Hello,

I'm trying to choose a motor to build a long(ish)-endurance quadcopter. I will be using the RCTimer x650 frame to lift a go-pro and small brushless gimbal. I want to use 2x 4000mah 4s packs for a total of 8000mah 4s

I want to use ~16 inch propellers on either the 3508 320kv motor, or the 4108 380kv motor running 4s

Can some one experienced in brush-less motor design help me understand the differences between these 2 motors? The weight of the motors is very close, The main difference I can see is the 3508 motor has 14 poles, while the 4108 motor has 24 poles. I'm not sure what this means in terms of efficiency though. In the charts posted, the 3508 motor uses slightly less current, but aso has slightly less g/w effeciency compared to the 4108 motor

.

Thanks for any help!

Nick

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Replies

  • You should note that the 380kv motor may actually be 480kv...see the picture and comments below the picture. 

    • The 4108 is a slight higher wattage motor than the 3508. You have to look at the charts to really see this as Sunnysky is bad about not specifically listing the maximum watts the motors can handle. Practically, what this means is a higher wattage motor has more torque and will have a better ability to turn larger props and still hold speed.

      I'm guessing a bit from the charts, but I'd say the 3508 can handle around 275 watts while the 4108 can handle around 325 watts.

      Either motor might work, but I couldn't find any Sunnysky motor data charts for the 3508 that tested on 4S. The data all seemed to be for either 5S or 6S. The fact there's no data being presented for 4S would make me hesitant on the 3508 until I found out why.

    • I think that's just the pic they used... They are both actually 380kv, I just made a typo when posting for the first motor.

      I think I'm leaning towards using the 4108 380kv motor. I think the wider motor with 24 poles will have more torque for about the same amount of current as the smaller motor.. good for a larger propeller like I plan to use. but still don't fully understand.. I'm sure the 3508 motor has some advantage or they wouldn't make it?

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