[Flying fisho]

Am on the home stretch with my eratix. Power setup as follows.
60 amp plush speedie, 15 x 6 prop, Turnigy G32 motor 770kv. (HK specs say max 42 amps Max 620 w)
Fired up on 3s 4500. Full power showed 48amps & 520 w.
Exceeded max amps, not sure what to tone down. HK suggested props 12x8 - 14x10.

[Raptorfly]

Hey Wayne
15x6 on G32 sounds very big.
Prop down and you will reduce the amps.

[Flying fisho]

Being a 3D plane, want to achieve thrust greater than its 1.8kg flying weight. Had an 11x6 on Moneyshot but with 1100 kv motor on 4s, so dont think 11x6 on 770kv 3s will suffice for thrust. Will a static test draw more amps than in flight.

[gbanger]

Try droping down to a 14 x 6 and re test

[smuzz]

Yes Gazz, I was going to say 13 x 6 as that's what I've got on the G32 in the Eflite Beaver I got from Darren. Goes really well on 4S with that combination.

[Flying fisho]

Had a 14x8. Tested - 43amps & 471 watts. Static test. do amps reduce in flight.

[Flying fisho]

Sorry, not trying to disrespect advice, looks like I did not order enough variety of props to try out. Have ample for higher KV motor but do not have a 13x6 or 14x6

[gbanger]

Ive got a 13 x 6.5 you can try mate.
Its a spare for my Deuces Wild and surprise surprise, I'm running a Power 32 on 4S in that.

[wingtipper]

your watts are low and your amps are high . indicating your not getting the power down . 15x6 way to big , 13x6 . and 4s is what your after . but try the 14x6 . still big for that size motor .

in theory yes amps drop in flight , because your model is moving forward . but i did a test in my mx2 98 amps static , and 98 amps in verticle flight . !!!!
i have since changed the motor to run less amps and bigger prop . that was a 5055 700kvwith 13x6 on 6s . i now run 5050 580kv with 15x6 on 6s and its 87 amps static , 90 amp/2000w motor . so can take it .
a big prop for yours is 14x6 max , but 13x6 on 4s will be far better , and bring the watts up to about 800 watts static , which is ok for a 10 second verticle . your not running full throttle often with 3d models , so go for it . 45 amps is ok for 10 seconds in air too , much cooler in the air thrust wash cooling everything . if i were you i'd run 13x6 4s/3s . your labouring the motor with 15x6

[Flying fisho]

Thanks Gazz, will take you up on that offer, save wrong prop order again

[gbanger]

No worries, I will throw it in my flight bag.
What size is your shaft/ shaft to prop adapter.

[Flying fisho]

Thanks Gaz, prop adaptor shaft is 8mm.

[samste]

Hi Claudio,

With The Extra 300s what is the Cog Measurement on Yours.
I have set my Up Light as you Suggested 3s 1000ma.

Thxs

Steve

[Claudius]

With The Extra 300s what is the Cog Measurement on Yours.
I have set my Up Light as you Suggested 3s 1000ma.
[/quote]

Just checked. Looks to be about 120mm back from the wing-root with a 3S/1000mAh (more or less right on the second wing spar), and 110mm back with the 3S/1300mAh.

[samste]

With The Extra 300s what is the Cog Measurement on Yours.
I have set my Up Light as you Suggested 3s 1000ma.

Just checked. Looks to be about 120mm back from the wing-root with a 3S/1000mAh (more or less right on the second wing spar), and 110mm back with the 3S/1300mAh.

[/quote]

Thxs Claudio, I actually gave it a maiden Today and position the lipo all the way forward as possible and pot lucked it, Took off from Hand and Had 5 flights Today using 3s 1000ma.
I found my Lipo sits basically right at the Front and still has a slight tail heavy feel but it flys cool.
Using 10x4.7 prop max amps on full throttle 18 amps.
The motor is a 1100kv, i bought ages ago for a project that never happened and is very Light and the Esc is Mega Light 25 Amp.
I think i may need to relocate Esc to underside to Tidy Up away from lipo, But i had to get it in the Air to see how it Flies.
Its alot of Fun, i can see why you enjoy it, and your Right Keeping it Light is the Key, as i tried a heavier Lipo and made a huge Difference to its Flying.
It Flies so nice Being Light.
Not Sure how you set yours Up but I'm Thinking Possibly move Rx & Esc to the Underside near Front to Give it a Little more Weight to The Front and then i may be able to bring the lipo back a bit so the front Closes up.
   

P.s I Actually Plastic Hinge all my Control Surfaces, Super Strong
Steve

[wingtipper]

ok guys . technical question .
i have a 6s 3000mah battery . now using a light socket and an xt60 plug , i ran the 2 wires from the xt60 plug into the 2 light socket terminals , bc type fitting . then i put a 240volt 60w globe in the light socket , and plugged in the battery .
the result is the globe produces no light , but gets warm to touch .
i tried this also using the watt metre source plugged into battery and then load plugged into the plug ,

WHY DOES THE WATT METRE NOT SHOW ANY READING , OTHER THAN BATTERY VOLTAGE , YET THE GLOBE IS GETTING WARM TO TOUCH ?
2NDLY how long should the battery take to discharge ???

my guestimate says , its a 3 amp hour battery , therefore 3 amps will send it flat in 1 hour . ( which is now proven wrong; after 1 hr only dropped .02v per cell )
the globe is a 60watt globe .
therefore 24v x 2.5a = 60w roughly an hour should flatten the battery . RIGHT OR WRONG ? ( wrong)

OR IS THE FORMULA 24/60 = O.4 AMP = 7.5 HOURS TO FLATTEN BATTERY . ????


ANYONE ??

[smuzz]

Frank - your 6S battery (roughly 24 volts, as you say) doesn't seem to be high enough voltage to drive enough of a current through the bulb to make it glow. The low current that you are putting through it is enough for some heat loss, but that's it. I presume it's a standard incandescent light-bulb? I don't know what Wattmeter you're using, but it's possible that the current is lower than it's lowest detectable reading which is why it sees the voltage but reports no current.

Your first calculation of 24 Volts * 2.5 Amps = 60 W is fine, but you're not putting 2.5 Amps through it and so the power consumption isn't 60 Watts. 60 Watts is what the bulb is capable of, but it won't necessary consume that much power - only up to 60 Watts. It's probable that the current you're putting through it is only a few hundred milliamps, which means it will take quite some time to discharge.

I presume you're wanting to discharge a battery in order to dispose of it in salt water? If so, discharge it in one of your planes mate, it will only take 6 or 7 minutes

[Claudius]

Ok, so smuzz was more concise and faster to boot, but I'll just leave this here.

my guestimate says , its a 3 amp hour battery , therefore 3 amps will send it flat in 1 hour . ( which is now proven wrong; after 1 hr only dropped .02v per cell )
the globe is a 60watt globe .
therefore 24v x 2.5a = 60w roughly an hour should flatten the battery . RIGHT OR WRONG ? ( wrong)

Short answer: Wrong. Your 240V/60Watt light bulb only is only a 60 Watt light bulb when you give it 240 Volts.

Long answer: (To the EE's, excuse the odd gross simplification here...)

There's a couple formulas from high school you might remember:

1) V (Volts) = I (current, in amps) x R (resistance, in ohms)
- this one is called Ohm's Law
2) P (Power, in watts) = I (current, in amps) x V (Volts)

With these, we can figure out your problem.

Let's pretend that your light-bulb is really a ideal resistor (EE's look away here), and figure out what current it draws at 240 Volts using formula 2:
60 Watts = I * 240 V => I = 0.25 Amps

Now using formula 1, we can figure out the effective resistance of the light bulb:
240 V = 0.25 Amps * R => R = 960 ohms

Now, when you're putting your 6S battery on the light-bulb, it's putting out maybe 24 Volts. So, using formula 1 again, how many amps will it be pulling with 6S?
24 V = I * 960 => I = 0.025 Amps1

And, using formula2, how much power is this?
P = 0.025 amps * 24 = 0.6 Watts

Or not a heck of a lot. Probably lower than your watt-meter can detect, and not enough to make the filament glow, but enough to warm up the bulb (which has very little thermal mass).

And it'll take more than 5 days to discharge your LiPo at that rate (3 Ah / 0.025 Amps = 120 hrs = 5 days... but it'll be more than 5 as the current will drop as the battery voltage sags...).

Solution: to discharge a 6S battery quickly, instead use a pair of (for example) 60W/12V halogen bulbs, wired in series. This will discharge your 6S LiPo at a rate of about 10 5 Amps (initially), and will therefore well and truly kill it in a half-hour or so - be careful!

Feel free to call and drop past my place to pick up a couple - I've got a surplus of them, and the pigtails for them too which will might make wiring them up easier.

#1 except the filament is tungsten, which has a positive temp coefficient, which means the resistance is actually lower at lower voltages because the filament is colder, and so the current will really be a good bit higher than we've initially calculated... and so on

[wingtipper]

hahahahahah . thankyou very much claudio , i love the explanation and the humour mixed in .
im now discharging them with the chargers in storage mode .after 2 hours on the light bulb i realized not much was happening , explains why the wattmetre wouldnt read anything , surprising with the heat though . its all good . just dont feel good about them sitting there at full charge for weeks . they have been charged for 5 days , so i figure i wont be using them for a few more weeks , ill discharge them down a bit . cheers .
seriously though , i really appreciate the breakdown and simplified explanation you gave , always love learning these things and it helps when the expertise is available to pass it on , cheers mate .

[secant0give]

Nice explanation Claudio!!, I wonder what difference the induction caused by the 240v being 50hz AC makes to the overall impedance of the globe ?? It would be lower than just a factor of 10 as the 24V is pure DC. Probably wouldn't come to much tho' as it'd be more a resistive load than an inductive one,


It's also worth noting that the turn down ratio of those watt meters is very poor their accuracy is probably only one or two percent of their full scale reading if your lucky. Which mind you is quite close enough for checking large current draws. However you shouldn't expect to measure 50 mA with a 100A meter. Even of you discharge with the meter in line with the battery and check the mAh at those low rates it will be wildly wrong........... mine was

[Flying fisho]

Thanks Claudio, I have read your response a few times, and even though this thread is called Electrics for Dummies, I have come to the realisation that I have not yet increased my electrical knowledge sufficiently to understand any of your equations.
Now my head hurts.

[wingtipper]

missed your post smuzz . also worthy of a thanks . cheers .

[smuzz]

All good Frank, no worries - we have to give Claudio a 10 out of 10 for effort though, he's obviously not getting enough homework to do already

[samste]

Solution: to discharge a 6S battery quickly, instead use a pair of (for example) 60W/12V halogen bulbs, wired in series. This will discharge your 6S LiPo at a rate of about 10 Amps (initially), and will therefore well and truly kill it in a half-hour or so - be careful!

Typo in the Amps Discharge, It will be approx 5 Amps with the two 12 volt 60 watt bulbs in series at 24 volts.

Sparky auto correct Feature In Use


Well Explained Claudio
Steve

[smuzz]

Typo in the Amps Discharge, It will be approx 5 Amps with the two 12 volt 60 watt bulbs in series at 24 volts.
Steve

Yes, you're right there Steve - it will be initially more like 5 Amps, dropping exponentially over time as the voltage sags.

[samste]

Sometimes it easier to explain like this.
http://www.flashscience.com/electricity/...globes.htm
If You want to know More, Move the mouse over voltage and switches in the Flash program exercise on each section and learn what it does etc.

[Claudius]

Typo in the Amps Discharge, It will be approx 5 Amps with the two 12 volt 60 watt bulbs in series at 24 volts.

Oops, thanks... fixed.

Sparky auto correct Feature In Use

That's why we should leave these things to the professionals

[BenR]

I have a question that I was hoping not to have to ask so soon.

The blu-baby I have got some damage recently, where it got a nasty knock side on. The damage has caused 2 large cracks in the right hand side of the plane and 1 crack on the underside starting small on the good side and widening to the bad side. The result makes the plane appear kinked. The horn for the rudder control also popped off (see photos for what I mean). The depron is also cracking on both sides of the battery bay (from a mix of a hard landing pushing the undercarriage out, and fingers trying to get to the battery bay). Undercarriage has been solved at least for now with cable ties reinforcing the legs to hold together.

Looking at the inside of the plane, the cracks are just aft of the main balsa section of the plane, right near the servos for elevator and rudder. Both cracks are in front of a piece of depron reinforcing piece holding the 4 pieces together. It is possible to get to the inside of the plane where the damage is, but it is not possible to replace the damaged panels (without essentially remanufacturing 90% of the plane).

My plans for repair? Glad you asked. I am thinking of buying some thin sheeting of balsa and cutting out 2 long panels (about 30-45cm long by about 10cm or so wide) and using them as outside cladding running from the nose of the plane (just before the battery bay) as far back as they need to for covering the cracks. I will also use CA to fill the crack on the underside. (Actually thinking about this, I might CA fill all cracks, then do balsa sheeting). Once the sheeting is attached, I would then check the plane and see if that is enough, or if it needs sheets of depron over the balsa for extra stiffness. The horn for the rudder would get sanded on its base to clean it up, then attach it somehow (not sure yet, the attaching may include a need to insert some filler).

Are these plans reasonably sound, or does someone have a better sugggestion?

[kizza42]

Heh, I'd just sticky tape it with some fibre tape

[wingtipper]

BUY A HOT MELT GLUE GUN , and some glue sticks . go to lincraft or something like that , even the 2 dollar shop has them . gun about 10 bucks . glue sticks 6 bucks .
time to fix . 5 minutes . .
or simply araldite with 5min araldite .