Monday, March 10, 2008


A note about the McWire design

I know that many of you are quite taken with the McWire cartesian positioning system design and several of you are making one. I know I quite like it and am stealing several sweet design tricks off of it for use in Tommelise 2.0.

I've spotted a problem with the design that I discovered, however, which I will pass along to you.

One of the really cool things about the McWire design is the way he handles the connection between the steppers and the threaded drive rods. He has a fixed stepper mount and a flexible connection between the stepper and the drive rods. He also makes no attempt to secure the other end of the drive rod.

What that means is that his design is remarkably insensitive to misalignments. It self-corrects. That's utterly brilliant.

It is that very portion of the design that gives me trouble, not that I disagree with it. What the design implies is that any thrust generated by friction with the guide rails is going to go straight into the stepper motors. That's not really a problem with the beefy NEMA's that he uses. They can handle a substantial amount of axial thrust and have little, if any play in the drive axis.

(Read the whole story)

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