Motor MN3110 700kv , 3S or 4S?

[afernan]

I´ve just bought a set of MN3110 for my hexa. Looking at the performance table (attached) the effitienty (gr/watt) decrease significantly with the number of cells.

Por instance, a copter of 2.6 Kg requires 433gr/motor, so you can get it with:
204watt using 3S or
288watt using 4S wich is 41% !!! higher and this is proportional to flight time.

This clearly indicates to use 3S intead 4S for this reason. In a small quadcopter I have (1 Kg) I´ve experienced this big difference (I use 3S, with MT2212 and 2200mAh). When using 4S with same h/w I clearly obtain much lower effitiency.

Any experience on this phenomenon?

Angel

[LPR]

Angle

I've looked at a lot of charts and I see that using lower voltage often gives a little better efficiency. These charts look a bit off because they must have used different 12*4CF props when making the charts for 3s and 4s.
The 3s chart @ 65% has 500 grams of thrust for 4500 RPM.
The 4s chart @ 50% has 420 grams of thrust for 4800 RPM.

The same prop should have at least the same thrust at higher RPM.

Larry

[afernan]

Larry:

you´re right. There´s something wrong in the table.

I can´t imagine any reason why the effitiency should be higher for lower voltage. In fact I thought it was the oposite (higher volt, lower current then lower heat losses, then higher effitiency).

Anyway I´ll test at home to see if there is some effect.

Angel

[chschmid]

Hi Angel

I use the 3508 on my hexa with 4s and 12x4 Tiger Props. Nice Combo.
They just draw around 20Amps.
I had to chenge the switching frequency to 12KHz and advance to 22°.

STARTUP_MODE 0.0
FF1TERM 4.92449e-08
FF2TERM 0.00137331
MAX_CURRENT 25.0 // amps
PWM_RPM_SCALE 6500 // RPM equivalent of maximum PWM IN in CLOSED_LOOP mode
CL1TERM 0.240078
CL2TERM 0.00138354
CL3TERM 0.061492
CL4TERM -4.20862e-05
CL5TERM 0.656795
SWITCH_FREQ 12.0 // output PWM frequency in KHz
ADVANCE 22.0 // electrical degrees

Cheers

Christof

[afernan]

Christof, thanks for your info. I´ll try that.

Angel