heli motors

[benngunn]

Hello hello.

This is a bit of a run on question from my earlier one about torque and battery etc.

on to motors we go! so sifu's, please enlighten me yet again!

SO I notice that some helis are recommended with lower Kv motors.. like a Trex I saw on some site recommended with a 3800kv unit..

Then I saw smaller helis, lik Piccolo size, recommended with a 4100KV!!

Realizing that the motor might be bigger for the Trex, how come it runs on lower KV and what would happen if:

I run higher KV motor on the Trex

and smaller KV motor on the Piccolo

=================

here is another one..

in the motor specs, I noted that they post up the lo and Ri values.. what relevance is that to motor performance or power consumption?

Thanks once again, one and all!

Dr. Bennjamin Gunn

[benngunn]

motors?

Any sifus out there can explain?

Thanks

BG

[Super-Hornet]

I not be expert here... here is my thought.

The bigger the heli is, the more heavier the head. That means u need a lot of torque to start the blades spinning and maintainning the blades speed especially when changing pitch.

Smaller heli head is lighter so no need to have hight torque.

When blades spin fast, your heli become more stable and better cyclics control (assuming your heli is in balance or not bended shaft)

With that, all helis required high speed motor but for TRex sizes, u need high torque motor to sustain its speed.

Bottom line... U need high speed motor to produce high speed spinning but u also need high torque to sustain it.

Super-Hornet

[9VDXN]

Here's another explaination....

For my way of thinking, KV isn't exactly a good representation of motor's torque.

KV is motor RPM per volt....so technically, to achieve the headspeed you want, you need to determine your running voltage & your gear ratio.

Most micro helis are limited to 11.1v as voltage, and a specific gear ratio.
so given these two 'fixed' constant, you cannot vary much by motor seletion to attain your desired headspeed.


Again, for larger helis, you can play with a lot of factors....

eg. My Voyager E likes to run at about 45,000 motor rpm with a 13T pinion gear to attain a headspeed of about 1800rpm..

With these figures, I can have options to run a lower KV motor at a higher voltage to attain my desired motor RPM.

Now, I use a 4000kv motor to run at 11.1v, which will give me close to 45k rpm. I can have the option to use a 2000kv motor and run at 22.2v (6S lipo pack) and I still can attain my desired motor rpm.

Previously when using 8cell NiMH pack, I was using a 4800kv motor, which gave slightly higher desired motor RPM (4800x 9.6v = 46,000 rpm)...so with motor being a bit too fast, I actually have to change a pinion to tame down the headspeed a little.

Get the idea?
Basically, besides motor selection, u gotta know what voltage u want to run at, what is the gear ratio of the specific heli, what range of pinion gears are avilable to u, and what is your desired headspeed.

Then again, calculations are calculations, and theory is theory....when it comes to the real thing, it's a different ball game.....If it was so easy, i would have spent so much money buying and trying different BL motors, pinions & battery packs for my VE....







Here are some picts of my VE to tempt u with larger scale electric helis..

[jerahteo]

In regard to motor , can anybody advise me why is it that my aline motor seem to lost power when it gets very hot. Recently I notice that , when I fly the heli for more than 10 mins and when the motor get very hot , I can just lost power and my heli can just come down.

Anybody had such experience before !

[9VDXN]

losing power usually is a result of ESC cutoff....
can be a temperature cutoff or low voltage cutoff.....

When either cutoff happens, it means there's something wrong with your setup somewhere....

[jerahteo]

If its a temperature cutoff what can you do about ?

It its a low voltage cutoff do you just charge your battery or there are some other problem ?

All I know is when I touch my motor the align 3200 model it was hot enough to make me ouch !