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Trunk Snake
The main challenge in designing snake robots deals with putting actuated
joints in a tight volume where we minimize the length and cross sectional
areas of the links between the joints. 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 snake robot. There are three main schools of designs for
these kinds of robots: actuated universal joints, angular swivel joints and
angular bevel joints.
Actuated Universal Joints
Figure 1: Double orthogonal revelute 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. As the name suggests, he design incorporates
a universal joint with two motor to actuate each of the two degrees of
freedom of the universal joint. There are many variations of this design: The
simplest of which is just stacking revolute joint orthogonally and as close
to each other as possible, as seen in Figure 1. These kinds of designs tend
to be bulky and slow, hence not appropriate for many snake robot applications.
Another variation of this design approach is by using bevel or worm
gears train as seen in Figure 2 or using push-pull rods, as seen in Figure 3.
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Figure 2: Using worm gears. |
Figure 3: Push-pull design approach used in EOD snake robot. |
The main challange in this design approach is to make the joint as compact as
possible, yet strong enough and with appreciable bending range. One of the main
benefits of this design is that you need only one motor to actuate one degree of
freedom as oposed to the rest of designs in the webpage where two motors are
actuated at all times. However, the torques transfered to the motor are relatively
larger hence the need of higher reduction. Usually the high reduction is done by
using power screws of worm gears hence the slowness of the mechanism.
Angular Swivel Joint Design
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The second design that evolved was the angular swivel joint, which is present
in the JPL Snake Robot. These are much more compact two DOF joints. The design
is simple: starting with a sphere, then slicing the sphere into two parts such
that the slice plane is transversal 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 north pole as it traverses a cone of revolution. Connecting two adjacent
snake bays via a passive universal joint and then by coordinating the rotation
of the two spherical cups generated two degrees of freedom: In-plane bending
and orientation. This is the most compact joint design till now. However here
we are trying to develop a new compact two DOF joints.
Angular Bevel Joint Designs
Here we are trying to develop a new compact two DOF joints. We work on
optimizing the size, strength, reachability and flexibility of these joints.
So far we have designed three new types of joints. We have already designed and
built many prototypes:
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Angular Bevel |
Orientation Preserving |
Gearless |
Double Angular Bevel |