Snake Robot Design - The Robotics Institute Carnegie Mellon University
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Snake Robot Design
Contact: Howie Choset

Snake robots are a new type of robots, known also as serpentine robots. As the name suggests, these robots possess multiple actuated joints thus mulitple degrees of freedom. This gives them superior ability to flex, reach, and approach a huge volume in its workspace with infinte number of configurations. This redundance in configurations gives them the technical name: hyper redundant robots. Here we develop new snake robot designs. Ideally, the future snake design will consist of three degree-of-freedom stages — roll, pitch, and extension. Sometimes stages are called bays.

For the applications that we are interested in, the main challenge in designing these robots deals with putting actuated joints in a tight volume where we minimize the length of the stages and their cross-sectional areas. For the next design iteration, we will omit the extension degree-of-freedom in favor of having a shorter bay length. Therefore, the main concept of our design, as well as many others, is to stack two degree-of-freedom joints on top of each other, forming a serpentine robot. There are three main schools of designs for these kinds of robots: actuated universal joint, angular swivel joint, and angular bevel joint.

The simplest design that first comes to mind is stacking simple revolute joints as close as possible to each other and this led to the actuated universal joint design. However these kinds of designs are bulky and not appropriate of lots of serpentine robot applications. Another kind of bulky two DOF joints are pnuematic snakes.

The second design that evolved was the angular swivel joint, which is present in the JPL Serpentine Robot. These are much more compact two DOF joints. The design is simple: starting with a sphere, slice the sphere into two parts such that the slice plane is transverse to the south-north pole axis of the sphere. Now rotate one half sphere with respect to the other and notice the motion of the poles. Putting the snake bays orthognal to the sphere at the poles and coordinating the motors that rotate those hemispheres leads to a two DOF joint.

Until now, this was the most compact joint design. However, here we are trying to develop a new compact two DOF joint. We work on optimizing the size, strength, reachability, and flexibility of these joints. So far we have designed three new types of joints. The first prototype was designed and built using off-the-shelf componnents and using simple manufacturing machinery.

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