I’m liking the idea of using the current motors and chain for support and
movement, and Kevlar cord running from the sled to the bottom corners for
position encoding. The tension on the measuring cords would also serve to
reduce sag in the chain, and thus improve accuracy in the bottom corners.
sag in the chains wouldn’t matter as we are positioning based on the measuring
I’m visioning it something like this: one end of cord on another ring or
linkage at the bottom of the sled, going to a very small pin or pulley beyond
bottom corner (mirroring motor placement?), then up to encoder shaft/spool
mounted on top bar (axis parallel to top bar), two turns around encoder shaft,
then down to a weighted pulley, then up to anchor point on top bar.
have some sort of cap on the router so that the measuring cords can attach to
the top of the router directly above the bit.
the encoders should be above the workpiece so that they are less likely to catch
sawdust and chips.
We can save money by using relative encoders rather than absolute,
the difference in cost between relative and absolute encoders is pretty small.
This would also get the measuring cords out of the way while loading and unloading sheet stock…
so would having them above the workpiece, and there they would be out of the way
of chips as well.
One problem I see with the thought of driving the sled with a triangle above,
and locating it with a triangle below, is that the opposite corner vectors
will seldom be collinear. I can imagine a scenario when the sled is somewhat
off-center, and the direction of motion desired is collinear with one of the
sensor vectors, but not collinear with either of the chains, so the intuitive
use of the bottom right sensor encoder to control the top left motor by simply
flipping the sign in the current code would fail.
the control is not that trivial, you don’t control the left motor based on the
right encoder, you use the encoders to figure out where you are and then power
the motors to move you towards where you want to be.