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Constructing a Spider

exploded view This is not - yet - a complete `howto', but those of you with some mechatronical experience will find enough information here.

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Most of the bits and pieces above are quite recognizable - but what are those white bits in the legs? It is ABS tubing, a somewhat flexible and easy to shape plastic. A sharp knife is all you need for cutting to length, while the holes for the legs (1 mm steel wire) were `drilled' by pushing a pin through. Each leg-pipe rotates on a nylon M3 secured to the frame; the end of the M3 rests on the steel wire, thus taking the weight supported by the leg. The ABS tubing serves only as a double hinge.

When they are not supporting the robot, something has to prevent the leg-pipes from slipping down. This is the task of the strips of pcb material mounted below the four `hip joints' on each side. They are secured by longer nylon M3's, with bits of ABS tube around them to keep the assembly from squeezing the hinges. In the photo above you see them on the side I didn't take apart, but they aren't visible as loose items. And in fact I forgot them when I put the Spider back together - I was concentrating on my camera - so in the photo below (and in the others) they are missing. Despite that, the Spider walked fine, so it took me a while to discover what had happened!

The plastic gears are part of a low priced package sold by the mail order house Conrad, where I also bought the high quality geared motors.

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side view

PCB chassis

As you have probably noticed, the rest of the framework is also made of pcb material. The glass/epoxy has a good strength to weight ratio, and it is easy to transfer the Spider drawing to it, using spider_print.ps. It is a drawing in Postscript, giving very high accuracy, without bitmap jaggies. The accuracy has to be about 0.1 mm to make sure that the gears will mesh correctly. My own pcb was made by simply laserprinting the drawing on transparent paper and transferring it onto light-sensitive pcb material. With excellent result!
The drawing also positions patches of copper foil so the frame can be soldered together, a fast, easy and quite sufficiently strong method. And of course it is easy to integrate traces for connecting the yet to be done leg sensors. Which brings me to the `brain'.

previous (Spider performance) / next (Spider brain)