Robotics 2012-10-21

I finally got around to resolving the collision problem with the leg assembly that was limiting its range of motion. The solution was to insert five extra 6/32″ nylon washers on each side to jack up the assembly just enough that it would clear the frame and the screw.

mechanical_linkage_with_clearance

Of course, now that I’ve adjusted one thing in a tightly coupled system, I’ve created another issue, that of the front feet hanging in the air when the robot is in a neutral position.

unbalanced_front_view

As it turns out, there isn’t just the problem of the front feet hanging too high, but also the rear feet, and the heavy servos in the rear confuse the issue.

unbalanced_side_view

Fortunately, I’ve got a little bit of play with the rubber feet, as they can slide up and down in a fashion that helps to level things out. I don’t have quite enough play to make it perfect, but probably enough to be OK, as the six-legged arrangement means that it operates on tripod pairs, presumably making perfect vertical alignment non-critical. One of the engineering lessons reinforced here is how nice it is to have easily adjustable components that can take up or play out slack to compensate for imperfections in individual components, either from manufacturing flaws or work-induced changes. I certainly appreciate the barrel adjusters on my bikes’ shifter cables as they make minor adjustments trivial without even requiring tools.

Next up is the task of affixing the micro-controller’s board to the chassis. Then I’ve got to code up a basic algorithm for operating the legs, at which point I’ll know if I can get away with the less-than-perfect foot heights or if I will have to re-saw a few pieces of square aluminum.

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