Quite an Unusual one

[Jonathan]

Clive, sorry I'm not sure what you mean ?
To clarify, by driver I meant motion control board. Feedback should go to that and not via the bob.

There's actually a lot of debate on this topic when using LinuxCNC. Since LinuxCNC is real-time, you can implement the PID controller within the computer (instead of the motor drive), and have the computer output speed instead of position (step/dir) signals. That can work well, especially if you use a PCI card. Some people consider that better as then the computer is always tracking the following error... but just saying that is really oversimplifying the situation so if interested, Google it.