Modeling motor control

[Ether]

Originally Posted by kamocat

Here's a drill motor, with no gearbox or pinion attached . I think it's from a 6v Ryobi.

Unfortunately, there's no encoder on it, so I'll have to assume the speed is proportional to voltage.
The current curve seems a lot more regular; there's less noise, and it looks like a continuous function [perhaps 1/x*log(x) ].

Why is the plot of current a series of horizontal lines?