Tips for a successfull D.I.Y. Pendulum Latest change 2019-12-15
Experiments with a Foucault Pendulum generally last days or weeks.
good part of the message is that you can do something else in the
time, but only if you have the means to precisely log the
your pendulum. My approach with electronics and software allows
Many parts needed to construct a working pendulum are not
regular shops. You simply need to make them yourself. I regard
to) a lathe and a stable column-type drilling machine as a
milling machine makes several jobs to a pleasure.
People who are used to d.i.y. work in the home often have enough
tools and experience for the woodworking required. Manufacturing
coil members to the required precision may ask for some
You don't need to be a professional for this, but basic
of working with operational amplifiers, Ohms Law, Voltage and
levels, etc. is required. Basic experience with (and access to) an
oscilloscope is as good as mandatory.
It is almost inevitable to (be able to) modify the Arduino
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
electronic engineer and yes that means a certain math background,
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
and understand the messages there.
Suppress (the effects) of
the elliptical path any
pendulum tends to follow. See the Ellipse
I use only the method according to the Schumacher Equation with
good results. That means that the timing of the drive-pulse is
I have no Charron ring or some similar mechanism to reduce the
of ellipse. My experience so far is that a correct timing also
the amount of ellipse.
Use a drive coil of small
The Schumacher equation predicts that a bob with a high Q needs to
driven very close to the center. So, to make your coil effective,
it around the same radius. However, you generally won't know the Q
advance and maybe need to redesign your coils after some
Use a Center-Detect coil of sufficient diameter such that
it will give enough signal, even when a substantial ellipse has
Do implement a Rim Coil as
did. Give it a radius of around 2/3 of the intended amplitude of
pendulum. It will be very helpfull in accurately determining and
controlling the amplitude of the swing.
Use a simple clamp to fix
wire at the top. There exists a variety of bearing constructions
balls, cylinders, knife-edges etc. These all are difficult to
with the required precision and / or may introduce asymmetry or
which -even in the slightest amount- cause problems like
substantial elliptical path or complete absence of Foucault
because of stalling at some angle.
Try to use a bob as compact as
The weight itself is not that important, although mass goes with
3rd power of linear dimension and surface (as seen from the side
determining air friction) goes with the 2nd power of linear
A bob made from high density
material is smaller and has less air friction compared with a
density bob. I use lead, which is quite dense (11kg/dm3) and
cheap. Besides that you can easily melt it and pour it into your
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
appears to have a Q over 3000.
I use Piano Wire, also
Music Wire and family of Spring Steel. Piano Wire has a tensile
strength around 6 times that of normal iron wire and is
with very narrow tolerances. It is made to withstand all tortures
and amateur pianists without going out of tune.
I once used normal iron wire of 1mm diameter (tensile strength 36
with a bob of 6 kg and a period of 4.2 seconds. It broke after
12 days of operation because of material fatigue.
Stranded steel cable can be a good alternative, but is probably
easy to aquire. A disadvantage of stranded cable is that it
and rotates when it is loaded, and that it has a low torsion
constant. This may cause your bob to rotate along its axis for