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fastbaja5b
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11.07.2011, 07:21 PM

I find it a bit insulting that because I choose to question what I consider issues I am being labelled as a 'basher' as I don't maintain the status quo.

What happened to informed intelligent discussion?

The numbers don't lie, I am curious how the SCT combo is specifically labelled as 2s only (no 3s with that motor on that ESC) yet the Flux XS uses an ESC with similar specs, a motor which is clearly less efficient, but they pretty much invite you to run 3s through it.

I've been told here that a 30 odd amp jump is reasonable for 200kv, so by that logic, if I go down from the 4000kv to a 2000kv, my battery should be getting charged as every 200kv drop is a 30 amp drop? Doesn't make sense.

I have no problem proving my data:

Flux XS, stock esc, stock motor



Compared to Flux XS, stock esc, Castle 3800 motor


And when placed in a Hyper 10SC, with a HPI Q Base esc, geared for around 30-35mph, the 4000kv motor still pulls huge amps (and runs hot)



..the numbers don't lie. (Esc's both run with default settings, deans plugs, Turnigy Nanotech 65/130C 2s Hard Cased Lipo)


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Pdelcast
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11.07.2011, 08:05 PM

Quote:
Originally Posted by fastbaja5b View Post
I've been told here that a 30 odd amp jump is reasonable for 200kv, so by that logic, if I go down from the 4000kv to a 2000kv, my battery should be getting charged as every 200kv drop is a 30 amp drop? Doesn't make sense.
Well that's just silly.


Going from a N38UH magnet to an N35UH magnet is about a 8% decrease in air gap flux. This causes the kV to rise by about 8%.

A Castle 3800kV motor is about 3770kV actual.

An HPI 4000kV motor is about 4050kV actual.

They have exactly the same DC resistance.

So the difference in current maximum is determined by back-EMF. Because the HPI motor has lower back-EMF, when using the same gearing and throttle ramp rate, the maximum currents will be significantly higher.

Your observed 30% maximum current difference is about right, and doesn't have anything to do with how the motor is constructed. If we made you a custom 4070kV CC 1410 motor (by shortening the stator stack and magnet) the peak currents would also be about 30% higher than the CC3800kV motor.

IF you change the gearing so that the HPI motor is geared approx. 8% lower than the 3800kV CC motor, you should see about the same peak currents.

OR - if you change the throttle ramp rate by 8% (using punch control or torque limiting) you will see about the same peak currents.

It's just that you can't compare peak currents on two different kV motors side-by-side without making a similar gearing or throttle ramp rate adjustment.


Patrick del Castillo
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Castle Creations
   
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fastbaja5b
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11.07.2011, 09:15 PM

Ok, well I'll gear both for the same speed and do a back to back test.

Can we use the 1410 rebuild kit (specifically the rotor) in the HPI branded motor?


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Pdelcast
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11.07.2011, 09:18 PM

Quote:
Originally Posted by fastbaja5b View Post
Ok, well I'll gear both for the same speed and do a back to back test.

Can we use the 1410 rebuild kit (specifically the rotor) in the HPI branded motor?
You sure can. :)


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fastbaja5b
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11.07.2011, 09:24 PM

Now will that improve the efficiency I am seeing (obviously not KV as that is Stator based?), or with it being the magnets as you stated, will putting in a rebuild kit bring this HPI motor to the same spec as the 3800 Castle?


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Last edited by fastbaja5b; 11.07.2011 at 09:25 PM.
   
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Pdelcast
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11.07.2011, 09:35 PM

Quote:
Originally Posted by fastbaja5b View Post
Now will that improve the efficiency I am seeing (obviously not KV as that is Stator based?), or with it being the magnets as you stated, will putting in a rebuild kit bring this HPI motor to the same spec as the 3800 Castle?
If you change the rotor, the kV will drop because of the stronger magnets in the CC rotor.

The efficiency of the motor will go up slightly, but still won't be as good as the CC3800 motor because of the difference in the stator lamination thickness. Thicker laminations = lower cost = higher iron losses = higher maximum flux density. Thinner laminations = higher cost = lower iron losses = lower maximum flux density.

The .2mm laminations in the CC motor are rated at 150watts loss / kilo @10khz, the .35mm laminations in the HPI motor are rated at 230watts loss / kilo @10khz (for comparison.) But the .2mm laminations are three times as expensive as the .35mm laminations.

Both perform well. But the .2mm laminations have a small advantage in high speed motors, at a large cost disadvantage.

We make both .2mm and .35mm lamination versions of many of our motors. Really depends on whether the application and cost target can justify the extra expense for the thinner laminations.

All of the CC branded motors use .2mm laminations. For OEM motors, some use .2mm laminations, some use .35mm laminations. Really depends on the application.

Thanx!


Patrick del Castillo
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crusey_aus
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12.14.2011, 02:00 AM

Apparently HPI are swapping failed ESC's with a new version

Any comment on what has changed Patrick ?

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