Quote:
Originally Posted by biddy
nuz69's theory is based on the assumption that the efficiency of the 1518 will be the same as that of the 1515, with a 4S lipo pack. This is incorrect as the 1515 will have the most efficient top RPM of 32,560 whilst the 1518 will have a max RPM of 26,640. At 26,640 the motor is in a lower portion of its power curve, and is not as efficient compared to an RPM of around 30,000.
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No I am damn sorry, this statement is correct for two motors of same weight and different Kv due to different windings, BUT we are talking about two motors wich have same windings and different weight.
"lower portion of its power curve", This is not a nitro motor, the efficiency of a brushless motor is not measured by varying the voltage, but the LOAD or the AMP going through the motor, while the motor is under a given voltage.
The 1518 motor, with its longer rotor, produce more torque at the same amp, so puting an higher pinion on it will compensate the lack of RPM and will result of the same working point in terms of current, however the shaft of the motor will be strain of an higher torque. Moreover, the 1518 will have to handle the same power in a larger can and on a longer rotor, so the temperature will necessarly drop a little, and efficiency will go up.
That's exactly the reason why here in europe in our large tracks we use the 1515 2200Kv on 4S instead using 1512 2650Kv on 4S because it always overheats, too small motor...
On the other part, in our practical application, a lower Kv motor will produce lower amp spikes during acceleration, and amp spikes are responsible too of the heat and bad efficiency, that's where the 1518 win the efficiency test too.
I have done the test between a 1515 and a 1520 on 4S geared for the same speed in my mbx5T, I always had lower temp and longer runtimes with the 1520. I suggest you to do the test.
Anyway I race my truggy on 6S with the 1600Kv but with adapted ESC parameters to avoid as possible the amp spikes...
==> Xsmoker you can begin by increasing the punch control, and maybe drop one pinion tooth, I know by experience that most of the pilots have a too large gearing for the track they race.
After that if you have some dollars to spend, don't buy larger 4S batteries, it will add more weight, not good for the driving behavior and strain on the system. Buy some 5S 4000mAh and reduce the pinion of 4/5 x actual number.