Another possibility for bumpers are the piezo film elements made by Amp. I
recently ordered information from their web site at
<http://www.amp.com/sensors>. The packet included a small sensor and some
expirements including one using it as an impact sensor. Unfortunately, I
don't have an oscilloscope which would be really helpful in determining if
the sensor would work well for a mowbot.
-- Doug Smith * dsmith nospam at execpc.com <http://www.execpc.com/~dsmith>