Views: 130 Author: Site Editor Publish Time: 2020-06-12 Origin: Site
There are 4 caster wheel in the shopping cart in the general supermarket or the trolley running in the airport. It can be found that the axle of the caster wheel and the car body are not fixed, but can rotate freely around the vertical axis. Because if the axle and the body are fixed, the caster wheel can only go straight ahead, and the car can't turn.
In addition, when you push the cart forward, the caster wheel always follows the axis of rotation. If you change from forward to backward, the caster wheel will suddenly turn 180 degrees around the vertical axis and still be in the position following the rotation axis. Under normal circumstances, the rolling direction of the caster wheel must be consistent with the forward direction to make the shopping cart move smoothly. Once the rolling direction of the caster wheel is inconsistent with the forward direction of the car body, the friction of the ground will generate a torque on the vertical rotation axis in front, pushing the caster wheel to a position consistent with the walking direction.
Similar to the caster wheel of shopping carts, bicycles have a similar phenomenon. If the rotation axis of the bicycle front fork is extended to the ground, the intersection point with the ground is always in front of the contact point between the front wheels and the ground. When you hold the cushion forward and push the cart forward, the front wheels follow the direction of travel very obediently. If you push the cart backwards, the relative positions of the front wheels and forks are exactly opposite, and the direction of the lateral friction is also reversed, and the front wheels will shake left and right. The relative position between the rotation axis of the front fork of the bicycle and the contact point between the front wheel and the ground has a very important role in ensuring the driving stability of the bicycle.