Chop Gesture

I'd like a "chop" gesture, like the double-chop gesture Motorola uses for toggling the torch.  Similar to the action you would use with a small hatchet, or bouncing a hammer off the head of a nail.  Each "chop" is a short, abrupt, single shake down and back up.

The gesture should have settings for:

1. Sensitivity (how aggressive and/or fast the chop must be) 

2. Number of "chops".

The current "shake left to right" gesture doesn't work as a good replacement.