Switchable Magnets.

[synchro1]

@sveinr,

Thanks. I uploaded some good photos: We can see how the magnet connects the ferrite  keepers in the "ON" position in the bottom photo: This variety only has to throw 90º.

[synchro1]

Here's a Dual Switch model of that type from "StrongHand":

Adjust-O™ 90° Dual Switch Magnet Squares

Angle magnet squares with the convenience of On/Off switches.

For professional jobs that demand strong hold down forces. Hold flat and round metal work pieces.
•Two On/Off switches for independent operation.
•Turn the magnets Off when setting up, turn On when you're ready to work. Easy and safe set-up!
•Precision machined flat and V-surfaces are ideal for round and square tubing, angle, and flat stock.
•Choose from 120 - 265 LBS (55 - 120 kg) pull force.

A small servo and trigger switch would deliver 265 pounds of pull force at TDC to the ferrite rotor from one face! This model would spin a very large and heavy iron rotor. Saturation's our enemy, so slow and heavy is best. This model could probably power a large 360º pendulum. Naturally, "High Permeability" rotor material would allow for higher R.P.M. It might be possible to use both 90º magnet switch faces with an "L" shaped rotor.

[synchro1]

This video shows a 90º magnet base in action:

https://www.youtube.com/watch?v=n0vX8VTiiDg

[synchro1]

The Noga DG0039 1300 Newtons. Most powerful magnet switch in the Noga line: 1300 Newtons is 292.2516270323 pounds of force.

[lumen]

This video shows a 90º magnet base in action:

https://www.youtube.com/watch?v=n0vX8VTiiDg

Yes! but the video never shows how it becomes much harder to turn to the on position when it's not on the steel surface.
In fact if you turn it half way on and remove it or tilt it on the steel surface it will switch itself to the off position due to the increased pull to the off position.

I have about four of these and they all work the same.
One would need to do some testing but I believe no OU here.