Iuse an MPIServo Driver. The female connector on the bottom goes to a battery. The male connector on the top gets the servo lead. With the knob line vertical the servo is centered. Rotating the knob will provide partitial to full activation. I use this to ensure that the throws are good during the pre-covering full assembly.

Took a closer look at this MPImodel - mine is older - the operation looks like it will be different with the new model.