14 Feb 2002 ROB.T.   » (Master)

I've finally completed an axis prototype - and everything is working great (1 down, 22 to go...). I ended up using some aluminum rectangular tube-stock, and I found some channel stock which I will use to mount the Pot to the side of the axis - I'll call joint - for position sensing. I have to tighten some things up but so far so good.

I plan to CAD parts using TrueSpace 5.1 so I can head off physical problems before they occur. I'm also thinking about taking pictures of the project at various stages - but where to post this stuff? I've never learned how to put a web page together, and at this point I would rather build Predecessor. Maybe I'll ask one of my TCRobots buddies to help me out, or maybe I'll just save it for my book ... ;-)

I asked Jeff Sampson, one of our resident guru's, what motor driver I should use. He's recommending the LMD18200. I was going to try another more complicated controller from Allegro, but I don't think it delivers enough power.

I anticipate having the legs done in about a month, the motor controllers within 3 months.

Other concerns -

I want to have some current sensing ability for each motor.

Each leg needs some sort of foot sensor, probably a strain gage derivative.

Do I include a rudimentary form of direction at this level? Probably not. Should I have one controller a leg? Seems like a waste. I'll try for one controller a plate, maybe a third controller for the extra motors, maybe balance or part of the balance, and to handle the interface with the rest of the system.

My ideal would be this component , the base (most gearheads would call it a platform) , should only accept higher level commands from the robot system, and this is where the integration of these systems gets tricky. If I include stuff like direction and body orientation in relation to gravity, then the robot system can simply send the base commands like `get up' or `walk over there'. But then where does it end, after all it wouldn't be too much of a leap to add clinometers, GPS, and accelerometers at this level. At some point the base would need some sort of rudimentary decision software just to deal with relative position in the real world.

Of course this is all on the premise that the controllers will be configured like a tree. What if the controllers communicate more like peers instead of Master/slaves?

Anyway, these are some of the problems I'm struggling with. Luckily I can model (as in UML) these systems out and come up with a better solution - probably along the lines of KISS. I should also work on getting a solid definition of what I'm trying to accomplish before I risk scope creep.

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