Sounds tough. To capture the spirit of the device, the gears need to appear to turn at different speeds and in different directions - that rules out a simple alternating edge, unless you made teeth sufficiently different shades that the eye you can track them. Otherwise you’d only be able to fit 4 teeth on the 12 space perimeter of the smaller gear. 4 copies of the 4x4 eats 8 pixels across your texture in both axes, so you’ll probably want to depict the outer overlapping (red) gear rather than the meshed (green) gear. With the large gear overlapping the smaller ones, at least one of the 4 teeth will be obscured, leaving it looking a little bare. That suggests that 6 shading hinted teeth might look better. There is also the issue of looping the animation: with 4 teeth, the animation loops on a multiple of 3 frames; with 6 shaded teeth, the animation loops on either 6 or 12 frames. None of these is ideal - your other animations all appear to be either 8 frames or an integer factor of 8 frames (I’m guessing there’s a “tick mod 8” line somewhere in your renderer?). Ideally, the smaller gear would be 5x5, with a perimeter of 16 - but I don’t think you’d fit that in.
Anyway, I’m sure you’ll make something that looks awesome as always - I just worry that that specific device is ambitious.
Mentioning shading and gears in the same thought just reminded me - the reason the gearboxes are hidden in the screenshot I posted is that they currently aren’t spray-paintable and I didn’t fancy bright orange boxes in my grey-on-grey-chic interior. Is spray-paintability something that might be possible, or do the gearboxes use that same space to track other state? (I can imagine a world in which the presence or absence of a gear is tracked as a flag within the colour field, for example.)
(ps. I do hope you realise that the addition of axles/gearboxes/transforming gearboxes is rapidly creating a context in which a quick-response variable output burner/boiler/turbine will soon be coveted by all…)