Design, Control and Fabrication of Snake Robot
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Gaits of Biological Snakes
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! 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. |
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. 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. |
Kinematics
Where, n is the motor number when motor at each joint is numbered sequentially. A_x, A_y represent the amplitudes; delta_x, delta_y represents the spatial frequency; omega_x, omega_y represent the temporal frequency and phi represents the phase difference between the sine waves in horizontal and vertical plane
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Prototypes
The above photos show the pictures of the 2 prototypes we made before making the actual snake. The 1st prototype was made from PVC pipes mainly to experiment with the circular cross-section. But after looking at the results, we found out that even a small unbalance in center of mass or inertia would cause the robot to roll away on the ground.One of the mistake made by us was mounting all the servo motors on the same side of the link we should have mounted the servos such that the consecutive axis are 180 degrees apart from each other.
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Hence we made a second prototype out of aluminium keeping a square cross-section and this time we gave alternate Pitch and Yaw degree-of-freedom to each link as compared to the earlier design where the axis of rotation of all the joints were parallel. We successfully achieved the side winding motion in this prototype and hence we made our final robot on the basis of this design.
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Electronics Architecture
Mechanical Design and Fabrication
Team
This project was done by the 3 of us:-
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The project was under Prof. C. Amarnath (Mechancial Dept. IIT Bombay).The following people really helped us with their opinions and advice throughout the project and I would like to thank every one for all the help:
Tim John, Keshav Kumar, Murtuza Patanwala, Ashay (IIT Bombay). |