The plastic blade needed a lot of speed to work. I was running it at about
15000RPM. The soft rubber blade worked, but hit anything ard and you need
to replace the whole blade. The nylon trimmer just made a mess of the
grass, it's best against a hard surface like a fence, but less successful
when the grass can move away. The hedge trimmer also left a mess of uncut
grass. The handmower would have been dead simple to convert to robotic
operation, but you need to go back and forth over the same spot to get a
proper cut.
In the end the best system was the razor blades.
Dave Everett
Domestic Droids Website
http://members.xoom.com/Mowbot/