For this project, a physical model of the system was
developed using available materials, as can be seen in Fig. 1.
The frame is 12" x 21.5" and is made from a 1x2x8 furring strip
[1]. A Jameco ReliaPro 161382 geared motor that was
salvaged from a previous project is used to provide the periodic
input force [2]. The eccentric and DVA masses are machined
pieces of brass stock which we were given for free from the
RIT machine shop. For the platform a machined aluminum bar
is used that has four #8-32 clearance holes drilled at each
corner, in which eye bolts are mounted [3]. A tapped #8-32
hole on the bottom in the center of the platform provides the
mounting location for the eye bolt from which the DVA is
suspended. Motor clamping to the platform is accomplished
using two 2" #8-32 cap screws from the machine shop in
tapped holes. A Lexan motor mount was made and sanded to
give a frosted texture after being recycled from a previous
project. The DVA mass is constrained similarly using a Lexan
piece with two 5/16" holes for the motion constraining rods,
and is connected to the DVA mass using a #8-32 eye bolt. 1/4"
steel tubes that are mounted through the furring strips at the top
and bottom of the frame are used as constraining rods for
system motion. To reduce pitching of the platform, 2" pieces
of 3/8" copper tubing were secured through holes in the
platform using adhesive. These work as minimal friction slides
on the steel constraining bars which do not bind. Four
extension springs are attached to eye hooks in the top of the
frame and are used to hang the platform [4, 5]. A spring that is
slightly less stiff is used to hang the DVA from the platform.