Electric motor diameter...

[Externet]

How could a permanent magnet electric motor be built/designed for slower rpm turning shaft but with 'normally' high commutation speed (passing of magnets in front of coils) ?

 

Would a 60cm - 100cm diameter motor just ~5 cm thick -disc shaped motor, with a large number of magnets placed at the peripheria and a corresponding large number of coil poles do it ?

 

Being the magnetic propulsion forces at a 'large' distance from the shaft with a large tangential speed use less force to produce same high shaft torque ?

 

It is hard to express in writing, I hope the above is understandable...

[tvp45]

As opposed to just using a gearhead? Or, alternatively, why not a controller?

[Mr Skeptic]

If I understand you correctly, the answer to your question is that energy is conserved. The higher force farther from the shaft produces more torque, yes, but it has to go a longer distance so there is no increase in energy output. It would probably be far cheaper to just use gears to accomplish a similar effect, as motor is quite expensive.

[Externet]

Hi. Thanks; it is getting really hard to put this in the right wording.

 

It is not about avoiding a gearhead. Such motor would be driving a gearcase. A speed controller would be used too.

 

It is about decreasing the components ratings and stresses.

A power source, a controller, the wiring and the motor itself are subject to greater stresses when starting to spin a motor under load because the slow commutation speeds and very large currents.

 

For a given torque need starting under load at -say 0.5 rev/sec- demands a lot of current.

 

That same given torque need can be achieved with smaller forces (weaker magnetic fields) applied more distant from the shaft

 

It is not about increasing energy output. Comparatively, it takes less force to manually spin a wheel by turning it as far as possible from the shaft than turning it near the shaft to produce the same torque.

 

It is about using less force x larger distance from the shaft to achieve the same torque and at the same time getting high tangential speed.

 

Would that demand less current ?

 

Trying again :

As a smaller force far from the shaft (large disc shaped motor) can achieve the same torque than a much larger force near the shaft (conventional shape motor);

 

a weaker magnetic force (smaller windings, current and ampere turns) far from the shaft can achieve the same torque than a much larger force near the shaft (large windings, current and ampere turns)

 

[Mr Skeptic]

Oh, that makes sense then. I don't know if it would work. An alternative would be to have a clutch like a car, and you could instead start the motor without a load, but if you have a lot of start/stop it would wear out.