When FSA where first introduced, I was thrilled. I do a lot of
> mechanism design with complex relative motions and FSA looked like they
> would be a tremendous productivity boost. Unfortunately, they haven't
> panned out. Sure it works OK when you have one very simple FSA, but
> anything beyond that is extremely flaky. As an example, I have an
> assembly with two FSAs in it. The FSAs are very simple, and as
> mechanisms, they are identical. One is a linear actuator, and the other
> is a linear slide. Each has has a limit mate to constrain its stroke,
> and each has one DOF along its axis.
>
> The slide is 'fixed' in the main assembly, but flexible. The actuator
> is mated such that each of its two components is fixed relative to a
> corresponding component in the slide. It is also mated such that the
> limit mate on each is not violated.
>
> A grand total of 2 mates, and SW chokes on it. Neither mate can be
> solved. Also, the limit mate in each FSA fails as well. Open up the
> FSA and rebuild and it corrects itself, but the main assy fails. If I
> suppress the limit mate in one of the two FSAs, all is well, except that
> the mechanism doesn't work properly. Without both limit mates, one FSA
> can move beyond its internal limit.
>
> Jim S.
>
I ran into a similar issue, and I think the problem is with the limit mates and not necessarily the FSAs (although I agree that FSAs can be flaky).
The issue is that once a limit mate is applied, no other mate can be applied that defines the limit mate's exact position. Ex.: Create a simple cylinder and use a limit mate to define its stroke limits (10-20 for instance). NOW, apply another mate that defines the exact stroke length that does not violate the limit mate (15 for instance). This will immediately cause errors, even though all conditions are/can be met.
Thus, in my case, I wanted to crate a ramp that was actuated by a couple of cylinders. My main assy would contain the ramp, base, and FSA cylinders. The cylinders had limit mates applied defining their motion limits. Then, in my main assy, I would apply an angular mate to define the ramp. BOOM!! mate errors due to fully constraining the cylinder length with my angular dim, even when the angular mate caused the cylinders to be in a position that satisfied the limit mate.
I wish an error would only occur if the angular mate caused the limit mate(s) to become unsatisfied.