Simple throttle curve question

[drakenn]

How do I tell the RPM of the motor? I know all the math to calculate the head speed, just how do I tell the top RPM of the motor so I can set my throttle curve appropriately. Stock align motor and esc. Thanks!

[GreenCello]

Two choices. A monitoring device such as the Eagletree E logger with Rpm sensor or a tachometer. The Eagletree will give you a lot more valuable information such a Voltage, Amps,etc. An optical tach is the safest tach but requires a helper.

[Bob O]

Originally Posted by drakenn

How do I tell the RPM of the motor? I know all the math to calculate the head speed, just how do I tell the top RPM of the motor so I can set my throttle curve appropriately. Stock align motor and esc. Thanks!

kilivolts * volts.....is that what you're looking for?

For instance, my 430L 3550kv motor running from a 3 cell Li-Po battery:

3550 X 11.1 = 39,405 RPM.

Hope this helps.

[widower]

I believe 1 KV stands for 1000rpm at 1Volt. As BobO mentioned, that's the simple way. I've seen some web pages that get really fancy and start including drag and many other things.

Regarding the optical tach, you want the tach with the shutter mechanism. You look through it and adjust a dial until the main rotors appear stationary. Then take your reading. Their usually in the price range of $80. There is a sticky thread on helifreaks that shows how to build your own.

A data loger like the EagleTree V3 is around $75 plus sensor. I think it's the way to go. You can also use it to monitor battery current, servo current etc. There's even an optional gps attachment that logs your heli travels in 3D and then you send the log info to google maps to view your flight patterns.

[mwillack]

Originally Posted by widower

I believe 1 KV stands for 1000rpm at 1Volt. As BobO mentioned, that's the simple way. I've seen some web pages that get really fancy and start including drag and many other things.

Regarding the optical tach, you want the tach with the shutter mechanism. You look through it and adjust a dial until the main rotors appear stationary. Then take your reading. Their usually in the price range of $80. There is a sticky thread on helifreaks that shows how to build your own.

A data loger like the EagleTree V3 is around $75 plus sensor. I think it's the way to go. You can also use it to monitor battery current, servo current etc. There's even an optional gps attachment that logs your heli travels in 3D and then you send the log info to google maps to view your flight patterns.

I beleive it is 1000kv for 1000rpm at 1Volt. My 3700kv motor runs at 3700rpm at 1 volt.

[MXDURO]

3700kv motor with 3s pack of 11.1v = 41070 rpm
That means on the trex 450 se v2 : 150t main gear the head speed will be:

12t: 150\12 = 12.5 = 41070\12.5 = 3285.6 rpm
13t: 150\13 = 11.538461 = 41070\11.538461 = 3559.40 rpm
without taking blades and drag in calculation? Does this sound correct?????

[haywire]

Yea, you need to step down from your gear ratio too.

[pwoodyp]

Assuming (for the examples):

KV: 3700KV (ALIGN 430XL)
Volts: 11.1V (Lipo 3s1p)
Main Gear: 150T (Trex 450)
Motor Pinion: 11T
Drag Co-Efficient: 85%

To Calculate the Headspeed

((KV * Volts) / (MainGear/Pinion))*DragCoefficient
Example: Copy and Paste into Google: ((3700*11.1)/(150/11))*0.85

To Calculate the Motor Pinion, assume 2560.3rpm headspeed

HeadSpeed*MainGear/KV/Volts/DragCoefficient
Example: Copy and Paste into Google: 2560.3*150/3700/11.1/0.85

To Calculate Motor RPM

KV*Volts
Example: Copy and Paste into Google: 3700*11.1

Some Links to play with: References - Headspeed Calculators

DarkHorse: http://www.dhrc.rchomepage.com/calcAdvanced.htm (WOW)
Headspeed Calculator for Windows: https://www.helifreak.com/showthread.php?t=55471
ReadyHeli: http://www.readyheli.com/Online_Head...lator_s/81.htm

Source:

https://www.helifreak.com/showthread.php?t=41692

I maybe right I maybe wrong however I'm certainly opinionated, check the equations your ownself

[DominicD]

The KV actually changes depending on the current draw and other factors.

[Mr.Andersen]

Can you explain deeper?

[DominicD]

Perhaps another day.