> Needless to say, the blades get dull fast and rarely last more then 2
> years and have to be re-sharpened every month or so.

Count yourself lucky, I know a lady that's gone through three sets of blades
this year. (and a new quill :-(

> I'd like to put some sort of sensor in that would disengage the
> blades automatically when the blades hit something solid and I would
> like some suggestions from the group.

My first thought for an engineering solution would be a shear pin. Find a
way to put something soft, cheap, and easily repairable between the motor
and the blades. (think of lead for the key on the blade shaft) That way it
limits the damage to the rest of the parts. Or maybe you could make the
blade attachment squeeze between a couple of washers, sort of a torque
limited clutch.

> Any ideas? It has to be cheap and simple. I can handle the
> interfacing to the solenoid.but need suggestions on what type of sensor to
use.

I don't really think a technological solution is the best idea here. You
could try the solution I'm using for the lady I mentioned above, charge a
*lot* every time I have to fix it. I'm hoping it will help her to remember
to quit running over large hard objects. Hasn't worked yet, but we'll see...

Good luck,
-Denny

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