Motor selection for vertical lift door with balanced counterweights

[davemech]

I'm having trouble selecting a suitable motor to lift a single leaf 1000kg door. To cut down on power costs i plan to use perfectly (or as close as i can get) balanced counterweights. The door is to be lifted 4m vertically using wire rope hung over two sheaves connected to the respective counterweights (each weighing 500kg). The door is to be accelerated from rest at 0.05m/s^2 to a speed of 0.1m/s, kept constant until an equal decceleration occurs. As the weigth of the door is balanced by that of the counterweights it seems that the power required to operate the door is absolutely minimal. The only power input necessary seems to be that needed to overcome the inertia of the sheave (which will weigh 50kg and have a diameter of about 0.6m) and the friction associated with the roller bearings which i plan to fit the sheaves on, which according to my calculations seems negligible. The only additional source of friction i can think of is the anti-friction cam followers which will guide the door.
All of this seems to reuire a Very small motor,only a fraction of a HP at most, which seems a bit odd to me! Any insights would be greatly appreciated!

 

[davemech]

got it