APPENDIX I
HANDLING TIPS FOR BALL BEARINGS
While they are tough the small bearings typically used in Model Solar Cars are not
indestructible. And in fact the general information presented here holds for large bearings
as well. In ball bearings rolling of the balls carries the relative motion of the inner section
of the bearing to the outer. Whereas in a sleeve type bearing this is a sliding action of two
surfaces relative to each other. The rolling action has lower friction provided the
surfaces are smooth. Typically bearings are produced with very fine tolerances and
smooth operating surfaces.
If the loads being carried by the balls onto the races are too high the races and or balls
will be damaged permanently by denting of the races and by producing small flats on the
ball surface. The bearing will then run rough and friction will have gone up significantly.
This type of damage can occur due to incorrect handling, usually during installation, or as
the result of the car crashing. When mounting or dismounting bearings onto shafts or
into housings NEVER push on the bearing in such a way that the assembly forces are
carried through the balls. That is when mounting bearings into a housing only push on the
outer. When mounting bearings on a shaft only push on the inner. If necessary make
pushers to ensure the loading is correct. Mounting and dismounting forces are often high
enough to damage bearings by denting the balls or races.
Be careful not to mount bearings into a housing that is too small or on a shaft that is too
large, excessive forces on the bearings will deflect the bearing and reduce clearances
which will increase bearing friction. I have seen a bearing mounted in a nylon wheel so
tightly that the bearing had deformed to the point that it would not rotate.
Cleanliness and lubrication are also important. Cleanliness is obvious, shielded bearings
will normally not suffer with dirt ingress in the relatively clean area of the track. Even
open bearings give no trouble so long as a little care is taken in handling.
Lubrication is a little more tricky. Bearings are commonly supplied lubricated with
grease (they may be ordered oil lubricated if required).
We devised a test to give an indication as to the losses due to lubrication, it entailed
mounting the bearings under test in a test wheel then spinning the wheel with a known
amount of energy input. By counting the number of revolutions the wheel did before
stopping a relative measure of the friction due to the lubricant was obtained. To input the
energy the wheel had a pin on its periphery, the pin was aligned horizontally a 10 gm
weight hung from it and the wheel let free to rotate. This always gave about the same
energy input.