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Old Mar 14, 2012, 11:15 AM
Tossing planes into the snow
Canada, BC, Smithers
Joined Nov 2011
3,168 Posts
I never had a problem with the stock batteries coming down warm with the stock prop until recently. Now the poor RP is trying to pack a 180 gram camera, which is about the equivalent weight of 2 1300 batteries. I know it's not ideal but it's what I have for now and it takes good videos. It has to work hard for over 2 minutes to get it "up there" to an altitude that I am guessing is about 500 meters. Even after one run, the battery is a bit puffy, and fairly warm (not hot).

Am I pushing my luck here? How can you tell if a battery is just "comfortably warm" or is hot enough to be a cause for concern?
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Old Mar 14, 2012, 11:26 AM
Zor
Suspended Account
Ontario,Canada
Joined Feb 2007
9,742 Posts
Quote:
Originally Posted by kaptondave View Post
There are instruments available that will measure and record power parameters in flight but I do not believe that you would find a significant difference from static test measurements. Props do not "unload" in flight. If anyone has actual measurements to show that this is true or false please post them.
kaptondave,

Responding to your invitation to post even though I do not have actual measurements.
I am anxious to see if anyone has actual in flight measurements and will post them

I agree with you that "Props do not "unload" in flight if you mean that their load completely disappear.

In reality the load is reduced but of course does not fully "unload".

When an engine or motor and its prop is running on a bench (static condition) without any forward speed the angle of attack of the prop is determined by the pitch of the prop blades. At least some area of the prop is actually working beyond its stall angle with a lot of drag needing more torque from the engine or motor.

Some part of the prop may not be stalled if the pitch is very small but that would not be a practical prop that would not load the engine or motor properly.

Once in the air the prop blades angle of attack is considerably reduced and the engine or motor increase in RPM and the torque is reduced.

I believe that less torque on an electric motor would reduce the electrical current to some degree.

I also think that in the air the motor windings would be cooler, have less resistance and that may reduce the current difference.

We are not talking very large differences.
I supose that motor designers and manufactuers may be using telemetry to measure current load or wattage while airborne.

I see wattage and/or current maximum ratings on motors but I have never seen actual values defining a specific motor and prop versus speed.

I find this an interesting subject.

Regards from Zor.
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Old Mar 14, 2012, 12:04 PM
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Old Mar 14, 2012, 12:12 PM
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Joined Jan 2010
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Doing a Google search on the prop unloading issue shows that there has been and is a lot of discussion but no concise answer. The reason seems to be that there are too many variables, one being rpm which is hard to measure in flight. I have found some reports comparing inflight and static measurements that indicate there might be 15% to 20% reduction in flight. I am not going to get wrapped up in a debate on this but agree that if static test measurements show safe power levels you can fly without worrying about letting the smoke out.
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Old Mar 14, 2012, 01:40 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,549 Posts
Quote:
Originally Posted by Stregalicious View Post
Is there a way to test if I'm overloading the battery while using the 11x8?
As stated by others, a wattmeter is an essential tool for anyone who plans to stray from the RTF world. Once you start setting up your own motors, changing props, etc, you really need a wattmeter to see the results of your work.

I have had club members wonder why they have battery, motor and ESC failures or why their plane crashed. Then we put the wattmeter on the set-up and found that they were seriously overloading their systems.

Sometimes problems blamed on radio links are actually ESC overheating and the BEC shutting down, cutting power to the receiver. By time you get to the plane the ESC/BEC has cooled and everything is fine.

BAD Radio, BAD receiver they cry.

Nope, just an electric pilot fooling around with mixing and matching stuff without a wattmeter.
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Old Mar 14, 2012, 02:23 PM
Kool Kats Fly RC!! AMA 30462
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United States, CA, Baywood-Los Osos
Joined Feb 2009
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Originally Posted by Patchitagain View Post
Just make sure none of the loctite gets on the plastic cowling... It will weaken and/or melt it..
Just a dab will do ya, (as the old commercial said). I just put a tiny drop on the threads only, as Loctite is a form of CA it can melt foam and/or plastic, so a little goes a long way and care should be used when it's applied near foam and/or plastic.

Quote:
Originally Posted by Jovanx View Post
Even after one run, the battery is a bit puffy, and fairly warm (not hot).

Am I pushing my luck here? How can you tell if a battery is just "comfortably warm" or is hot enough to be a cause for concern?
I also fly edf's, and pushing lipos and esc's to their limit is an everyday thing in those high-discharge situations. It's the difference between "very warm" to the touch and "definitely hot" to the touch. If it's the latter you may be pushing your luck, but if you can touch it and hold it in your hand comfortably you'll be fine. In my edf's after a WOT flight my lipos are good and warm, but not so hot I can't hold them and put them in my pocket, (they make a nice pocket-warmer on a cold day). A little puffing while still warm isn't so concerning, but if they stay puffed up after cooling down that's a different matter, and you may want to replace a lipo that puffs up and stays that way. I've found also that most esc's can be pushed to their amperage limits, but the same applies to them, warm is ok, but too hot to touch is too much. In my RP the amp draw is, like I stated earlier, around 20-22 amps. The "stock" esc is rated at 35 amps, so you could very realistically run it at 30 amps and you shouldn't have any issues. All the above applies to motors also, warm is ok, but too hot to touch is pushing it. I use an E-flite Watt Meter to test my all of my power systems, if flying electric power it's really a necessary piece of equipment.

Sonny
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Old Mar 14, 2012, 04:04 PM
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United States, TX, Austin
Joined Jul 2009
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I just got mine yesterday along with a DX8, I'm having trouble figuring out what servos to plug into what ports (besides the obvious ones). I'm using the radio program provided on the Spektrum site, and elevator, throttle, and aileron work pretty much right but the right flap doesn't move and wont stop buzzing (it seems to be the only one constantly making the sound), lol. I'm using the receiver that comes with the DX8. Sorry if It's been asked before here, 550+ pages is a bit much to look through
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Old Mar 14, 2012, 04:30 PM
NE Texas, USA
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Quote:
Just a dab will do ya
Wow, that goes way back up memory lane... was it the Brylcreme commercial ?
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Old Mar 14, 2012, 05:33 PM
Kool Kats Fly RC!! AMA 30462
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United States, CA, Baywood-Los Osos
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Originally Posted by Patchitagain View Post
Wow, that goes way back up memory lane... was it the Brylcreme commercial ?
Yes it was! I couldn't remember how to spell it so I didn't try, but that was their advertising phrase and the lyrics for their jingle. That was the look for guys back then, (50's early 60's), my dad smeared his hair down every morning with that stuff! Guess I'm revealing my age, bet most of the guys out there don't remember such things as having only three television channels, (ABC, CBS, NBC), no remotes, (rocket science back then), and cartoons only on Saturday morning til noon! Those were the days of Howdy Doody, Captain Kangaroo, who had my fave cartoon hero; Tom T Riffic, and of course Popeye, (I should include Mighty Mouse in that list; "Here I am to save the day, that means that Mighty Mouse is on the way!!"). Remember "Pop pop fizz fizz oh what a relief it is"?

(Sorry for the brief departure from the subject of the thread, but nostalgic nonsense sometimes creeps up on those of advanced age and decrepitude).

Sonny
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Old Mar 14, 2012, 05:38 PM
Proud member of LISF and ESL
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Originally Posted by Patchitagain View Post
Wow, that goes way back up memory lane... was it the Brylcreme commercial ?
Brylcreme, a little dab will do ya,
Use more, only if you dare.
But watch out, the gals will all pursue ya.
They'll love to get their fingers in your hair!

Guess I watched too much TV as a kit?
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Old Mar 14, 2012, 05:43 PM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
United States, CA, Baywood-Los Osos
Joined Feb 2009
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Quote:
Originally Posted by aeajr View Post
Brylcreme, a little dab will do ya,
Use more, only if you dare.
But watch out, the gals will all pursue ya.
They'll love to get their fingers in your hair!

Guess I watched too much TV as a kit?
Ha!! Me too!

Sonny
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Old Mar 14, 2012, 07:15 PM
Gerry M
Canada, BC, Victoria
Joined Mar 2010
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Quote:
Originally Posted by pow-wow View Post
I just got mine yesterday along with a DX8, I'm having trouble figuring out what servos to plug into what ports (besides the obvious ones). I'm using the radio program provided on the Spektrum site, and elevator, throttle, and aileron work pretty much right but the right flap doesn't move and wont stop buzzing (it seems to be the only one constantly making the sound), lol. I'm using the receiver that comes with the DX8. Sorry if It's been asked before here, 550+ pages is a bit much to look through

Pow-Wow, try the summary of all the tips in this thread located at: http://www.Radian-Pro.com put together by Stregalicious.

There are some set-up tips in there for the DX8...
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Old Mar 14, 2012, 07:22 PM
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Joined Feb 2012
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Thanks for the info on the watt meter, I've just ordered mine and won't fly again until I have it in hand to test it out. If I find I'm overloading the ESC but the prop works very well on the RP, can I just go with a higher rated ESC to solve that issue?
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Old Mar 14, 2012, 07:33 PM
The "Foaminator"
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United States, CA, Los Angeles
Joined Mar 2007
2,211 Posts
Quote:
Originally Posted by Stregalicious View Post
Thanks for the info on the watt meter, I've just ordered mine and won't fly again until I have it in hand to test it out. If I find I'm overloading the ESC but the prop works very well on the RP, can I just go with a higher rated ESC to solve that issue?
Good joice first off, this is a tool you will use anytime you do a new setup to verify what your amp draw is and you can also tell imediately if you have a failing battery

Yes you can install a larger ESC if your way orver spec, but first consider, are you also over spec of the motor?
You should always know the max ratings of your motor, either in Amps or Watts and then try to get about 90% of that on the ground if you want the most from it. I know this can turn into a whole nother discussion, My point is this is safe as it will unload a bit in the air.
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Old Mar 14, 2012, 08:51 PM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
United States, CA, Baywood-Los Osos
Joined Feb 2009
2,793 Posts
Quote:
Originally Posted by Stregalicious View Post
Thanks for the info on the watt meter, I've just ordered mine and won't fly again until I have it in hand to test it out. If I find I'm overloading the ESC but the prop works very well on the RP, can I just go with a higher rated ESC to solve that issue?
Didn't you say in an earlier post that you have 11x8 prop blades? As I and others are getting around 22 amps using 11x6, you will probably be in the 25-28 amp range, maybe as much as 30 amps, which is totally doable with the stock esc, (rated 35 amp continuous), and most probably the motor as well. However, I would use at least a 25C lipo, and preferably 30C to be sure it has enough discharge capability. A wattmeter is something everyone who flies electric power should have, but you would be safe to fire the system up using the 11x8, run it for 30 seconds or so at WOT then see what if anything is hot to the touch. If the esc/motor/lipo are just warm you'll be fine.

Sonny
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