A Sub-meter Foucault Pendulum              Latest change 2025-03-13
End of 2024 I started a project to build a foucault pendulum with a rather short length, and constructed as a all-in-one transportable unit.
With this project I have a number of goals in mind:

a/ Prove that it is possible to limit ellipse growth to a minimum by driving the pendulum with the resonance frequency of the major axis of the elliptical path it will follow anyhow, so avoiding to excite the slighty higher frequency of the minor axis. There will be no other means to limit ellipse growth.
For background see my article about the Period Time

b/ Prove that it is possible to combine this with the "Schumacher" timing principle to eliminate the intrinsic ellipse precession.

c/ Prove that sensing the bob's posiion, center passes and rim passes can be done using a capacitive method, so avoiding the use of magnets.

d/ Prove that the bob can be driven, based on forces generated by eddy currents induced by a radially phase shifted AC magnetic field. Again to avoid a permanent magnet in the bob.

e/ Prove or disprove that the alternating direction of the ellipse and the change over at N-S and E-W orientations  is real and not depending on the orientation of the equipment.

 

a/ requires a pendulum with a sufficient separation of the resonance frequencies of both axis. That calls for a pendulum with a large amplitude (frequency difference) and a high Q (spectral separation) Also a generator is needed, tuneable in very small frequency steps.

b/ most likely requires an elaborated control algorithm.

c/ requires dedicated electronic circuitry.      Per march 2025 most of this part has been realized and tested.

d/ requires two concentric driving coils which are driven with out-of-phase AC signals.

e/ This is now easy possible because the whole unit can be rotated. With the 4 meter pendulum that was not possible.


"Look Mom......No Magnets"   

My planning has no numbers on the time scale, but certain things do come before others.

I started with the making of the bob. To achieve a high Q I thougt that a disk-like shape would be the best.
A first test indicated a Q of around 3000, which I think is sufficient.

Next came the frame and the Top Mount.

The new magnet free Position Measuring System PMS was developed in several steps of improvement.

The first tests will be done with conventional drive-coil-and-magnet methods. These test should show that the whole construction is sufficiently stable, an absolute requirement for the further experiments a/ and d/.