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HomeAircraftHelicopterMain Discussion › Whats More Efficient?
06-03-2009 03:38 AM  9 years agoPost 1
Sean Williams

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Santa Clarita CA

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So I always hear that brushless motors run their most efficient at 100%. If that is true, then would it mean that if I flew the same exact flight under the same conditions, I would take less out of a battery at 100% vs say 80%? Maybe somebody could give me a technical explanation as to why this happens?

Thanks.

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06-03-2009 03:47 AM  9 years agoPost 2
jbdww

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Round Rock, Texas

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The energy gets lost in the ESC. The lower you run the throttle the more the ESC has to take away from the motor and also the hotter the ESC gets. The motor is going to use the energy you give it, but the ESC is like putting a resistor before the motor to throttle it down.

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06-03-2009 03:51 AM  9 years agoPost 3
Sean Williams

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So does this run your battery down any faster?

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06-03-2009 03:53 AM  9 years agoPost 4
Spitfire1

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Perth Australia

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Im no expert Emag, but I can tell you from personal experience if you run low T/curves, something like 100 80 75 80 100 you can get 8 minute flights, but its not much fun I wouldent recommend it.
You could probly run 60% on all points and hover for over 10 minutes but how crappy would that be.

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06-03-2009 03:59 AM  9 years agoPost 5
Sean Williams

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Santa Clarita CA

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Well lets put it this way Spitfire, on my 600e, at 100%, I'm getting 2500 rpm on the head. There are no alternate gearings, so this is why I'm asking.

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06-03-2009 03:59 AM  9 years agoPost 6
Spitfire1

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Perth Australia

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Hey just curious.

emag remrofni/informer game.

Always wondered where that comes from?? surely not just coincidence is it?

Jason.

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06-03-2009 04:00 AM  9 years agoPost 7
Sean Williams

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No not a coincidence. I just wanted a different name and that turned out to be an interesting combination.

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06-03-2009 04:00 AM  9 years agoPost 8
Spitfire1

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^^^
Cool! I think its a name of a movie or something.
Typeing the same time, maybe just try 90 90 90 90 90 and see how it goes.

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06-03-2009 04:04 AM  9 years agoPost 9
Spitfire1

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Perth Australia

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****!!

I just put a mug of milk in the microwave for 5 minutes instead of 50 seconds, ive got a real disaster going on here!!

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06-03-2009 04:11 AM  9 years agoPost 10
Terrabit

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Seattle, WA - USA

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In my experience, ESC's have a sweet spot - particularly if you are running a governor. The Jive seems to run best between 75 and 85%. The Jazz is decidedly lower, 65 to 75%. I gear to match my targetted throttle curve with my targetted headspeed.

Also, ESC's do not like v-curves. It causes them to heat up ... more. Comming from RC cars I can tell you that from experience. The more constant the curve the more efficient and cooler.

Ultimately, headspeed is the biggest factor in efficiency. A 10% increase in headspeed will consume more than 10% of your available mah. The relationship is exponetial.

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06-03-2009 04:17 AM  9 years agoPost 11
Sean Williams

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Santa Clarita CA

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Ultimately, headspeed is the biggest factor in efficiency. A 10% increase in headspeed will consume more than 10% of your available mah. The relationship is exponetial.
But please tell me this, will a flat 80% curve be exponentially more efficient than a straight 100% curve? Or does this only apply if you re gear it?

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06-03-2009 04:26 AM  9 years agoPost 12
Terrabit

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It would not be exponentially more efficient and yes, you'd need to regear it. 2200rpm at flat 90% curve would be marginally more efficient than 2200rpm at a flat 80% curve. But, 2000rpm at a 90% curve would net you greater efficiency than the 10% change in headspeed or throttle curve. These are ofcourse arbitrary numbers.

Do you follow me?

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06-03-2009 04:27 AM  9 years agoPost 13
Spitfire1

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Perth Australia

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Are you running the ALign ESC??
If so, in my opinion it doesent like anything below 88%, so to be honest I would not run any lower than 90%. IMO.

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06-03-2009 04:29 AM  9 years agoPost 14
Sean Williams

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Santa Clarita CA

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Do you follow me?
Yes
Are you running the ALign ESC??
If so, in my opinion it doesent like anything below 88%, so to be honest I would not run any lower than 90%. IMO.
This is not even on an Align heli, let alone an Align esc.

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06-03-2009 04:29 AM  9 years agoPost 15
Terrabit

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I have a tendency to smoke Align ESC's. So, don't take my advice on how to set one.

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06-03-2009 04:35 AM  9 years agoPost 16
Spitfire1

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Perth Australia

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OK.

If its not ALign you could run gov mode.

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06-03-2009 07:22 AM  9 years agoPost 17
DKNguyen

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N/A

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The lower the duty cycle you run, the lower average voltage that is applied to the motor, which means the motor spins slower, which means less BEMF. THis BEMF is what opposes the battery voltage and what causes a fast spinning motor to consume less current and causes a slower spinning motor to consume more current (all the way to stall).

But the ESC puts a square wave through the motor that jumps between battery voltage and 0V. THis stays the same no matter what the duty cycle is. So even though decreasing the duty cycle decreases the average voltage, the peak voltage stays the same. This means that ESC applies to the motor is the full voltage of the battery, but for less time as you decrease the duty cycle.

THat's a problem because there's less BEMF to oppose the full battery voltage which means high currents. THe result is that a motor running off 20V@50% looks like it is more heavily loaded (running closer to stall) than the same motor running off 10V@100%, even though they are running at the same speed outputting the same torque.
Yes inductance slows down how quickly the current rises and falls through the motor as the square wave is put through the motor, but it still rises and falls fast enough to make a noticeable difference (the inductance isn't infinite after all). THis is a motor, not a switching BEC so not as much attention is paid to increasing the inductance of the motor to smooth out the current in it.

THe larger the inductance is relative to the battery voltage, the slower the voltage rise/fall is, the less ripple there is relative to the overall current waveform, the farther the motor runs away from stall at a low duty cycle. That's one reason some ESCs have selectable switching frequencyes- high frequency for low inductance motors and low frequency for high inductance motors. Lower switching frequency is preferable because it means less heat due to switching, but in low inductance motors the current rises/falls faster and a low switching frequency allows the the current too much time causing it to rise to intolerably high levels.

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06-03-2009 08:31 AM  9 years agoPost 18
Terrabit

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Seattle, WA - USA

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That's all fine and dandy Mr Nguyen. I believe what you are saying is that it depends on the motor and the ESC. Now, can you clearly express that in laymen's terms and shorten it down to four sentences or less? I have a very short attention span! Like a nat.

When will you engineer types learn how to speak to us administrative types?

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06-03-2009 09:02 AM  9 years agoPost 19
Hamo

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Ireland

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So I always hear that brushless motors run their most efficient at 100%. If that is true, then would it mean that if I flew the same exact flight under the same conditions, I would take less out of a battery at 100%
If you fly the same path, the same distance and the motor is more efficient at 100% speed, then the quick answer is YES.
Hamo

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06-03-2009 09:04 AM  9 years agoPost 20
Spitfire1

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Perth Australia

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uurrgh plug in, push lever thingy forward, woohoo up she goes!!!!

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