In the spirit of my latest thread this is one of the things I kept thinking about. I kept asking why the induction motor was not evolved by this seemingly simple looking principle. Most of us know (or at least think we know) the principle of a classic induction motor. You establish a rotating magnetic field. (In most simplistic case of having one current loop as the rotor) The loop tries to remain in a non changing flux thus induces a current which acts in such a way that it will counter act the change. In the induction motor this will result in the rotation of the loop which will try to keep up with the rotating field until it does and the net torque becomes 0.

Now a dc motor on the other hand uses a "different" principle for the main rotation, namely the Lorentz force. But while the current loop is rotating this in itself will see a changing magnetic flux and thus will induce a voltage in your conductor circuit that will lower you current through your conductor and thus make the lorentz force vanish the higher the rotation gets and again you'll reach a point with 0 torque.

Now why not marry these two motors and get the good from both worlds.

The idea is fairly simple. You establish a rotating magnetic field through coils (like in an induction motor) and push your own current through the loop windings (like in a DC motor, but unlike a DC motor here the current doesn't have to flip polarity). That's it! The HUGE key point here is SYNCHRONIZATION. If the loop and the rotation of the field are synchronized, no lenzlaw, now back emf, now moving conductor in a field....is seen from either the loop's frame or the magnetic field's frame. Thus if the setup is synchronized (mainly that the rotating magnetic field increases in speed along the loop) you will get free rotation. To the point you'll by far exceed the input needed to run the system. The big genius here is Tesla's rotating field. He managed to have this feature WITHOUT mass rotation. This is a very important feature in this setup. This means that the magnetic field can rotate with the conductor while the REACTION FORCE (newton's third law) is felt on the coils themselves! But this is okay since the coils themselves are stationary.

Let's do a little energy analysis here. How much energy is needed to keep this going? Well to be theoretical NONE! The coils that form the field can be in theory a perfect non damping LC-tank. The rotating loop itself can be a super conductor thus at no point absorbing any fields that change the coil induction AND having an indefinite current flowing without any applied voltage. So both stationary coils and rotating loop are independent of each other. So as a result we have a net torque if synchronized correctly can maintain itself without any other cost.

I can make simple drawings if that is needed, as I'm in a bit too busy right now. Please post your feedback.

Edit: Just a small addition.

http://www.freepatentsonline.com/result.html?query_txt=constant%20torque%20motor&sort=relevance

This proves the saying "once you know what you're looking for you'll find plenty of it".