And as promised, prototyped in the system I love to hate:

The upper red bar is attached to the heartbeat generator, swinging the sense arm back and forth.
The long black bar is the actual feeler. If it should brush against something, the impact retards the feeler in relation to the sense arm. This applies a load to the thread running through the sense arm's pivot, drawing the lower red arm up.
Originally, I wanted a co-axial shaft for the pivot, Lego doesn't offer any useful part in that category.
So 'necessity being the mother ... ' lead to the thread and a simpler mechanism.

Occasionally I get a bee in my bonnet about a certain mechanism.
Today's case in point: I wanted the cogwheel driven robot to have a pair of long flexible feelers that it swung before itself, feeling for obstacles. In other words, I want a trigger that rotates through ~180 degrees and is only triggered if the feeler fetchs up against an obstacle.
The trick seems to be to rotate the entire pawl and ratchet assembly, and take the activation motion off the spindle by pushing upwards.
A picture will be worth a thousand words, if I can get the scanner running.

What would comprise an important scene in the Coolest Movie Ever?
Robotic T. Rexs fighting skeletons. Skeletons that are on fire.

Too bad the reflective metal film in CDROMs is so thin, because than a stack of CDs could be turned into a dandy capacitor by grinding away the plastic and affixing bus wires.
Layering foil between the disks just does not seem as elegant.