Discussion Will It Blow Up?

 #1 The_Red_Baron Oct 11, 2012 03:31 PM

Will It Blow Up?

Hello All,

I'd first like to state that I've done research about power systems, and it seems the more I do, the more I get confused. I've used WebOcalc and have made the best educated guess I could and now I ask all here, to let me know if it will blow up (Granted, I could use a multi-meter but there should be a non-experimental answer).

Model: GWS Slow Stick

Motor: Turnigy 950 Kv, 243 W max, 23.2 max Amps,

http://www.hobbyking.com/hobbyking/s...ner_Motor.html

ESC: Red Brick 30 Amp

Battery: 2200 mAh, 3S, 11.1 Volt, 25C

Prop: APC 10 X 5

Total Weight: Approximately 30 oz

Thanks to everyone for the help!

-Red

 #2 Dr Kiwi Oct 11, 2012 03:39 PM

At 70g, ~210W is probably a more prudent maximum... but looking at these test results:

static tests on 3S:
Prop/A/W
8x6 8.3 98
10x6 12.5 140
10x7 16.2 190
11x7 21 230
13x4 21.8 240

11x3.8SF 16.2 190
11x4.7SF 20.5 225

a 10x5 should certainly be okay for it [in fact well below its rating!... it may well draw <12A]

 #3 The_Red_Baron Oct 11, 2012 04:06 PM

Thanks Dr. Kiwi, that makes me feel better.

I forgot to mention we are at an elevation of 8,000 ft.

 #4 Dr Kiwi Oct 11, 2012 09:32 PM

At 8000' I'd bet you can go up in prop diameter quite a bit and still not be over-taxing the motor.

 #5 scirocco Oct 11, 2012 10:22 PM

I used the D2836/11 that is in ECalc, then modified for Kv=950, and just tweaked the I0 and Rm a little, and got a similar 11x7 sea level current as Dr Kiwi's test data.

In eCalc, sea level to 8000 feet, same prop is a drop in static current from about 20.5A to 15.3A. The 10x5 estimate is only 10A at 8000ft.

I'd recommend the extra pitch because for the same indicated airspeed the wing is flying on, at altitude the prop is seeing a higher true airspeed and thus will want a higher blade angle/pitch speed.

 #6 jackerbes Oct 12, 2012 10:27 AM

The Slow Stick tend to pitch the nose up as power is increased because the motor mounting does not allow the thrust line to be set down and to the right a little.

A mount like this one will let you put some washers between the back of the motor and mount to get some thrust angle change:

http://www.horizonhobby.com/products...mount-EFLM1915

I used three flat washers on the top hole to get the down thrust and 2 on the left to get some right thrust.

The mount will work on a 16mm x 16mm or 16mm x 19mm hole pattern. You may have to shorten the screws a little to make sure they do not go into the motor more than 4-5 turns. If they go in too deeply they can damage or short out the windings.

Jack

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