Understanding motor guide spreadsheet calculations

1

Hi,

I’m struggling to understand some of the assumptions in the motor guide spreadsheet. In particular, no load speed is calculated as speed constant x supply voltage, but then this value is used as if it were base speed and used to calculate power output, along with a value for torque based on the motors’ torque constant and max current value. My understanding is that base and no-load speeds are different, as at no-load speed you effectively have zero torque as explained here. I also see these assumptions being used elsewhere, e.g. Skyentific’s videos on youtube, where he talks about getting the full torque (based on max current x torque constant) at max speed, which is surely wrong?

More broadly, I’m trying to understand roughly what the torque-speed curve for the D5065 and D6374 look like. I understand that cooling is a significant factor, and this will affect the continuous torque capacity.

Any pointers are much appreciated.

Thanks,

Luke

2

No-load speed and base speed are effectively the same for a PMAC assuming no field weakening.

No-load speed is more relevant for async and series / parallel wound motors. A PMAC motor can run at the base speed at max torque (aka corner power). If you use field weakening, you can run a higher speed at lower torque.

ODrive doesn’t currently support field weakening, so the Torque-speed curve is a flat line from 0 to 0.7*Vbus*Kv