Skywalker 168cm FPV plane - Page 525 - RC Groups
Jun 22, 2011, 09:22 PM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by Cralis Thanks man! I'll keep that formula in mind. I'm not sure how it works out though. To me, the mah is the mount of petrol the tank can hold... So how does a tank with more capacity, effect the C (Which I am not sure what that represents, but I thought it was how tough a battery is...). Wait, this is way off topic, so let me add ... Anyone else flying 500mah packs in their Skywalkers ?
C=Current rating. A 20C 1000mAh pack means it's rated to deliver 20x1000mA (or 20x1A) for 20A of constant current while holding voltage. A 20C 5000mAh pack is cable of 20x5A for 100A of constant current. That doesn't mean your power system will draw more amps though. Your power system will only use what it requires. A higher capacity and higher C rated battery is able to supply the current easier than a smaller capacity and smaller C rated battery.

Okay, I said a higher C rated battery doesn't mean your power system will draw more amps...sorta. In most cases it actually will. That is because of the voltage drop under load. A lower capacity/C rated battery will have a reduced voltage under load. A higher capacity/C rated battery will hold a higher voltage under load. Amps=Voltage/Resistance. Resistance is pretty much fixed via the windings in the motor and design of the ESC. Consider resistance a fixed value that doesn't change. Let's say a low capacity/C rated battery only holds 10v under load and a larger capacity/C rated battery holds 11v. Both batteries are connected to a power system measured at 2ohms. The 10v battery will draw 5A (10v/2ohms). The 11v battery will draw 5.5A (11v/2ohms). So the larger capacity/C rated battery will actually allow the system to draw more amps, which equates to more power. All very confusing at times. Just consider larger capacity and higher C rating means easier ability to provide the amps the power system wants at a higher voltage.

Lastly (on the C rating stuff). Don't take C rating as gospel. It is often exaggerated as part of the marketing. I just knock of a couple of C's for a rough guesstimate of what it can actually do. So a 20C battery if probably more truthfully like an honest 15C, A 30C like a 25C, etc. Either way, the larger the pack and the higher the C rating the easier the battery can provide amps while holding a higher voltage level.

As for the second part of your question. Yes, I fly my SkyWalker with a 5000mAh, 3S, 40-50C Turnigy battery. The SW handles the weight with no issues. I cruise around in the 6A-8A range at ~24mph/38kph.
Jun 22, 2011, 09:27 PM
OSUFPV - KF7VFT
Quote:
 Originally Posted by Vantasstic So the larger capacity/C rated battery will actually allow the system to draw more amps, which equates to more power.
Actually, in your example it equates to a constant power. (P=IV)
Jun 22, 2011, 09:39 PM
'FPV'er...not a "LOS'er
Quote:
 Originally Posted by Blueshy Actually, in your example it equates to a constant power. (P=IV)
Well, maybe more to 'apparent power' (P=IV), where 'real power' is P=I2R. All mute really as the higher the current and voltage the higher the power in Watts. A higher C pack should provide higher amps since it's holding a higher voltage under load so the overall power is also increased.
Jun 22, 2011, 09:41 PM
Registered User
Quote:
 Originally Posted by Blueshy Actually, in your example it equates to a constant power. (P=IV)
Actually no. That was the whole point of the example. Read it again.
The current draw is more or less fixed by the demand of the motor, but the voltage of a
lower C battery may drop under load so P=IV means less total power delivered.
A higher C battery is less likely to drop the voltage under high load, so
given a fixed current draw, and higher voltage, it delivers more power.

Before one jumps to the conclusion that higher C is always better, remember the SW
and most other FPV planes only need 30-40Amps at most, so a 20C 5Ah battery (capable
of delivering close to 100A draw) won't sag at all, and a 25C or 30C battery offers no
benefit at all. It'd be a different story if we were talking 2000mAh batteries at 15-20C rating
for a small fast plane like a Funjet with a hot motor.

ian
Last edited by Daemon; Jun 22, 2011 at 10:02 PM.
Jun 22, 2011, 09:57 PM
OSUFPV - KF7VFT
Quote:
 Originally Posted by Daemon Actually no. That was the whole point of the example. Read it again. The current draw is more or less fixed by the demand of the motor, but the voltage of a lower C battery may drop under load so P=IV means less total power delivered. A higher C battery is less likely to drop the voltage under high load, so given a fixed current draw, and higher voltage, it delivers more power.
Oops, you're all right. I totally missed the point that he was trying to make.
Jun 22, 2011, 10:14 PM
SLO Flyer
Beautiful video, Tom. Favorited.

Quote:
 Originally Posted by tom223866 little flight with my skywalker, lawmate 2,4 500 and scherrer uhf http://vimeo.com/25464739
Jun 22, 2011, 10:36 PM
Fly Chitty Chitty Bang Bang!

# Has anyone vertical flown the SW?

I am thinking about doing a vertical strait lift for about a min on the SW.
If moto calc calculates right This configuration will do 2419ft(737m)/min @ 90°.

Here is the analysis.

1000ft above Sea Level, 29.92inHg, 55°F

Motor: Scorpion SII-3026-1190; 1190rpm/V; 3.26A no-load; 0.008 Ohms.
Battery: 11600 LIPO (25C); 3 series x 2 parallel cells; 11600mAh @ 3.7V; 0.0015 Ohms/cell.
Speed Control: Scorpion Commander 110A; 0.0008 Ohms; High rate.
Drive System: APC 10"; 10x6 4-bladed (Pconst=1.11; Tconst=1) direct drive.
Airframe: Skywalker; 550sq.in; 92.5oz RTF; 24.2oz/sq.ft; Cd=0.068; Cl=0.87; Clopt=0.95; Clmax=1.72.
Stats: 156 W/lb in; 136 W/lb out; 19mph stall; 26mph opt @ 47% (255:04, 87°F); 27mph level @ 48% (264:21, 87°F); 2419ft(737m)/min @ 90°; -177ft/min @ -4.4°.

AirSpd Drag Lift Batt Motor Motor Input Loss MGbOut MotGb Shaft Prop Thrust PSpd Prop Total Time
(mph) (oz) (oz) Amps Amps Volts (W) (W) (W) Ef(%) Ef(%) RPM (oz) (mph) Ef(%) Ef(%) (m:s)

17.0 2.8 35.9 83.9 83.9 10.8 909.9 119.7 790.2 86.8 84.9 11662 106.7 49.3 28.5 24.2 16:36

I think the stiffening of the tail will need to be done. The plane oscillates with speed.
All opinions accepted.
 Jun 22, 2011, 11:46 PM I love FPV! Elevator throws... Are you all using maximum deflection, or are you dialling it down a bit? I am going to maiden mine soon, and wondering if I will battle with full deflection.
Jun 23, 2011, 12:08 AM
FPV junkie
Quote:
 Originally Posted by Cralis Elevator throws... Are you all using maximum deflection, or are you dialling it down a bit? I am going to maiden mine soon, and wondering if I will battle with full deflection.
I put mine into the ground for not having enough deflection.

I have it at full deflection.

& I am using the mechanical Anti reverse yaw technique that is described in previous posts.

essentially offset the servo horns one notch to the back, so you get more upward deflection than down.

When you go into a bank, it helps to pull it around, instead of the lower one pushing it in the wrong direction.

Mike
 Jun 23, 2011, 12:12 AM Registered User My SW does loops and dodges between trees with +/- 5 to 7 mm of elevator deflection and the CG somewhere beyond 30mm behind the servo wire slot. The further ahead of that your CG, the more elevator throw you'll need. ian Latest blog entry: 2015 Best of FPV vid and wrap up...
 Jun 23, 2011, 12:14 AM FPV junkie Earthorbiter, I have seen some steep climbs in youtube. search Skywalker FPV, and Clouds. I think that will pull up what you are looking for.
 Jun 23, 2011, 12:15 AM I love FPV! I just put in my 5000mah pack, and find I am still tail heavy. So I added an extra 2200mah pack (dead weight - not functional), and it's perfect. So, might have to fly with dead weight... OR ... remove my power for my camera/vtx from my harness, and power it off the spare 2200mah pack... Maybe that would be a good idea? Lots of work though...
 Jun 23, 2011, 12:24 AM Registered User Define "tail heavy"? Where is your CG? If it's anywhere near the wiring slot, then it's actually severely nose heavy. 25-35mm behind the wiring slot is a better range. Where I run the CG, I can't put a 4 or 5Ah battery anywhere near the nose. If you need 7A worth of battery to balance it, something is very wrong. ian Latest blog entry: 2015 Best of FPV vid and wrap up...
Jun 23, 2011, 12:29 AM
Fly Chitty Chitty Bang Bang!
Quote:
 Originally Posted by m_beeson Earthorbiter, I have seen some steep climbs in youtube. search Skywalker FPV, and Clouds. I think that will pull up what you are looking for.
Thanks, M B.
I will look for a 1 min climb there.
 Jun 23, 2011, 02:22 AM Registered User Short of reading all 500+ pages, is there a synopsis of the "must-do" mods for the SW? Mine arrived yesterday, and I'd like to know what's in front of me, assembly-wise.