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08-03-2011 12:08 AM  6 years agoPost 1
GyroFreak

rrProfessor

Orlando Florida ...28N 81W

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I used to think KV was a good indication of motor power, but not anymore. The power in watts is the only good indication of true power. I have some 730 KV motors which are about the size of a shot glass.
I used to think that would be about the size of my big 600 Kv, but it's not, the 600 Kv is giant compared to the 730.
So when you state you are installing a xxx Kv motor, you really should state the power also in watts.

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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08-03-2011 04:35 AM  6 years agoPost 2
SkySurfer

rrApprentice

usa

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Funny you bring up this topic. I was looking at purchasing a 4035-330kv motor for my scale project, instead of using my 4035-560kv motor. The 330kv is rated for a peak of 3500watts, while the 560kv is rated for 5200watts. I think the 330kv wouldn't have near the power of the 560kv in a 20 pound chopper, even though its out of the KV range thats recommended?

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08-04-2011 04:59 AM  6 years agoPost 3
Josh Moen

rrApprentice

Denver, CO

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Motor kV should only be looked at as RPM per volt. A 330kv motor will output 1,386 RPM per LiPo cell. So going back to SkySurfer's selection process before you decide on a motor how many cells are you running and what is the main gear ratio? If you don't have a pinion selected how many teeth on the main gear?

The wattage of a motor IS the indicator of how much power the motor is capable of outputting.

Thanks,

Josh Moen
Team Synergy Factory Pilot
Team Futaba

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08-04-2011 10:05 AM  6 years agoPost 4
rexxigpilot

rrProfessor

Florida

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Make sure when selecting a motor you choose one with the amount of continuous wattage rating you want and at the voltage (most are rated at 12S) you plan to use. Many are being fooled by the high peak wattage figures some manufacturers list in their motor specifications. The problem with peak wattage is that there is no set standard on the time a peak must be sustained. Most manufacturers don't list the time either. So they misrepresent the true power of their motors by posting some ridiculously high peak power number that may only be capable of being produced for less than a second before the motor would fail. They also post input wattage, which must be multiplied by the efficiency of the motor at that particular input current and voltage to determine the output power.

Heat is the motor's enemy. A motor should be chosen to run at its most efficient point under the specific operating conditions. This will keep heat buildup to a minimum. This allows the longest flight time and puts the least amount of stress on the electrical components. Everything will last longer. The most efficient point is typically between 85-95% of the unloaded RPM at the specific operating voltage.

When I select a motor I choose one that has approximately the listed continuous wattage I'm looking for. Then I choose a KV that is correct for the gearing I have and the voltage and headspeed I plan to use. Again, I use 85-95% of full voltage, unloaded RPM to maintain efficiency and prevent unwanted heat buildup. Then I look at the max. continuous current spec. I then multiply the max cont. current by the number of cells and 3.75V/cell and the motor efficiency at the wattage input planned to determine the available continuous output power I can expect.

Getting back to KV, most high KV motors are less efficient than a similar lower KV motor due to winding differences.

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08-16-2011 01:58 AM  6 years agoPost 5
johnnie eagle

rrApprentice

Florham Park, NJ 07932

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Kv
So it's safe to say you should only match your esc max current to the continuous current of the motor ?

Team Minicopter - Peak Aircraft, Team Kontronik USA

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08-16-2011 01:32 PM  6 years agoPost 6
rexxigpilot

rrProfessor

Florida

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That would be safe, but you can always go bigger on the ESC for more headroom. The thing to remember is motor efficiency. Once you slect a motor series with the power you want, you should select a specific motor that will operate in the peak efficiency range based on your gear ratio, desired headspeed, voltage, etc.

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08-16-2011 05:00 PM  6 years agoPost 7
johnnie eagle

rrApprentice

Florham Park, NJ 07932

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@ Rex
How would you know your overall efficiency?

Team Minicopter - Peak Aircraft, Team Kontronik USA

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08-17-2011 01:46 PM  6 years agoPost 8
rexxigpilot

rrProfessor

Florida

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Overall efficiency, that would be nearly impossible for a hobbyist to determine. Hovever, if you are only interested in the ESC/motor portion of the power system it is easier. Most manufacturers will provide specifications if asked. Sometimes this is already published information.

The typical ESC is in the low to mid 90% range for peak efficiency. Most of our brushless motors are in the high 80% to low 90% peak efficiency. So the product of the two is typically around 80% efficiency.

The motor is most efficient at close to (85-95%) its unloaded speed in rpm. Note that this is not the most powerful point for the motor to operate, just the most efficient. Less heat is produced and the motor will last a long time.

Peak power occurs at the midpoint between stall and unloaded speed. By choosing a motor KV that will provide the desired headspeed at around 75% of the unloaded speed, you strike a good balance between power and efficiency. My prefference is to go more for efficeincy than power. So I like a KV on the lower side where the motor will run at about 85% of unloaded speed.

Most often when someone has a motor that runs hot, it is because they have too high a KV for the gearing, voltage and set headspeed. They may have lots of power, but the motor is not running efficiently. In this case it is better to use a smaller pinion and higher throttle/governor input to get back toward the peak efficiency range.

Hope this helps.

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09-29-2011 02:39 PM  6 years agoPost 9
flynlyons2

rrNovice

Fairbanks, AK

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Thanks for all the great info Rex! One question...

Kontroniks just confirmed with me that "freewheeling" is very efficient with the Jive controllers. So I can govern at 70% and be fine, unlike Castle ICE HV 160 which needs 90-94% range. My only question is that if I run the Kontroniks ESC at 70-80% with a 330-400KV motor (which won't hurt the Kontroniks ESC) on my larger Vario models, will the motor run hotter? Think motors at lower KVs are best governed at 90% also? Or am I confusing something?

David

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09-29-2011 03:30 PM  6 years agoPost 10
rexxigpilot

rrProfessor

Florida

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David, you have it right. I would use 80% and a lower Kv motor even though the Kontronik ESC is efficient when freewheeling at lower values. The ESC may not get hot at lower throttle percentages, but that won't stop the motor from getting hot when under heavy load. 80% gives some headroom for proper governing and allows for voltage drops through the system and as the battery wears down. Otherwise, if voltage to the motor could be held constant (never going to happen in our systems) using 90% may be better for low Kv motors.

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09-30-2011 06:34 AM  6 years agoPost 11
Stolla

rrKey Veteran

Port elizabeth South Africa

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Kontronik recommends 65 -70 percent on the jive for best governing (check h/jive manual) That is the rule if uncalibrated which is completely unnessecary anyways.
Running lower no problem, higher not good governing.
Second there are issues with the scorp 330 and jive apparently fixed on h/jive, i rewinded mine so cant say.
For scale ships u want the lowest kv to do the job but on the jive
leave enough room for the gov to work so perhaps a little higher kv at a lower percentage.
I've seen a couple of surprise faces when i reduce headspeed on friends machines and they then seem to have mre power where in fact i only created headroom for the gov so speed stays more constant.
If u have a setup where u are running higher than 70 percent on the jive up your pinion to get in the range and you will have a much improved machine.

Common sense may not be common after all

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09-30-2011 08:35 PM  6 years agoPost 12
flynlyons2

rrNovice

Fairbanks, AK

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Great information guys... Currently I'm in the mindset of 90-94% in governor mode with my CC ICE 100's. That's the word from CC is to use THEIR ESCs in governor mode at 90+% if at all possible. They say excessive heat and undue spikes will result otherwise. Not that it is "terrible" to run a CC ICE HV2 160 at 85% or some. But I'm just repeating what I've been told.

So basically if I go with Kontroniks I can operate (and should operate) at 65-70% and the appropriate Motor KV
-OR-
90-94% with CC ICE HV2 160s in governor mode with Xera 4035Y4/300KV motor(12S based on 9.09 gearing on Vario Bell 412) and (10S based on 7.53 gearing on Vario BK117). My only options at the moment.

Thanks,
David

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09-30-2011 09:30 PM  6 years agoPost 13
rexxigpilot

rrProfessor

Florida

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Take the ESC out of the equation!!! The ESC's average voltage output is not necessarily linear/proportional to the throttle percentage from the TX. Even calibrating to the TX is only good for the upper and lower limit of the input signal. All points in between can be way off. Including the ESC just adds non-linearities of the ESC into the mix and makes it seem harder than it is.

Just use nominal voltage (about 3.85V/cell with LiPo), motor Kv, desired headspeed, and main gear teeth to figure correct pinion teeth count. For example: Kv = 480, 12S packs (voltage = 12*3.85 = 46.2V) and desired headspeed = 2200 RPM, and main gear of 106T. 1/(480Kv * 46.2 * 0.80 /106T / 2200) = 13.14T, you should select a 13 tooth pinion. If you want more efficiency but less governor headroom and less total power, use a 12T pinion. You will be at 88% throttle.

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10-01-2011 05:39 AM  6 years agoPost 14
Stolla

rrKey Veteran

Port elizabeth South Africa

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"Take the esc out of the equation" Yes with normal esc's not with the jive the normal calculations doesnt allow u to run in the 65 to 70 percent bracket youll be more likely in the 80 percent bracket so u have to bring that into play. My advice is to look at the motor calcs then get at least one larger t pinion than anticipated to be able to run at 65 to 70 perent on jive.

Common sense may not be common after all

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10-01-2011 04:18 PM  6 years agoPost 15
rexxigpilot

rrProfessor

Florida

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Stollo, so you are saying the Jive, like all Kontroniks, breaks the laws of physics!

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10-01-2011 05:42 PM  6 years agoPost 16
flynlyons2

rrNovice

Fairbanks, AK

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Well this is how I'm getting my numbers and I've verified (through actual data and worked backwards) that I'm very close...

Just one example... I've got a T-Rex 600 ESP in a Century Jet Ranger body. Stock mechanical flybar. Head speed is governed with CC ICE 100. So I take ((22.2V * 1100KV) * .9) = 21978. 170 main / 13T pinion = 13.07 ratio. 21978/13.07=1681 full speed rpm. 1681*.92(governed %)= 1546 governed rpm at 92%. Which is almost exactly what I'm getting in real world performance from the CC ICE 100 ESC.

On the Castle stuff it's my understanding to keep governed mode near 90%. Less than that and it's not as efficient, but I'm not an engineer, so I have no concept of why that is on the Castle stuff. Kontroniks is different in that regard I know, but I really like the software of Castle and the numbers are almost dead on accurate.

David

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10-01-2011 05:57 PM  6 years agoPost 17
Mojave

rrElite Veteran

Palos Verdes, Ca. USA

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After reading this entire thread and seeing many good points, I think that your best bet is to start with a good motor/gearing/lipo baseline and set the esc during the tuning phase of your build. Go to blackhorse head speed calculator and plug the numbers in, then pick a motor/lipo/pinion combo that will give you the desired headspeed, then govern the jive based on your test flight real world head speed. There are so many factors involved, including lipo health etc.. This way you know that you have components that are in the ballpark for your desired headspeed and you're not asking the electrical components to operate outside of their happy zone, just to change your head speed. That's my .02
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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10-02-2011 06:03 AM  6 years agoPost 18
Stolla

rrKey Veteran

Port elizabeth South Africa

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"Stollo, so you are saying the Jive, like all Kontroniks, breaks the laws of physics!"
Haha you may say so but really it's not generally known that kontronik's range should be within 65 to 70 percent. most people alibrate the jive endpoints to tx to get real values which is the first "mistake" as you dont know where you are in "kontroniks recommended range"
Throw in the 5 Percent variance in motor kv you can see how easy it is get the maths wrong.
In my personal experience i've found that generally most people fly too high percentages on the jive to get the headspeed they want. Only way to get it absolutely right is to measure headspeed within the recommended range.
With the jive you'd rather be in the too low than too high range as it can handle partial loads without problem but too high and your motor will not be governed properly. This different on "normal esc's as you want to be in the highest range possible as they cant handle partial loads well

Common sense may not be common after all

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10-02-2011 07:19 AM  6 years agoPost 19
Band1086

rrElite Veteran

Kennewick, Wa. USA

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Torque X RPM = Power

With this it's easy to see why the Scorp 4035 series motors go down in power as they drop in KV. The lower the KV the lower the RPM on any given voltage. If the torque is the same on all the 4035's, but the RPM is less, the power will be less. If you know the torque value(which is the hard part) of any given motor, you can easily find the power value.

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