Re: Information
It is pulsed. I think that a motor winds up a spring which then knocks a weight downward into the tip of the thing, hammering it into the ground. There's another weight (or something) fired upwards to conserve momentum, and this runs into some kind of spring buffer & so gets rid of its momentum more slowly & doesn't hammer it back up again. this (PDF) is what to look at, I think.
Biting the hand that feeds IT
