motor selection for ball mill

AC motors do have less torque compared to DC motors but that is usually compensated by "oversizing", about 20-30%. AC motors have good speed stability, mostly locked to the line frequency. If you are using a regulator, it is essentially reducing the effective voltage and speed is controlled by allowing greater slippage. You can certainly use an AC motor but use a somewhat larger size

The only suitable method to operate an induction motor with variable speed at higher load torque is VFD (variable frequency drive). DC or universal motors can be easily speed controlled versus motor voltage, e.g. using a triac or SCR controller. That's why they have been preferred for washing machines and other home appliances for many years. Most serious disadvantage is running noise and limited lifetime. I won't expect more than 5000 maximum 10000 hours. That's not much for a continuously operated ball mill.

What you need is torque at a low speed. As FvM says washing machine motors use DC motors and turn a heavy drum. They also have a big step down between the two pulleys, say 6/10 : 1 The loading of a typical washing machine would be 5 KG of dry clothing, but with the water I would think they are turning over something more like 15 kG. The motor ratings are typically 500/50 W. The higher power is required for the spin cycle, the lower for the washing cycle.
So one of these running at the lower rating - say 50V at an amp driving one of the rollers and relying on the roller to drum ratio for your reduction. You will need a very good friction material on the rollers else they will not start the drum. washing machines normally have a soft start on the motors to over come this.
Frank

I am not very sure but my LG washing machine says that it takes 300W during the spin cycle (it is a 6kg rated front loading machine) and it goes back and forth (the motor reverses periodically) during the normal wash. The motor is regulated from the microprocessor and hence I will assume (??) that it is using some kind of PWM (because that is the popular thing to do). It also has a good soft start (I wish it had a vibration sensor too) but the power ratings are not given.

just a reference for the wiper motors :

they have very low speed.

@Chuckey , I think you mean AC motors not DC.
@FvM, The speed of washing machine are in range of 16,000 RPM. VFD are really expensive. I would use pulleys for coarse speed adjustment and fine speed tuning with XXX (not defined yet)

Universal motors life time is very low and need lots of maintenance specially to the brushes Pffff
I like they have strong torque but as I indicated before, I lost one motor due to overheating

mr_byte31 said:

@FvM, The speed of washing machine are in range of 16,000 RPM. VFD are really expensive. I would use pulleys for coarse speed adjustment and fine speed tuning with XXX (not defined yet)

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The drum rotation during the spin cycle is about 1000RPM. During the wash cycle it is around 0.5-2sec. The motor is a single phase connected to the drum by pulleys and belt. I have not measured the reduction ration.