closed loop control of solenoid frequency and stroke

Tear apart an old hard drive..

• Voice coil designs are rather good in those 3 regards; look at speaker voice coil positioning can be controlled by use of an arbitrary waveshape and hard drive positioning is definitely by arbitrary drive.

Not everything needs to be quantifiable. For a big and expensive project development you'd definitely want to nail down your specifications as much as possible to minimize a costly redesign. For things like communication equipment that have to interface with existing technology, the numbers pretty much define your project. But this hypothetical gizmo is for an artist, so knowing that the force needed is "pretty small" tells me enough. You build a mechanism that can overcome its own inertia by a large enough margin to make you confident that it'll work and then go out and test it. Is it really cost and time effective for me to go out and try to measure this force just to provide a number? I doubt it. I could be wrong, but that's a chance I'll take.

Besides, I'm not asking anyone here to design this thing for me. Just for general ideas. Thanks for everyone's suggestions.