"There is no real mystery about how
unicyclists stay upright — they pedal
so
as
to
keep
their
point
of contact with the ground under their center of
gravity.
But
pedaling
is
confined
to
the plane of the wheel, and so a sideways
fall
has
to
be
countered
by
first turning the wheel-plane. This may be
done
by
upper-body
rotation,
using
angular
momentum conservation and
wheel/ground
friction.
As
a
result,
a
competent
rider can control the machine near upright by
continual
small
adjustments
of
the
wheel-plane
plus minor pedaling to and
fro.
This
may
be
either
static
balancing (‘idling’) or a subsidiary component
of
steady
progress." -
Johnson
It is possible to gain both longitudinal and lateral
stability on a unicycle. These depend on the pitch and roll angles. Pitch
is the rotation made in the horizontal (x) axis and Roll is the vertical (y axis) rotation. Longitudinal stability is attained by
pedaling faster or slower. Pedaling involves your thighs and shanks
and gives them a good work out even after a short ride. The two sides
of the rider's thighs and shanks are used alternately and not
simultaneously. Longitudinal stability is also controlled by the rider
moving their torso and arms forward or backward. Lateral
stability
depends
on
longitudinal
stability.
Lateral
stability
is
obtained
by
going
in the direction the rider feels that
they are falling in. Unicyclist are constantly correcting themselves in
order to stay stable. In order to go in the direction the rider is
falling they must lean their torso sideways, countering their shift in
weight by pulling in or pushing out their arms and twisting their hips
to physically turn the seat. Turning with the hips makes enables
rider's to make sharper turns.
Stability
of
the
pitch
and
roll angles are needed for the rider to
control the speed of the wheel, which is directly related to the Yaw
angle (z axis). Neither the pitch or roll angle may exceed 90
degrees for the rider to maintain their stable posture. If a rider
cannot maintain their posture on the unicycle for more than one second,
they are not in control. Once in control, the rider may chose which
direction they would like to go in. A
rider must maintain constant control in order to overcome the influence
to fall. The rider can never stop moving or else they will lose
control. It is possible to maintain control at very low speeds, but
that is usually takes lots of skill. A rider's posture is maintained by
the centrifugal force created by the rider's movements dynamically. Stability
is
possible
even
on
uneven
terrain. A skilled rider will be able to
shift their weight and change their pitch, roll and yaw angles so that
they will still be vertical with respect to gravity's pull.
Elements of A Human Riding
a Unicycle
Diagram from Sheng
If you want to see 12 pages of mathematical proof of how a human can
ride a unicycle click here!
