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HomeRC & Power✈️Aircraft🚁Helicoptere-Electric Motors-Controllers-ESCOther › How to choose the right Motor Kv
12-18-2011 08:15 PM  9 years ago
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boomstrike5

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Sacramento, Ca, Usa

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How to choose the right Motor Kv
Do you decide what head speed you want to run and figure for 20% more head speed and muliply by gear ratio, divide by voltage to get the kv for your motor. How would you figure this out when you run multiple head speeds like N 1900, IU1 2000 and IU2 2100. Which head speed would you add 20% to to figure out motor kv. Thanks leon

Added voltage to the formula, sorry.
MA Graphite 46, MA 98 SE, MA Ion X2, Whiplash EX, Synergy E7SE
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12-18-2011 09:36 PM  9 years ago
NoLuckChuck

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Leesville, LA

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Yes, and determine what nbr of cells you want to run and what pinions are available. You will generally want to set the ESC around 85% if you use governor. Keep in mind as the battery dies the ESC will regulate to keep the headspeed constant. If you are at 100% it cannot do this. Post what you got and let us help.
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12-18-2011 10:00 PM  9 years ago
boomstrike5

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Sacramento, Ca, Usa

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This is a general question. Looking for how much head room for running a gov on any setup. I understand you need to account for what voltage your running and gear ratio. Thank you for your reply, LeonMA Graphite 46, MA 98 SE, MA Ion X2, Whiplash EX, Synergy E7SE
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12-18-2011 10:43 PM  9 years ago
AnneThe Man

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Ireland

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I asked the same question but didn't really get a satisfactory answer. I suspect this is because the majority run at one headspeed, and therefore the question is relatively easy to answer. If you fly in normal, idle1 and maybe idle2 and there is a relatively wide headspeed band I suspect you have to use the highest headspeed you plan to fly to do the calculations and then choose an ESC and motor that can handle throttle curves of maybe as low as 30 or 35%.
I'm using a Kontronik and run a Normal curve as low as 30% with no overheating or other problems.
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12-21-2011 09:29 PM  9 years ago
bustedmp

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Shamokin, PA

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I'm no expert on this matter, but from what I understand if you are using a gov built into an esc the throttle curve % you set in your tx isn't the % the esc puts out to the motor. I know for my Swift NX with an 880kv motor and 9.6 gear ratio in the high gov setting, 44% throttle in the tx is about 94% output from the esc to the motor to turn about 1800. The flat line throttle curves are just to tell the esc what speed to turn to motor, If the load on the motor is high and the esc commands 100% battery power to the motor, any extra load and the headspeed will get bogged down.

I was told to take the highest headspeed I planned on running and figure for 10% more. I was also told running the esc at less than 70% throttle output is not very good for them. But like I said I'm not an expert, just know enough to get myself in trouble, but that is my understanding of esc and gov operation.
The world is yours!
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12-21-2011 10:21 PM  9 years ago
Pistol Pete

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Seffner, FL

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Head speed.
You need to know your desired max head speed for given model.

RPM = Motor KV x Batt V (3.7 per cell) x Motor Efficiency (80% = .8)

Gear Ratio = RPM / Head Speed

Pinion = Main Gear Teeth (MGT) / Gear Ratio (GR)

If using governor, multiply desired max head speed by .15 (15%)
~~Enjoying the hobby one flight at a time~~
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12-22-2011 01:28 AM  9 years ago
Gregor99

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Western Wa

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I use the Castle Link in demo model for modeling different motor Kv, cell count and gear ratio combinations. The resulting throttle position will only be an average. So they will be little high if you have good collective management and a little low if you are smacking hard.

http://castlecreations.com/downloads.html

I find this method easier to use and more accurate than the online HS calculators. Sometimes the online calculators give you headspeed for a fresh pack which only lasts for 30 seconds.
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12-22-2011 03:37 AM  9 years ago
bustedmp

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Shamokin, PA

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I have done just that, but I also used another calculator on castles site to help get me a rough idea of different motor/gear ratio combos. I picked up an 1100kv motor for my nx, but even with an 8t pinion on a 6s pack the esc was cutting back too much and was hotter then with the 880kv. I am sure it was due to the fact that the 1100 with the 8t pinion would be happier at a higher headspeed. The 880kv that I have will work from 1600 to 2200 depending on the pinion I choose to run and be happy with it.The world is yours!
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12-22-2011 12:38 PM  9 years ago
Pistol Pete

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Seffner, FL

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On 6S swinging 550's, no gov.

880Kv needs 12T to get @ 2000RPM
1100Kv needs 10T to get @ 2000RPM

Ive read 8T are not the best due to meshing issues and or greater potential for stripping main gear.
~~Enjoying the hobby one flight at a time~~
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12-22-2011 09:28 PM  9 years ago
Richardmid1

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Leeds, England

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I go with the packs nominal voltage and leave the efficiency out and get very accurate results.

Castle gov requires about 20% headroom so if say you want to run 2000 headspeed you want to gear the heli to run at 2400 max. All governors are different though, Kontronik governors for example only need about 15% headroom.
60% of the time, it works every time!
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12-22-2011 10:46 PM  9 years ago
bustedmp

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Shamokin, PA

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My flying skills are not good enough to need or want 2000rpm yet. I like the smoothness it has at 1600, 1550 and below it gets scared and shakes. I have tried 1700 and 1800 which makes the response very nice, but I kind of like a nice smooth flight so 1600 rpm is good enough for me for now. Even if I did run it at 1800 with the gov on the castle i couldn't push it hard enough to need the overhead and keep the heli in one piece. Even at 1600 the esc is using 87% of the battery power. I am happy with how smooth my NX is at that headspeed, or should I say was before it got flooded along with everything else in my basement. I am still working on getting back in the air the way I want it.The world is yours!
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