Inside Neato's Bumper
Construction of the bumper is shown disassembled. Nylon bearing pads at corners of the cover top surface, and 1/4" deep ribbing of the bumper underside. Vertical sensing switches therefore belong in the bumper underside instead of under the top cover.
Small tact switches from Radio Shack shown fit into the ribbing cavities, and springs from retractable ball point pens fit on the stems to provide more positive bumper support than weak switch internals.
A standard flat washer 1/32" thick fits between the bumper and the nylon pads when the bumper is secured at the top by a lip on the grab handle, showing some clearance. Thin 30 gauge wirewrap wire goes over to the bumper spring pillar holes, and slits can be cut in the ribbing as needed. Limited horizontal play leaves the corner of those holes open for wire passage inside the case, then on to the front bumper switches for connection in parallel.
The wall sensor should be unscrewed when detaching the bumper; the cable connector is very tight and poorly accessible, fragile and could be damaged -- best leave in until the sensor is dismounted.
The top edge of the bumper is still poorly positioned for vertical sensing as the flange of the grab handle is at the same height and protrudes close to the front, capable of being vertically squeezed, though over little area before a bumper strike would be sensed. To avoid higher turret traps, sensing should really be done at the turret top level, with a hoop on the bumper front. Bumper level strikes would then mostly be horizontal, except at the corners. But Neato does do a lot of turning, working it's way into everything, unpredictable.
Edit: more use for the ball point pen -- the body, sliced section, is a tube around the spring, usable with the low stem switches to hold the spring over the too short stem stub. Then a #6 pan head nylon screw can be used as the top, and adjust the length easier, provide better bearing etc. The pen is mightier than the neato.
Edit: the 9.5mm long stem switches could be mounted under the cover positioned to bear on the bottom of the ribbed underside wells. The cover is about 1/8" thick, the wells 1/4" deep (varies with curve in the cover), and 3/8" is 9.5mm. Only a 1/8" hole for narrow stems, nothing major. Depends on the wells being wide enough for the bumper travel -- not sure. They can be filled in to reach the stem tops. For nylon screw stems only the shaft can be used, for enough travel. Very thin bearing points, but not much pressure on them. Switch travel only 1/64".