RC Motor Turns and kv

R

reload

10 mW
Joined
Sep 8, 2009
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So I'm trying to put together a RC bike kit and I am wondering about how to choose the best config for a motor.

I'm specifically wondering about astro 3220 motors. It looks likes alot of builds are based on the 4 turn version but why not go for a higher turn count, get a lower kv and have less reduction gearing etc.
 
Higher turn count will mean smaller gauge wire meaning less current capability meaning lower power. The other way to look at it is the motor size determines the amount of torque you can get, so the faster you can run the motor, the higher the power.
 
yeh that makes sense. more turns, means smaller wires in the same space = less amps.

are the watt ratings the same for all the configs? so...i guess that means a higher voltage ratings for higher turn counts.

i tried asking astro fore more specific info on the diff versions but they only pointed me to the general spec page. anybody have experience with diff voltages and currents that have been used with the astro motors?
 
In the case of the Astros, all of the different winds are effectively identical motors with identical efficiency, power and torque. What varies is the Kv, but an inverse relationship of voltage and current in the same proportions gets you to the same end result, since the motor limits are rpm and temperature. Miles shared a link with a performance chart listing each winding of an Astro 3110 that displayed this commonly misunderstood relationship very well. I tried searching and couldn't find a link for you. The bottom line is that as long as the copper fill is the same, the motor is identical.

In the case of hubmotors, the inability to vary gearing due to limited wheel sizes along with the practical limits of voltage means you can't effectively consider different windings of an otherwise identical motor to be the same motor like you can with RC type motors. For hubmotors the higher turn count motors with the lower Kv are slower and lower power, and the will often be more effective on hills and in stop-n-go traffic because they are more efficient at lower speeds. Higher Kv hubbies are faster and higher power because they are can handle greater current resulting in the same torque but at higher rpm, so greater power is possible with the same voltage limitation.

John
 
reload said:
i tried asking astro fore more specific info on the diff versions but they only pointed me to the general spec page. anybody have experience with diff voltages and currents that have been used with the astro motors?
Click to expand...
I've used several different Astros. Notably, 3220 in 4, 5 and 8 turn. You get the most power out of the motor at high RPMs if I understand right. To get to high RPMs, you need higher voltage if you choose a low kv wind. Me, I like the Castle Creations HV-160 controller - it's small, reliable, and it's really the only controller I know. Notably, it's max voltage is 50v. So, for me the best choice for motor is one that gets to 7500-8500 rpm at 50v. That's the 4 or maybe the 5 turn.
 
John in CR said:
In the case of the Astros, all of the different winds are effectively identical motors with identical efficiency, power and torque. What varies is the Kv, but an inverse relationship of voltage and current in the same proportions gets you to the same end result, since the motor limits are rpm and temperature. Miles shared a link with a performance chart listing each winding of an Astro 3110 that displayed this commonly misunderstood relationship very well. I tried searching and couldn't find a link for you. The bottom line is that as long as the copper fill is the same, the motor is identical.

In the case of hubmotors, the inability to vary gearing due to limited wheel sizes along with the practical limits of voltage means you can't effectively consider different windings of an otherwise identical motor to be the same motor like you can with RC type motors. For hubmotors the higher turn count motors with the lower Kv are slower and lower power, and the will often be more effective on hills and in stop-n-go traffic because they are more efficient at lower speeds. Higher Kv hubbies are faster and higher power because they are can handle greater current resulting in the same torque but at higher rpm, so greater power is possible with the same voltage limitation.

John
Click to expand...


Hm. I noticed that the Adaptto Maxi-e controller has a ERPM limit of 70,000.
So if I go for a higher motor turn for an Astro 3220 I should be able to use stock firmware with the Adaptto controller while running an astro 3220? And all this without loosing max power?

It seems most people limit their voltage to 48v for the Astro motors. would there be possible to explore higher output power by increasing voltage - as long as I don't exceed 70,000 ERPM?
 
It's actually 60000 erpm.

You cannot simply overvolt rc motors because they have their max power declared at max rpm, and if you go above that max rpm losses become too large and you gain nothing. So what you should do of you want max power is make sure that your rc motor can work up to its declared max rpm, no matter what voltage you use, you have to pick suitable kv motor according to your voltage.
 
It seems that Astro themself says:
AstroWebsite said:
Typical Voltage Range 24 to 80 volts for the Astro 3220.
Click to expand...

If there was no point of over volting why would they not state that on their website?

It should then say max voltage 48v?

Adaptto claims on their website max 70,000 ERPM.

AdapttoWebsiteIndexPage said:
Ability to use in conjunction with high-speed engines to 70000 ERPM (1ERPM = rev / min motor * number of pole pairs).
Click to expand...
 
Oh ok. So different Kv will handle different volt, yes?

Didn't remember they launched their English website. I read their .ru website via google translate and there is says 70,000 e-rpm.
But yes I saw the English says 60K. Don't know what is correct. But it seems those astro motors can come in different turns so if it is 60K limit a higher turn will work or lower voltage I guess.
 
The different winds of that motor will have the same power limits (same torque at the same rated erpm), so the reduction is the same too, as well as noise. You just have to look at the voltage and current limits of the controller to make sure it's a match if it can handle the erpm. Since in this case you're looking at the controller being fixed, if there's leeway in both the voltage and current, then opting for a higher voltage so you can run lower current through it would be the better choice.

Keep in mind that Astro posts the range of voltage to take into account the different windings. The limits are the physical limits of rpm, which is the same for all winds. IOW, there's no such thing as over-volting, because it's not like a hubmotor which aren't run at their rpm limits. Astro tells you the limits, and it would be unwise to run a voltage that exceeds the rpm limit.
 
macribs said:
Oh ok. So different Kv will handle different volt, yes?

Didn't remember they launched their English website. I read their .ru website via google translate and there is says 70,000 e-rpm.
But yes I saw the English says 60K. Don't know what is correct. But it seems those astro motors can come in different turns so if it is 60K limit a higher turn will work or lower voltage I guess.
Click to expand...

yep been talking with them via email, its 60k.
 
OK 60K it is. It seems even astro 3220 4T will work. 169 kv @48v = 8281 rpm.Rpm x poles pairs = E-rpm
8281 x 4 = 33,124 E-rpm.

And no need to over volt seems to be consensus.
 
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