Well, the first movement on the Mantis just happened, and for a start I guess it wasn't too bad! Admittedly this is under electrical control, not hydraulic, but still, its good progress.
The PID filter seems to be working pretty well, although as I found out its not a good idea to leave power switched off to the motor amplifer, and leave the FACU running, allowing the integrator to wind up.. when power is restored to the motor amp, you can guess what happens.. and boy does it happen fast!! ahem, partly operator error, and partly badly tuned PID.
The back to back actuator arrangement works ok, but as you can probably guess they tend to get out of sync with each other, which doesn't help, so I may have to go back to single unit.