RPM and rollout question/decision help?

[nuz69]

No!
The both motor can handle the same power, that mean geared for the same speed, they will consume EXACTLY the same amout of current (amps).
You can put a higher pinion on the 1850kV BECAUSE it provide more torque for the SAME CURRENT than the 2650kV. Both motors will work exactly as hard.
BUT, the 1850kV will have less RPM, meaning less losses from bearing drag (that mean better efficiency) AND higher bearing lifetimes.
The 1850kV is lighter too, mean less weight in the car and a little less current consumption.
Other than that, the lower kV possess more controlability due to the higher self inductancy of the winding, Although the punch control can help to get some controlability...

[VintageMA]

nuz69 - I don't agree with your arguements.

- Both motors are 1512 motors and will weigh the same.
- Neu motor are actually more efficient up around the 40K range. It is the cheaper motors which are more efficient in the lower RPM ranges primarily because they are, well, cheaper.

Listen to what Jeff is saying - he knows his stuff.

IMO if you use the 1850kv motor you should really be going up to 5S to bring the RPMs closer to 35K. If you go with the 1850kv motor with 4S and taller gearing you are going to pull many more amps on acceleration than you would with the 2650 with shorter gearing. The 2650 motor will just have an easier time spooling up.

I would say run the 2650 with 20-30% punch and you'll be pretty happy.

[nuz69]

IMO you are wrong,
The torque per amp is higher when the kV is lower, meaning for the same acceleration force, both motor will consume exactly same current. Its all about energy, you need it to accelerate your truck, and it comes from your battery depend only of voltage and current ==> same voltage and acceleration ==> same current.

Neu 1512 1.5 : 10.23 oz
Castle/neu 1512 1Y : 13.1 oz

It appears that the Castle/neu has a little less efficiency than the real american neu.

The electromagnetic efficiency depends a lot of the load, not of the RPM : between 25k and 40k efficiency is the same. But mechnical losses are higher at 40k.
==> For the same top speed and same voltage, the 1850kV will always provide better results for in matter of temps and runtimes...
==> I would keep the neu.
Who is jeff ? ^^
Can someone qualified confirm or negate ?

[VintageMA]

Originally Posted by nuz69

Neu 1512 1.5 : 10.23 oz
Castle/neu 1512 1Y : 13.1 oz

Hmmm... fair enough - should have looked up the specs instead of making an assumption.

Originally Posted by nuz69

It appears that the Castle/neu has a little less efficiency than the real american neu.

Previous research and threads from Patrick have shown that the Castle Neu's will run about 10* hotter than the hand-built Neu's, IIRC.

Originally Posted by nuz69

The electromagnetic efficiency depends a lot of the load, not of the RPM : between 25k and 40k efficiency is the same. But mechnical losses are higher at 40k.
==> For the same top speed and same voltage, the 1850kV will always provide better results for in matter of temps and runtimes...
==> I would keep the neu.

What is your source of this information?
In my own personal experience, many years of testing and many $$$ spent on about 15-20 different Neu motors has shown me that 35-40K is the sweetest spot for these motors. Heli guys run them up in the 50k rpm range - which I have found in surface gets them hot way fast.

The truth of the matter is that 4S is not the sweet spot for heat and efficiency - 6S and higher is. More voltage = less current for the same power and that equals less heat. But if 4S is a requirement - go with the 2650 motor. Going with the 1850 and trying to gear for 40mph is going to create a lot of heat.

Just my opinion -

Originally Posted by nuz69

Who is jeff ? ^^

jhautz

[nuz69]

I took this from my personnal experience. In europe we compared different configurations such as tekin buggy 1900kV and CC/neu 2650kV, on track. Both setup geared for the same top speed, the 2650kV ran a little hoter than the 1900kV, and the motors are theoritically capable of handling the same power, ~ 1200Watts.
And its logical, as you said, power is volt x amp, the same acceleration and voltage you have, the same current you will drop and so the same heat, end of story no ?
But it's true I don't have your kind of experience... Just wait someone else to confirm this all kV thing...