Im not sure how much help I can offer, but I am somewhat interested in some of the specifics of this type of control. Are you using an optical encoder, hall effect, or does your motor have a built in tach? Which ever you have, how many pulses per revolution does it generate? Are you designing a speed control around a washing machine that already exists, or are you building everything from the ground up? I know the commercially built machines have a dampening system in place to absorb some of the energy from load imbalances. How much does it over/undershoot? It seems to me that, given the nature of the load, that a bit of allowable error or hysteresis or something would be needed. Well thats just my 2 cents. I'm sure some of the pros will be on here shortly to better help you.