Chain SOP - how to maintain point distance along curves?

[cdenny]

Hey all, I've been having an issue figuring out the best way to make panels move along a curve - constrained to each other. Like chains, tank treads, sectional garage doors, etc. I've attached an image of the issue, the black dots would be wheels on a rail.

It looks like the chain sop uses curveu to control the objects position along the curve, which fails when the movement axis changes from a single direction to a mix of the two. IE as it rounds the bend the top pivot point travels a longer distance than the bottom pivot point. I've got one thought which is to create points that are constrained via distance to the previous point, which are all constrained to slide along a path. Is this possible in vellum now with the slide constraint? Each point would be a position constraint for the bottom of one object, and a 'look at' constraint for the next object down the path. If the distance is maintained between each point then theoretically it'll always be a seamless assembly of chain-links or a tank tread.  I just can't believe there isn't a simpler way or something that has been done before, it seems like this would've been solved years ago. Maybe there's some math or CHOP to interpolate point distance along the path? Maybe some sort of for loop where it changes a points curveu attribute until the correct point distance is achieved?

Thanks much for the advice!