A 1/4 HP Garage Door Opener ought to be plenty, really. But they are not cheep.

Q: Where exactly did you com up with the figure "100lbs of cloths".

 

I would also suggest, responding to post #18, that the voltage does not describe the power of the motor. You need to know the horsepower of the motor to estimate how much load it can move. The load in this case has a lot to do with the quality of the pulleys, the configuration of the lines, and the weight of the clothes. The only requirement of the motor is that you have "enough" horsepower. Unfortunately, I can not calculate this answer.

 

One thing no one has addressed yet is, with clothes hung on the line, the line will have to be very long. At least twice as long as the amount that the clothes are hung on. As the line moves under cover if there is a mid-support the clothes will be knocked off as they move past any type of support. From hanging clothes out on a line years ago, the 'props' (supports) are normally placed about every ten feet.

 

Yes, we're waiting for the promise of post #19...pictures of how to do this without knocking the clothes off the rope.