It is said, that synchronous motor is rotating at the same speed as magnetic field rotates. But three-phase made magnetic field rotates as the frequency of current, i.e. 50 or 60 times per second, which means 3000 or 3600 RPM.
How can synchronous machines on Aliexpress have other RPMs, like below?
There multiple of these, no any mistake expected. Many of them has 3 explicit inputs.
Sorry I agree that in slow RPMs reduction gears are most probable inside.
But can I be sure, that if motor is "synchronous", then magnetic field is rotating at 50/60 Hz and inner rotor is rotating at the same speed?