"Is his mechanical system capable of the KiloHertz behaviour he seems to want from it ? "

You are right in asking that. In fact a few posts back I had asked Mehmmet if he had been able to work out the Step response of his load. Unless one has a knowledge of this, implementing a a smooth closed loop velocity control is going to involve plenty of trial and error and frustration.

And that stuff about the D term being the Velocity parameter in a position control is lovely. Old wine in a New Glass ? Good.

Raghu