Here I would like to describe various motions performed by biological snakes which are the main source of inspiration for the snake robot.
- Side-winding Motion
This motion is performed by desert snakes which move side ways by lifting a part of their body from the ground. Hence there are only a few (shifting) points of contact between the snake and the ground. This really helps the snake when it has to move in the desert where the ground is really hot!
- Lateral Undulation
This is the typical motion performed by snakes. Here the snake is actually producing a propagating wave motion. The key to the snake moving forward using this motion lies in the an-isotropic friction present in the skin of the snake. The friction coefficient of the snake is high along the direction perpendicular to its body and less in the direction along the body. This difference in friction causes the snake to move forward.
- Concertina Motion
A concertina is a small accordion instrument. The name is used in snake locomotion to indicate that a snake stretches and folds its body to move forward. The folded part is kept in a fixed position while the rest of the body is either pushed or pulled. Then, the two parts switch roles. Forward motion is obtained when the force needed to push back the fixed part of the snake body is higher than the friction forces on the moving part of the body.Concertina locomotion is employed when a snake moves through narrow passages such as pipes or along branches. If the path is too narrow compared to the diameter and curving capacity of a snake, the snake is unable to progress by this motion pattern.
- Rectilinear motion
The slowest mode of snake locomotion is rectilinear locomotion, which is also the only one where the snake does not need to bend its body laterally, though it may do so when turning.In this mode, the belly scales are lifted and pulled forward before being placed down and the body pulled over them. This motion is also known as Caterpillar Motion as the snake moves like a caterpillar.