OT? sorting rocks from potatoes

[Tony]

i live in a farming community.. though most of my work comes from the industrial centers a few miles out, i get the frequent farmer come through with ag equipment: tractors, tillers, harvesters, stuff like that. i weld alot of old iron.

potato season has come and gone with most of the potato crops already harvested. its very labor intensive. they plow the earth, turning everything up, and collect the potatos by hand. its hard work,
sorting through the dirt and rocks, and selecting the good potatoes. these are the two weeks where the town is dead quiet at night.. even the teenagers asleep by 10.

anyway, to make a long story short, there is a piece of equipment out here that makes the job lighter.. essentially its a plow with two vibrating grates immediately behind it.. it leaves behind a tidy row of potatoes.. and rocks. its easier to sort through, but still leaves alot to be desired. not to mention
the thing is probably 80 years old.

i'd like to build them a new one. theres not really much to this design-- its all mechanical with two moving parts (the grates and a cam that keeps them hopp'n).. its dragged along by a heavy tractor and powered via PTO.

in the good old American spirit.. i'd like to make it better. better means no rocks.

for the life of me i can't figure out how to sort the rocks from the potatoes. potatoes are about the same size and weight. theyre even the same color, they don't float on water, i can't use a blower to separate them.. i'm stumped.

i know somewhere out there, there is equipment that can do this.. and i know there are some pretty sharp beans on this forum.

any body have even a remote idea on how this could be(or is) accomplished? preferably without a microprocessor based vision system.

if i get this thing built with the help of the forum, i'll post the complete CAD drawings here.

i'm essentially doing this for free anyway.. a farming collective is footing the materials bill. though i do get free fresh potatoes. the lucky winner gets a big sack of grade A potatoes, how's that?

-tony

[Steve Stube]

<font face="Verdana, Arial" size="2">for the life of me i can't figure out how to sort the rocks from the potatoes</font>

Rocks don't have eyes, so take a vote and the "eyes" have it,(get bagged).

Yes this will take more thought but don't wait on me.

[Evan]

Rocks don't float in salt water.

[This message has been edited by Evan (edited 09-27-2005).]

[vinito]

And if the water was hot enough you could sell the potatoes pre-cooked & seasoned.

[ahidley]

Easy..........
1-dig em all up. Now they are up on your machine
2-sort/sift off the dirt. Maybe vibrating/rolling over a screen of some sort.
3a-now the tricky part! make some kind of trough filled with water, with a conveyer running down the center at the botom. As this dirty mess travels down the trough the rocks will be heavier than the potatoes so the water and/or air jets (that you have not yet desigened to the proper dimensions)will gently lift the more boyant potatoes and they can be directed in a differant direction....
3b-You could also seperate them with something like a trough flowing into a spinning washing machine tub. this would use centrificagle force and whirlpool cleaning action.. Just how fast is the key to maxamize seperation. (Boy if RED GREEN could see this)

Remember - potatoes almost float, rocks dont

p.s. I like my potatoes home fried

[digger_doug]

the way it's done around here is called
a "wind machine"
a large squirrel cage blower powered by
a v-8 engine sucks the potatoes up to the
underside of a slat conveyor, which in turn
pulls them 90 degrees off the conveyor.
they then are out from under the suction,
and fall onto another (the clean) conveyor.

[winchman]

Have a drum rotating just fast enough so the potatoes are held in place as they go over the top. The rocks would fall onto a conveyor belt running through the drum, and would be carried away to fill in New Orleans.

The drum would be inclined slightly so the potatoes would work their way to the lower end, where they would fall on a conveyor of their own.

Roger

[winchman]

Here's how it's really done:

"Modern potato harvesters are able to sort rocks from potatoes with amazing success. They do this with air. A huge fan within the harvester blows across (actually, under) the potatoes and rocks. The potaoes, being lighter per unit volume than rocks, "float" upwards and move into a different part of the machine. The rocks settle out and are stored in another compartment, to be later dropped onto the field."

From: http://www.geo.msu.edu/geo333/spud_harvest_now.html

Roger

[Steve Stube]

Interesting link winchman, thanks.
A quote from the link doesn't quite fit all operations anymore.

<font face="Verdana, Arial" size="2">Like many of Michigan's crops, seasonal or migrant workers are imperative to the success of the industry.</font>

I remember migrant workers out in the pickle fields picking and paths for the tractor and crates to haul in the crop, then fewer paths and wide sweeping walk behind or sit on conveyors for the workers to put the harvest on. A month ago I stopped along side the road to see a pickle crop being harvested. The field was solid pickles no roads or paths or migrant workers on the ground. Two really really big machines with what looked like A/C'd glass enclosed sports annoncer size cabs/boxes on board. It took a swath maybe 40 or 60 foot wide pulling the vines and everything up a harvester head conveying them to a separating drum or drums the description of which I won't try to explain (frankly I was too far away to see it well) but could see that where it had already traveled the vines and perhaps the reject pickles were discarded in a sliced and diced foder sprayed out on the field behind the machine. I assume these machines had large hopper capacity because the only trucks I saw were positioned at one end of the field. Next time, if I don't have passengers I will stop for a closer look but that is like going to be next years crop.

[charlie coghill]

Tony, that is how I made some of my high school money. If I could I avoided picking the patatoes but would pick up the sacks and load them on the trucks.

That will put you into shape.

Maybe they could move down a trough and pass in front of some kind of urta sound. A gate could open and drop the rock out or maybe drop the patatoe out into a convayor belt.