mAh @ 3.7V; 0.012 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: Plastic; 12x8 (Pconst=1.06; Tconst=0.995) geared 6.6:1 (Eff=95%).
Airframe: Anything you want.
Motor Amps = 16.0
Motor Volts = 10.4
Input (W) = 166.5
Motor RPM = 38211
Prop RPM = 5790
Thrust (oz) = 33.5
PSpd (mph) = 43.9
Sep 29, 2005, 04:49 PM
Registered User
Thanks for the vote of confidence Dr Kiwi. This is my first ever self configured motor system so I am constantly second guessing myself.
Sep 29, 2005, 09:43 PM
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Dr Kiwi's Avatar
Originally Posted by johnhay73
Thanks for the vote of confidence Dr Kiwi. This is my first ever self configured motor system so I am constantly second guessing myself.

Please test it with a Whattmeter to see if Motocalc is to be believed. Generally it is in the ballpark, but sometimes it doesn't model particular motors too well.
Sep 30, 2005, 12:33 AM
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BEC's Avatar
Just looking at that and thinking about my own Himax experience, you should heed the good Doctor's advice and MEASURE it. I suspect a little smaller prop would be better (i.e. the 11x7). A little more useful thrust will be had with the APC prop vs. the GWS. An APC 12x6SF might be worth trying, too.

The T-18, as long as you don't exceed 18A by much or often, will be fine.

Dr. K - the Thunderbird-18's specs aren't quite as good as the Phoenix-25 but it's probably close enough for estimating with MotoCalc.

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