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'[OT] [EE]'
2005\08\15@094840 by KY1K

picon face
Good day all,

I have to mow lawn that has rocks and similar lawnmower blade
damaging hazards. I use a John Deere riding lawnmower that has a
solenoid to engage and disengage the drive to the blades.

It's hard on the blades when they hit rocks and other obstructions
because I can't react fast enough to disengage the solenoid to stop
the blades from turning.

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.

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.

I know cars have knock sensors to detect pinging, but I'm not sure
how these work. A vibration detector with an adjustable threshold
might work. Or, perhaps a microphone could just detect loud noises
above some adjustable threshold?

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.

Thanks,

Art





2005\08\15@105129 by Mark Scoville

flavicon
face
Hi Art,

My gut reaction is that it will be hard to do what you want. I would guess
that by the time you *detect* a blade strike the damage is already done -
sort of like using an impact sensor to detect a parachute not opening :)
Whenever I hit rocks with my tractor (Not a John Deere, I have a cheap MTD
brand) there is a loud high pitched scraping noise. Like you suggested,
*maybe* you could detect this sort of noise and disengage the blades, but
again, it's probably too late too be any help. As far as a vibration
detector, my tractor shakes like crazy even if I haven't hit anything. Maybe
you could just hook up the solenoid to a "dead-man" switch on the steering
wheel. If you hit something let go of the switch - this would save the
reaction time of having to reach for the disengage switch. Might lengthen
the blade life a little. Maybe some others will have some clever ideas.

Good luck to you.

-- Mark

> {Original Message removed}

2005\08\15@164745 by Josh Koffman

face picon face
While not directly applicable, search out that little video of the
capacitive sensor for table saws. It can detect a finger, stop the
blade rotation and withdraw the blade all before the finger gets much
more than a semi-deep cut. I'm on the road at the moment (well, in an
airport) so I don't have the link. I'm sure someone does though!

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

On 8/15/05, KY1K <spam_OUTky1kTakeThisOuTspampivot.net> wrote:
> 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.

2005\08\15@165623 by Robert Young

picon face
>
>
> While not directly applicable, search out that little video
> of the capacitive sensor for table saws. It can detect a
> finger, stop the blade rotation and withdraw the blade all
> before the finger gets much more than a semi-deep cut. I'm on
> the road at the moment (well, in an
> airport) so I don't have the link. I'm sure someone does though!
>
> Josh
> --

I believe those use something similar to a blank pistol cartridge as the
prime mover for the blade brake.  

It is neat to watch them shove a raw hotdog into the blade and it stops.
Not very practical if you are mowing rocks though.

Rob

2005\08\15@170923 by Josh Koffman

face picon face
Interesting...I was wondering there they got that much kinetic engery
so quickly.

I wasn't suggesting it would work in this situation, but might stir
some creative juices in the list!

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

On 8/15/05, Robert Young <.....rwybeakerKILLspamspam@spam@hotmail.com> wrote:
> I believe those use something similar to a blank pistol cartridge as the
> prime mover for the blade brake.
>
> It is neat to watch them shove a raw hotdog into the blade and it stops.
> Not very practical if you are mowing rocks though.

2005\08\15@180009 by olin piclist

face picon face
Robert Young wrote:
> It is neat to watch them shove a raw hotdog into the blade and it
> stops. Not very practical if you are mowing rocks though.

Or trying to saw hotdogs.

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