■ FIGURE 6.
Your belt can be made of nearly
any insulator — Rayon, Dacron,
neoprene, rubber. I’ve even used very
wide rubber bands with “adequate”
results. When looking for a belt, black
rubber (such as used in tires) is usually
not ideal, because carbon is added to
get the black coloring and is
conductive. Thin belts always seem to
give the best performance, but the
trade-off is that they take a beating and
don’t last long.
Commercial belts (available from
science supply stores) are usually
neoprene and thick. A commercial belt
may last 500 hours or more, and has become my belt of
choice only because of durability/simplicity. However,
homemade belts often outperform them.
Probably the best belts I made myself were cut from
the wide exercise stretch bands available from Amazon
and all over the Internet. You can get a pack for a few
dollars that contains several sizes and thickness.
Simply cut out the length of belt you’d like, and
super-glue the ends (a diagonal cut on the ends is
strongest) to form a truly excellent belt.
Your generator has many points to help adjust the
run of the belt, including the slots on the top roller
(allowing you to adjust its tilt) and the hose clamp at the
base (for belt length). It usually takes a few minutes the
first time you run it to get
everything positioned just right.
Once you do, your generator
should run for many hours without
Keep your face clear of the top
terminal while doing this setup,
unless you’d like your generator’s
first bolt to strike there. (Not that I
would know, of course.)
easy spinning needle bearing. (I also coated all surfaces
with corona dope, except the tips.)
When placed on top of your running Van de Graaff,
the sharp points will have the highest electron density,
and the electrons at this point will leak off into the air.
Thanks to Newton’s Third Law, the motor will spin
rapidly. Though the design of this motor is humble, used
in frictionless space ion motors have already propelled
large rockets such as NASA’s Dawn mission to visit
asteroids, and at speeds and thrust durations chemical
rockets cannot attain. This simple idea may be our best
bet for future deep space exploration.
Figure 7 shows a Franklin motor. Invented by
Benjamin Franklin, this is possibly the world’s first electric
motor. Construction is also simple. A set of metal spheres
(I used sling shot pellets) are glued around a circle which
is balanced on a needle bearing. When spinning, the
A Few Classic
Figure 6 and Figure 7 show
two electric motors that can be run
from your Van de Graaff generator.
Figure 6 is an ion motor. A metal
bar or wire is bent in the Z shape
shown, and the ends are sharpened
to a point. This assembly is
balanced on a point, forming an
■ FIGURE 7.
September 2012 45