Brushless motor torque

[Saull]

Hi,
I cant finde rating on torque for brushless outrunner motor. I am not interested in exact number but something that I can roughly estimate what motor I need. So what torque can I expect from 100 watt 1000 kv outrunner ?

Thanks.

[Benta]

The relationship is:

Torque = Power / Angular frequency

The angular frequency is 2 * pi * rpm / 60 (you need revs per second)

If you run your motor at 6 V, it will rotate at 6000 rpm

So Torque is 100 W / ( 2 * pi * 100 ) = 0.159 Nm

[W9GFO]

If you know the power and rpm, you can calculate torque.

Torque (Nm) = Power (W) / (Speed (RPM)/9.5488)


A 1,000 kV motor running at 10V would be turning 10,000 rpm.

100W / (10,000 rpm / 9.5488) = 0.95 Nm

[tatus1969]

The relationship is:

Torque = Power / Angular frequency

The angular frequency is 2 * pi * rpm / 60 (you need revs per second)

If you run your motor at 6 V, it will rotate at 6000 rpm

So Torque is 100 W / ( 2 * pi * 100 ) = 0.159 Nm

+1, W9GFO's formula is also correct but the result seems to have a typo.

On the other hand, torque is (in a wide range) proportional with current. The 1000kV / 6V motor will happily deliver twice that 0.159Nm if loaded correspondingly, and draw (more than) twice current from the battery. Of course it can only do this for a short period and heat up quickly. Therefore I tend to look more at wattage and required rpm. Depends on the application of course. Also keep in mind that the numbers of typical BLDCs are often peak power, they often cannot deliver this continuously.

[Benta]

W9GFO's formula is also correct but the result seems to have a typo.

No typo, W9GFO is just calculating at a different rpm. Both results are correct.

[tatus1969]

W9GFO's formula is also correct but the result seems to have a typo.

No typo, W9GFO is just calculating at a different rpm. Both results are correct.

100W / (10,000 rpm / 9.5488) = 0.095 Nm

[Benta]

Man! Missed the decimal error. You're right, of course.

[Saull]

Hi,

Thanks all for help, like I said I need ballpark number so those equations will help.