Self-propelling beach animals like Animaris Percipiere have a stomach. This consists of recycled plastic bottles containing air that can be pumped up to a high pressure by the wind. site 
YOUTUBE XDn6Cj4p-Z8 Published on Dec 20, 2015.
Beach animals have pushing muscles which get longer when told to do so. These consist of a tube containing another that is able to move in and out.
Muscles can open taps to activate other muscles that open other taps, and so on. This creates control centres that can be compared to brains.
The articulated legs translate rotary motion into steps. page
The beach animal doesn't lurch. When the toe reaches the end of the base, the leg is lifted whereupon it rapidly describes the other two sides of the triangle. During that time the animal is supported by the other legs which at this stage are on the ground.
Fifteen hundred legs with rods of random length were generated in the computer. It then assessed which of these approached the ideal walking curve. Out of the 1500, the computer selected the best 100. These were awarded the privilege of reproduction.
The ultimate outcome of all this was the leg of Animaris Currens Vulgaris. This was the first beach animal to walk. A new computer evolution produced the legs of the generations that followed.
These linkage dimensions are the holy numbers: a = 38, b = 41.5, c = 39.3, d = 40.1, e = 55.8, f = 39.4, g = 36.7, h = 65.7, i = 49, j = 50, k = 61.9, l=7.8, m=15 . It is thanks to these numbers that the animals walk the way they do.
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Theo Jansen is a Dutch artist. He is best known for creating kinetic sculptures that appear to walk. wikipedia
Imagine this machine, scaled down to the size of a bike where the back wheels are replaced with legs. post