Alien/Turnigy c80-100 130kv vs 80kv

[Ratking]

Hello

I've been trying to find out what the drawback with a low kv motor is compared to the same motor with a higher kv.
The case is that I want to lower the speed of the motors so the total reduction is lower making the sprockets and chain lighter and shorter.
I understand that there are some disadvantages with the lower motor speed, but what would the difference between these two motors be?
http://alienpowersystem.com/shop/80mm/c80100-outrunner-brushless-motor-80kv-7000w-2/
http://alienpowersystem.com/shop/80mm/c80100-outrunner-brushless-motor-130kv-7000w-2/

And would the 80 kv motor be easier for the controller or harder?
Is there less power potential in the 80kv version compared to the 130kv?

I tried to mail Alien Power Systems about termination(star/delta) but did not get an accurate answer. If anyone else have experience with the motor, please tell me.

Thanks

 

[Ratking]

From the chart at astroflight we can see that the 3220's Kt and best amp combined gives the same torque regardless of Kv.
But I suspect that I would need a higher voltage to get the same power?

It seems that a lower kv will give a higher resistance for the same termination.
That means that a low resistance motor have a better potential regards to heat build up.


http://www.astroflight.com/3220.html

 

[Arlo1]

If wound properly the performance from the motor will be the same one will just need more voltage to spin as fast as the other.

The LOWER KV motor will be EASIER for the controller to run. It will have more inductance which is much more important that the higher resistance it will also have.
I think a 80kv is still pushing the limits of a Chinese controller with out phase current sensing. Maybe PM thud to post on this thread he really knows the limits here.

 

[Ratking]

If wound properly the performance from the motor will be the same one will just need more voltage to spin as fast as the other.

The LOWER KV motor will be EASIER for the controller to run. It will have more inductance which is much more important that the higher resistance it will also have.
I think a 80kv is still pushing the limits of a Chinese controller with out phase current sensing. Maybe PM thud to post on this thread he really knows the limits here.

But if I have a voltage limit of 50v due to using a castle creations hv 160, would I be able to put the same amount of current in to the motor as the 130kv version? I want to have a lower motor rpm to get the benefit of a slightly less noisy system and less reduction.
My understanding was that I would get a higher Kt and therefor more torque for the same amps with a lower Kv.

 

[Thud]

I'll jump in here,

But if I have a voltage limit of 50v due to using a castle creations hv 160, would I be able to put the same amount of current in to the motor as the 130kv version?.

That depends on the method they used to arive at that KV....if its simply re-terminated in wye, then the combined current carying capacity of the wire should still carry = current values.
(i have no clue what those are wound with from the factory or what the wire insulation is rated for)

I want to have a lower motor rpm to get the benefit of a slightly less noisy system and less reduction.

we all want that, but you never get a free ride.
By lowering the kv....& not re-ballancing the equation with higher voltage, you are effectivly lowering the horspower potential of the system.
(horspower being: tourque/time)

Study the astroflite charts.... they all equill about 4500 watts of energy input on the continuous ratings chart.
this is the reasonable limit of a motor that size....they can rewind for higher KV with fewer turns of heavy wire...& feed it amps to reach 4500 watts...
or wind many turns with lighter wire(less current carying capacity) & feed it voltage to achive the exact same potentials...

The key thing to focus on is....every variable on the chart is measured at nearly 8krpms....from 12v to 288v.....(tourque/time)

My understanding was that I would get a higher Kt and therefor more torque for the same amps with a lower Kv.

this is a true statment...but missing 1/2 of the equation as it applies to driving a vehicle.
the amount of Kt gained is not proportional to the loss of HP by staying with the previous voltage.
by spinning the motor slower you are cutting its power potential...how much? I can not say.

Do not expect maximum output of any motor at less than optimal speed/rpm. (& forget the 7kw thats stated on the websites....I have unsoldered internal connections on a few of these motors looking for true 6kw continuous rattings...they won't do it....continuously.)

My point:
Just be aware that your de-rating your motor to less than optimal. Operate is inside those parameters & you'll be fine.

examples:
all the Astro motors that got smoked on the race tracks were lower KV units to ease gearing issues....then over driven in amperage to try to drive the bikes at 30+mph....
the smaller wires used to achive high Kv couldn't sustain the high amperage needed to make the required HP to deliver target performance.
Instead of 6 & 8 turn motors on limited voltage....they should have been 3 or 4 turn motors.

 

[Miles]

My understanding was that I would get a higher Kt and therefor more torque for the same amps with a lower Kv.

Addressing this directly:

If you halve Kv, you double Kt. So, you get twice as much torque per Amp and copper losses are proportional to the square of the current (I²R). In order to double Kt, you need to double the number of turns in the windings. When you double the number of turns, not only is the cross-sectional area of each turn halved, the total length of the windings is doubled, also..... So, the resistance goes up in proportion to the square of the number of winding turns.

As long as the fill factor remains the same, the amount of heat produced per unit of torque is not changed by varying the number of turns in the winding.

 

[Ratking]

Thank you for your replies guys, great help.

I asked the seller for more information, I hope they are winded in such a way that the fill factor is as close to the 130kv version as possible.