A weight suspended by a string is swung around by a variable speed motor. The angle made by the weighted string to the vertical increases with the rate of rotation.

Notes

This sort of driven conical pendulum is actually rather complicated. The paper below details a similar system as a way of understanding a spinning chain. https://iopscience.iop.org/article/10.1088/1361-6404/abe6b2

What I observed was that the pendulum would often oscillate around an azimuthal angle, and when driven faster it the pendulum could cross over the axis of rotation. In short, don't spend too much time trying to get it to behave; it won't.

PIRA DCS 1D50.25