Anyway ,,what made you say that rpm would multiply?
I can see how someone might think that without going through it carefully. After all, that's what would happen if you connect a 1000RPM motor to a 1:1000 gearbox. With motors stacked, you use the relative motion equations which are sums of different motions and not products.
lol, yup curosity killed the cat! i was just looking at these stepper motors which have limited RPM,
**broken link removed**
in the example you see the "charge coils" around the ceramic magnetic rotor, now we could design the same thing with the rotor on the outside and the "Charge coils" on the inside instead, right?
so what if we put the charge coils around the outside, put the rotor in the middle, then put an inner set of coils, now what if instead of hooking the inner coils up to a stepper controller we set them up so that one of the inner coils would pick up the flux force of the outter coil and used it to distribute power to the other inner coils causeing thoes coils to push from the center ceramic rotor?
the total would be summed, i was thinking factored too, but maybe we could still use this?
THe concept of cascaded motors isn't practical for quite a few reasons:
-mechanical balancing
-inertia for dynamic loads
-vibration
-transfering power to rotating components is difficult and require slip rings which are really expensive, let alone for one that is strong enough to support mechanical loads and large enough to pass motor-level currents
-slip rings introduces brushes (or for brushed motors even more brushes) increasing noise and wear while decreasing efficiency thus limiting power levels
-motors are expensive enough to wind as it is
-requires redundant controllers (you are really controlling two motors after all)
-motors almost always run too fast anyways. I can't think of any application where a motor runs too slow.
As far as steppers are concerned, their advantage is not in the power or speed departments. It is more for their ability to hold positions and move predefined amounts in open-loop control (assuming sufficient motor torque so steps aren't skipped), and to a lesser extent good direct-drive torque which reduces or eliminates the need for expensive gearboxes makes them good for "servo-like applications" where you don't want to pay for the servo feedback systems or gearboxes.
The design of a stepper makes more vibration and their torque rapidly decays as the speed increases which makes them not so good for high speeds. Other motors easily spin much faster while actually maintaing their torque at these high speeds while using simpler drives. THere's really no need or reason to use a cascade steppers for higher speeds. What stepper motors do is eliminate feedback for closed loop control and gearboxes at the expense of other things in low speed applications.