The device is made up of a trench, for instance made from aluminum with magnets mounted upon it.
The most important thing is the positioning of the magnets: they must be positioned so that the magnetic poles are all facing the same direction on each side of the trench, e.g.
on the left, all magnets are mounted with the south pole facing inward; on the right, all magnets are mounted with the north pole facing inward.
In the experiment shown in the video, small cube magnets
were used, but one could also use discs.
On the assumption that the discs are magnetized axially, they would have to be placed vertically, like small wheels.
The distance between the magnets doesn't make a big difference, but in order to achieve a decent acceleration, they have to be close enough to each other.
The distance depends upon the strength of the magnets: in our experiment, the magnets were placed approximately 5 mm apart.
At the end of the ramp two magnets rather than just one are place on top of each other on each side.
This creates a magnetic trap: a strong magnetic field, which stops the sphere in place.