Joined Sep 2005
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
* 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.
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
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.
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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