Skid steering
- Steering method relies on velocity difference of wheels to turn a vehicle using frictional force
- It is the simplest method to implement, and can be found in heavy construction vehicles and tanks (using tracks instead of wheels)
- This is found to be the most popular method for robots for its simplicity to model mathematically as well as how controllable it can be through software
- Because it relies on DC motors, it is not perfect and wheels will not drive in a straight line unless tuned or corrected with additional sensors and filters
Top & Left: Example of skid-steer demonstrating velocity control of separate motors, as well as an example of a Bobcat S510 Loader implementing skid-steer.
Ackermann steering
- A mechanical configuration which turns wheels in a direction with greater precision and control
- It is found in every production car in the consumer market, and is more ideal for faster vehicles which need greater turning control at high speeds
- It is difficult to model accurately but is usually simplified with the bicycle model, and velocity of the wheels are equal for both motors
- This method is the most taxing, requiring an additional servo to control steering, proper wheel alignment needed, and more complex mechanical design required to properly implement
Top Left & Right: Examples of Ackermann steering demonstrating mechanical linkage to influence the turning radius on a Ferrari F1 car
Omnidirectional steering
- Omni-directional wheels have additional wheels to allow a vehicle to drive in all directions and even on the spot without wear and tear from skid-steering
- It’s the only method of the three to achieve ‘non-holonomic’ motion on the ground, meaning it can move in any direction at any orientation
- Due to the wheel design, wheels may experience more wheel slip due to friction between the rollers and surfaces, and the wheels are only efficient and safe to park on directly flat terrain
Top: Model of a robot implementing omni-wheels
