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The Spider

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• Performance
• Construction
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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:

1. Everything touching the ground has to be powered. Otherwise mobility will be impaired in all but easiest environments.
2. More than two motors are out of the question. Adding motors increases complexity and thus makes construction more difficult. Cost also goes up fast, and not only because good motors are expensive; you need more power to move the extra weight, and that means larger batteries and/or solar cells.
3. The robot must be able to turn around its top axis, that is on the spot. Otherwise horizontal mobility just won't be good enough.

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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