Can a cylinder with magnets also be used?
Conclusion
It seems to work.
Can the current also be supplied outside the magnetic ring?
Conclusion
It does not seem to make any difference whether the current flows from the axle through the magnetic ring or is supplied directly outside it.
How far can the distance from the sliding contact to the magnet be?
Conclusion
The distance from the sliding contact to the magnet can also be further away and over bridges, but the magnet must be stronger for this.