Robot Driving Styles

Nonholonomic vs Holonomic

Holomonic Drive

When it comes to movement there are two main differences. One is a system of movement where we can go in whatever direction we want. This would be an example of a Holonomic system. The other system is one where we cannot move however we want. This is called a Nonholonomic system. This is the type of system in which a car fits. To parallel park we cannot just slide into the spot. We must take many steps to achieve the result that a slide would get us. As we can see in the video above, the forklift is fitted with special wheels that allow it move in a Holonomic system. It can move forward, backwards, side to side, as well as turning.

Quick terms

Some words we need to know are defined in the part.

Vector - A Vector is a direction and magnitude. Going 50 miles per house is just a magnitude but going 50 miles per hour heading west is a vector. The magnitude can be any unit of speed. Such as miles per hour or meters per second. A direction can be a compass heading or degrees.

Nonholonomic Example

Let's look at how a car moves. The tires use friction to move the car. The tires can only produced motion in the way they are pointed. You use the pedals to apply a magnitude of speed and the steering wheel to apply a direction. These two values come together to create a vector. You can see the vector as a red arrow in the picture below.

Classic Tires

Tank or Differential Drive

Tank drive keeps the wheel locked into one position. All the direction part of the vector comes from a difference in magnitude of the two sides. This is best illustrated in the picture below. One side is going forward and the other backward. This creates a stationary turn. Check out vectors below.

Holonomic Examples

Here are two examples of Holonomic driving systems.

Omni-wheels

Omni-wheels

Omni-wheels are wheels that In the picture below check out the individual vectors on the left and the sum total on the right.have rollers along the circumference. They rotate like normal tires but due to the rollers, you can move side to side. They are usually found at 90 or 120 degree differences to each other. Unlike a car that would have all the tires facing the same direction. By combining the vectors of multiple wheels you can achieve a Holomonic drive system. In the picture below check out the individual vectors on the left and the sum total on the right.

Omni-wheel Vectors

Mecanum Wheels

Mecanum Wheels

Mecanum wheels are mounted similar to normal tires and have rollers like omni-wheels. However, their rollers are positioned at 45 degree angle to how like rotate. This allows them to create the same vectors as omni-wheels but in a simpler layout. In the picture below check out the individual vectors on the left and the sum total on the right.

Mecanum Wheel Vectors