The motor was spinning way out of its efficiency range probably. Too numerically high of a final drive ratio, and it doesn't put enough load on the motor. Still haven't figured out why brushless motors like a certain amount of load to run cool...

There's a general rule of thumb to not overgear, but also not to undergear a motor.

ok thanks...

guys take a look on this motor can it is useless to put a heatsink on this ?

http://img33.picoodle.com/data/img33...2m_73de019.jpg

its a giant heat sink itself, maybe screw a fan in the vanes ? <ducks from thrown vegetables>

yeah true..

whats about if I use a heatsink + fan combo on this already integrated huge heatsink does it can work just fine or ... ?

I run my 2s 7.4v lipo pack at 6.3v cut-off does it got a big difference in runtime from 6.0v and 6.3v cut-off if yes how much ?

The runtime difference won't be more than a few seconds, and is definitely not worth the risk. If possible, it wouldn't hurt to run the cutoff as high as 6.6v. If the battery is any good it won't have any problem staying above this limit.

ok thanks for your reply. and whats about a 3500kv brushless motor and 4300kv does I can notice about 5min more runtime with the the 3500kv instead of the 4300kv ?

Geared for the same speed they should theoretically have the same runtime. There are a number of other factors which determine runtime, including driving style, battery choice, etc.

hmm for now im geared 18t pinion 84t spur and I get 30mph on the 4370kv motor with the 3500kv for get the same speed ( 30mph ) I should use 84t spur and 22t pinion so the runtime will be almost the same ?

The 22t should give approximately the same top speed. Which motors are you comparing? That will make a difference. For example, the VXL 3500 uses a larger rotor than the Castle motors, and so runtime is affected accordingly.

for now I use this one :

http://cgi.ebay.com/4300KV-9T-Brushl...QQcmdZViewItem

--->

MAX AMPS FOR THIS MOTOR IS : 40AMPS

do larger rotor give more or less runtime ?

In this case the VXL 3500 should theoretically give less runtime due to its larger rotor. It doesn't work like this all the time though, because you have to factor in the efficiency of the motor given a certain load.

if the esc and battery stay cool and only the motor get damn hot whats its can be ?

undergeared?