Why the unicycle balance scooter will not fall down?

For the Chinese consumers, the first time to know about the electric balance scooter may dates back to the 2008 Olympic Games. At that time, the guards in the Olympic gym were riding on the electric balance scooter provided by American balance scooter manufacturer-Segway Inc, as a means of patrolling. But the balance scooter was the new darling attached with “military” and “import” etc tags, so many people stop looking at this new gadget, and self balance scooters are always cast a layer of mystery. Today we would like to explore the scientific principles behind the balance scooter with everyone.

The working principle of the unicycle (single wheel) balance scooter

Unicycle balance scooter

Why unicycle balance scooter will not fall down ?

On one hand it is due to people can adjust their body gravity and the balance scooter moving direction , the change of moving direction of the scooter will balance the gravity of the rollover moment due to inertia .There is also an important point is that high speed rotating wheel has a large angular momentum which can resist the external torque, same like the top does not fall. In university physics, this phenomenon is called precession, and the autobiographical body rotates the direction of the external moment by 90 degree,while here the wheel turns the rollover torque into the “steering torque”.

motor improve the scooter balance

On this basis, the self balancing electric unicycle scooter improved to be driven by the motor, use the gyroscopes and circuit board for controlling to ensure the scooter will not fall.The body can be tilted forward to start,speed is controlled by the degree of body tilt, If you want to speed up just lean forward, slow down during backward. Overing the active control, to ensure the normal working of single wheel balance scooter,the acceleration sensor and angular velocity sensor (gyroscope) can’t be separated.


The acceleration sensor can measure the acceleration caused by the gravitational force of the earth or the movement of the object,when measuring the acceleration value in one direction, we can compute the inclination of the scooter. For example, using acceleration signal in X axis, when the scooter is upright, acceleration will be fixed in X axis direction,and the output signal will be zero bias voltage signal. When the car is tilted, the acceleration of gravity g will form the acceleration component in the X axis direction, causing the output signal changes of the axis.But in the actual scooter running process, the acceleration signal produced by the motion of the balancing scooter itself will produce a large interference signal superimposed on the above mentioned measurement signal, so that the output signal can not accurately reflect the inclination of the true tilt angle. Therefore, the attitude information required for the upright control can not be completely obtained by acceleration sensor.

Angular speed sensor

Gyroscope can be used to measure the angular speed of the object. Balancing scooter installed with the gyroscope, you can measure the angular speed of the scooter, after integral processing on the angular speed signal,the scooter tilt can be obtained.

Core components of balance scooter

When it comes to balance,we have to talk about gyroscopes, the principle of gyroscopes is that the direction of the rotation axis of a rotating object will not change if do not affected by external forces.With this principle, something created to maintain direction was called gyroscope.It is also the principle when we riding a bike.


The quicker the wheels rotated the harder it can be fall down, because the axle has a level of power to maintain horizon. So once the unicycle balance scooter was running, it won’t fall down.