Actually, there is a yardstick in the pic. That steel plate is a common enough item - it's walkway sheeting. The bumps would typically be around and inch and a half long, I suspect.It's not easy to get a sense of scale, though, without knowing how large that motor or steel plate are.
I've tried doing a cursory search for the plating, but have not found anything so far (lack of time). The material could be aluminium, but is most probably steel.
That would make that motor/alternator thingy in front maybe a foot long? <thumbsuck>