I'm trying to select a motor for a design application that cares mostly about efficiency. Given a required torque and RPM output from the motor, I feel like it should be possible to calculate the efficiency of that operating point given a spec sheet. However, take the spec sheet on page 8 of this pdf for example: https://www.magneticinnovations.com/wp-content/uploads/2020/07/Brochure-Frameless-High-Torque-Motors_MI-F18V1web-std-res.pdf
There doesn't seem to enough information to calculate the efficiency for a given operating point. I feel like you would need the viscous drag (Nm/rpm) and static torque (Nm) as constants to be able to then multiply by the RPM to get the iron losses, and add them to the copper losses which can be found using the resistance (which is included). The total loss can be then compared to the output (torque * rad/s) to get efficiency. However, most data sheets don't have those two constants. Is there another way using the other constants? Is there something obvious I'm missing? This is a PMSM. With some BLDCs, given the no-load current, Kv, and R, you can match a supply voltage to get to the right torque-RPM point, and then find the efficiency that way, using (torque * rad/s)/(V * I).