Lies, Damned Lies, and Sean

The rock picker

Thanks to Noelle, I now know how to run a Bobcat.  Her next door neighbor has a horse arena, constructed with layers of gravel, small gravel, and sand.  She kindly lets Noelle use the arena.  Unfortunately, the gravel rocks, being larger than the sand, move to the surface, which leaves the horses lame when they practice jumping in there.  Noelle's neighbor said she would pay for the many tones of fresh sand it now needs (though she doesn't jump, so the rocks are less of a problem), but Noelle had to remove the rocks first.  To this end Noelle rented a Bobcat with a rock picker attachment.  The rock picker mounts in the front where the scoop normally resides.  It has a hopper to hold the rocks and tines that dig into the ground and throw the rocks and some unlucky sand into the hopper.  Mostly it worked.  

The problems we had are:  

• With the rocks we dumped about 10 cubic yards of sand, which seems quite a waste.


• I had to go in reverse all the time because it scoops up too much sand otherwise


• Adjusting the picker's tilt and elevation was tricky -- too high, and it didn't pick rocks; too low, and the hopper fills with sand, which we must dump with the rocks, wasting it.


• Noelle directed from outside the Bobcat because it wasn't possible to see where the picker was relative to the ground or how full the hopper was from within.


• Dumping the hopper was slightly dangerous, as the back wheels sometimes raise off the ground, causing Noelle some consternation.


• Not all the rocks are picked.


• The gravel base is chewed up in places where the sand is too shallow, resulting in more rocks.


• It is deafeningly load, in part because the picker works best when the Bobcat's throttle is at maximum.


• The steering of the Bobcat uses two leavers rather than a wheel, so hitting a bump can produce a forced oscillation:  I'm thrown backward, and inadvertently move the handles backward with me, which slows down the bobcat, which throws me forward, and I inadvertently move the handles forward, which speeds the bobcat, which throws me backwards even further, etc.


• The edge of the arena is surrounded by a nice fence, so we don't dare get too close to the fence with the machinery, but the horses are often run near the fence, so having the rocks removed from such a high-traffic area is desirable. As a result, I spent four hours picking the rocks out by hand.  Noelle spent a few hours hand picking too, and our friend Laurie spent perhaps an hour.

The job we did by hand around the periphery was superior to the picker's.  I think five men paid minimum wage would cost as much as the picker and do a better job.

We discussed making a small robotic rock picker that would work like the robotic lawn mowers.  They stay confined to an area defined by a wire antenna.  They randomly mow about, and as time goes on they probably will reach all locations.  The rock picker would be more complicated and need a greater power source, a sifter, a kind of conveyor, a hopper, and a way to empty the hopper.