This is great, with or without hue shifts (although to me it seems like you've already used hue shifting, doing a grey ramp for the metal tinted yellow/brown). The design and metallic look are lovely!
Something that pops out at first glance is the perspective of the side cogs, which should follow the perspective of the coil (indicated by its highlight) instead of being perfectly horizontal. Also, to convey a more mechanic feel, which is usually associated with perfectly aligned parts, the feet should point in the same direction, or perhaps somewhat outward, instead of slightly inward as they are.
The hue shifted version is a nice alternative, although i don't think it's needed in this piece. But practice is practice!