Book 3

Ways of balancing. The worst method is this one
(top), from a Champ 507. with long slashes
ground in the pole surface. The Dyna method,
filing up notches (next down). The best method
of removing weight, drilling holes in the pole
surface (bottom). The arm here turned out
fairly well balanced after winding, so only two
small holes were needed
Now for balancing, with the method that at least 99% of the readers m ust be
familiar with - the Razor Blade Method. Check that edges of blades really are
parallel. Heating the lead epoxy on the arm. Shift between placing the arm with
the lead epoxy top and bottom, so that it will not flow out too much.
18 balancing (static)
Now the armature is wound and epoxied. but we are not out of
the woods yet: it has to be balanced first.
Why balance? Well, when doing the armature, we have usually not
quite managed to get the wire and the epoxy on evenly, with the result
that the armature will be heavier on one side. Only once in my
nine years as a racer have I seen an arm that turned out perfectly
balanced (static), but unfortunately, it was not mine. Anyway, you
can see that happens very seldom, so chances are your armature will
need a little work.
If we put our unbalanced arm in a motor and have it run. centrifugal
forces will try to force the heavy side away from the shaft,
causing vibrations, friction and heat. Friction and heat have already
been discussed in general and it should be obvious that these are bad
for performance, but let us consider vibrations. Vibrations - any
vibrations - in a car are detrimental, since they will spread everywhere
in the frame. And you can easily imagine what kind of roadholding
you will have with the rear axle trying to jump up and
down . . .
(You should watch worn gears, bent axles and out-of-round
wheels, too, since these can cause serious vibrations. Ideally, gears
and wheels should also be balanced for maximum performance.)
So it is clear that the armature should be balanced, and the obvious
way is to either remove weight from the heavy side or add weight to
the light side.
For static balancing (we will discuss dynamic in a moment), the
tried and true method is to place the armature on a pair of razor
blades stuck into a piece of balsa. Blade edges must be parallel and
horizontal. When the arm is placed on the blades, it will turn until it
17