Back in the days when dinosaurs roamed the computer labs ... some hard disks, and even some (Persci) floppy disk drives used voice coils to position the heads. The hard disk drives had very massive positioning mechanisms and multi-ampere drivers for their voice coils.

One thing about loudspeaker coils is that they return to their neutral position when power is removed, and the coils get VERY hot, and, quite promptly, melt when one attempts to keep them in one position for too long. They are, after all, supposed to move (oscillate), constantly, when power is applied.

IIRC, Chico wishes to draw pictures with his laser light source, projecting them onto the wall of a room. Open loop methods may, in fact, be quite adequate, if he has, say, a 12-bit DAC, that might be adequate to drive a voice coil with sufficient accuracy (repeatability) and precision (probably only 9 or 10 of those bits in actual performance) with a properly designed and constructed circuit.

The limitations that either a loudspeaker voice-coil (usable because of his application) or a fixed-disk's voice-coil-driven head stack actuator, impose are mostly mechanical. Each of these will "start slowly and accumulate momentum" along the way. The mass of the moving parts is a major factor. The other factors are probably quite important, too. The viewing angle of the projected image will be nominally 90 degrees, i.e. once on the wall, the image will be consistently proportioned. However, as the projection angle deviates from 90 degrees, the relative velocity of the light beam increases. That can be managed with a cam/follower mechanism, but that increases the mass and reduces his speed.

I'd suggest he study the problem with a stepping motor, which he apparently already knows how to use, accepting, along the way, the rather pedestrian performance of which it's capable, and simply learn about the "other" problems with that system before proceeding to a voice-coil implementation, which will be more complex in both electronics and mechanics.

The drive electronics for that old 1970's-generation 8" floppy disk drive occupied a PCB of about 500 square cm. and required several amperes on each of its four power supplies. The DAC was discretely implemented. There are, today, and have been for decades, monolithic high-power audio amplifiers capable of driving a massive voice coil at audio frequencies with quite reasonable linearity. Even a pixelated (raster) display could be considered with such a device, as the audio power amp would drive the deflection system, but a video speed display driver would modulate the laser signal.

Isn't that worth a thought?

RE