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Old May 12, 2011, 12:39 PM
I think I forgot how to fly RC
cryhavoc38's Avatar
United States, WA, Woodinville
Joined Mar 2007
8,061 Posts
Quote:
Originally Posted by egaus View Post
My understanding is that the ESC delivers as much amps as the engine wants, determined by its Kv, but the ESC pulses the power to lower the load it delivers. ESC will get hotter at lower throttle as they are working harder there. Motors will get hotter at WOT and fail faster at sustained WOT because there is relatively no pulsing going on at WOT.

This has been my understanding and from what I've read from Lucien to Vitter recently, I believe it is correct. It was explained to me that what you see in your amp/watt meter is just an average of the amps due to the pulsing. Some serious pulsing going on at 8k/sec.

I think all manufacturers underrate their motors so they don't have to deal with as many unsatisfied customers w/ burnt/broken motors.

e
I've read and read and read all the "explanations" on how an esc magically learns what max amperage is for a given system combination and I understand the theory behind pwm modulation and pulses at a given throttle range, ie the esc will "know" what the system's max amperage is and will deliver that constantly, regardless of the throttle settings, ie 100% of the power delivered x amount of the time...

But what has ALWAYS troubled me is that our systems have no way of knowing what max amperage is before the throttle is moved one millimeter...if you know what I am saying.

theoretically, if a user hooks up a 6s 5000mAH pack to a 4025-540 motor with a 15x7 prop, the possible max amperage would be approx 90amps

but if the user never moved that throttle to WOT, the system would have no way of knowing what max amperage delivered would ever be.

Theoretically, its only until the throttle was moved to WOT that the "system" would be able to ever know what maximum amp draw is for that battery, kv, and prop..

its one of those circle jerk conversations that can go on and on over many beers, cigarettes and wildly articulating gestures..

never would a group of 5 come to an agreement as to the actual facts, even if it were the design engineer of Castle giving the lecture him/herself.
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Old May 12, 2011, 01:04 PM
Quadrophenia
egaus's Avatar
Seattle
Joined Mar 2009
915 Posts
The ESC always delivers as much amps as the motor wants and battery can provide in order for the motor to spin at its 'programmed' RPMs, determined by the motor's Kv.

Again, that's just my oversimplified understanding and how you put that theory in to practical use is more the mystery to me. I just go with setups that are recommended and proven to work good. I measure my amps at WOT and try to use a motor/battery/ESC/prop combo that has ratings that match those numbers, as do all of you.

Sorry this isn't very helpful, Chris.. Call Ben/Ken.

e
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Old May 12, 2011, 01:10 PM
Training to be a cage fighter.
bicyclechris's Avatar
Woodinville, WA
Joined Apr 2010
499 Posts
That whole theory confuses me as well.
First of all, I've flown "Hot" setups that were above manufacturer's spec.
Such as my HET 3W-25 on 6 cells, it was about 7 amps over the recommended spec.
At low throttle the ESC doesn't get hot at all.
In fact, when flying it the whole time at low throttle, everything came down cold.
Also, the amps being pulled is a result of the specific size and pitch of the propeller being used.
I don't think that the motor will require the same amount of current, or work as hard when turning a given prop at 800rpm vs let's say 8,000rpm.
There are other forces at work such as wind resistance which will increase the faster the motor turns the propeller.
It seems to me that the manufacturer's are looking at this from en engineering standpoint versus a practical use point of view.
What seems confusing to me, is that Vitter discussed the issue of motor selection for the 70" Electric Slick last year and the 4035-380kv motor was recommended as the best overall setup for that plane by either Scorpion or Innov8tive designs.
Now another person from Innov8tive, Lucienne I think, is saying that Victor is putting too small of a motor in his plane and over-working it on 6s with a 19x10E prop.
Note, the 3DHS 71" Slick is "Electric Specific" and is much lighter than standard 30cc sized gas planes.
It doesn't require a larger true 30CC motor to fly it the way it was intended to.
On paper the Scorpion, Infinite, Motrofly, and Hacker motors look veerrry similar to each other in terms of specs and performance.
So why would a Motrofly motor perform any better or last longer than the Scorpion?

Even if a design engineer at whatever company gave a lecture, I'd like to know what some of the real-world results would be in a plane vs. in a lab.
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Old May 12, 2011, 01:11 PM
Ride Blue
jholen's Avatar
United States, WA, Sammamish
Joined Aug 2006
1,495 Posts
Lucien just wants him to buy a bigger motor lol

Yeah, I've heard it explained, but can't wrap my head around it.
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Old May 12, 2011, 01:17 PM
Training to be a cage fighter.
bicyclechris's Avatar
Woodinville, WA
Joined Apr 2010
499 Posts
Ya, and that bigger motor weighs over 200 grams more, nearly half a pound heaver!
lame-o man.
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Old May 12, 2011, 01:24 PM
Gonna need a bigger plane . .
FlopGun's Avatar
Kitsap County, WA, USA
Joined Jul 2007
2,951 Posts
You guys are giving me a headache.

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Old May 12, 2011, 01:24 PM
Quadrophenia
egaus's Avatar
Seattle
Joined Mar 2009
915 Posts
I run a Hacker A50-16S using 6S on my 65" Vyper, I don't recall off-hand what the max amps/watts that I pull are but I'm running a Xoar 18x10 and it comes down warm. It isn't a rocket, but it is certainly capable and I've had no problems with it. If I could do it again, I'd want a motor that could deliver more thrust/speed on 6S using that prop. FWIW.

e

ps. Good one FG!
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Old May 12, 2011, 01:24 PM
I think I forgot how to fly RC
cryhavoc38's Avatar
United States, WA, Woodinville
Joined Mar 2007
8,061 Posts
Quote:
Originally Posted by egaus View Post
The ESC always delivers as much amps as the motor wants and battery can provide in order for the motor to spin at its 'programmed' RPMs, determined by the motor's Kv.

Again, that's just my oversimplified understanding and how you put that theory in to practical use is more the mystery to me. I just go with setups that are recommended and proven to work good. I measure my amps at WOT and try to use a motor/battery/ESC/prop combo that has ratings that match those numbers, as do all of you.

Sorry this isn't very helpful, Chris.. Call Ben/Ken.

e
totally understandable, but this is exactly why I take the recommended and then go from there.

I won't use a recommended motor/esc combination based on the simple fact that a manufacturer who sells or endorses one line of hardware will not recommend another brand of hardware because they do not sell it.

3dhs will never tell you online what scorpion motor to use, because they want you to use a hacker or torque

EF won't tell you what motrolfly to use because they want you to use a torque.

Hyperion (their planes) will only give you specs and recs based on their line of motors.

Eflite/horizon will only tell you what Eflite motor to use..

etc

Some of us, at times, want to "soup" things up a bit and do something different.

sorry if I sound harsh in any of my replies today.
I'm just in a bad mood today.

Oh and I have to add..

a prime example of when NOT to listen to a manufacturer's recommendations is when they say to use a servo that costs $94.99, but is only capable of about 170oz of torque, when the same servo brand has a much better servo at the same price that produces three times as much torque and a much faster speed.

hs7985mg versus the hs7954sh
tower prices used ONLY as an example.

7985mg 94.99
7954sh 99.99

if a person took the recommended servo and bought 5 of them for $475 and then wanted to build a larger plane after the smaller one crashed..they are stuck with $475 bucks worth of servo's that could not be used in the larger plane.

if they would have done their own research, they would have spent $500 on servo's that are capable of being used up to a 40% class airplane, versus spending $475 for servo's that could only be used in a 26% class or lower airframe.
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Old May 12, 2011, 01:26 PM
I think I forgot how to fly RC
cryhavoc38's Avatar
United States, WA, Woodinville
Joined Mar 2007
8,061 Posts
Quote:
Originally Posted by FlopGun View Post
You guys are giving me a headache.

what the hell else am I suppose to be doing at work
working?? yeah right!

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Old May 12, 2011, 01:31 PM
Training to be a cage fighter.
bicyclechris's Avatar
Woodinville, WA
Joined Apr 2010
499 Posts
You're right Cryhavoc, each manufacturer will always push their brand of motors to sell with their planes.
I also don't think you've been harsh at all, this is exactly the kind of discussion that I was looking for.
I wanted everyone who has knowledge and experience to give their thoughts, and so far they have.
Super Cool!
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Old May 12, 2011, 01:36 PM
Quadrophenia
egaus's Avatar
Seattle
Joined Mar 2009
915 Posts
Quote:
3dhs will never tell you online what scorpion motor to use, because they want you to use a hacker or torque
http://www.3dhobbyshop.com/65-Vyper--Red_p_15262.html

See that 3DHS provides an alternate configuration for this plane: Scorpion 4025-12 on 8S under components. Not to nit-pick, but ...

Now I'll be getting back to my Kool-Aid, mm... tasty.

e
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Old May 12, 2011, 01:39 PM
Ride Blue
jholen's Avatar
United States, WA, Sammamish
Joined Aug 2006
1,495 Posts
I can believe that the ESC sees full amperage even at half throttle. That makes sense to me.

When it comes to the motor however, I think the danger is heat. Overheat the motor and it's gonna be fried. And I think we can all agree that heat can be managed by throttle management - run something at WOT for the whole flight and it's going to be a heck of a lot hotter than if you ran it at half throttle with only short bursts of WOT.

That isn't from a book/education viewpoint, that is just from my experience.
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Old May 12, 2011, 01:42 PM
Gonna need a bigger plane . .
FlopGun's Avatar
Kitsap County, WA, USA
Joined Jul 2007
2,951 Posts
I think I'm with egaus there, what I've noticed is EF and 3DHS are motor independent with their setups.

I agree with Jolene. The enemy is heat, as long as you are not too hot, who cares about the math. I like to read the threads and just choose what the experienced 3D guys are using.

On the infinite motors I think the brand name works as it seems they are infinitely delayed........

And guys, I was at Walgreens today and saw where they have a big sale, graph paper, protractors and mechanical pencils. Stock up!
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Old May 12, 2011, 01:42 PM
Training to be a cage fighter.
bicyclechris's Avatar
Woodinville, WA
Joined Apr 2010
499 Posts
True, ultimately heat is the brushless motor's Kryptonite.
I'm thinking that Vitter simply received a Scorpion 4035 motor that was from a
not-so-awesome production run.
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Old May 12, 2011, 01:53 PM
I think I forgot how to fly RC
cryhavoc38's Avatar
United States, WA, Woodinville
Joined Mar 2007
8,061 Posts
egaus is correct.
I was going off old info.

At one time, EF, 3d, PA, etc only recommended one motor choice.
Seems times are a changing.

I stand corrected.

HOWEVER comma...
whats their alternative motor for a 6s setup...



So an example..I do like that a manufacturer will give you a basic starting point with regards to whats recommended..and 99times out of a hundred, they have to recommend what they sell..

a perfect example is the Hanger 9 sundowner 50
Their recommended hot setup would give approx 65mph at wot on a 4s pack.

I used their basic starting point to then purchase a scorp 4025 on 6s with a 12x12 prop to get a pitch speed of 106mph..

its all good though.
this is suppose to be a fun and relaxing hobby.
how come it isn't sometimes?
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