My pendulum goes elliptical.
Ellipticity is a natural consequence of the Earth's rotation. A small amount can be expected. If it becomes unacceptably large it is because of poor suspension or misaligned drive.
My pendulum progresses for a while, then stops. It will only swing in one axis.
This is called a Primary Axis. It is always due to the suspension favoring one axis. Radial symmetry is of critical importance in the design of pendula.
Can I have a powered system, but without magnets?
Most powered systems have magnetic drive because this is simplest. Alternatives are possible such as variable length wire that lengthens on the outswing and shortens on the inswing.
Does the length of the pendulum matter?
In theory any length pendulum will work, but larger ones are more forgiving of errors.
Is the launch important?
Only in an unpowered system. A well tuned powered system may be launched quite roughly and within a few minutes the unwanted actions will be damped out.
Can wind and vibration interfere with operation?
Air currents can throw off a pendulum, particularly an unpowered one. Vibrations are a problem if they are intense or if their frequencies are a harmonic of the pendulum motion.
What is a Charron Ring?
It is a ring at the top near the suspension point that the wire passes thru. It is used to suppress ellipticity and, in some cases, to trigger the drive.
What role does the Earth's magnetic field play?
None.