Inspiration

 

Interesting Parallelograms

The parallelogram shape of the legs has an overlooked unique advantage; a parallelogram is a four-sided shape with sides parallel to one another of the same length. The angle at a corner of a parallelogram will always be equal to the angle at the opposite corner. So long as that rule is followed, the angles can be changed without affecting the lengths of the sides. By changing the angles of the corners, the entire shape is altered. These principles give a parallelogram the unique ability to collapse itself to a point where it appears to be a single line.
There are two different ways that the parallelogram can be collapsed into a line.

Case1 (D is above A)
-The distance from B to D is great.
-The distance from C to A is small.		 Case2 (D is below A)
-The distance from B to D is small.
-The distance from C to A is great.

If the C and A corners are pulled together, corners D and C will rise up (relative to the other two corners). If the D, and B corners are pulled together, corners D and C will be forced down.

 

 

Inspiration from 1930

The use of a pulley had bean overlooked in the design of the legs since a pulley is only capable of pulling object together, and the legs require a pushing motion. However with the collapsing principles of a parallelogram, it is clearly possible to transform the pull of a pulley into a push. Pulling the different corners of the parallelogram shaped legs together causes the end of the leg (foot) to push against the ground, or rise up.

To the best of my knowledge this is the first walking robot to use any sort of pulley system to move its legs. However the idea is far from new. By chance, an image of the noble steam shovel presented itself, and lead to a breakthrough in mechanical design.


Not unlike a servomotor, a steam engine was very weak but still had the ability to lift massive amounts of earth. Even more impressive is that the steam shovel existed decades before the innovation of the hydraulics used by modern excavators. The weak steam engines used a winch to pull on a cable. The cables ran through a system of pulleys to produced enough strength to move a lever with a bucket on the end.
historic steam shovel
Image Source: New York Online Library.
Once the legs were improved by ideas inspired by the steam shovel, they were capable of lifting themselves twelve centimeters above the ground. The limitations on the height no longer have anything to do with the strength of the motor. The legs cannot lift any higher because pieces of metal are in their way. The steam shovel was the inspiration, which lead to the realization that pulleys could be used, but the design of the pulleys and levers themselves are completely original.

 

Pulley Possibilities

Interestingly, pulleys and the muscles of living animals behave in very much the same way. Just like a pulley, our muscles cannot push only contract, which is why animals, and the robot have at least two muscles in all joints.


This robot is certainly not the first to experience have problems with a poor system of leg movement. Many designers of walking robots, which use the previous design and others frequently mention that improving the height their legs can move would be a large improvement. The pulley muscles may be a step forwards for walking robots. Pulley legs are simple, powerful, have no distance limits, and are extremely versatile.

 

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