View Single Post
Old Jan 01, 2013, 05:56 AM
modisc is offline
Find More Posts by modisc
modisc's Avatar
United States, MI, Ann Arbor
Joined Aug 2011
895 Posts
Originally Posted by Odysis View Post
If you have a sinusoidal magnet, the flux distribution will be sinusoidal, and so will the bEMF (roughly). In this case, it doesn't matter what the winding is.

With a "square" rotor flux distrubution, caused by lumped magnets as normally seen in RC motors, you may or may not get sinusoidal bEMF. With concentrated, full pitch windings like we all use, the bEMF will be roughly trapezoidal. If you use a distributed winding scheme though, you can get a bEMF that's sinusoidal, even will a hobby rotor.

It makes a few % difference in efficiency, but that's it. If a sinusoidal machine (magnet or winding distribution) is driven by a sinusoidal signal, you can get almost perfect torque (FOC for example).

If you use a trapezoidal machine and a sinusoidal signal, there are some regions where the motor is capable of producing 100% torque, but the signal commands as low as 86% (off the top of my head). The result is a torque ripple and noise.

If that doesn't make sense, let me know and I'll see if I can draw some bEMF and current waves.

(sorry for the OT!)
How about sinosodial machine driven by trapezoidal signal. To be more specific, a sinosodial rotor, with concentrated winding, driven by RC ESC (trapezoidal signal), how is this combination?
modisc is offline Find More Posts by modisc
Reply With Quote