Very Large Diameter Electromagnet (solenoid)

[CS Bence]

I am toying with an idea and not sure if it's feasible. Here is the setup: There is a 6' diameter steel pipe that is 30' long standing up vertically. Inside, among other stuff, are ~20 small 'trolleys' on tracks that run from top to bottom, spread out evenly among the cross sectional area of the pipe. There is a strong permanent magnet of to-be-determined size on each trolley, with north/south axis parallel to the pipe. Around the pipe would be the windings of an electromagnet to create a flux which would move these trolleys slowly up and down the length of the pipe continuously. I expect to see 20 lbs of resistance from each trolley going down, and 20 lbs + the weight of the trolley going up.

The big picture questions are:

Would an electromagnet of that diameter be feasible? Would it even act as an electromagnet without a massive current?

Do the coils of the magnet need to run the whole length of the pipe, of could I have one coil in the middle, or possible multiple coils evenly spaced?

To balance the trolley force would I simply adjust the size (strength) of the permanent magnets for each trolley such that the trolleys nearer the center would have larger magnets than those nearer the edge of the pipe?

Thanks in advance!

 

[mfb]

To move them up and down, you'll need a segmented coil over the whole pipe where you can power each segment individually, so you can change the position of the magnetic field over time. Getting a really slow and smooth motion sounds challenging.

I expect to see 20 lbs of resistance from each trolley going down, and 20 lbs + the weight of the trolley going up.

What happens to the weight of the trolleys going down?

 

[CS Bence]

The weight is still there going down... That should read ( 20 lbs - weight ) going down.

Does the large diameter not give you any pause?

 

[mfb]

What do you mean by "pause"?

Forces from magnets nearby tend to be inhomogeneous - once a trolley starts moving towards a field, it feels an even stronger field and accelerates faster.