BUILT BETTER THAN
A MOUSETRAP: The
illustration shows the
basic elements of the
WPV. Besides 4 wheels,
a couple of axles, and
a frame, the most
prominent feature is
a 12" mast. This mast
serves as the support
for a falling 1-pound
weight, allowing it to
drop precisely 1 foot,
thus propelling the
The central feature of the vehicle is a 1'-high mast
made from the yardstick. At the top is a pulley, over
which the fishing line is wrapped, bearing the 1lb
sinker. This drive mechanism is similar to that of an
MPV car, but its string-wrapped axle is propelled by
a falling mass instead of a spring. In addition, the
drive axle has a collar (aka drive hub) to give more
leverage to the string when conveying the 1lb force.
can build WPV vehicles that can travel much greater
distances using the same amount of energy.
» Within a narrow range, gross vehicle weight didn’t
affect elapsed distance, because very little coasting
occurred. The only thing affected was elapsed time.
» Because the WPV uses less force than the MPV, it
requires more precision in its construction. Bearing
designs that can be used with little performance
degradation in an MPV are too crude and apply
too much drag in the WPV. The difficulty we experienced in trying to minimize rolling resistance
and power-train drag was tougher than originally
envisioned, because of the subtle forces involved.
Testing and Results
We tested the vehicle with 3 different wheel diameters ( 2", 2¼", and 3"), 2 drive hub diameters
( 1" and ¼"), and 3 sinkers ( 6, 10, and 16oz). The
vehicle itself, without the sinker, weighed 4oz. The
values that worked best for our vehicle design were
2¼"-diameter wheels and a ¼"-diameter drive hub.
Illustration by Julian Honoré/ p4rse.com
When tested with the minimum weight, 6oz of
lead, the vehicle failed to move even when pushed.
This we attributed to friction and drag. With the
10oz weight, the vehicle rolled from a standstill without assistance, covering 10' in 9 seconds. When the
16oz weight was put to the test, the vehicle spanned
the same 10' distance in 12 seconds. We attributed
this slower speed to increased rolling resistance of
the soft sponge-rubber tires, caused by the increase
in vehicle gross weight.
Phase II: Energy Recovery
If converting potential energy into kinetic energy
gets boring, Phase II could be an “energy recovery
of applied force” competition. Within a limited distance, the vehicle that covers the greatest distance
— and recovers the greatest amount of kinetic
energy when the brakes are applied — wins.
» Overcoming this challenge is ideal for a contest
of ingenuity and skill.
» Our proof-of-concept WPV used 1 ft-lb of energy
to travel 10'. As we experiment, we’re confident we
Richard B. Graeber and his son won Saratoga High School’s
mousetrap-powered vehicle competition and then evolved
the concept to the next level.