Originally posted by bb99
You might be able to get away with three motors. I see two potential ways:
1. Each corner of the table has two legs. If you were to fix one of these legs to the base, then you would only need to move the other leg. This however would involve more complex math for some simple movements. For example, if you wanted to simply tilt one edge of the platform down, you would have to take into account a slight twisting of the platform since only one of the corners supporting legs is moving, the corners position ins 3D space will travel proportionately in the same direction as the moving support leg. This would necessitate a counter rotation of the entire table to counteract.
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I don't know that this is true. You can get reverse threaded screws -- a turnbuckle is a perfect example of this. One rotation, and even motion out both sides. This would eliminate the twisting.
Down side is that it would also remove the rotational aspect of the construct -- we'd be back down to 5 DOF, but that's more than enough for most purposes.
Thinking about it, though, I'm not sure that would work. It'd raise and lower the corner of the platform, but I think it would eliminate any side to side movements that were available. I think that two legs *have* to be independently adjustable.
Check out the motion in these videos...
http://www.hexel.com/video.htm
-- Chuck Knight