Dr Mel Siff Blog

Dr Mel Siff responders to a members enquiry about Force Plates on the Supertraing List as found at www.yahoogroups.com

<< Re: lab equipment—I use an interface called “Data Studio” to gather,
plot, and analyze data of impulse phenomena involving lab carts, fans, model
rockets, etc. This Pasco apparatus and software quite nicely allows for
variable force graphical analysis to be used with high school freshman long
before they are ready to perform calculus. It allows older students to
confirm their calculations and easily go into areas previously reserved only
for university labs. This system is unable to handle forces the size of
which we speak in training applications.

I assume the force plate apparatus does much the same thing on a larger
scale? An earlier post mentioned a “cheap force plate”. Could someone
inform me if they work similarly to my smaller lab apparatus and how cheap
is cheap? If you could point me in the right direction to find this
information, I would appreciate it. >>

***A force plate or force platform in essence is a sophisticated type of large
bathroom scale which can measure forces in the X, Y and Z directions and the
torque about each of these axes. An athlete carries out typical sporting
actions on this device or runs across it, while the information is fed
through an Analogue to Digital (A-D) card into the computer, where the
required analysis is carried out.

Construction of a relatively inexpensive force plate to measure the forces in
the X, Y and Z directions is not at all beyond the capabilities of the
average competent engineer. All that one needs to do is to construct a
suitable “load cell” using strain gauges secured by means of special epoxy
resin at appropriate locations on the deformable elements of the cell and
install four of them at the corners of a heavy wooden or metal platform. One
has to be sure that the resonant frequency of the platform is nowhere near
the sort of frequency of vibration produced in any activities that you wish
to study.

My Civil Engineering colleague who manufactured them still works at my former
university and still makes a limited number of these force plates, so if you
are interested, you could contact him in South Africa at:

hofmeyr@civen.civil.wits.ac.za

Failing that, you can also buy piezoelectric film that may be placed under a
platform to enable you to measure vertical reaction forces. In fact, you can
place it on any surface to measure forces like that, but remember that it
only gives information in one direction. You need to locate it in a few more
positions if you wish to measure three dimensionally. Remember, too, that
piezoelectric devices do not measure static or isometric forces, but they are
fine for dynamic measurements.

All that you need to do is buy a suitable amplifier (“signal conditioning
unit”) and A-D card for your computer and you have your basic force measuring
device. All of these devices may be found readily via the Web. A
biomechanics colleague of mine, Dr Gideon Ariel, has a great deal of
information on his website about such devices, plus a lot of free software to
help you along. Go to:

http://www.arielnet.com

Students can easily make their own crude force measuring devices with this
sort of film. Quite often, you will see simple force devices (typically for
measuring jumping force or reaction times) being sold for several hundred
dollars by sports performance and machine companies, but they are little more
than devices using such film being sold at a huge profit.

Dr Mel Siff

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Tags: Axes, Dr Mel Siff, force plate, Force Platform, Load Cell