Tips for a successfull D.I.Y. Pendulum                                    Latest change 2017-09-10
 
Required skills:

Patience:
Experiments with a Foucault Pendulum generally last days or weeks. The good part of the message is that you can do something else in the mean time, but only if you have the means to precisely log the behaviour of your pendulum. My approach with electronics and software allows for this.

Metal working:
Many parts needed to construct a working pendulum are not available in regular shops. You simply need to make them yourself. I regard (access to) a lathe and a stable column-type drilling machine as a minimum. A milling machine makes several jobs to a pleasure.

Wood working:
People who are used to d.i.y. work in the home often have enough tools and experience for the woodworking required. Manufacturing the coil members to the required precision may ask for some improvisation.

Electronics:
You don't need to be a professional for this, but basic understanding of working with operational amplifiers, Ohms Law, Voltage and Current levels, etc. is required. Basic experience with (and access to) an oscilloscope is as good as mandatory.

Software:
It is almost inevitable to (be able to) modify the Arduino firmware and the PC software I present here to your particular needs. So if you don't know already, learn programming, or find a friend who knows to. I use C and Pascal


Study the theory as good as you can. I am certainly not a skilled mathematician or physicist, I am a retired electronic engineer and yes that means a certain math background, but most of the math I've seen in the articles I mention go beyond my skills. Not withstanding that I could mostly "read between the lines" and understand the messages there.

Suppress (the effects) of the elliptical path any pendulum tends to follow.  See the Ellipse chapter.
I use only the method according to the Schumacher Equation with very good results. That means that the timing of the drive-pulse is extremely important.
I have no Charron ring or some similar mechanism to reduce the amount of ellipse. My experience so far is that a correct timing also limits the amount of ellipse.

Use a drive coil of small diameter. The Schumacher equation predicts that a bob with a high Q needs to be driven very close to the center. So, to make your coil effective, give it around the same radius. However, you generally won't know the Q in advance and maybe need to redesign your coils after some experiments.

Do implement a Rim Coil as I did. Give it a radius of around 2/3 of the intended amplitude of your pendulum. It will be very helpfull in accurately determining and controlling the amplitude of the swing.

Use a simple clamp to fix the wire at the top. There exists a variety of bearing constructions with balls, cylinders, knife-edges etc. These all are difficult to construct with the required precision and/or may introduce asymmetry or friction which -even in the slightest amount- cause problems like developing a substantial elliptical path or complete absence of Foucault Precession because of stalling at some angle.  

Try to use a bob as compact as possible. The weight itself is not that important, although mass goes with the 3rd power of linear dimension and surface (as seen from the side and determining air friction) goes with the 2nd power of linear dimension.
A bob made from high density material is smaller and has less air friction compared with a lower density bob. I use lead, which is quite dense (11kg/dm3) and modestly cheap. Besides that you can easily melt it and pour it into your bob's shell.
Also the shape of the bob is not critical. A sphere might be the optimal compromise between mass and air friction, but is hard to manufacture. A cylinder is much more easy to fabricate. My pendulum appears to have a Q over 3000.

I use Piano Wire, also known as Music Wire and family of Spring Steel. Piano Wire has a tensile strength around 6 times that of normal iron wire and is manufactured with very narrow tolerances. It is to withstand all tortures of master and amateur pianists without going out of tune.
I once used normal iron wire of 1mm diameter (tensile strength 36 kg/mm2) with a bob of 6 kg and a period of 4.2 seconds. It broke after around 12 days of operation because of material fatigue.
Stranded steel cable can be a good alternative, but is probably not easy to aquire. A disadvantage of stranded cable is that it lengthens and rotates when it is loaded, and that it has a low torsion spring constant. This may cause your bob to rotate along its axis for long time.