Which Brushless for the HBK2?

[gregor]

I'm new to brushless motors and having a little trouble determining which motor should be used in the HBK2. There is the Esky 3800kv but I've heard the frame needs to be modified to get it too fit. Helidirect used to carry a HDX300 3800kv but it looks like it's been replaced by a 3.17mm spindle version with the same specs. It seems like most pinions are 2mm or 2.3mm. I'm just starting out so I'm not looking for super head speed.

Recommendations?

[borocouncilman]

I run the 3100kv E-Sky outrunner. It's a perfect fit and is a bit lighter than the 3800kv. That said, with other motors, don't let the trimming scare you off as the HBK2 frame is soft enough to be trimmed with a fresh xacto blade.

[George1234]

I'm using the Esky 3900 on mine. Light weight, no mods required,and more power than the 3100.

George

[gregor]

OK, thanks. I have a dremel, and I'm not afraid to use it :) About the motors it looks there are 3 Eskys to chose from, 3100kv, 3800kv, and 3900kv. The 3800 seems to be the heaviest. What are the differences between these motors? I know that kv is rpms per watt. So it would seem that the higher number would always be better for efficiency. But perhaps not provide as much performance? Is that true? Other comments about these three motors appreciated.

[George1234]

Kv is rpm/volt, not watt. Power is calculated in watts, (volts x max. current in amps) the 3800 is the most powerful, in that it's max current is the highest of the three. the 3100 will give you the longest flight time, but at the cost of power.

George

[gregor]

George,

Thanks for clearing that up. So Kv is more "gearing" ratio number than a power output number. Really only helpful in determine which pinion to use. Correct? So how can you tell what a motor's output would be compared to another motor? I notice some web sites give an amp rating on motors.

[George1234]

Multiply the max amps x volts. Nominal voltage for a 3 cell lipo is 11.1 volts, fully charged should be 12.6 volts, although under load it would drop from 12.6 pretty fast. I use the
11.1 volts when I'm calculating. I think the 3100 motor has a max draw of 13 amps 13x 11.1= 144 watts. 3900 is 17 amps I think, so 189 watts. 3800 is 20 amps max, so 222 watts.
You're right about the rpm/kv being a speed indicator.

George

[gregor]

Thanks George. I ordered the 3800.