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A good balance between mobility, ease of construction, and cost - that is what I tried to design. To me this means:
It is possible to conform to those three rules using four or more wheels. One motor to drive them, the other for steering. But the result will be rather complex. A tracked vehicle is better, but also complex, and things tend to get between the tracks and wheels. A simple walker is much easier to construct. Reasonable balance and traction come within reach when using six legs, but eight legs provide superior mobility. And so the Spider took shape on my drawing board...
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